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HUNGER AND POVERTY: CAUSES, IMPACTS AND ERADICATION

SUSTAINING FUTURE FOOD SECURITY IN CHANGING ENVIRONMENTS

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HUNGER AND POVERTY: CAUSES, IMPACTS AND ERADICATION

SUSTAINING FUTURE FOOD SECURITY IN CHANGING ENVIRONMENTS

DIVYA PANDEY AND

ABHIJIT SARKAR EDITORS

New York


Copyright © 2017 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. We have partnered with Copyright Clearance Center to make it easy for you to obtain permissions to reuse content from this publication. Simply navigate to this publication’s page on Nova’s website and locate the “Get Permission” button below the title description. This button is linked directly to the title’s permission page on copyright.com. Alternatively, you can visit copyright.com and search by title, ISBN, or ISSN. For further questions about using the service on copyright.com, please contact: Copyright Clearance Center Phone: +1-(978) 750-8400 Fax: +1-(978) 750-4470 E-mail: [email protected].

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Library of Congress Cataloging-in-Publication Data ISBN: (eBook)

Published by Nova Science Publishers, Inc. † New York


CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

vii Aquatic Bioresources: Utilization of Diversified Species, Products and Services for Strengthening Alternative Agriculture in Rural India P. K. Mukhopadhyay and R. N. Mandal Impact of Tropospheric Ozone and Particulate Matter on Plant Health Pallavi Saxena, Saurabh Sonwani and Umesh Chandra Kulshrestha Productivity of Major Crops Worldwide: Reviewing Food Safety and Security Neelofar Mirza, Amit Kumar Singh and Dhammaprakash Pandhari Wankhede Plant Growth Regulators, Plant Adaptability and Plant Productivity: A Review on Abscisic Acid (ABA) Signaling in Plants Under Emerging Environmental Stresses Prasann Kumar, Bansh Narayan Singh and Padmanabhh Dwivedi Global Climate Change and Mung Bean Production: A Roadmap towards Future Sustainable Agriculture Moushree Sarkar, Sambit Datta and Sabyasachi Kundagrami


1

19

61

81

99

vi Chapter 6

Chapter 7

Chapter 8

Chapter 9

Chapter 10

Contents Impact of Seedling Diversity and Their Survival Strategy in Modern Day Agro - Forestry Services Parasuram Kamilya and Ayan Das Management of Stem Rot of Jute Using Plant Growth Promoting Rhizobacteria (PGPR) and Plant Growth Promoting Fungi (PGPF) Consortium: A Step towards Integrated Disease Management in Modern Agriculture S. K. Bhattacharyya and Chandan Sengupta

121

177

Impact of Rising Carbon Dioxide (CO2) on Plant Health and Efficacy: An Insight to Cell Metabolism Pratika Singh and Amrita Srivastava

195

Toxicological Study of Organo- Phospohorous Pesticide and Proposed Detoxification Methodology Md Shabbir, Samar K. Saha and Mukesh Singh

211

Food Security in the Changing Environment: Challenges and Solutions Divya Pandey and Abhijit Sarkar

221

Index

237


PREFACE Following the late twentieth century, changes in environment propel profound challenges towards agricultural production, food security and development worldwide. Negative impacts from changing environment are major issues especially in those regions that are currently food insecure and / or might have made progress in reducing food insecurity over the past years. Scientists along with policy makers are continuously developing strategies to adapt to addressing environmental change adaptations, and are providing assistance to farmers and common people to implement appropriate riskreduction measures. Adaptation in the agricultural sectors have always been given high priority because of the inherent sensitivity of food production towards environmental fluctuations, and their inter-connected relations with economic growth and development. This book volume analyses linkages between agriculture and environmental changes, major challenges and potential solutions to secure food security. We have tried to organize and articulate such works / views / opinions together which collectively might pave a roadmap towards a sustainable future. Chapter 01 entitled Aquatic Bioresources: Utilization of Diversified Species, Products & Services for Strengthening Alternative Agriculture in Rural India by P. K. Mukhopadhyay and R. N. Mandal mainly focused on the rich diversity of aquatic bioresources which includes several economically useful plant and animal resources. Besides benefiting us through generous supply of food, fodder, vital bio-active components, recreational support, thatching materials, scope of new raw materials, these also provide multiple ecological functions. These resources form the foundation on which the gene pool of species stock. Floral group comprises wide range of organisms starting from micro-algae to different higher plants of diverse families like- Nymphaeceae,


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Divya Pandey and Abhijit Sarkar

Hydrocharitaceae-(major submerged flora), Convolvulaceae, Azollaceae, Lemnaceae, Trapaceae, Papillionaceae; and the faunal group starts from zooplankton to rich ichthyofaunal diversity, crustaceans, molluscs, amphibians and so on. Some of the valuable bio-resources are fulfilling the essential requirements of the societal needs in the hundreds of religious rites and festivals in the region. It is essential, therefore that proper scientific management strategy should be drawn based on long term planning so as to harness the potentiality of such priceless bioresources in providing micronutrient nourishment, stable livelihood support, buffering the emerging threats due to impact of climate change in the particular environment, conservation of precious biodiversity to balance the two extremes-utilization and conservation for significant social benefit. Chapter 02 entitled Impact of Tropospheric Ozone and Particulate Matter on Plant Health by Pallavi Saxena et al. focused on two major air pollutants tropospheric ozone and particulate matter, and their effects on agricultural production in developing countries which largely cover the tropical belt. Tropospheric ozone is a major phytotoxic agent because of its reactive nature and that it can actively participate in the mechanism of reactive oxygen species formation. There are strong evidences that indicate ozone as perhaps the biggest air pollution threat to food production. Atmospheric particulate matter is a key indicator of air pollution. It is injected into the air by a variety of natural and anthropogenic sources. Alkaline dust may cause leaf surface injuries. Deposition of such particulate matter may affect rhizosphere which provides more probable route for metabolic uptake of nutrients and impact on vegetation and ecosystem. Chapter 03 entitled Productivity of Major Crops Worldwide: Reviewing Food Safety and Security by Neelofar Mirza et al. on elevation of atmospheric carbon dioxide concentration, and its effect on crop yields. Atmospheric CO2 level has greatly increased since the advent of the industrial revolution, largely due to the fossil-fuel combustion, increased emission of greenhouse gases (GHGs) such as e.g., carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and changes in land management. The atmospheric concentration of CO2 has increased to more than 400 ppm as compared to 280 ppm in pre-industrial era. Elevated atmospheric CO2 (e[CO2]) will promote growth of plants through fertilization effect and enhanced photosynthesis. Given the complexity of the subject, it is difficult to cover effects of elevated CO2 on all the aspects of plant function. Chapter 04 entitled Plant Growth Regulators, Plant Adaptability and Plant Productivity: A Review on Abscisic Acid (ABA) Signaling in Plants Under


Preface

ix

Emerging Environmental Stresses by Prasann Kumar et al. focused on plant health and responses under different stresses and how they can be controlled with the use of plant growth regulators, especially abscisic acid (ABA). Our improving understandings of plant hormones also increase the chances that plants can be genetically modified to enhance their tolerance towards diverse environmental stresses. Here, authors have presented an overview of abscisic acid, and how it can provide a possible strategy to increase plant adaptability to future climate change. Chapter 05 entitled Global Climate Change and Mung Bean Production: A Roadmap towards Future Sustainable Agriculture by Moushree Sarkar et al. portray effects of climate change on mung bean production. Mungbean is an important legume crop in terms of both food value and its beneficial role in biological nitrogen fixation and soil fertility. It is primarily cultivated in the developing nations of Asia, especially India, Pakistan, China, Myanmar, and Bangladesh. Its importance in food security globally is unconditionally important as it provides essential dietary protein, carbohydrate, vitamins, and minerals, cheaply to the poorest of the poor. Already the effects of global warming are evident in many parts of the world, which has reduced agricultural outputs especially in the economically backward nations. Severe droughts, flash floods due to unseasonal rainfall, salinization of arable lands have negated agricultural productivity. Here authors presented the effects of climate variables on mungbean cultivation, especially at quantitative and qualitative production level. Chapter 06 entitled Impact of Seedling Diversity and Their Survival Strategy in Modern Day Agro - Forestry Services by Parasuram Kamilya and Ayan Das focused on the diversity and survival strategy of forest seedlings. According to authors, a range of diversity is found among the seedlings of monocot and dicot species. Apart from the number of cotyledon, some other typical juvenile features vary significantly among them. Coleoptile is the tubular elongation of the cotyledonary sheath. A conspicuous collar is observed in almost all monocot seedlings, which is the transitional zone between hypocotyl and primary root. Whorls of trichomes or rhizoids are found to develop from the collar in some species. Typically branched primary root system is found in many species, which is supposed to be an ancestral condition. A derived condition of lacking the primary root system is observed in four families (Eriocaulaceae, Lemnaceae, Poaceae, Zosteraceae) of Liliopsida. The upper part of the cotyledon is a storage organ and photosynthetic in nature. The seeds of monocots lack endosperm, and the reserve is stored in the embryo or in the


x


cotyledon or hypocotyl during seedling stage. Both epigeal and hypogeal conditions are found among monocots. Also depending on the extension of cotyledonary axis, two types of germination can be found in monocots – adjacent and remote. In case of remote germination, the cotyledon extends profusely promoting development of plumule away from seed, whereas, embryo develops next to seed in adjacent germination. Chapter 07 entitled Management of Stem Rot of Jute Using Plant Growth Promoting Rhizobacteria (PGPR) and Plant Growth Promoting Fungi (PGPF) Consortium: A Step towards Integrated Disease Management in Modern Agriculture by S. K. Bhattyacharya and Chandan Sengupta discuss the major biotic stressors and their probable sustainable management. Plant diseases caused by variety of pathogens pose a serious challenge and economic threats to various agricultural crops all around the world. It has been evidenced that despite wide use of chemical pesticides in crop production, the losses due to pests, viz. insects, diseases, nematodes, rodents is significant. These are the major groups of organisms that live in diverse habitat and continue to threat variety of agricultural crops all around the world. Since early times the major agricultural crops have been plagued by these noxious organisms that fed on various plant parts viz. roots, rhizome, tubers, seedlings, stem, leaves, buds, crowns and damage worth more than 100 billion dollars annually. Stem rot of jute caused by the phyto-pathogenic fungi Macrophomina phaseolina (Tassi) Goid. [syns. M. phaseolina (Maubl.) Ashby] [= Rhizoctonia bataticola (Taub.) Butler] is a major disease occurring in almost all the jute growing areas of the world. In India, particularly in West Bengal, Assam it occurs every year in moderate or severe form, occasionally taking epidemic form based on several parameters. Here authors reviewed some sustainable management procedure using plant growth promoting rhizobacteria (PGPR) and plant growth promoting fungi (PGPF). Chapter 08 entitled Impact of Rising Carbon Dioxide (CO2) on Plant Health and Efficacy: An Insight to Cell Metabolism by Pratika Singh and Amrita Srivastava portrays a better way of understanding the symbiotic and integrated mechanisms associated with plant growth and productivity under the alarming rise in the global atmospheric concentration of greenhouse gases (GHGs) especially carbon dioxide (CO2). Many research efforts have been initiated to understand the response of plants and ecosystems to rising CO2. Plants acknowledge and respond to increasing carbon dioxide concentration CO2 through increased photosynthesis (A) and reduced stomatal conductance (gs).


Preface

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These two fundamental responses help in the derivation of all other effects of increased CO2 on plants and ecosystems. Supplement to being a greenhouse gas, atmospheric carbon dioxide is also the source of carbon for most of the plant species. Its rapid increase is likely to affect the quantity and quality of a number of agriculturally relevant crop species and earthy plant species including those with C3, C4 and crassulacean acid metabolic (CAM) pathways. The lenience of horticultural commodities to CO2 is also restricted. Chapter 09 entitled Toxicological Study of Organo-Phospohorous Pesticide and Proposed Detoxification Method by Md. Shabbir and Mukesh Singh discuss a major issue in modern agriculture, i.e., chemical pesticide and their toxicity. The use of these chemicals have resulted in contamination of all the basic necessities of life, i.e., air, water and food. Among these compounds, Organophoshorous have become most popular and have wide application during cropping seasons and postharvest period. Chlorpyrifos is one of most broad spectrum chlorinated organo-phosphorous insecticide. Chloropyrifos is extensively use in the agricultural field to control various types of pest and insects. But its extreme toxic behaviour on the non-target species of all groups including humans has raised several criticisms. It causes cytotoxicity, genotoxicity, mutagenicity, carcinogenicity, immune-toxicity and physiological disorders. It has potential to persist in environment for long time. Overall it becomes a major problem around the world. Simultaneously, researchers around the globe started working on bioremediation of chloropyrifos looking into the adverse environmental effects. Many countries banned the use of such insecticides. In rural areas of many countries including India, uses of this pesticide are still in practice. Bioremediation is an ecological approach which has several advantages over other remediation. Extensive researches are going on at several research stations in exploiting soil microbes and optimizing bioreactors to degrade chlorpyrifos. Chapter 10 entitled Food Security in the Changing Environment: Challenges and Solutions by Divya Pandey and Abhijit Sarkar focused on the global food security issues under changing environmental variables. Modern agriculture is a pivotal system to human sustenance. As population grows, the food production also must continue to increase, but limited land and water resources do not allow agriculture to expand indefinitely. Moreover, environmental changes like global warming, climate change, land and water contamination and some air pollutants are negatively affecting agricultural productivity. Interestingly, agricultural practices also play important role in environmental degradation. It is a major contributor to anthropogenic greenhouse gas emissions and a significant cause of water pollution. Therefore,


xii


to ensure food security, adaptation of agriculture to environmental changes along with making agriculture optimally resource efficient while reducing its environmental footprints is needed.

Dr. Divya Pandey Research Associate Stockholm Environment Institute at York Environment Building University of York, York, UK Email: [email protected]

Dr. Abhijit Sarkar Assistant Professor Laboratory of Applied Stress Biology Department of Botany University of Gour Banga Dist.: Malda, West Bengal, India Email: [email protected]


In: Sustaining Future Food Security … ISBN: 978-1-53610-279-6 Editors: D. Pandey and A. Sarkar © 2017 Nova Science Publishers, Inc.

Chapter 1

AQUATIC BIORESOURCES: UTILIZATION OF DIVERSIFIED SPECIES, PRODUCTS AND SERVICES FOR STRENGTHENING ALTERNATIVE AGRICULTURE IN RURAL INDIA P. K. Mukhopadhyay and R. N. Mandal Regional Research Centre of ICAR- Central Institute of Freshwater Aquaculture (ICAR – CIFA RRC), Rahara, Kolkata, West Bengal, India

ABSTRACT Aquatic ecosystem possesses rich biodiversity of economically useful plant and animal resources of biological origin. It also benefits us through generous supply of food, fodder vital bio-active components, recreational support and thatching materials. These also provide multiple ecological functions. These resources form the foundation on which the gene pool of species stock and strain are based. Floral group in aquatic system exhibits wide range of organisms starting from micro-algae to different higher plants of diverse families like Nymphaeceae, Hydrocharitaceae-(major submerged flora), Convolvulaceae, Azollaceae, Lemnaceae, Trapaceae, Papillionaceae; and the faunal group starts from zoo-plankton to rich ichthyofaunal diversity, crustaceans, molluscs, amphibians and so on. 

Corresponding author: [email protected]


2

P. K. Mukhopadhyay and R. N. Mandal Given the inadequacy and nutritional deficiency in the diet of the most rural population in India, the role of such aquatic bioresources should be regarded as vital not only for providing nutritional support (especially micronutrient security), but also can provide a scope for gainful employment to those living in the rural regions. Some of the valuable bioresources are fulfilling the essential requirements of societal needs in the hundreds of religious rites and festivals of the region. Of the many ecosystem services provided by these recourses, the maintenance of nutrient flow for the sustainability of aquatic ecosystem as well as their dwellers, needs special mention such as, bioremediation of sewage and other wastewater, contributing to primary productivity in particular and ecosystem services in general. Keeping aside all these, if we just consider only the small indigenous fish species, for example, which are selfrecruiting in nature and continuously provide enormous benefit in terms of nutritional and economic support to farming and to fisher-folk community in particular. It is essential, therefore that proper scientific management strategy be drawn, based on long term planning, so as to harness the potentiality of such priceless bioresources in providing micronutrient nourishment, stable livelihood support, buffering the emerging threats due to impact of climate change on environment, conservation of precious biodiversity to balance the two extremes-utilization and conservation for significant social benefit.

Keywords: ecosystem, aquatic plants, fishes, bioresources, rural development

INTRODUCTION India and especially the state of West Bengal is endowed with vast and varied aquatic resources. Besides streams, rivers and reservoirs, there are ponds, pools & tanks, beels & jheels, canals & karanjalis, deepwater rice aquatic system and many shallow impoundments. These are not just idle water bodies as such, but provide a range of invaluable services like promoting nutritional security, providing a source of uncultivated food and fodder, enabling livelihood and employment opportunities to many people in the vicinity rendering multiple ecological functions (cultural, regulatory, supporting, provisioning) upholding the life support system, recharging groundwater reserve- to mention a few (Mandal and Saha, 2007). With the strong gene pool of varied floral and faunal bio-resources, in the form of amazing species diversity as well as by virtue of having physical resources for farming, viable technology and extension backup, local availability of critical inputs, and innovative capability of our farming communities/resource users in transforming knowledge into productivity, it is


Aquatic Bioresources

3

our onus and responsibility to ensure that with the application of scientific principles focused on sustainable natural resource management overall production, income and nutrition are enhanced and diversified both in terms of quality and quantity This should accompany promotion of climate change adaptation, mitigation and coping without much constraint. These have high relevance in the present context since till now, the farming practices for some unknown reasons have been emphasizing only on a few selected species and overlooking the unique potential of so many others which also need to be appropriately harnessed for our benefit (Yadugiri, 2011). The vast array of natural food organisms for example, plankton, periphyton, nekton, benthos etc. exemplify the richness of aquatic biodiversity. Phytoplankton as the primary producer and constitutes the basis of nutrient cycle of an aquatic ecosystem. Zooplankton are the primary consumers which convert plant biomass into animal tissue and further become food for consumers of higher order in the ecosystem. Advantage of such cycles of nutrient generation system are to be continuously utilized to the fullest for supporting the supply of good quality plant & animal groups and services given the availability of abundant sunlight, favourable temperature during most part of the year. Again, since water is both a receptacle of waste and the vital source for production of human food resources, pragmatic water resource planning also is of value to facilitate sustainable productivity for improving climate-resilient livelihood initiatives (Mandal and Jayasankar, 2014). Our database are still inadequate with regard to the various precious aquatic bioresources, and their optimum potential for host of human benefits including the source of sustenance and stability of nature. There is an urgent need, therefore, to ascertain linkages among the different components of biodiversity, input recycling, existing needs, goals and aspirations including establishment of a sense of community empowerment for resource productivity. This article emphasizes to document the uniqueness and potentiality of some of the aquatic floral and faunal bioresources in the context of better human health and economic prosperity in general and strengthening rural development in the region in particular.

AQUATIC FLORAL BIORESOURCES Our freshwater habitats sustain diverse plant communities starting from microalgae to different higher plants as potential bioresources. Aquatic vegetations directly used as human food resources are many such as water lily,


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P. K. Mukhopadhyay and R. N. Mandal

lotus, makhana, ipomoea, water chestnut etc. There are many other aquatic macrophytes including azolla, duckweeds which can form cattle and fish feed components apart from having their role as organic manure in the farming.

Lotus (Nelumbo nucifera) As an aquatic bioresource, lotus, a rooted floating macrophyte needs special mention. It has substantial societal importance if harnessed appropriately from the economic viewpoint. A great part of our vast water bodies often remain either under-utilized or in weed chocked conditions. Even in such perennial as well as fallow seasonal waters, lotus may be cultivated following a package of practices with defined set of standards. Its rhizomes are long used as food having medicinal values, leaves are used as plates in eateries and the flower itself is in continuous demand from various sources throughout the year (Shen-Miller, 2002; Mandal et al., 2007; Mandal and Bar, 2013).

Water lily (Nymphaea odorata) Water lily (commonly called sapla) is found in several attractive colours like lotus. The long flowering stalk develops directly from the rootstock and bears single flower which opens up during daytime and closes as evening approaches. All part of the flora are preferred as food. It is a common experience that waterbodies where sapla and lotus are grown, form the natural breeding place for some of the prized catfishes like magur and singhi thus providing a support to aquafarming also (Chopra et al., 1986; Mandal and Jayasankar, 2014).

Makhana (Euryale ferox) Makhana, an aquatic herb with floating leaves (with green on top and purple beneath) can be a very good alternative cash crop. This plant needs hardly any attention except that during harvesting (period: June - August) some care and expertise are required. The puff made out of it forms delicious food items and is highly demanded throughout northern India including Bihar and Jharkhand (Mandal et al., 2010)



5

Water chestnut (Trapa bispinosa) Trapa or water chestnut is an annual herb, the kernel of which is both delicious and nutritious. Seedlings generally take three months for flowering followed by fruiting. Though the potential of this cultivable species is recognized but it is yet to be fully explored. The fallow rural ponds can be used for intensive farming as a remunerative venture (Kalita et al., 2007).

Figure 1. Some of the aquatic floral bioresources. A. Flower and other parts of lotus plant (Nelumbo nucifera); B. A boy is carrying a bunch of water lily (Nymphaea odorata); C. Makhana plant (Euryale ferox) [inset – final processed product ready for consumption]; D. Rural people are harvesting Water chestnut (Trapa bispinosa).

Ipomoea (Ipomoea aquatica) Ipomoea is a common perennial aquatic plant which can be propagated by seeds (viable seeds are easily available in market) or stem cutting. First time harvest may take place one month after seed sowing but then it can be done on a weekly basis. Its efficacy as an ideal leafy vegetable component is reflected by its richness in nutritional content and taste (Mandal et al., 2008; Dewanji, 1993; Gopalan et al., 2007).


6


Azolla (Azolla pinnata) Azolla occupies a prominent place for its unique role as bio-fertilizer in both agriculture and aquaculture. Its high atmospheric nitrogen fixing capacity, fast propagation and rapid decomposition rate result in quick release of nitrogen in the field making it an ideal biofertilizer in the farming system. Azolla is a free floating fern in symbiotic association with a cyanobacterium, Anabaena azollae, present in its dorsal leaves. The entire vegetation appears to be a mat floating freely on water surface and grows in varied range of ecological factors. Azolla enriched feed elicits excellent growth response in all the carp species. Nutritive evaluations indicated presence of high crude protein and carotene content (Singh et al., 1967; Gaigher et al., 1984; Kalita et al., 2007; Mandal et al., 2012b).

Figure 2. Azolla (Azolla pinnata) cultivation and its multiple uses. A. Mass cultivation of Azolla [inset – magnified view of Azolla pinnata; B. Azolla as potent biofiertilizer; C. Azolla as cattle feed; D. Azolla as fish feed; E. Azolla can also be used for Sewage Water Treatment.



7

Shola (Aeschynomene aspera) Shola (Aeschynomene aspera), a species of flowering plant in the family Fabaceae,is a aquatic plant of special importance. Seeds are sown in the April which grow up into matured plant within six months and the stems are collected before the waterbody dries up. The outer brown skin is removed to get cortex which has a characteristic lusture, and demanded for its malleability and sponginess. Without the use of any specialised tool (only simple knives are needed), the artisans (generally known as Malakars can create superb handicrafts having aesthetic values. Again despite having high demands, cultivating shola has not generated much interest and people have to depend on sola from wild sources thus the artisans are compelled to adopt other means of livelihood means leaving behind their in born talent due to such uncertainty in supply of raw material (Nguyen et al., 2005; Mandal et al., 2014).

Figure 3. Shola (Aeschynomene aspera) and its uses. A. Shola plant growing at its natural habitat; B. Harvested dried stems of Shola plant; C - E. Different workers are working with Shola; F. Final finished product of Shola.


8


Pati Bet (Schumannianthus dichotomus) The shrub, Schumannianthus dichotomus belonging to the family Marantacea (known commonly as ‘Pati Bet’) grows in the swampy and derelict waterbodies mostly in the northern part of West Bengal (in Coochbehar district mainly). High value export quality handicrafts can be made out of the bark of the mature stem of this plant. Again artisans depend on the wild ones because cultivation is yet to be taken up on a large scale.The ‘sital pati’ is one such widely used household product in the eatern India. If the pati bet can be made available through systematic cultivation, the craftsmanship can also survive with high revenue earning (Chowdhury et al., 2007; Mandal et al., 2014).

Figure 4. Pati Bet (Schumannianthus dichotomus) and its uses. A. Pati Bet plant; B. Harvested dried stems of Pati Bet plant; C. A worker making strips of Pati bet; D. Final finished product made from Pati bet.



9

Similarly other aquatic vegetations (shown in Table 1 & Table 2) are potentially nutritious. Without care and management measures, these can thrive and grow and continue to provide nourishment to rural and urban people alike. These are rich in antioxidants and simultaneously full of important phytochemicals - qualities which can protect the vulnerable ones in particular without any extra effort or expenditure. Table 1 and Table 2 summaries the common leafy vegetables grown naturally without any special effort or systematic culture; some of these are well known for their medicinal properties.

AQUATIC FAUNAL BIORESOURCES Large number of indigenous fish species form the prime aquatic bioresources (plate-2). Production of fish through aquaculture accounts for almost 50% of the total fish production and consumption in the country and is perceived as having the highest potential to meet the growing demand for fish. The bulk of this production is generated through small scale farming. It is estimated that at least 40 million tonne of additional fish will be required by 2030 to maintain the current per capita consumption (Nadeesha, 2002; Aflabuddin and Hasan, 2013).

Figure 5. Diverse aquatic faunal bioresources. A. Rohu fish (Labeo rohita); B. Catla fish (Catla catla); C. Mola carplet (Amblypharyngodon mola); D. Banded gourami (Colisa fasciata); E. Fresh water prawn (Macrobrachium rosenbergii); F. Fresh water crab (Scylla scerrata).


Table 1. Certain aquatic vegetations contributing towards household nutrition & health benefit in rural West Bengal, India Scientific Name

Family

Local Name (in Bengali)

Parts Used

Purpose as Food Item

Current Status

Traditional Use

Medicinal Importance

Ipomoea aquatica

Convolvulaceae

Kalmi

Entire plant

Leafy vegetable

Wild and partially cultivated Wild

for relief of general constipation Remedy for chronic Amoebiosis and blood purification

Leafy vegetable and medicine

Wild

Leafy twig


Wild & non conventional management

Leafy twig


Wild

Use for remedy of anemia, especially female Increase memory function for children Remedy of common skin rashes and maintenance of blood pH

Considered wholesome for females suffering from nervous and general debility. Useful tonic in diseases of skin, leprosy, nerves and blood tonic for improving memory, syphilic skin disease for internally and externally. Tonic for jaundice, dropsy, rheumatism, anasarca and disease of the urinogeneital tract. Tonic useful for asthma, epilepsy, insanity, hoarseness.

Centella asiatica

Apiaceae

Thankuni

Leaves


Hygrophilla auriculata

Acanthaceae

Kulekhara

Leafy twigs

Bacopa monneiri

Scrophulariaceae

Brahmi

Mollugo cerviana

Ficoidacoae

Nalte


Febrifuge, used for promoting the flow of lochial discharges and as cure for gonorrhea.

Scientific Name

Family

Local Name (in Bengali)

Parts Used

Purpose as Food Item

Polygonum plabejum

Polygonaceae

Kharkol

Leafy twig

Leafy vegetable

Enhydra fluctuans

Asteraceae

Gime

Leafy twig

Marsilea minuta

Marsileaceae

Susuni

Foliages

Colocusia esculanta

Araceae

Kachu

Rhizom e& Petiole

Alternanthera sessiles

Asteraceae

Sachi Sak

Entire plant

Current Status

Traditional Use

Medicinal Importance

Wild

Use for remedy of bowel complaints


Wild

Leafy vegetable and medicine Vegetable

Wild

Remedy of skin disease and purification of blood Remedy for insomnia

Given in bowel complaints, dried and powdered taken in internally in pneumonia. Laxative, useful in skin and nervous affection, antibilious, and dedulcent.

Wild & cultivated

Remedy for bowel complaints

Leafy vegetable

Wild

Use for remedy of constipation

Medicinal importance; source: Glossary of Indian medicinal plant by Chopra et al., 1986.


Tonic useful for remedy of insomnia. Petiole juice styptic, stimulant, rubifaceant, and corm juice used in alopecia and in scorpion sting. Not known

Table 2. Nutritional statuses the following wild leafy vegetables Scientific Name Ipomoea aquatica Centella asiatica Hygrophilla auriculata Mollugo cerviana Polygonum plabejum Enhydra fluctuans Marsilea minuta Colocusia esculanta Alternanthera sessiles

Moisture (g) 90.3

Protein (g) 2.9

Fat (g) 0.4

Minerals (g) 2.1

Fiber (g) 1.2

Carbohydrate (g) 3.1

Energy (Kcal) 28

Ca (g) 110

P (g) 46

92.7

0.9

0.3

1.3

2.1

87.2

3.0

0.4

2.8

1.4

5.2

36

330

21

91.7

2.4

0.4

1.0

2.2

2.3

22

370

67

83.2

3.2

0.7

3.9

2.1

6.9

46

194

48

94.1

1.2

0.25

1.0

1.4

86.9

3.7

1.4

2.1

1.3

4.6

46

53

91

82.7

3.9

1.5

2.2

2.9

6.8

56

227

82

77.4

5.0

0.7

2.5

2.8

11.6

73

510

60

Fe (g) 3.9

Carotene (μg) 1980

Riboflavin (mg) 0.13

Vitamin C (mg) 37

10.0

10278

0.26

12

16.7

1926

0.14

17

12.3

Source: Nutritive value of Indian foods by Gopalan et al., 1987.



13

Fish has uncomparable nutritional merit over all other animal meat and its uniqueness is due to its excellent protein make-up (high proportion (65 – 70% ) of myofibrillar protein (low proportion (5 – 6%) of stroma protein). Its chemical score is 70 and PER is about 3.5; it is also rich in long chain n-3 PUFAs like EPA (20 : 5 n-3) & DHA (22:6n-3) so effective in raising HDL (protective type of lipoprotein) and confer greatest health benefit. The selected micronutrient contents in some small fishes are depicted in plate-8, The fatty acid profile of Labeo bata is indicated in the chromatogram here showing nutritional richness in terms of long chain n-3 fatty acids. There is a large amount of scientific literature on the merits of eating fish on human health such as supply of animal protein with high biological value, reduction of cardiovascular ailments due to polyunsaturated fatty acids of n-3 series, supply of vital cyanocobalamine, mineral elements like - Fe,Ca, P, Zn, iodine, selenium & K. It is also now known that one can tailor farmed fish quality through application of nutritional principles. Even in a semi-intensive system, it is possible to modify the long chain n-3 PUFA for better human health and nutrition. Plate-9 summarises the power of fish in terms of contributing towards human health and nutrition (Nandi et al., 2012).

Figure 6. Chromatogram of fatty acid profile of fillet of Bata fish (Labeo bata). Arrows show major fatty acid fractions with RT values (Source: Nandi et al., 2012).


14


Besides fin fishes, edible crustaceans including prawns and crabs, molluscs like mussels, snails also form unique resources. The mussel species of the genus Lamellidens are found in freshwater ponds and tanks (Plate-6) Generally slightly alkaline water is conducive for its growth and survival. Freeshwater pearl culture still remains an unexplored area despite having vast freshwater resources and abundant natural stock of freshwater mussels. Besides freshwater mussels are in great demand because of their use in shell button industry, handicrafts and lime production in particular. Moreover their role in maintaining the waterbody as a natural cleaner is a boon for the fish farmers. Plate-7 shows the available water resources in the country. The streams, beels, and similar wetlands are rich source of fascinating varieties of freshwater ornamental fishes which also contribute to the aesthetic requirement and deserve to be commercialized rather than looking for the imported species for no valid reason (Nandeesha, 2002, Nandi et al., 2012).

DUCKWEEDS IN THE BIOREMEDIATION OF DOMESTIC SEWAGE Certain aquatic macrophytes have been found to be extremely useful in bioremediation processes of waste effluents like domestic sewage. An aquaculture sewage treatment plant comprising duckweeds (Spirodela polyrrhiza; Lemna minor; Wolffia arrhiza) can significantly reduce the BOD & COD levels of sewage effluents (plate-5) transforming it fit for use in fish culture. Such wastewater based aquaculture system will have immense relevance in the foreseeable future especially in regions where water shortages are imminent. All these autotrophic aquatic vegetations as well as some others like the green manure, Sesbania roxburghii can be considered as potential support to the rural economy and therefore need conservation through better understanding of the sustainable provision of ecosystem goods and services.

CONCLUSION Fisheries and its management in general has a major role to play in providing basis for better human health. The sector provides livelihood support to over 14 million people through the chain of seed production, grow-out fish



15

culture, fish harvesting, input supply, trading, marketing as well as processing. It is important therefore that available waterbodies under all panchayets /talukas be utilized for production of edible aquatic organic food. Further, if possible social aquaculture in the line of social forestry be introduced wherever possible utilizing the small indigenous fish species. This may serve the dual purpose of conservation of these species, some of which are becoming endangered, as well as production of cheap and best edible animal product for better human health. In the name of bringing more area for large fish like major carp culture, natural habitats of a wide range of indigenous small fishes and prawns are being encroached. These species of small fishes used to contribute significantly towards rural household food basket. Such management strategy seems to have a negative nutritional impact on household nutrition and poverty alleviation. Only a few years ago these were readily available in fairly good quantity. The scenario is not the same today with the introduction of culture practices of major carps that advocate eradication of smaller fishes mostly in rural Bengal where micronutrient deficiency is now a common sight among school children and womenfolk. On one side we claim to be the connoisseurs of fish and grow most of the fishes in the country and the other side under-nourishment among school children is among the highest in the country. Such nutritional deficiencies might cause enormous national loss and need to addressed before it is too late. Micronutrient deficiencies impair cognitive development and impair immunity as well as increases susceptibility towards infection, While fortification of food items of daily diet may be a recommended intervention strategy, but food base approach at increasing micronutrient status by increasing fish availability is a very simple and sustainable approach of prevention given the vast water resource availability much of which still remains unexplored.

REFERENCES Aftabuddin, M and Hassan, M A (2013) Nutrient enrichment potential of floating aquatic macrophyte Eichornia crassipes. J Inland Fisheries Society of India 45(2) 8-13. Chopra, R. N., Nayar, S. L and Chopra, I. C. 1986. Glossary of Indian Medicinal Plants, Publication and Information Directorate, CSIR, New Delhi-12. Chowdhury, M. S. H.; Uddin, M. S., Haque, F., Muhammed, N. and Koike, M. (2007) Indigenous management of Patipata (Schumannianthus dichotomus (Roxb.) plantation in the rural homesteads of Bangladesh. Journal of Subtropical Agricultural Research and Development 5(1) 202 – 207.


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Dewanji, A. 1993. Amino Acid Composition of Leaf Proteins Extracted from Some Aquatic Weeds. J. Agric. Food chem. 41: 1232-1236. Gaigher, I. G., Porath, D and Granath, G. 1984. Evaluation of duckweed (Lemna perpusilla and Spirodella polyrhiza) as feed for Nile tilapia (Oreochromis niloticus x Oreochromis aureus) in recirculating unit. Aquaculture. 41: 235244. Gopalan G., Rama Shatri, B. V and Balasubramanian, S. C., 2007. Nutritive Value of Indian Foods. Revised and updated by Rao, B. S. N., Deosthale, Y. G and Pant K. C., National Institute of Nutrition, ICMR, Hyderabad, India. Gopalan G., Rama Shatri, B. V and Balasubramanian, S. C., 2007. Nutritive Value of Indian Foods. Revised and updated by Rao, B. S. N., Deosthale, Y. G and Pant K. C., National Institute of Nutrition, ICMR, Hyderabad, India. Kalita, P, Mukhopadhyay, P K & Mukherjee, A K (2007) Evaluation of nutritional quality of four unexplored aquatic weeds of north-east India for cost effective fish feed formulations. Food Chemistry 103 : 204-209. Mandal, R N, Chattopadhyay, D N & Mukhopadhyay, P K (2012) Potential of aquatic plant bioresources. Water Garden Journal 27 : 12-19. Mandal, R N. Pandey, B K, Chattopadhyay, D N & Mukhopadhyay, P K (2012) Azolla- an aquatic fern of significance to small scal aquaculture Aquaculture Asia 17(1) 11-15. Mandal, R N, Saha, G S, Kalita, P & Mukhopadhyay, P K (2008) Ipomoea aquatica- an aquaculture friendly macrophyte. Aquaculture Asia 13 (2) 1213. Mandal, R. N and Saha, G. S. 2007. Aquatic vegetation – A potential support for rural economy. Agricultural Situation in India. LXIV: 251-255. Mandal, R. N. And Bar, R. (2013) The Sacred Lotus: An Incredible Wealth of Wetlands. Resonance 1 – 7. Mandal, R. N. And Jayasankar, P. (2014) Aquatic Weeds as Potential Future Foods. In ‘Future Crops’ (vol 2), Eds. Peter, K. V., Daya Publishing House, New Delhi, India. pp. 17 – 50. Mandal, R. N., Bar, R. and Chakraborty, P. P. (2014) ‘Pati bet’, Schumannianthus dichotomus (Roxb.) Gagnep. – A raw material for preparation of livelihood supporting handicrafts. Indian Journal of Natural Products and Resorces 5(4) 365 – 370. Mandal, R. N., Bar, R. and Chattopadhaya, D. N. (2014) Shola, Aeschynomene aspera L. used for making indigenous handicrafts revealing traditional art



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needs conservation. Indian Journal of Traditional Knowledge. 13 (1), 103110. Mandal, R. N., Saha, G. S and Mukhopadhaya, P. K. 2007. Lotus – an aquatic plant of versatile qualities. Aquaculture Asia. X11 (1): 11-13. Mandal, R. N., Saha, G. S. And Sarangi, N. (2010) Harvest and processing of Makhana (Euryale ferox Salisb.) – An unique assemblage of Traditional Knowledge. Indian Journal of Traditional Knowledge 9 (4) 684-688. Nandeesha, M C (2002) Diversity enhances profitability and sustainability Aquaculture Asia 7(2) :53-56. Nandi, S Majumder, S and Saikia, S K (2012) Small freshwater fish species (SFF) culture: issues from nutrient security, carp-SSF integration and feeding ecology. Reviews in Fish Biology and Fisheries Doi 10 1007/s 11160-012-9294-2. Nguyen TV, Nguyen KH & Vu XP, Checklist of plant species in Vietnam, (Agriculture Publishing House, Hanoi), 2005. Shen-Miller, J. 2002. Sacred lotus, the long-living fruits of China Antique. Seed Science. 12: 131-143. Singh, S. B., Pillai, K. K and Chakraborty, P. C. 1967. Observation on the efficacy of grass carp in controlling and utilizing aquatic weeds in ponds in India. Proc. Indo-Pacific Fish Counc. 12 (2): 220-235. Yadugiri, V. T. 2011. M. S. Swaminathan, Current Science, 101(8): 996-1002.




Chapter 2

IMPACT OF TROPOSPHERIC OZONE AND PARTICULATE MATTER ON PLANT HEALTH Pallavi Saxena, Saurabh Sonwani and Umesh Chandra Kulshrestha School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India

ABSTRACT Air pollution is a widely known problem which can have significant effects on plant health. In this regard, pollutants such as air particulates, ozone, nitrogen oxides, sulphur dioxides have a negative impact on plant physiology and morphology. Recently, it has been noticed that most of the plant species are affected by tropospheric ozone and particulate matter, especially in developing countries which largely cover the tropical belt. Tropospheric ozone is a major phytotoxic agent because of its reactive nature and that it can actively participate in the mechanism of reactive oxygen species formation. There is strong evidence that indicates ozone as perhaps the biggest air pollution threat to food production. The atmospheric particulate matter is a key indicator of air pollution. It is injected into the air by a variety of natural and anthropogenic sources. Alkaline dust may cause leaf surface injuries. Deposition of such PM may affect rhizosphere which provides more probable route for metabolic uptake of nutrients and impact on vegetation and





20

Pallavi Saxena, Saurabh Sonwani and Umesh Chandra Kulshrestha

ecosystem. Since interactions of particulate matter with other pollutants and with the climate change components is an important area for research for the further understanding of ecosystem sustainability. The present chapter discusses the effects of these important pollutants on plants.

Keywords: tropospheric ozone, particulate matter, plant health, phytotoxicity, food security

INTRODUCTION In urban areas, an increase in industrialization, growing in the vehicular fleet, population growth, and unplanned development are the important reasons behind the increase in the air pollution levels (Jayanthi and Krishnamoorthy, 2006). Substantial scientific interest has been developed linking health of living beings (plants and animals) to air pollution in the world. Air pollutants such as particulate matter (PM), ozone, persistent organic pollutants (POPs) are of great concern to human society. According to World Health Organization (WHO), air pollution due to particulate matter contributes to approximately 800,000 premature deaths each year, ranking it the 13th leading cause of global mortality. Various studies on exposure assessment of several pollutants were carried out in the developing world (Saxena and Ghosh, 2015; Garg et al., 2015, Saxena and Ghosh, 2013; Han and Naeher, 2006; Agrawal et al., 2003; Oliva and Mingorance, 2006) and it has been recognized that both outdoor and indoor pollutants are associated with acute adverse effects on health of human and plants (Dwivedi et al., 2008; Lebowitz, 1995; Tripathi et al., 2008). Air pollution can directly affect plants via entering through leaves or indirectly via soil acidification. When exposed to air-borne pollutants, most plants experience physiological changes before exhibiting visible damage to leaves (Liu and Ding, 2008). The effects observed through plants are a time-averaged result that is more reliable than the one obtained from the direct determination of pollutant in the air over a short period. A huge number of plants have been recognized and used as dust filter to check the increasing pollution levels of urban dust. (Rai et al., 2010). A number of workers have reported air pollution effects on plant morphology (Ninoval et al., 1983; Bhatti and Iqbal, 1988; Anbazhagam et al., 1989; Jahan and Iqbal, 1992; Ali, 1993; Chronopoulos et al., 1996; Preeti, 2000; Stevovic et al., 2010). The effects of pollution on the morphology of plants are quite diverse and depends on the component of the pollutants and plant type.


Impact of Tropospheric Ozone and Particulate Matter on Plant Health

21

Ninoval et al. (1983) in their study on London planetree (Platanus acerifolia) showed changes in leaf morphology of plants as a result of the adjustment to atmospheric pollution. One of the premier study on air pollution which has been reported by Sodnik et al. (1987) demonstrated the reduction in the size of leaf blade of five tree species growing in the area of thick dust and SO2 pollution. Stevovic et al. (2010) found that Tansy (Tanacetum vulgare) plant leaves from the polluted site were significantly thinner as compared to the clean site. Significant reduction in length, breadth, area of leaves and length of petiole of the plants growing in a polluted area has also been reported (Iqbal, 1985, Jahan and Iqbal, 1992). While plants improve the air quality to some extent, air pollution may adversely influence the plant life and can reduce yields of crops, vegetables and fruits substantially. Several authors found that many pollutants such as ozone may cause serious damage to the DNA, proteins, and lipids by raising the level of reactive oxygen species (ROS) after it’s entry to plant tissues through stomata (Jaleel et al., 2007; Kuźniak and Urbanek, 2000). To control the air pollution, first of all, we need to monitor Physico-chemical parameters of air followed by biochemical analysis of plants and reanalysis of physicochemical parameters of air with method validation steps. Out of these methods, the biological approach can be inexpensive for extended surveys of air quality with the effects of several environmental factors (Yu-mei et al., 2005; Fernández et al., 2007). Any oxidation stress of the plant is produced by plant cells which have several antioxidative defence mechanisms such as tocopherol, carotenoids, glutathione and glutathione reductase enzymes, superoxide dismutase, catalase, ascorbate peroxidase, polyphenol oxidase to protect plants (Kangasjarvi et al., 1994; Pell et al., 1997; Dat et al., 2000; Mittler et al., 1999). However, the activation of antioxidative defense mechanisms requires high consumption of energy which may consequently inhibit the plant's growth (Ghorbanli et al., 2007). Considering all these aspects the present chapter discusses the effects of tropospheric ozone and particulate matter on plant health and yields.

TROPOSPHERIC OZONE Ozone is found both in the troposphere as well as in the stratosphere. The stratospheric ozone layer is naturally occurring jacket of ozone molecules while most of the tropospheric ozone is formed via manmade sources (Aneja et al., 2000). Stratospheric ozone is helpful in protecting biosphere, but the tropospheric ozone is harmful to the plants and human health (Aneja et al.,


22


1991). Ozone is heavier than air it is brought down from the stratosphere by vertical winds produced during electrical storms (Kasibhatla, 1993). However, the tropospheric ozone is produced when sunlight reacts with nitrogen oxides and hydrocarbons emitted by the combustion of coal or petroleum fuels (Finlayson-Pitts and Pitts, 1997). Ozone levels can be relatively constant throughout the day and night (Seinfeld and Pandis, 1998). Tropospheric ozone is of universal curiosity as when oxidant levels in the air are high at that particular time range the most of the air is ozone ( >90%). These levels are usually at their highest point in the afternoon and are relatively low at night (Atkinson, 2000). Plants are another major source of VOCs. Due to different weather conditions NOx and VOCs both easily transported to long distance and react to form ozone in the atmosphere, where it can persist for many weeks. Ambient concentrations of ozone are maximum during calm, sunny, spring and summer days when primary pollutants from urban areas are present. Rural areas have high ozone level as compared to the urban areas, while at high altitude the main source of OH∙ (the major tropospheric oxidant) and as well as its action as a greenhouse gas. Consecutive age group of models has been developed over the past decades to recognize the aspects controlling tropospheric ozone and to prepare emission control strategies (NRC, 1991). These models have still an only limited success in reproducing observed concentrations of ozone and its precursors (HOx, NOx, hydrocarbons). Uncertainties in the emission inventories, transport, and chemical mechanisms may all contribute to the model deficiencies. There is an indirect effect of wet deposition on ozone and rather marginal, involving mostly the scavenging of HNO3 and H2O2 which are pool for NOx and HOx. According to Giorgi and Chameides (1985), a simple rainout parameterization for HNO3 and H2O2 is enough to explain wet deposition in ozone models. Lawrence and Crutzen (1998) have recommended that Cirrus precipitation could be a significant sink of HNO3 in the upper troposphere.

Gas-Phase Chemistry of Tropospheric Ozone Figure 1 is a diagram of gas-phase ozone chemistry in the troposphere highlighting the union between the cycles of O3, HOx, and NOx. Ozone is transported from the stratosphere to troposphere via stratosphere-Troposphere exchange (S-T exchange). Dry deposition removes it on to the surfaces. A fraction is consumed in a chemical reaction within the troposphere. For budgeting purpose, one has to calculate the chemical production and loss of



23

ozone with all precautions to reduce uncertainty especially in the troposphere (Wang et al., 1998c; Hauglustaine et al., 1998).

Ozone as Phytotoxic Agent Ozone was first described to have toxic effects on plants in the form of foliar injury and suppressed growth in grape (Vitus sp.) (Richards et al., 1958). Researchers have found that ambient ozone concentrations significantly reduces the yields of susceptible crops, that leads to significant crop loss, and many countries can further have adverse economic implications (Fiscus et al., 2005; U.S. EPA, 2006; Wang and Mauzerall, 2004)

Figure 1. A schematic diagram of the sources and sinks of ozone in the troposphere.

Damaging effect ozone may be the highest during afternoon period when its ambient concentration are high (Kulshreshtha et al., 1996, Long and Naidu, 2002). Ozone initiates toxicity in plants mainly via uptake by the foliage (Runeckles, 1992). Once it entered a leaf through open stomata, it gets dissolved into the aqueous phase of the cell wall (Laisk et al., 1989). It can react with apoplastic and symplastic components of the cell (Runeckles and Chevone,


24


1992; Pryor and Church, 1991; Fiscus et al., 2005; Fuhrer and Booker, 2003; Long and Naidu, 2002). In the apoplast, ozone reacts with water, ascorbic acid (AA), phenolics, transition metals, and thiols to form reactive oxygen species (ROS) (Long and Naidu, 2002). The ROS are thought to include superoxide, singlet oxygen, hydroxyl radicals, and hydrogen peroxide (Heath, 1987). Studies reported that in addition to being toxic, ozone-derived ROS interact with signaling pathways that control plant stress reactions, together with programmed cell death (Sandermann, 1998; Schraudner et al., 1998; Wohlgemuth et al., 2002; Overmyer et al., 2003; Kangasjarvi et al., 2005). It is assumed that the ROS formed directly from ozone or indirectly by promoting plant-derived oxidative bursts are not detoxified within the extracellular space, but such ROS can initiate reactions that lead to damage (Sandermann, 1998; Rao et al., 2000; Overmyer et al., 2003; Kangasjarvi et al., 2005). The introduction of ozone is responsible for the harm of ion regulation, promote stress ethylene formation, stimulate antioxidant and phenylpropanoid metabolism, and eventually suppress carboxylation activity and carbon assimilation (Heath, 1987; Guidi et al., 2001; Runeckles and Chevone, 1992; Fuhrer and Booker, 2003; Fiscus et al., 2005 Pell et al., 1997). Ascorbic acid (AA) in most of the cases reported such compounds localized in the apoplast are potential scavengers of ROS that could attenuate ozone injury (Conklin and Barth, 2004; Plo¨chl et al., 2000; Chen and Gallie, 2005). After synthesizing ascorbic acid into the cell, it is transported to the apoplast of the leaf. Several authors suggested that ascorbic acid plays a crucial role in the several cell wall processes (Smirnoff, 2000; Smirnoff et al., 2001). According to Chameides (1989), ascorbic acid scavenges ROS and reacts to ozone to reduce the chance of damage caused by ozone whereas, It also serves as a substrate in enzymatic reactions that scavenge ROS (Chen and Gallie, 2005; Fiscus et al., 2005; Polle et al., 1990). Ascorbate biosynthesis and transport have been implicated in cell wall biosynthesis and signaling (Conklin and Barth, 2004). Several studies also suggested that apoplastic ascorbic acid is oxidized during ozone exposures, resulting in the production of dehydroascorbic acid (DHA), which is then transported back into the cytoplasm where it is reduced again to AA by coupled reactions involving DHA reductase and reduced glutathione (Luwe et al., 1993; Noctor and Foyer, 1998; Horemans et al., 2000). Apoplastic AA concentration and redox status change in response to ozone in some plants, suggesting that extracellular AA may be involved in ozone detoxification processes (Luwe and Heber, 1995; Castillo and Greppin, 1988; Conklin and Barth, 2004; Burkey and Eason, 2002). Sensitivity to ozone among



25

genotypes of snap bean (Phaseolus vulgaris L.) (Burkey, 1999; Burkey et al., 2003; Burkey and Eason, 2002) and Plantago major (Zheng et al., 2000) is correlated with concentrations of extracellular AA. Arabidopsis thaliana mutants with low foliar concentrations of AA (vtc1) exhibit hypersensitivity to ozone (Conklin and Barth, 2004). Transgenic tobacco (Nicotiana tabacum L.) plants with altered expression of DHA reductase exhibited changes in leaf AA concentrations that positively correlated with their tolerance to ozone (Chen and Gallie, 2005). However, the efficacy of AA in protecting plants against ozone injury has been questioned in some studies because apoplastic concentrations are insufficient for effective detoxification of ROS (Turcsanyi et al., 2000; Luwe et al., 1993). Also, the differential ozone sensitivity of NC-S and NC-R clover (Trifolium repens L.) clones was not correlated with apoplastic AA concentrations (D’Haese et al., 2005). Therefore, there are some unresolved issues regarding some mechanisms involved in a relation with ozone with plant health.

(Source: Gills and Tuteja, 2011). Figure 2. Mechanism of ozone entry into plant cells.


26


Characterization of Ozone Exposure In order to relate ozone exposure to its effects, it is necessary to summarize concentrations averaged over 1-hour intervals in a biologically meaningful way (Aamlid et al., 2000). In principle, the exposure index must be based on the concept of effective dose (Alscher and Amthor, 1988), i.e., it must capture the characteristics of exposure that most directly relate to the amount of ozone that is absorbed by vegetation. Uptake of ozone could be estimated by multiplying the concentration near the leaf surface by the leaf conductance for ozone, and the absorbed dose would then be the integral of the rate of uptake (flux) over time (Bassin et al., 2007). This concept could be expanded to take into account the conductivity of the atmosphere (Feng et al., 2008a). In situations with sufficient air mixing (high air conductivity), the diurnal pattern of ozone flux is determined by leaf conductance and ozone concentration. This is the case in open-top exposure chambers. Owing to the lack of leaf conductance data, the use of radiation as a surrogate for leaf conductance has been suggested in crops (Forster et al., 2007), and the most simple approach is to use ozone concentrations measured during daylight hours (e.g., > 50 W/m2 global radiation) to characterize exposure. For species with substantial leaf conductance at night, however, no such discrimination should be made. Other factors, e.g., air humidity, soil water availability, and temperature, are also known to influence leaf conductance, but to date, these factors have not been used to characterize ozone uptake or dose in long-term experiments. Long-term exposure to ozone can lead to growth and yield reduction. Hence the most suitable exposure indices to be related to long-term effects are cumulative, i.e., they integrate exposure over time. Long-term effects means that the arithmetic mean over the growing season of the daily mean concentrations during a specific 7-hour period (usually 09.00–16.00 hours). The use of a mean concentration over a given period implicitly gives equal weight to all concentrations. However, experimental exposure–response studies with ozone suggest that this is not appropriate and that it is the intermittent exposure to higher concentrations that is most important in causing long-term effects (Heagle et al., 1999). This can be explained physiologically by the capacity of the plant to detoxify ozone and other oxidants; it is only when the concentration or flux of ozone exceeds this capacity that adverse effects result. In order to calculate the cumulative exposure index, the positive differences between the actual hourly mean concentration and the threshold concentration are then summed for the exposure period of interest (Karlsson et al., 2003).



27

This concept was adopted by the United Nations Economic Commission for Europe workshop at Egham in 1992 when a threshold concentration of 40 ppb was tentatively suggested (UNECE, 2010). This exposure index has been called the AOT40, i.e., accumulated ozone exposure above a threshold concentration of 40 ppb, expressed in units of ppb/hour or ppm/hour. Statistical examination of yield data from European open-top chamber experiments has demonstrated that the use of this threshold provides better linear fits to exposure–response data than the use of higher thresholds (2005). A linear exposure–response association presented a good statistical foundation to explain severe levels resultant to a particular outcome than do other types of exposure–response relationship (Utriainen and Holopainen, 2001). The use of 40 ppb as the threshold has been favoured over lower threshold concentrations. Though, the option of this threshold does not mean that the concentrations below 40 ppb have no effect (Paoletti et al., 2010). Hence, the threshold level is not for threshold effects but acts as a cut-off concentration. Due to the rise in the quantity of background ozone with rising elevation, the use of a cut-off level of 40 ppb may not be appropriate for higher altitude. The index would be calculated with concentrations during daylight hours only (i.e., hours with a potential worldwide radiation equal to or larger than 50 W/m2) because only small rates of ozone deposition have been determined over crops and forests during night time (Lefohn et al., 1997). However, it should be noted that in wellmixed fumigation chambers, substantial ozone in trees can occur (see below). Based on a typical exposure duration, the AOT40 is calculated for crops over three months (e.g., May–July) and for forest trees over six months (April– September).

Ozone Deposition Mechanism Ozone deposition comprises several processes that can be described at different scales of resolution (Jonson et al., 2006). One scale focuses on atmospheric processes above the plant canopy, which are governed by wind turbulence and the roughness of the terrestrial landscape, including altitude and type of vegetation. The second scale, very much used in ozone dose–response studies, concerns the individual leaf; ozone is deposited to vegetation canopies through uptake by leaves, mainly through the stomata. Reactions inside the leaf drive the third and finest scale of resolution. In forests, sinks other than the stomata may also play a role in ozone deposition, such as cuticles, bark, litter, soil and canopy air space, where ozone can be scavenged by biogenic


28


hydrocarbons or oxides of nitrogen emitted from organic decomposition in the soil or by the foliage (Grini et al., 2005). The extent of gas exchange via the stomatal pores, i.e., the ozone flux, depends on the total pore area per unit leaf area, i.e., pore density (number of stomata per mm2 of leaf surface times area per pore). In most plants, the pore area comprises 0.5–1.5% of the leaf surface (Islam et al., 2000). The degree of opening of the pores, and thus the stomatal diffusion resistance, depends on the environment and on the interior state of the plant. The most important external factors are light, temperature, humidity, water supply, wind speed and altitude, while the internal factors include the partial pressure of carbon dioxide in the intercellular system, the content of water and ions in the tissues, and plant growth regulators (gibberellic acid and cytokinin promote opening and abscissic acid promotes closing). Ozone uptake by crops in highly turbulent situations is directly related to leaf (stomatal) conductance and follows the diurnal pattern of radiation (Gravano et al., 2004). Under less turbulent situations, however, and especially over low-stature crops (e.g., grassland), the canopy may be decoupled from the atmosphere, and ozone deposition depends primarily on atmospheric transport with little control exerted by the stomata. Because of their structure, forest canopies are strongly coupled to the atmosphere under most conditions, and the flux or deposition of ozone strictly depends on leaf conductance (Fiala et al., 2003). Looking at the uptake, i.e., the absorbed dose, the specific leaf area as a measure of the leafiness of the tree on a dry weight basis (i.e., the area of assimilatory leaf material per unit dry weight) becomes the primary determining factor. Measurements at different altitudes using branch cuvettes on spruce trees revealed that the pattern of ozone deposition velocity differs between high- and low-elevation sites (Duenas et al., 2002; Bartholomay et al., 1997). On an average midday, conductance increases with increasing altitude. Finally, there is evidence from transpiration measurements that some stomatal uptake of ozone may also occur at night in certain coniferous species (Ashmore, 2005). However, because of the lack of a substantial rate of ozone deposition to forests at night in most circumstances, for trees, the calculation of an accumulated exposure (e.g., AOT40) should only consider the daylight hours (as for crops).

Effects of Ozone on Physiology and Biochemistry of Plants Ozone may affect the cellular level through the level of individual organs and plants to the level of plant communities and ecosystems (Bytnerowicz et al.,



29

2007b). After passing through the stomatal pore, ozone can react with organic molecules (e.g., ethylene, isoprene) in the intercellular air space or with components of the extracellular fluid. In both the cases, secondary oxidants (e.g., primary ozonides, hydroxyhydroperoxides) may be formed, which in turn could react with the protein component of the cell membrane (Calatayud et al., 2011). This reaction is prevented to some extent by the presence of radical scavengers, such as ascorbic acid and polyamines (Coyle et al., 2002). Formaldehyde, formate, and acetate accumulate in damaged tissue, possibly as a result of the reaction between ozone and ethylene or between ozone and the phenylpropanoid residues of lignin. There is evidence that ethylene formation determines the sensitivity of plants to ozone (Eckmullner and Sterba, 2000). High levels of ozone cause target cells to collapse, leading to local visible tissue destruction. The effect on the plasma membrane can cause changes in membrane functions that may affect the internal concentrations of ions (e.g., Ca2+) (Larsen et al., 1990). This changes the osmotic potential of the cytoplasm, which in turn can reduce photosynthetic processes in the chloroplasts. Reduction in carbon dioxide fixation by the enzyme ribulosebisphosphate carboxylase is a typical symptom found in leaves exposed to ozone over longer periods of time (Matyssek et al., 2008). Further, inhibition of carbon dioxide assimilation results from direct or indirect inhibition of stomatal opening that reduces uptake (Nali et al., 2002b). Stimulated dark respiration often occurs together with reduced photosynthesis (Oksanen et al., 2004), probably due to increased respiration associated with maintenance and repair (Peterson et al., 1999). The combined effects of reduced assimilation and increased the respiratory loss of carbon dioxide consist of an overall reduction of assimilate production and export from the source leaves. In the leaves of crop species exposed long term, the onset of senescence is advanced and accelerated catalysis leads to the rapid loss of protein and chlorophyll (Repo et al., 2004). As a result of the reduction in leaf duration, the period with the positive net assimilation of carbon dioxide is diminished, and the overall production of assimilates declines. Under conditions of reduced assimilate supply through photosynthesis, allocation of carbon to different organs may be altered, leading to altered growth responses of these organs. Typically, higher priority is given to the shoot about roots and other storage organs (e.g., seeds). This results in reduced root: shoot weight ratios or in a reduction of the ratio between seed yield and total biomass production. In crops, this results in reduced grain or seed yield (Ro-Poulsen et al., 1998).


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Concentrations and Trends of Ozone in the Troposphere According to Marenco et al. (1994), naturally, ozone occurs at low concentrations ranging from 5 to 15 ppb. The earliest ozone measurements were made in the mid-1800s when ozone concentrations were found more than 300 recording stations in separate parts of Europe and the USA. Re-evaluation of Table 1. Approximate percent loss in yields of different crops due increasing ozone concentration in different parts of the world Crop Wheat Rice Winter wheat Wheat Rice Maize Soybean Winter wheat Wheat Rice Maize Soybean Winter wheat Winter wheat Wheat

Maize

Soybean

% Yield loss 6 – 17% 10-14% 34.8-46.7% 13.2-17.6% 5.7-8.3% 2.0-4.0% 4.7-19.1% 52% 9.8-19.0% 3.1-39% 4.7-7.1% 11.4-20.8% 51% >10% 10.4% 5% 9.4% 2-4% 3-5.8% 6.8 4.7% 1.9% 1.7% 2.8-3.0% 10.6% 15.2% 6.2% 3.4-4.3% 0.0-7.0%

Location Different states of India Varanasi, India Lahore, Pakistan India

References Ghude et al., (2014) Rai and Agrawal, (2008) Wahid et al., (1995) Van et al. (2009)

Vietnam China

Van et al. (2008) Van et al. (2009)

China Southern China South Asia East Asia Africa and M.E. North America & Latin America E 25 & East Europe South Asia East Asia Africa and M.E. North America & Latin America EU 25 & E. Europe South Asia East. Asia Africa and M.E. North America & Latin America E 25 & East Europe

Feng et al. (2003) (Chameides et al. 1999) *Avnery et al. (2011) [Reported estimated change in regional relative yield loss (%) (Year 2030 – 2000) under the with A2 scenario of IPCC (35-40 ppmh) according to the M7, M12 and AOT40 metrics and the metric average.]



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daily ozone concentrations over Athens (Greece) during the period from 1901 to1940 provided a mean concentration of about 20 ppb (Varotsos and Cartalis 1991). Several studies on ozone have been reported across the world in term of daily, monthly, annual average (Table 1). As given in the table, ozone potentially affects the percentage production of wheat, rice, soybeans and many other crops.

PARTICULATE MATTER Particulate matter (PM) is a heterogeneous material and a mixture of solid particles and liquid droplets suspended in the air. The abundance of PM varies temporally and spatially and hence, the prediction of regional impacts is tough. The deposition rate of PM to plant surfaces depends on particle size distribution and atmospheric the chemistry both. However, chemical characteristics of PM play a significant role in the impact of PM on plants. PM with aerodynamic diameter < 10 µm diameter (PM10) and < 2.5 µm diameter (PM2.5) are of high significance to public health due to the presence of heavy metals and PAHs (Prajapati and Tripathi, 2008a-c, NEPC, 1998). The particulates can either be directly emitted as primary particles from their sources (construction sites, unpaved roads, fields, smokestacks or fires) or forms in the atmosphere from gas precursors like sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles while secondary particulates form by chemical reactions in the atmosphere. Coarse (PM10) and fine particulate matter (PM2.5) have a number of contrasting properties that affect their impact on vegetated systems since two decades. PMs are having a great matter of concern due to its impacts on ecosystem function and great potential significance for human welfare (Prajapati and Tripathi, 2008a-c; Telesca and Lovallo, 2011, Gupta et al., 2015a,b,c). Many recent studies observed that the concentrations of PM10 and PM2.5 airborne aerosols show a significant relationship with traffic, coal fire power plants and other combustion-related processes (Prajapati and Tripathi, 2007). Whereas, resuspended road dust, crustal material, and longrange transport events are mainly identified as sources of the coarse particles (Park and Kim, 2005; Gupta et al., 2015a,b; Vallius et al., 2005).


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Characteristics of Particulate Matter (PM) Physical as well as chemical characteristics of particulate matter are important while considering its impacts on plants. PM can have direct physical effects like effects of mineral dust on vegetation at relatively high surface load (>seven gm-3) (Farmer, 1993) and indirect effects on ecosystems like particle bound sulphates and nitrates present into the cement dust (Grantz et al., 2003). Krajickova & Mejstrik, (1984) suggested that a particular size of the particle is also important, as the stomata diameter ranges between 8-12 µm for a range of crop. In any study, the chemical effect is much more important than physical effects, as a particle of different origin have different chemistries. Several authors have reported wide verities of particulate matter according to their size fraction (Dzierżanowski et al., 2011, Chen et al., 2015). Whereas, some author focused on the particulate matter of specific source like Darley, 1966. Table 2. Comparison of the basic properties of PM with respect to particle size: fine (PM2.5) versus coarse (PM10) mode particles Fraction Respirable suspended particulate matter (RSPM) or Coarse mode particles or PM10

Size range ≤10 μm diameter

Accumulation mode or Fine particles or PM2.5 (respirable fraction)

≤2.5 μm in diameter

Ultrafine particles (UFP)

≤0.1 μm

Source Resuspension of soil dust, from process like farming, mining, industrial dusts, construction, and coal, oil combustion, and ocean spray Combustion of coal, oil, gasoline; transformation products of NOx, SO2, and organics including biogenic organics, e.g., terpenes; high temperature processes; smelters, and steel mills Metal fumes, Sea salt nuclei, oil smoke, and diesel smoke, etc.

Lifetime in atm. Minutes to hours

Reference Atkinson et al. (2010)

Days to week

Cheung et al. (2011)

Week to months

Srimuruganandam and Nagendra (2012)



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Schuhmacher et al., (2004) focused on cement kiln related particulate matter. Particulates with toxic compounds released into the atmosphere from motor vehicles, thermal power plants and other combustion related sources have ecological Rao, 1971, Ninomiya et al., 1971, Prajapati and Tripathi, 2007, Bignal et al., 2008). A number of factors are responsible for determination of the rate of particulate deposition. Peters and Eiden (1992) have worked on dry deposition velocity of particles to coniferous forest considering plant morphology and micrometeorological constraint. Whereas, Sæbø et al., (2012) worked on plant species differences in particulate matter accumulation on leaf surfaces and suggested that results may be helpful for the planning of urban green areas designed to capture air pollutants. USEPA has classified PM into fine (PM2.5) and coarse mode (PM10) particles listed in Table 2. Particles with a diameter of less than 0.1 μm are categorized as ultra-fine particles (PM ≤ 0.1) (Hashemi-nassab et al., 2013).

Deposition of PM Deposition of PM is the process by which the aerosol particles are deposited on various surfaces, which results in decreased concentration of particles in the air. According to McDonald et al., (2007), plants play a vital role in filtering ambient air through leaf surfaces. Trees with more leaf area are considered the most efficient type of vegetation for particle collection. Leaves of rough and broad surfaces area are more efficient in capturing PM than those with smooth surfaces (Beckett et al. 2000, Gupta et al., 2015a,b,c). Deposition of particulate matter (a mixture of organic and inorganic substances as solid and liquid) onto various surfaces at certain mass concentration causes various types of phytotoxic responses (Tasic et al. 2006). Deposition of particulate matter on vegetation includes (a) nitrate and sulphate and their removal in the form of acidic components and (b) trace element and heavy metals. Particulate-bound trace elements can be taken up directly via the stomata or be deposited on the leaf surface (McLachlan, 1999, Welsch-Pausch et al., 1995). By contrast, Polycyclic Aromatic Hydrocarbon (PAHs) may be accumulated in leaves by (i) kinetically limited dry vapour deposition; (ii) equilibrium partitioning; (iii) particle-bound deposition, depending on the Physico-chemical properties of the investigated compound and can also be absorbed through soil, after their deposition onto the soil surfaces.


34


Coarse (PM10) and Fine fraction (PM2.5) Particles Particle size is one of the factors related to the damaging effect of the PM, Coarse particles settle nearer their site of formation than fine particles. The size of PM correlated significantly with specific leaf area, but Chl a, Chl b, carotenoid and relative water content were inversely related with PM fraction (Chen et al., 2015). The size of the particle is also correlated with the chemical constitution of particles (i.e., most S, N and organic contents is present on fine particle while much of base cation and heavy metals is present on coarse particles). Fine particulate matters are found associated with the combustion related emission sources while coarse particle found related to crustal material. Various meteorological parameters like atmospheric humidity, precipitation and wind speed effects the deposition process through different mechanisms. Figure 3 is an example showing of particulate matter sources with particle diameter. Fine PM is secondary in nature and formed into the atmosphere by chemical reaction from gas precursors through series of process, nucleation, condensation and coagulation. Fine particles contain oxides of nitrogen and sulphur (NOx and SOx) along with some volatile organic compounds, volatile metals and products of incompletes combustion. Coarse PM is produced from mechanical processes like crushing, abrasion, soil disturbances and expansion of fine particle to coarse PM by the effect of humidity.

Figure 3. Particulate Matter, size ranges and their sources.



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Mode of Deposition The rate of particle deposition onto the vegetative surfaces depends on dust properties, characteristic of the location of plant and nature of receiving material (Grantz et al., 2003 and Chen et al., 2015). It also may be associated with the reduction in light required for the photosynthesis and an increase in the leaf temperature due to changed surface optical properties. The exchange of energy into and out of the leaves is highly influenced by particulate matter load, size and colour as compared to gasses (Rahul and Jain, 2014). The different type of mode of deposition and determinants of PM are listed in Table 3 given by Grant et al. (2003). The deposition of atmospheric particle onto vegetation surface has three major routes: (1) Dry deposition, (2) wet deposition, (3) occult deposition, uncertainty obtained from the measurements of dry and wet deposition, by fog, cloud water, and mist interception.

Dry Deposition The combined removal of particles from the atmosphere by gravity, Brownian motion, impaction and direct interception is known as dry deposition. Gravitational settling affects deposition of particles, especially those larger than a few micrometers in diameter. In comparison to wet or occult deposition, dry deposition of atmospheric particles to plant and soil is comparatively slower, but it is the continuous process that affects all exposed surfaces (Hicks, 1986). Gravitational sedimentation is one of the main depositional processes in dry deposition of PM, especially in the region where desert dust has significant influence on the atmospheric burden of plants. Dustfall is an important phenomenon in Indian region for the removal of coarse particles (Kulshreshtha et al., 2003, Gupta et al., 2015c). Dry deposition of organic compounds (e.g., dioxins, dibenzofurans, and polycyclic aromatics hydrocarbons) to plant surfaces is dominated in coarse PM relative to fine PM (Lin et al., 1993). PM deposition also influenced by fog formation through particle removal from air, by helping particle growth through aqueous phase oxidation reaction (Pandis and Seinfeld, 1989). Wet Deposition Wet deposition can be defined as the scavenging of soluble gases and aerosol particles from the atmosphere via precipitation. In wet deposition atmospheric hydrometeors (rain drop, snow, etc.) play very important role in the scavenging of particulate matter. Wet deposition is influenced by gravitational


36


pull, Brownian motion and/or turbulent coagulation with water droplets. Different type of wet deposition includes: 



In-cloud scavenging (Rainout): In this process aerosol particles get into cloud droplets or cloud ice crystals acting as cloud nuclei, or being captured by them through collision. They can be brought to the ground surface through rain or snow. Below-cloud scavenging (washout): it happens when falling rain droplets or snow particles collide with aerosol particles through interception, Brownian diffusion, impaction and turbulent diffusion.

Wet deposition of gases depends on the solubility of the gas based on Henry’s law. Whereas, aerosol wet deposition depends on the particle size and hygroscopicity, etc.

Occult Deposition The fraction of wet deposition which is not recorded by rain gauges is called as occult deposition, for example deposition through fog, and wind-blown mist. Occult deposition is linked with pollutant removal at high altitude sites where mists and ground-level cloud are more common (Fowler et al. 1989). The distribution of deposition of individual constituents and of total PM between wet, dry, and occult modes varies according to location (e.g., for both nitrogen and sulfur).

Deposition of PM onto Vegetation and It’s Effects Deposition of particulate matter on vegetation is affected by the particle size distribution, dimensions, and density of the foliage elements in the dispersion path. PM can cause adverse effects on plants like stomatal clogging, reduced photosynthetic activity, leaf fall and death of tissues (Farooq, et al., 2000; Garg, et al., 2000, Shrivastava and Joshi, 2002). Due to PM deposition many physicalchemical changes take place on aerial parts of plants (Grantz et al., 2003). A major proportion of stomata may cover by PM which reduces the rate of transpiration and rate of evaporative cooling (Sharifi et al., 1997). Leaf chlorosis also caused by dust pollution due to its effect on chlorophyll biosynthesis (Seyyednejad, et al., 2011). Several studies related to PM effects on vegetation were reported by different authors listed in Table 4.



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Table 4. Effects of particulate pollution on different aspects of plants Site Hubei Province, China

Plant species Trachycarpus fortune, O. fragrans, G. biloba, I. tectorium

Source Industrial emission

Sambalpur, Orissa

Pongamia pinnata, Tabernaemontana divaricata, Ipomea carnea, Ficus relogiosa, Ficus benghalensis, and Quisqualis indica Dalbergia sissoo

Traffic emission

Udaipur city

Chunar, Mirzapur and Banaras hindu University, campus, Varanasi Rajasthan

Tectona grandis, Syzygium cumini

Industrial and vehicular emission Industrial and road side area

Hibiscus cannabinus L.

Cement kiln emission

Ariyalur and Annamalai University, Tamil Nadu

Arachis hypogaea L.

cement dust

Riyadh, Saudi Arabia

(Leguminous crops ) Pisum sativum L., Vicia faba L., Glycine max and Vigna sinensis) Cucumis sativus L. and Phaseolus vulgaris L.

heavy traffic and industry related sources

Abutilon indicum, Croton sparsiflorus and Cassia occidentalis Shorea robusta, Maduka indica, Eucalyptus citriodora, Acasia moniliformis and Terminalia arjuna

Industrial and vehicle exhausts

Sakai 593, Japan

Kerala, India

West Bengal and Bihar, India

Mix dust (natural and anthropogenic)

Stone cursing and traffic related emission

Effect Loss in relative water content, total chlorophyll, pH and Inhibition in pigment content

References Chen et al. 2015

Chlorophyll degradation

Kapoor et al., 2013

Reduction in relative water content

Chaturvedi et al., 2013

Reduction in total protein, chlorophyll, sugar, lipid and starch Effects on germination growth and biochemical parameters Bioaccumulation of heavy metals in plant parts

Uma and Rao, 1996

Effect on leaf temperature and photosynthetic and transpiration rate Adversely effects on plant morphology

Hirano et al. 1994

Reduction in Chl a, b, total carbohydrate content, protein contents in foliar tissues

Padhy P.K., 2013


Prusty et al. 2005

Raajasubra manian et al., 2011

Alyemeni M. N., and Almohisen I.A.A. 2014

Sukumaran D., 2014

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Pallavi Saxena, Saurabh Sonwani and Umesh Chandra Kulshrestha Table 4. (Continued)

Site Mizoram, India

Gujrat, India

Plant species Ficus bengalensis, Psidium guajava, Bougainvillea spectabilis, Mangifera indica, Lantana camara and Artocarpus heterophyllus Arachis hypogaea, Sesamum indicum and Triticum species

Source Road dust

Effect Effects on biochemical parameters of leaves

References Rai and Panda, 2014

Cement industry emission

Effects on the photosynthetic pigments.

Chaurasia et al., 2013

The dust, such as soil, road, fertilizer, or lime, could produce a number of plant responses due to the dust chemistry. Rai et al. (2011) have studied risks on the yield of crops posed by air pollutants their emission patterns, atmospheric transport and leaf uptake including their effects on the plant’s biochemical defense capacity. Agrawal et al. (2003) have reported SO2, NO2 and O3 and related plant responses measured regarding physiological characteristics, pigment, biomass, and yield. These workers found that air pollutants affect the crop yield negatively. Several, chamber related studies also revealed that the particulate air pollution is responsible for negative commercial yield and adverse impact on biological parameters of several important crops (Heggestad and Lesser, 1990, Schenone and Lorenzini, 1992, Wahid et al., 1995, Rai et al., 2007). Joshi et al., (2009) reported the impact of industrial air pollutants (SPM, RSPM, NOx, and SO2) on biochemical parameters like Chl a, Chl b, Total Chl, Carotenoid, Ascorbic acid and yield in wheat and mustard plants. Parish (1910) is the earliest study, concerning cement particulate matter deposition onto shrub and grassland vegetation in California. Due to the cement industries, several plants such as Artimisia californica, Encelia farinosa, and Salvia apiana became extinct. The most effective deposition of the PM on grassland was reported by Krippelova (1982) around the magnesite factory in Czechoslovakia where the deposition was so high that surface crusts were often formed on the ground and the soil pH was raised to 9.5. Some studies related to limestone PM emitted from limestone processing plants may affect the lateral growth of the plant in vicinity. According to Padhy (2013), PM emitted from the stone crushing industry can affect the different plant parameters of some tree species like Sal (Shorea robusta), Mohua (Madhuka indica), Eucalyptus (Eucalyptus citriodora) Sonajhuri (Acasia moniliformis) and Arjun (Terminalia arjuna). Various types of the microscopic and macroscopic anomalies were



39

detected, including decrees in the amount of Chlorophyll and total carbohydrate in foliar tissue indicating reduction in photosynthesis. According to Anderson (1914), deposition of the PM on stigmatic surfaces may hinder the processes of fruit production. The effect of urban road and traffic emission related PM were also extensively investigated by several authors and reported various types of the morphological and biochemical affects (blocked stomata, reduced diffusive resistance, increase leaf temperature, reduced photosynthesis, reduced growth, fruit lesions and partial defoliation) on the plants (Populas trimula, Betula pendula, Rhododendron catawbiesnse, Acer campestre, Abies alba, Fraxinus excelsior, Vibumnum tinis and Mangifera indica, etc.) (Rao (1971), Eller (1977), Eller and Burnner (1975), Fluckiger et al., (1977, 1979), Thompson et al.,(1984), Ajuru et al., (2014). Deposition of urban dust on Morus and Arjun plants foliar resulted in biochemical changes in parameters of the plant. Such deposition are also clogged the stomata along with cuticular damage (Gupta et al., 2015c).

Plant Responses to Stress Caused by PM According to Billing (1978), minimum three types of interactions are involved between plants and PM. Firstly, the interaction between individual plant and environment, second, population and its environment and thirdly biological community and its environment. The response of any individual towards any stress depends on upon its genotype, growth phase, existing resources and microhabitat (Levin, 1998). Succession in the polluted environment or natural disturbed area, energy is shifted from growth and reproduction to maintenance, and thus succession reaches to its earlier stage (Waring and Schlesinger, 1985). Such disturbed environment potentially affects the ecosystem structure, processes and function like physiology and biochemistry of plants, energy flow, nutrient cycling, biogeochemical cycle (Odum, 1993). Deposition of the particulate matter onto soil can affect plant yield, reproduction, flowering and plant growth (Saunders and Godzik, 1986). Several studies suggested that chronic pollutant injury to a forest community may result in the loss of tree canopy, sensitive species, and safeguarding of a successional plant species (Smith, 1974; Millar and McBride, 1999). The deposition of PM to any plant surface may exert physical and/or chemical changes in the plant. This is generally associated with chemistry rather than the mass of deposited particles (Farmer, 1993). Some crustal particles having slightly alkaline pH may injure plant surface due to presence of


40


limestone (Brandt and Rhoades, 1972). Several authors reported that PM emitted from cement kiln industries may affect the leaf by destroying its cuticle, hydrolyses the lipid and wax component, and denature protein due to the rising alkalinity on the leaves surface by libration of calcium hydroxide on hydration through cement PM (Guderian, 1986, Darley 1966). Some of the microorganism, fungi, and arthropods residents on the plants play a very important role in decomposition of litterfall (Miller et al., 1982) Apart from direct effects, some of the indirect effects are also responsible for ecosystem response on PM. Indirect plant responses to PM are limited to soil environment (i.e., mineral, organic matter, water, air, verity of bacteria, fungi, protozoan, nematodes, and arthropods), depending on chemical composition of the each element present in PM. The soil environment is an active site for the poorly characterized biological interactions (Wall and Moore, 1999). According to Wall and Moore, (1999) rhizosphere organisms play a very important role in creating chemical and biological transformations, making inorganic minerals available for plant uptake. Indirect effects of PM on plant populations that occur through soil can affect the nutrient cycling important for plant growth, vigor and health of the biota. Guderian (1986) reported that many of the heavy metals and other constituents associated with PM and reaching to the soil surfaces are more harmful than component that penetrates the foliar surfaces. Biochemical effects due to dust fall deposition have been reported by Gupta et al. (2015a,b,c). They found that the plants have more sheer at the industrial site due to urban dust deposition on foliar surfaces.

EFFECTS OF TROPOSPHERIC OZONE AND PARTICULATE MATTER ON FOOD SECURITY World population has been predicted to rise to 9 billion by 2050 which causes another challenge to come into the picture is the food security. There are many air pollutants which pose ill effects on food security, but the most important is tropospheric ozone. A study in Europe indicated that over 30 crop species growing in commercial fields in 16 countries showed visible ozone injury symptoms and other negative effects of ozone such as biomass/yield reduction during the period 1990 to 2006 (Hayes et al., 2007, Mills et al., 2011b). Mostly all European assessments over vegetation were based either on AOT40 index i.e., accumulated amount of ozone over the threshold value of 40 ppb or 24h or 7h mean ozone concentration. These ozone metrics only focuses



41

on the ozone concentration in the air above the leaves of crops and not the uptake or flux of ozone. In another study of Europe, total crop losses across 47 LRTAP Convention countries were €6.4 billion (90% confidence interval of 4.5 to 9.3) in 2000 falling to 4.5 and 1.7 billion Euro for the 2020 baseline scenario and the RAINS model maximum feasible reduction scenario respectively (Holland et al. 2000). Wheat and rice have yield loss of 23.5% and 15.2% in 2000 respectively. Avnery et al. (2011a) also predicted that 12.1% yield loss of wheat occurred which is rising to 16.9% in 2030 using the IPCC A2 scenario (Avnery et al., 2011b). Van Dingenen et al. (2009) indicated that ozone effects on maize, wheat, rice and soybean in EU-25 resulted in losses of $US 0.86 to 1.05 million. Moreover, meta-analysis study was done of published data on ozone effects on crops compared with effects of current (31 – 50 ppb) and future (51 – 75 ppb) ozone against a baseline ozone concentration of < 26 ppb (Feng et al., 2010). Losses in current ozone were observed to be for potato 5.3%, barley 8.9%, wheat 9.7%, rice 17.5%, bean 19.0%, soybean 7.7%, and 10% higher for soybean, wheat and rice and 20% higher for bean in the concentration range predicted for 2030. Food and feed quality has also been affected by ozone. As per the studies based on agronomy, yield, and nutritional quality are of utmost importance, but less attention has been made towards nutritional quality as compared to yield (Ashmore, 2005). For example in wheat, the most important effects of ozone is increasing in grain protein concentration and changes in baking quality (Fuhrer et al., 1990; Pleijel et al., 1999; Rudorff et al., 1996a; Vandermeiren et al., 1992). Ozone increases grain protein concentration although protein yield per plant or ton of seeds was significantly reduced (Piikki et al. 2008). A significant reduction of grains of common millet was also found (Agrawal et al. 1983). P and K concentration of the flour was also decreased whereas total S concentration of the flour was increased (Anguissola Scotti et al., 1994; Vandermeiren et al., 1992). On the other hand, in sugar beet long-term exposure to ozone caused reduction of the sugar content, leading to an overall sugar yield reduction (De Temmerman et al., 2007). The study of effect of particulate matter on food security are still in process. This topic is untouched, and many researchers are still working on it. Many of the studies are on physiological or biochemical effects of particulate matter on plants (as we have discussed above). Hence, the researchers should pay attention to study the effects of pollutants on food security. In addition, the farmers should also be informed about the effects of different pollutants on plants which will help in the protection of crop quality and crop yield.


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CONCLUSION Tropospheric ozone and particulate matter significantly affect the plant metabolism and plant physiology that causes a reduction in plant produce that poses a significant concern for food security. ozone have huge impacts on quality and yield of crops, but the research related to the particulate matter is still under progress. Entry of these pollutants into leaf surfaces affects the photosynthetic machinery and enzymatic activities of plant cells as a significant mechanism. Mechanism of deposition which is common to both of the pollutants is very important for final consequences on the plants and plantderived food products. The deposition is the fundamental phenomena which deal with the preliminary way of injury to the plant cells and produce toxicity inside the electron transport system and antioxidant system of plants. Though, several studies have been reported with tropospheric ozone and particulate matter concentrating on deposition mechanism and also about the accumulation concept of these pollutants. Still, comprehensive research is required to explore and suggest proper options to control the adverse effect of such air pollutants.

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Chapter 3

PRODUCTIVITY OF MAJOR CROPS WORLDWIDE: REVIEWING FOOD SAFETY AND SECURITY Neelofar Mirza1,2, Amit Kumar Singh1 and Dhammaprakash Pandhari Wankhede1,* 1

ICAR-National Bureau of Plant Genetic Resources, Pusa campus, New Delhi, India 2 National Institute of Plant Genome Research, Aruna Asaf Ali Marg, New Delhi, India

ABSTRACT Agriculture is likely to suffer great losses due to erratic weather, increased temperature and decreased irrigation availability. Among the most important environmental impacts of climate change is the direct effect of elevated atmospheric carbon dioxide concentration (e[CO2]) on crop yields. Atmospheric CO2 level has greatly increased since the advent of the industrial revolution, largely due to the fossil-fuel combustion, increased emission of greenhouse gases (GHGs) such as e.g., carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and changes in land management. The atmospheric concentration of CO2 has increased to more than 400 ppm as compared to 280 ppm in pre-industrial era. Elevated atmospheric CO2 (e[CO2]) will promote growth of plants through fertilization effect and *

Corresponding author: [email protected].


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N. Mirza, A. Kumar Singh and D. Pandhari Wankhede enhanced photosynthesis. Given the complexity of the subject, it is difficult to cover effects of elevated CO2 on all the aspects of plant function. Hence, in this chapter, focus is kept on the effect of elevated CO2 on the productivity related aspects of important crops.

Keywords: agricultural productivity, global climate change, atmospheric carbon di-oxide, plant response

INTRODUCTION Agriculture is likely to suffer great losses due to erratic weather, increased temperature and decreased irrigation availability. The changing climate has the potential to alter crop productivity and affect food quality and supply, globally. Hence, comprehending its effects is vital to food security. A report by Hatfield et al. (2008) predicts that agriculture will face a more variable, future climate with an increased frequency of extreme weather events including, prolonged drought, intense heat waves, and episodes of drenching rains. Among the most important environmental impacts of climate change is the direct effect of elevated atmospheric carbon dioxide concentration (e[CO2]) on crop yields. Atmospheric CO2 level has greatly increased since the advent of the industrial revolution, largely due to the fossil-fuel combustion, increased emission of greenhouse gases (GHGs) such as e.g., carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and changes in land management (IPCC 2007). The atmospheric concentration of CO2 has increased to more than 400 ppm as compared to 280 ppm in pre-industrial era (IPCC, 2014). Elevated atmospheric CO2 (e[CO2]) will promote growth of plants through fertilization effect and enhanced photosynthesis. This positive effect of CO2 on plant growth is expected to be more pronounced in C3 crops such as wheat but less notable in C4 crops such as maize (Ghannoum et al., 2000). However, higher atmospheric CO2 concentrations also extend the active period of plant annual life cycles (Reyes-Fox et al., 2014). Increase in CO2 concentration also leads to elevation in temperature. Because atmospheric CO2 absorbs heat from the sun, global mean temperatures, over both land and water, increased to an average of 0.85°C between 1880 and 2012 (IPCC 2013). An additional increase of 3.7–4.8°C is predicted by the end of the current century (IPCC, 2014) which will have consequences for both mechanized and subsistence agriculture. Crop production is likely to be severely affected by global warming. Above optimal temperatures decrease both the vegetative and reproductive growth of crop plants which may


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be partially offset by greater rates of net photosynthesis due to CO2 enrichment (Sicher and Bunce, 2015). Elevated temperature will cause heat injury and physiological disorders resulting in reduced yield (Johkan et al., 2011). Elevated temperature as a result of elevated CO2 will have a major influence on food grain production depending on the locations. A proposed increase in temperature will mostly affect the hot tropics, mainly populated by developing countries as they are likely to suffer greatest loss in food production. The area of semi-arid and arid land could increase by 5–8%, with the disappearance of wheat production by the 2080s (Fischer et al., 2005). With a temperature rise of 1.0–2.0°C in tropical and subtropical countries such as India, food grain production is projected to decrease up to 30% (IPCC, 2014). Above optimal temperatures decrease both the vegetative and reproductive growth of crop plants but this may be partially compensated by greater rates of net photosynthesis due to CO2 enrichment (Sicher and Bunce, 2015). Given the complexity of the subject, it is difficult to cover effects of elevated CO2 on all the aspects of plant function. Hence, in this chapter, focus is kept on the effect of elevated CO2 on the productivity related aspects of important crops.

EFFECT ON CROP PRODUCTIVITY The agricultural industry is inimitably dependent upon climate and a changing climate has the potential to alter crop productivity and affect economic returns to farmers in turn global food supply. The impact of e[CO2] on plants has been studied for decades. Elevated CO2 affects the plants both at physiological and molecular level primarily by directly affecting the fundamental processes of photosynthesis and respiration and stomatal physiology of the plant (Bunce, 2000, 2001; Uprety et al., 2002; Leakey et al., 2009; Shimono et al., 2009). In the recent years, many research findings have proved that elevated CO2 have positive impact on yield and its components (Dubey et al., 2015) due to significant increase in growth and growth parameters such as leaf area index, plant height, leaf area duration, leaf net photosynthetic rates, total biomass and root mass (Long et al., 2004, 2006; Ainsworth and Long, 2005; Ainsworth et al., 2008). It also leads to decrease in stomatal conductance and alters water use efficiency (WUE) and (Rogers et al., 1994; Saxe et al., 1998; Reddy, 2010), in turn enhancing yield and crop productivity across many crop species (Ainsworth et al. 2008; Högy et al., 2009; Kant et al., 2012; Hasegawa et al., 2013). However, the e[CO2] might have negative effects as well. It has been observed that grain quality in some crops declined under


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e[CO2] condition. A reduction of upto 15% in the grain N content was reported in plants grown under elevated CO2 (Jablonski et al., 2002). When considering the impact along with other factors of climate change (viz. elevated temperature, drought etc), even though elevated levels of CO2 has potential to compensate and partially ameliorate some of the adverse effects of other changes in climate viz. elevated temperature (Qaderi et al., 2006), the positive response to e[CO2] might be less prominent in some crops. A rise in ambient temperature by 1–2°C might lead upto a 30% loss in productivity of major cereal crops (Johkan et al. 2011), particularly in central and south Asia.

Effect on C3 and C4 Crop Biology The effects of e[CO2], vary with species and developmental stage of the plant with a greater response during early growth stages (Kramer, 1981; Geiger et al., 1999). There are apparent differences in growth and developmental responses among plants of the two classes, C3 (rice, wheat) and C4 (maize, sorghum) crops to e[CO2]. In C3 crops, the primary acceptor of CO2 is ribulose bisphosphate (RuBP) and the reaction is catalyzed by Ribulose bisphosphate carboxylase-oxygenase (Rubisco). Rubisco catalyzes both carboxylation and oxygenation, hence CO2 and O2 compete for the same site. An increase in CO2 will decrease the oxygenase activity, decreasing oxygenation and photorespiration, while increasing carboxylation, in turn increasing the rate of net photosynthesis of C3 species (Bowes, 1996). C4 plants, on the other hand, do not respond as optimistically to rising atmospheric CO2. Classical response curves of C3 and C4 crops show that photosynthesis of C4 crops is at its saturation when [CO2] approaches 400ppm while for C3 crops, photosynthesis increases even beyond a [CO2] of 1000ppm (Taiz and Zeiger, 1991). The photosynthesis in C4 can be limited by phosphoenolpyruvate (PEP) carboxylase activity, Rubisco activity, or by RuBP-regeneration capacity. Unlike Rubisco, PEP carboxylase activity is saturated by ambient atmospheric CO2 concentrations. However, an increase in water use efficiency (WUE) might result in positive growth responses for C4 crops above 400ppm (Rogers et al., 1994). While an e[CO2] generally increases rates of photosynthesis biomass production and yield of C3 crops (Acock and Allen, 1985; Chen et al., 1995), it negatively affects the nutritional quality by significantly decreasing tissue concentrations of nutrients and proteins (Ainsworth and Long, 2005; Leakey et al., 2009). Loladze, (2014) showed that e[CO2] reduces the overall mineral concentrations and increases total non-structural carbohydrates in C3 plants.



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Elevated CO2 leads both to an increase in atmospheric and plant tissue temperature. In combination with high temperature, e[CO2] was proposed to have a positive impact on both C3 and C4 cereals (Rogers et al., 1994; Saxe et al., 1998; Leakey et al., 2009; Shimono et al., 2009; Reddy, 2010) though, yield components viz. number of panicles, number of spikelets, number of filled grains etc. showed varied response across different studies (Kramer, 1981; Geiger et al., 1999) predicted due to strong and variable genotypic responses, different treatments and varying experimental conditions. Increase in tissuetemperature affects both the sensitive reproductive process during anthesis and the pollen viability, leading to a significant decline in spikelet fertility that has resulted in sharp reduction in grain yield and other yield components across C3 (rice) and C4 (sorghum) cereal crops (Kadam et al., 2014). When compared with independent drought stress, both C3 (wheat and rice) and C4 (sorghum and maize) crops exhibited a relatively lower decline in grain yield and biomass under combined drought and e[CO2] conditions owing to a slightly positive effect on the physiological responses, including photosynthesis. Harvest index, however, decreased across both C3 and C4 cereals with e[CO2], mainly due to a greater proportion of increase in vegetative biomass. Xiong et al. (2015) reported profound effects of e[CO2] on the functional structure and metabolic potential of soil microbial communities associated with C4 plants and suggested a possibility of change in ecosystem functioning and feedbacks to global change in C4 agro-ecosystems.

Effect on Water Use Efficiency Decreased stomatal conductance and partial closure of stomata due to e[CO2], decreases transpiration and often leads to an increase in leaf or tissue temperatures by about 1–2°C (Madan et al., 2012). This higher tissue temperature increases vapor pressure inside and causes a greater leaf-to-air vapor pressure difference, decreasing transpiration and in turn improving WUE (Li et al., 2004). However, changes in single leaf conductance cannot be directly extrapolated to whole crop canopy transpiration under field conditions. Although, water use per unit leaf area is decreased, much of this decrease in transpiration is offset due to greater leaf area index at elevated e[CO2]. Thus, increased biomass might overturn the effect on total water use due to slightly increased WUE at e[CO2] (Kadam et al., 2014).


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Effect on Rice Rice is the major staple crop worldwide. It is predominantly a Kharif crop in India and covers one third of total cultivated area from north to south. A production of 157 million Mt was recorded in year 2014 (FAOSTAT, 2015) which is a 1.2 fold increase in the last decade. The effects of [CO2] have been studied in rice over the entire life-cycle (Baker et al., 1992; Ziska et al., 1996; Matsui et al., 1997; Baker, 2004; Cheng et al., 2009). An elevated [CO2] increases photosynthesis, growth, development, and yield in rice both in japonica (Kim et al., 2001, Sasaki et al., 2007; Yang et al., 2007) and indica cultivars (Weerakoon et al., 2005). When compared to plants grown at ambient [CO2], Shanyou 63, a three-line indica hybrid, (grown at 570 ppm CO2) showed an increase of 34% in yield (Liu et al., 2008) while Liangyoupeijiu, an inter-specific rice hybrid (grown at ~580 ppm CO2) had 24% and 20% higher grain yield and biomass, respectively (Yang et al., 2009). Photosynthesis in rice leaves increased significantly by 30–78% under e[CO2], and up to 63% when combined with high temperature due to the decreasing Rubisco specificity with increasing temperatures, thereby increasing the response of photosynthesis to e[CO2] (Long, 1991; Drake et al., 1997). Canopy photosynthesis showed an increase of only 21% under e[CO2] whch increased up to 143%, with combined high temperature and e[CO2], indicating a potential for alleviation of the negative effects of high-temperatures stress on C3 photosynthesis with e[CO2]. Madan et al., (2012) also reported increased vegetative and reproductive growth, including seed yield in three rice genotypes, a hybrid (IR75217H), a heat-tolerant check (N22), and a megavariety (IR64), under e[CO2]. The hybrid had significantly more anthesed spikelets at all temperatures than IR64 and resulted in a large yield advantage at both ambient (29ºC) and elevated temperature (35ºC). Rice plants grown under e[CO2] were able to maintain photosynthesis and other photosynthetic-related parameters to some extent, longer than plants grown at ambient CO2 in the drought conditions (Widodo et al., 2003). Although elevated [CO2] should increase productivity and yield in rice but it also leads to higher tissue temperature due to stomatal closure (Vara Prasad et al., 2006; Long and Ort, 2010) and a decrease in optimum and ceiling temperatures for seed-set by about 2°C (Matsui et al., 1997; Prasad et al., 2006). Increased tissue temperatures may cause a decline in pollen germination percentage on the stigma and also in number and rate of pollen tube growth in the style, resulting in a reduction of fertilization effect and lowering seed-set



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percentage. Improved WUE due to enhanced CO2 exchange rates and reduced evapo-transpiration (Vu et al., 1998; Baker et al., 1997) is known in rice but the advantage was lost when combined with high-temperature stress (Kadam et al., 2014). These effects are aggravated by the rise in atmospheric temperature. The increasing frequency and intensity of short-duration high temperature events (>33ºC) are posing a grim threat to crop production, especially in cereals like rice (Wassmann et al., 2009). Both high day temperatures (Jagadish et al., 2010) and high night temperatures (Peng et al., 2004) have negative effects on rice spikelet fertility and yields. Increase in temperature beyond the critical threshold during gametogenesis, flowering and grain filling stages have deleterious effect and lead to low seed-set (Madan et al. 2012). An exposure to temperatures, during developmental stages like gametogenesis and flowering leads to reduced seed set and hybrids were found to be twice as sensitive as the tolerant cultivar (Prasad et al., 2006; Madan et al., 2012). There was no yield advantage at temperatures beyond 350C. Increase in biomass with e[CO2] does not seem to alleviate the high temperature induced decline in spikelet fertility and hence yield (Jagadish et al., 2007, 2010, Madan et al. 2012). With a combination of e[CO2] and drought stress at the reproductive stage, the total Rubisco activity in the rice leaves declined by 44% and the photosynthetic advantage decreased significantly, ranging from 6% to 12% (Vu et al., 1999). The chalkiness also increased with increase in temperature during grainfilling (Lisle et al., 2000; Fitzgerald and Resurreccion, 2009) which in turn leads to increase in broken grains. Grain gel consistency in the hybrid, varieties was reduced when e[CO2] was combined with high temperatures, while the percentage of broken grains increased from 10% at 29°C to 35% at 38°C in the hybrid. Also, amylose concentration declined in many rice varieties and gelatinization temperature increases (Madan et al., 2012), affecting the texture and cooking time in rice. When combined with drought stress, an increase in leaf soluble sugars with a parallel decrease in leaf starch was generally observed at e[CO2] probably due to the conversion of starch to sucrose (Vu et al., 1998; Kakani et al., 2011). Higher carbohydrate accumulation leads to a dilution effect, particularly for nitrogen metabolites in shoots and grains (Wu et al., 2004; Johnson, 2013). An altered amino acids composition and grain mineral content was observed under e[CO2] (Wu et al., 2004; Högy et al., 2013; Madan et al., 2012).


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Effect on Wheat Wheat is the second most important staple crop after rice in our country. Wheat is the major winter or Rabi crop in India sown in October (temperature 10 – 15ºC) and harvested in March (temperature 21-26ºC). The production has increased from 72.16 million Mt to 94.48 million Mt in the past decade with an area of 31.19 million hectares (Mha) under cultivation in the year 2014 (FAOSTAT, 2015). Elevated CO2 often increases leaf area and mass per unit area, thus increasing the net leaf photosynthetic rates in wheat (Habash et al., 1995), most likely increasing the availability of carbon assimilates for floret development (Marc and Gifford, 1984) due to a reduction in floret death (Dias de Oliveira et al., 2013, 2015), improving tillering and potential grain number and hence, the yield (Slafer, 2003; Reynolds et al., 2009). The grain-filling rates were also observed to be higher under e[CO2] and 3◦C higher above ambient temperature. The effect of e[CO2] (from 365 to 550 lmol mol-1) was observed in wheat at various sowing times and irrigation regimes, and an increase in shoot biomass and WUE was reported (Wu et al., 2004; Högy et al., 2010; Thilakarathne et al., 2013; O’Leary, 2015). At the grain-filling stage, e[CO2] improved spikelet density, 1000- grain weight, panicle density, and harvest index (Madan et al., 2012; Högy et al., 2013). In some cases however, no effect of e[CO2] was recorded on grain number per ear (Högy et al., 2009, 2013), suggesting a variable response by different genotypes. A large variation however, exists for other growth and agro-morphological parameters (Kadam et al., 2014). A reduction of 67% in root biomass was reported, in a high vigour wheat line due to a reduction in root length, reducing total plant biomass by 26% (Benlloch-Gonzalez et al., 2014). With e[CO2], higher carbohydrate accumulation in shoots and grains led to a dilution effect, (Kadam et al., 2014). A lower nitrogen concentration while higher C/N ratios was reported in wheat grown under e[CO2]. The effect of e[CO2] was observed on the expression of genes involved in senescence, leaf carbohydrate, nitrogen metabolism and assimilate transport, from the stage of anthesis upto maturity in wheat, under field conditions (Buchner et al., 2015). A down-regulation of C remobilisation and up-regulation of N remobilisation was suggested during senescence (Buchner et al., 2015). Total grain protein decreased by 8–13% whilst the composition of amino acids and mineral content was altered (Kadam et al., 2014). Drought greatly reduces grain yield but when combined with e[CO2], a reduction in grain yield loss and an increase in 1000-grain weight (attributed to



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a faster grain-filling rate) were observed. Drought and e[CO2] combined, had a significant impact on later-formed tillers than on main stem spikes (Schütz and Fangmeier, 2001; Kadam et al., 2014).

Effect on Maize Maize (C4) contributes to significant global food grain production of which major share is contributed by the developing world. It is a versatile cereal crop cultivated in large part of world. In India, the crop is grown predominantly as a kharif (July–October) crop with 85% of the area under cultivation in the season. It is the third most important cereal crop after rice and wheat in the country accounting for about 9% of total food grain production with a production of 23.67 million Mt and an area of 8.6 Mha harvested in year 2014 (FAOSTAT, 2015). However, despite occupying large area in the country, productivity is low compared to other major maize producers. Similar to other crops, the growth, productivity and quality of maize is likely to be affected by elevated atmospheric CO2 and temperature (IPCC, 2007; Mendelsohn and Dinar, 2009). The reports on the effects of e[CO2] on maize yield are generally incoherent varying from no effect (Ziska and Bunce 2006), little positive effect (Ghannoum et al., 2000; Leakey et al., 2004) to as high as 50% increase in yield (Leakey et al., 2004; Vanaja et al., 2015). Elevated CO2 increased the number of flowers, pollen formation, leaf area index and also K content in grain whereas N and P content were decreased (Qaderi & Reid, 2009). An increase in biomass (32– 47%), grain yield (46–127%), grain number (25–72%), 100-grain weight (8– 60%) and Harvest index (11– 68%) was reported by Vanaja et al. (2015) at e[CO2] (550 ppm) in three different genotypes from semi-arid tropical climate of India. There is little or no stimulation of leaf photosynthesis at e[CO2] in maize, in general (Kim et al. 2007). An e[CO2] decreases photosynthetic thermal tolerance in maize (Hamilton et al., 2008) and brief episodes of elevated temperature along with e[CO2] inhibit photosynthesis in corn (Qu et al., 2014). Only sporadic CO2-dependent increases in photosynthetic rates were reported during water stress in a field study that reduces the stomatal conductance. A decrease in days to 50% tasseling, cob length, cob diameter, grain weight cob-1 and crude protein content in grain was also reported with e[CO2]. Test weight, stover yield and total biomass also decreased at e[CO2] with temperature 3.00C above ambient. However, both yield and yield related parameters decreased at elevated temperature alone (probably due to shortening of growth period) and also with e[CO2], in maize (Savabi and Stockle 2001). The loss of leaf starch


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content was lesser and was delayed in plants grown at e[CO2] and there was an increase in leaf soluble sugars indicates an alleviating response of e[CO2] to drought (Kakani et al., 2011). It may be noted that the most of the studies in this aspects were conducted under controlled environment facilities (phytotron, plant growth chambers) (Mendelsohn and Dinar, 2009). Studies on the impacts of e[CO2] concentration and temperature interactions on maize under field conditions are really scarce.

Effect on Sorghum Sorghum, another C4 grass, is considered the fifth most important cereal crop in the world and the most important millet serving as a staple food, feed and fodder for millions in the semi-arid tropics of Africa, Asia, and Central America and also as an industrial raw material, especially for ethanol production in developed countries viz. in US. It is a rich source of energy, proteins, vitamins, and minerals (Taylor et al., 2006). United States is the main world producer followed by India, Mexico, Nigeria and Argentina. In India, an area of 5.82 MHa is under sorghum production and a production of 5.4 million Mt was recorded in 2015 (FAOSTAT, 2015). The production however, has decreased many a folds in the last 30 years from 12 million Mt in year 1981, 11.68 million Mt in 1990, 7.53 million Mt in 2000 to 6.7 million Mt in year 2010 (FAOSTAT, 2015). Sorghum has great geographic and genetic diversity and is a good model to study the impact of e[CO2] in C4 plants. In sorghum, e[CO2] led to an increase in WUE rates and reduction on evapotranspiration (Conley et al., 2001) although, the increase in leaf photosynthesis was non-significant. When compared with ambient CO2 and well-watered conditions, approximately 13–20% and 35% less water was used under combined e[CO2] and drought stress conditions, respectively (Chun et al., 2011) and a 36% decrease in stomatal conductance was recorded (Wall et al., 2001). During the vegetative stage, canopy net photosynthesis declined by 9% at e[CO2] and by 7% with combined e[CO2] and drought stress. Studies show that plants grown at elevated CO2 led to decrease in optimum and ceiling temperatures for seed-set by about 2°C (Prasad et al., 2006). When combined with drought stress, an increase in leaf soluble sugars and decreases in leaf starch were generally observed (Vu et al., 1998; Kakani et al., 2011). Differential increase in leaf soluble sugars for both ambient- and e[CO2] -stressed sorghum plants indicates an alleviating response of e[CO2] to drought, achieved mostly at the expense of starch (Kakani et al., 2011). The rise in tissue



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temperature during anthesis stage due to e[CO2], results in higher spikelet sterility in sorghum (Prasad et al., 2006) as observed for rice. There was no effect of e[CO2] on either rates or duration of grain filling or grain size. With e[CO2], the harvest index of sorghum was found to decrease too and the decline was greater with combined drought stress due to a greater decrease in grain yield (Kim et al., 1996; Prasad et al.,2006).

Effect on Legumes Soybean is a C3 forage crop that establishes symbiotic relationship with nitrogen-fixing bacteria. Soybean yield has increased globally over the past 27 years due to the CO2 fertilization effect (Sakurai et al., 2014). In C3 plants, the optimum temperature for photosynthesis increases with the carbon dioxide concentration. When grown at elevated CO2, soybean showed considerable and long-term increase in leaf photosynthesis, in general (Bunce, 2014). However, during long-term growth experiments, the single-leaf photosynthetic rates were not increased by CO2 enrichment when measured at limiting light levels (Rogers et al. 2006; Bunce 2014) suggesting a decrease in the quantum efficiency of photosynthesis in soybean, comparable to various other species (Bunce and Ziska 1999; Bunce 2014). Sakurai et al. (2014) reported an increase of 5.84% of soybean yields on average during 2002–2006 corresponding to e[CO2] from 1980, slightly higher than that suggested by the results of previous free-air CO2 enrichment (FACE) studies i.e., 3%. McGrath and Lobell (2011) have also suggested a more than 2fold increase in the CO2 fertilization effect under conditions of water, increasing the historical CO2 fertilization effect at a global scale above that expected 3%.

CONCLUSION The increase in atmospheric CO2 along with other changing climate factors is expected to manifest quite differently in the different agro-ecological zones and the effect on crop production in apparent. An e[CO2] levels might encourage plant productivity but it also encourages fungal, microbial and most likely viral growth, thus increasing disease incidence. While e[CO2] has pronounced effects on crops, it is reported to effect weeds lesser. The overall reduction in protein and mineral concentration and increase in total non-structural carbohydrates might aggravate the global prevalence of ‘hidden hunger’ and obesity.


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For adaptation of crops to this ever changing climatic scenario requires understanding the dynamics of plant growth and development and the plantpathogen interactions. The response of crops to climate also depends on soil variability among other variables (Wassenaar et al., 1999). Differences in response of various cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO2 concentration could partially address the problem. Acclimatization might require a collective strategy of identifying resilient or less sensitive cultivars, moving planting dates, identifying locations by vigilant site-specific assessment and introducing new tillage practices for water conservation and new varieties. By 2050, the global atmospheric CO2 concentration is likely to increase to ∼550 mol mol−1 hence; the selection of traits for developing new cultivars must take into account these future environmental conditions.

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Chapter 4

PLANT GROWTH REGULATORS, PLANT ADAPTABILITY AND PLANT PRODUCTIVITY: A REVIEW ON ABSCISIC ACID (ABA) SIGNALING IN PLANTS UNDER EMERGING ENVIRONMENTAL STRESSES Prasann Kumar1,*, Bansh Narayan Singh2 and Padmanabhh Dwivedi1 1

Department of Plant Physiology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India 2 Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, India

ABSTRACT Global plant productivity is struggling against multifaceted emerging environmental stressors. Future food security strongly depends on the ability to minimize and manage the stresses on crops and trees. A significant development has been made in understanding of plant’s responses under different stresses and how they can be controlled with the use of plant growth regulators, particularly thegrowth hormones.Our improving understanding of plant hormones also increase the chances that 

Corresponding author: [email protected].


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Prasann Kumar, Bansh Narayan Singh and Padmanabhh Dwivedi plants can be genetically modified to enhance their tolerance towards diverse environmental stresses. In this chapter, we present an overview of abscisic acid, an important plant growth regulator, and how it can provide a possible strategy to increase plant adaptability to future increases in temperatures and soil contamination.

Keywords: abscisic acid, cadmium, heavy metal, stress, tolerance

INTRODUCTION Crop production is becoming the major concern for plant scientists due to unfavorable environmental conditions. Some of abiotic stresses such as excess light, phytotoxic components in soil and air, extreme temperatures, declining water and nutrients in soil negatively affect the plant growth and development. Among these, rising temperatures and increasing soil contamination with metals pose a great risk to crop production in future. These stresses directly alter physiological and biochemical processes of the plants leading to significant crop loss (Villiers et al., 2011). IPCC (2014) concluded that it is possible that some regions in the world might cross the 20C threshold by middle of the century and hence will face effects on agriculture and food production systems. Tropical countries will be the first to cross the dangerous temperature thresholds. These regions are among the most vulnerable to climate change related food crisis due to low adaptability; and high population load. Moreover, some of the most potential future food baskets lie in tropics. However, regarding temperature sensitivity, temperate and sub-tropical agricultural zones are more prone to yield losses as both day and night temperatures will likely increase in future (Teixeira et al., 2013). Plants have tendency to adapt to different environmental conditions, also referred to as plasticity. A number of physiological, biochemical and molecular studies have been made to investigate the these mechanisms and it is now known that plants have evolved different mechanisms of chelation and sequestration of toxicants, transcription and translation of heat shock proteins, the production of phytohormones such as abscisic acid (ABA) and antioxidants and other protective molecules (Maestriet al., 2002). Having insights into these mechanisms, researchers are trying to devise strategies to make future plants adapt to future stresses.


Plant Growth Regulators, Plant Adaptability and Plant Productivity

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SOURCES AND GENERAL PROPERTIES OF SOME HEAVY METALS ESPECIALLY CONCERNED WITH CADMIUM Cadmium is a soft, ductile metal which is usually obtained as a by- product from the smelting of lead and zinc ores. The principal use of cadmium is as constituent in alloys and in the electroplating industry. Other uses of cadmium include paints and pottery pigments, corrosion resistant coating of nails, screws, etc in process of engraving, in cadmium-nickel batteries, and as fungicides (Stoeppler, 1991). Cadmium is also naturally present in soils and mineral fertilizers. Origin of cadmium in soil is described as agricultural wastes (20%), sludge (38%), fertilizers (2%) and atmospheric fallouts (40%). Cadmium is one of the most toxic elements with reported carcinogenic effects in humans (Goering et al., 1994). Cadmium and its compounds, compared to other heavy metals, are relatively water soluble and mobile compound in most soils, generally more bio-available and tend to bioaccumulate. It induces cell injury and death by interfering with calcium (Ca) regulation in biological system. Cadmium is not essential for plant or animal life (IPCS monographs/WHO1995). It is more mobile than zinc but less mobile than nickel. Cadmium is readily accumulated by many organisms, particularly by microorganism and mollusks where the bio-concentration factors are in the order of thousands. Its mobility essentially depends on the pH; the metal’s adsorption to the soil’s solid phase can be multiplied threefold for every unitary increase in pH in a range from 4 to 8. Terrestrial plants may accumulate cadmium in the roots and cadmium is found bound to the cell walls (AMAP 2002). The pH level is one of the most important factors controlling cadmium absorption. Compared with other micro pollutants such as Cu or Pb, transfer of Cd to the above ground parts of the plant may be considered as significant. Concentration in roots represents only 2 to 5 times that in the above ground parts but cadmium is transferred only with difficulty to reproductive or storage organs of the plant. No deficiency level for cadmium is known. On the contrary, cadmium is well known as a highly phytotoxic element. Besides retarding growth, phytotoxicity also occurs above 5.0-30.0 mg/kg dry weight, through chlorosis, which can be followed in the case of acute cadmium poisoning by necrosis (Browen, 1979). Other compounds including Fe, Se, Mn and particularly Zn are antagonistic to Cd. A draft commission regulation process to set maximum level for some heavy metals in foodstuff as 0.05 mg kg-1 in fish, vegetables and fruits, excluding leafy


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vegetables, root vegetables and potatoes; 0.1 mg kg-1 cereals, except wheat grain and rice; 0.2 mg kg-1 in wheat grain and rice, leafy vegetables and mushrooms. The plant hormone abscisic acid (ABA) is a sesquiterpenoid synthesized from xanthophylls and appears to influence several physiological and developmental events. The level of ABA in plants increases upon their exposure to environmental stress, such as drought, high temperature, low temperature, salinity and flooding. It appears that ABA is a general endogenous inducer of tolerance to environmental stresses. Changes in ABA contents in Cd-treated rice seedlings of two cultivars were investigated by Hsu and Kao, 2003. According to Hsu and Kao, on treatment with CdCl2, the ABA content rapidly increased in the leaves and roots of Cd-tolerant cultivar (cv. Tainung 67, TNG 67) but not in the Cd-sensitive cultivar (cv. Taichung Native 1, TN1). The reduction of transpiration rate of TN1 caused Cd was less than that of TNG67. Exogenous application of ABA reduced transpiration rate decreased Cd content and enhanced Cd tolerance of TN1 seedlings. Exogenous application of the ABA biosynthesis inhibitor, fluridone, reduced ABA accumulation, increased transpiration rate and Cd content and decreased Cd tolerance of TNG67 seedlings was reversed by the application of ABA. Increase of endogenous ABA content is closely related to Cd tolerance of rice seedlings. ABA may exert its regulatory effect on transpiration rate, which reduces the transpiration of Cd to the shoot.

CREDENTIALS OF GENES THAT REQUIRES ABA FOR THEIR EXPRESSION In general, it is seen that, mutants that are inhibited for the synthesis of ABA have been established to be useful for the identification of genes that needs increased level of ABA for their expression at cellular level (Table 2). These deficient mutants also have been used to established another set of genes which become upregulated without increased level of ABA in the cellular environment but this become sensitive for low temperature (Yamaguchi-Shinozaki, K. and Shinozaki, K. 1993). In relation to this table, it makes the real sense to mention what is the benefit of identifying those genetic responses? Please describe how it may be used for better adaptation of plants to these stresses. In this chapter, we discuss the potential utilization of plant hormones, with special reference to ABA, aiming to make plants adapt to future environmental stresses, mainly temperature stress and contaminated soils.



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Table 1. Effect of fluridone (flu, 0.2mM) on chlorophyll and protein contents in the second leaf of TNG67 rice seedlings treated with CdCl2 (0.5 mM) and various concentrations of ABA Treatment CdCl2 Fluridone [ABA inhibitor] + + _ + + + + + + + + + + + + Source: Hsu and Kao, 2003.

ABA (µM)

Chlorophyll (mg g-1 FW)

0 0 0 0 2 4 6 8 10

2.51 ± 0.08 2.51 ± 0.03 2.47 ± 0.05 1.58 ± 0.08 2.09 ± 0.13 2.62 ± 0.03 2.73 ± 0.06 2.64 ± 0.07 2.74 ± 0.10

Protein (mg g1 Fw) 19.0 ± 0.08 20.5 ± 1.1 18.3 ± 0.5 11.1 ± 0.5 13.4 ± 0.8 17.8 ± 1.5 20.8 ± 1.0 19.2 ± 1.0 17.5 ± 1.8

Table 2. Genes regulated by Elevated Levels of Endogenous ABA resulting from environmental stresses using ABA-deficient mutants of Tomato and Arabidopsis Sl. No. 1.

2.

Mutant

Gene

Tomato

le4

Arabidopsis

Gene family

Stress

dhn/rab/group 2 Low temperature le16 nsLTP Low temperature le20 H1-histone Low temperature le25 D-113/group4 Low temperature Rab 18 dhn/rab/group 2 Low temperature Iti65 rd29/cor78 Low temperature

References Cohen et al., 1991 Cohen and Bray, 1990 Bray et al., 1993 Cohen et al., 1991 Lang and Palva 1992 YamaguchiShinozaki, K. and Shinozaki, K, 1993


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UTILIZING PLANT HORMONES FOR MAINTAINING HIGHER CROP YIELDS ABA are involved in abiotic stress tolerance in plants. Increased ABA level in stressed plants have adaptive significance because of their involvement in regulation of cellular ionic environment, maintenance of membrane integrity, prevention of chlorophyll loss and stimulation of protein, nucleic acid and protective alkaloids. Interaction of ABA with membrane phospholipids implicates membrane stability under stress conditions. ABA was identified 50 years ago as a growth inhibitor in abscising cotton fruit and sycamore trees (Wasilewskaet al., 2008; Cutler et al., 2010). As it is known as abscisin hormone, ABA does not control abscision directly during senescence in abscissing organ (Sharp, 2002). ABA is produced under various environmental stresses such as drought, cold, salinity, heat and pathogen infection. In most of the vegetative tissues of vascular plants, ABA is produced under water stress condition and regulates stomatal closure as well as various gene expressions related to dehydration tolerance (Rock et al., 2010). However, in non-vascular plants, ABA and some plant-specific transcription factor ABA INSENSITIVE3 (ABI3) are essential for seed desiccation tolerance. It is present in both gametophytic and sporophyitc developmental process of angiospermic plants under stress condition (Hartunget al., 1987). ABA is produced in plastids from C5 precursors i.e., isopentenyl pyrophosphate (IPP) ‘building blocks’ from which ABA is formed.It is derived from either cytoplasmic acetate/mevalonate pathway or plastidic methyl erythritol phosphate (MEP) pathway (Kirby and Keasling, 2009; Ruiz-Sola and Rodriguez-Concepcion, 2012). Carotenoids are the initial product for ABA biosynthesis and a series of condensation reactions involved in this process.Several mutant analysis studies suggested that metabolism and enzymes involved in ABA hormone synthesis are regulated by feedback processes under such environmental stresses like drought, cold, heat and temperature.

ABA SIGNAL TRANSDUCTION Several studies suggest that ABA signal transduction is associated with many second messengers such as phospholipid-derived signals, Ca2+, nitric oxide (NO), reactive oxygen species (ROS), cyclic ADP-ribose and cyclic GMP. These second messengers are involved in ABA regulation in various



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physiological processes. Among these messengers, NO and Ca2+ are most known ones which regulated the ABA signal transduction (Figure 1). Exogenous application of NO can trigger stomatal closure. It is well known that NO and ROS accumulated in the guard cell in ABA induced stomatal closure (Simontacchi et al., 2013). Another aspect of regulation of ABA by cytosolic Ca2+ concentration is dependent on either intra- or extra-cellular responses through plasma membrane channels. Several ROS (H2O2, O2-, OH*) are produced by oxidation reaction and activated plasma membrane channels. The level of intra-cellular Ca2+ is increased by induced of inositol triphosphate 3 (IP3). IP3 is catalyzed by phospholipase C activity and converted into phosphorylated inositide IP6 which participates in ABA inhibition of stomatal opening by promoting Ca2+ release leading to inhibition of K+ influx channels. Another product of PLC activity is diacylglycerol (DAG) which can be phosphorylated to produce phosphatidic acid (PA).PA is also produced by phospholipase D (PLD) activity. ABA also protect membrane from oxidative damage as they act as free radical scavengers. Response to abiotic injury and mineral nutrient deficiency is associated with the production of ABA in plants. The contents are altered in response to the exposure to heavy metals. These effectively stabilize and protect the membrane systems against the toxic effects of metal ions. Plants are adapted to synthesize a diverse group of metabolites upon the exposure of heavy metals that accumulate in the tissues in different ranges. In these metabolites specific amino acids such as polyamines, proline, histidine, peptides accumulate more. Scientist reported that, purines are also formed which indirectly attached to the synthesis of ABA. However, changes in the contents of these metabolites bear the functional significance in the context of metal stress tolerance. ABA contents are altered in response to the exposure to heavy metals. However, there is a strong possibility that they can effectively stabilize and protect the membrane systems against the toxic effects of metal ions particularly the redox active metals. Environmental stress severely restricts the distribution and productivity of plants. Heavy metal is one of the major abiotic factors which can limit crop productivity especially in arid and semi arid region. Land and water resources are worst affected under continuous stress, both biotic and abiotic, due to anthropogenic interventions. The soil is primary recipient by design or accident of a myriad of waste products and chemicals used in modern society. Cadmium (Cd) is of particular concern to human health as it can be readily absorbed by roots and be concentrated by many cereals, potatoes, vegetables and fruits. Elevated levels of Cd generally inhibit seed germination, cell growth as well as whole plant growth, nutrient uptake, distribution and photosynthesis.


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Figure 1. Effect of ABA on stomatal function.

According to the principle of soft-soft acid-base interaction (Pearson, 1963), the Cd ion can theoretically interact with the polarizable atoms of mono-, bi- and poli-dentate bioligands, such as the nitrogen of amino groups of histidine and polyamines, the oxygen of citrate, glutamic acid and glycine deprotonated carboxyls (Rauser, 1999). These small bioligands generally form less stable complexes than those formed with thiols, with mixed or different coordination geometry and have less specificity towards Cd. In particular, Cd binds octahedrally to O-bearing groups and tetrahedrally to S-bearing groups (Salt et al, 1995; Rauser, 1999). NMR studies of the formation constants of complexes suggest that GSH, a ubiquitous molecule in plant organs, can rapidly form relatively stable complexes as soon as it comes across Cd. This can lead to a 1:2 and, to a lesser extent, a 2:2 stoichiometry ratio of Cd:GSH coordination preponderant under the pH range 5-8 (Kadimaet al., 1990; Diaz-Cruz, 1997; Vairavamurthy, 2000). The formation of complexes with phytochelatins and metallothioneins is slower than the formation of complexes with glutathione, but the number of Cd complexed with these polythiols is higher than with glutathione (Satofukaet al., 2001). Thus, very probably, the formation of complexes with cysteine and glutathione is a primary response of plants to Cd exposure, replaced by polythiol-forming complexes with increasing stability. According to some experimental results, cysteine and glutathione complexes are more likely to form at very low and at very high Cd concentrations (VogeliLange and Wagner, 1996) when their formation is energetically less costly than



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phytochelatins, and when phytochelatin capacity to complex Cd is saturated. The Cd complex stability is thus a very important characteristic for the effective movement of Cd through the plant, and for its stable vacuolar sequestration. Exchange reactions of ligands occur at a reasonable rate when they lead to thermodynamically more stable complexes (Andersen and Aaseth, 2002). It is reasonable to assume that the exchange rate is high when Cd enters roots and very low when it forms the high molecular weight complex in the vacuoles. The mobilization of Cd from roots to shoots through the formation of complexes and ligand exchanges avoids the buildup of toxic Cd concentrations at sensitive sites. However, the possibility of exchanging ligands can lead to Cd binding with the many polarizable atoms of head groups projecting from surfaces of cell walls or membranes, or constituting the active sites of enzymes and of other molecules taking part in important cell processes (Salt et al., 1995; Das et al., 1997). These interactions can thus be the cause of numerous potential dysfunctions observed in plant roots exposed to Cd (Ederliet al., 2004). For example, prolonged Cd binding to root cell walls can be expected to alter their permeability and disturb the selective acquisition of some essential metals, particularly Mn, Ca, Mg and Fe (Das et al., 1997). It cannot be excluded that an enhancement of oxidative reactions is due to a Cd-induced deficiency of Mn or Fe by antagonistic root absorption (Sharma et al., 1985). This could, in fact, decrease the antioxidant capacity of the Mn or/and Fe superoxide dismutase. Similarly, a deficiency in Mn or its displacement by Cd could unbalance photosystem II activities, increasing the risks that photooxidative reactions take place on chlorophylls and other molecules (Baszynskiet al., 1980).

ABA AND SENESCENCE Senescence is the final stage of growth and development. It is an irreversible process. It will start with the hydrolysis of reserve materials and leads to remobilization of nutrients in the plant and finally lead to death of the plants. Leaf senescence and aging of leaf both are different. Senescence-related changes also occur under adverse environmental conditions, e.g., drought, heat, nitrogen deficiency, light limitation, and attack by pathogens or onset of disease. Leaf senescence is not simply the aging-dependent passive death of a leaf, but is a tightly organized and controlled process during which cell components are degraded in a coordinated fashion. When nutrients have been relocated to other parts of the plant body, the cell finally dies (Gan and Amasino, 1997; Noodenet al., 1997).Plants respond to these adverse conditions by initiating changes that


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may result in leaf senescence and abscission, precocious seed development, and a reduced plant life form. How do we study senescence? Generally we use the leaves and flower petals for the study. Yellowing is the visible manifestation of senescence. Physiological parameters used to measure the senescence include a loss of chlorophyll and a decline in the photosynthetic rate. Both are relatively easy to measure. The first symptoms of the senescence are a decline in the photosynthetic rate and an increase in the respiration rate. Chloroplast degraded first but mitochondria and peroxisomes remains functional. Senescence is not altogether a degradative process; many proteins as well as secondary products are synthesized during senescence (Buchanan et al.,2003). Table 3. SAGs and digestion of cellular molecules Sl. No.

Breakdown of molecules Remarks due to upregulation of SAGs genes 1. Digestion of proteins Genes encoding protease These proteases are found similar to those expressed in germinated seeds for digestion of reserved proteins Some proteases are similar to vacuolar processing enzymes, which take active participation in activation of other enzymes. Some are similar with protease of PCD in animal cells 2. Digestion of RNA The total measured amount of RNA in senescing cells show a declining trend due to increased RNase activity and associated genes responsible for the same. 3. Lipid mobilizations During senescence the regular supply of energy is essential at constant rate because high demand of energy is required for degradation and mobilization of the nutrients. Fatty acids released by the breakdown of membranes yield acetate by β-oxidation. 4. Remobilization of the Nitrogen is translocated in the phloem stream mainly in Nitrogen the form of amides, glutamine and asparagines. Glutamine synthase (GS) are the principle enzymes that convert ammonia to glutamine. Two types of GS occur in plants: GS1 is located in cytosol and GS2 is located in plastids. During senescence activity of GS2 decreases while that of GS1 increases. 5. Chlorophyll breakdown Due to activation of chlorophyllase, the chlorophyll will break due to degradation of phytol tail. Source: Buchanan et al., 2003.

Leaf senescence is regulated by different gene expression. Molecular approach established that, a number of senescence –associated genes (SAGs)



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have been identified (Lim and Nam 2005). SAGs encode enzymes involved in the digestion of number of molecules. These are summarized below in Table 3. We have discussed the natural senescence; there is also the senescence which can be induced by abiotic and biotic stresses. Based on the comparisons betweenthe gene expression profile of artificially induced senescence in detached leaves and that of natural senescence in intact leaves, it has been evident that many, but not all of these genes, exhibit similar patterns of expression (Becker and Apel, 1993).

CONCLUSION ABA is found universally in plants—angiosperms, gymnosperms, ferns, horsetail, mosses, liverworts and algae. ABA increases the tolerance level of plants to various kinds of stress caused by environmental or biotic factors. Plants cope with this problem by increasing the level of endogenous ABA quickly. Which leads to production of various osmolites via different tiers of signaling within the plants. Heavy metal stress especially cadmium and temperature stress, will leads to production of reactive oxygen species, this can be scavenge by the synthesized special protein and osmolytes within the cell. Here, ABA is the chief hormone involved in such protection. Besides this one, ABA also plays a central role in seed development, enabling seeds to withstand desiccation and to become dormant.

ACKNOWLEDGMENTS Authors are thankful to University Grants Commission New Delhi for providing Senior Research Fellowship to PK, and BHU for research fellowship to BNS.

REFERENCES Adriano, D.C. (1986). Chromium. In “Trace elements in the terrestrial environment” Springer, New York, pp. 58-76. AMAP. AMAP Assessment. (2002). Heavy Metals in the Arctic -Pre-print files. Arctic Monitoring and Assessment Programme; Oslo, Norway, pp. 870.


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Chapter 5

GLOBAL CLIMATE CHANGE AND MUNG BEAN PRODUCTION: A ROADMAP TOWARDS FUTURE SUSTAINABLE AGRICULTURE Moushree Sarkar1,, Sambit Datta2,3 and Sabyasachi Kundagrami1 1

Department of Genetics and Plant Breeding, Institute of Agricultural Science, University of Calcutta, West Bengal, India 2 Department of Botany, University of Calcutta, West Bengal, India 3 Department of Agricultural Chemistry and Soil Science, Institute of Agricultural Science, University of Calcutta, West Bengal, India

ABSTRACT Climate change has become a serious global problem and its ramifications on agricultural practices are threatening global food security. Changes in temperature, precipitation, rainfall pattern, soil degradation, pest and pathogen behaviors have serious implications on agricultural systems throughout the globe. Already the effects of global warming are evident in many parts of the world, which has reduced agricultural outputs especially in the economically backward nations. Severe droughts, flash 



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Moushree Sarkar, Sambit Datta and Sabyasachi Kundagrami floods due to unseasonal rainfall, salinization of arable lands have negated agricultural productivity. In this chapter, we have tried to present the effects of global climate change and its effect on the cultivation of a pulse crop, Vigna radiata (L.) Wilczek. Mungbean is an important legume crop in terms of both food value and its beneficial role in biological nitrogen fixation and soil fertility. It is primarily cultivated in the developing nations of Asia, especially India, Pakistan, China, Myanmar, and Bangladesh. Its importance in food security globally is unconditionally important as it provides essential dietary protein, carbohydrate, vitamins, and minerals, cheaply to the poorest of the poor. Changes in the environmental factors pertaining to the cultivation of mungbean can cause further lowering of productivity and production of mungbean, which already faces several challenges in its cultivation.

Keywords: climate change, food security, Vigna radiata (L.) Wilczek, temperature stress, drought stress, salinity stress

INTRODUCTION Food security, as defined by FAO (2003), states as, “When all people, at all times, have physical and economic access to sufficient, safe, and nutritious food to meet their dietary needs and food preferences for an active and healthy life.” It comprises of multiple food availability, food access and food utilization issues. Plant genetic resources, for food and agriculture are the basis of global food security. Kameswara (2004) stated that the genetic diversity provides farmers and plant breeders with options to develop, through selection and breeding, new, and more productive crops. The world population of 7.35 billion now is expected to cross 9.6 billion by 2040–2050 (Global population growth 2015). This increase in population will cause severe damages by changing the climatic condition as well as put additional constraints on food production. Hence, there is an urgent need to protect the environment. The resources of land and water have to be used more competently for crop production. Based on FAO released estimates, food production must be doubled between 2000 and 2050 to meet the increase in population. Additionally, consumers demand healthy food and with higher nutritional values (Lusser et al. 2011). Although there has been an increasing consciousness to deviate from monoculture cropping system that has a high dependency on inorganic ‘N’ fertilizers, very little attention is given on the crucial role of legume cultivation in sustainable agriculture. Legumes associate themselves with specific soil rhizobacteria in the process of biological


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nitrogen fixation and are estimated to fix 21.5 million tons of nitrogen in different agricultural systems around the world (Herride et al. 2008). Apart from this, legumes are a great source for providing high-quality food and feed. In spite of these benefits of legumes, considerable limitations are imposed on the cultivation of legumes, which needs to be addressed. Legumes are commonly known as grain legume, and are major source of proteins and commonly known as poor man’s meat (Reddy 2010). They complement the staple cereals in diets with proteins, essential amino acids, vitamins, and minerals. They contain about 22 - 24% protein which is almost twice the protein in wheat and thrice that of rice (Gowda et al. 2013). The intake of pulse protein is much higher than any other source of protein. About 89% of the population consumes pulse at least once a weak while only 35.4% consume animal protein at least once a weak in India (IIPS ORC Macro 2007). Pulses provide healthy proteins as compared to other protein sources like meat and meat products (Reddy et al. 2013). Among the several pulses cultivated globally, Mungbean (Vigna radiata (L.) Wilczek) is the third most important pulse crop and is highly valued as a grain legume. According to previous studies, Vigna radiata exhibits multiple benefits at farm and entire ecosystem level. They are, (a) rich protein source for human and animal consumption, (b) has a high capacity for biological nitrogen fixation thus increasing soil fertility, (c) has high potential for use as green manure, (d) multiple potential as biofuels, pharmaceuticals, and (e) with the introduction in intercropping systems has the potential of diversification as well as prevention of soil erosion. In the succeeding sections, a comprehensive outline has been attempted to find the effect of climate change on the cultivation and production of mung bean.

GLOBAL CLIMATE CHANGE AND ITS EFFECT ON AGRICULTURAL PRODUCTIVITY On 16 February 2005, at the Kyoto Protocol, a giant step towards mitigating global climate change because of human activities was placed in force. From the evolution of living beings on earth, there has been a gradual and regular change in its climate. The natural shifts in climate over millions of years have been gradual and regular which has helped organisms to evolve and diversify. But as a result of anthropogenic activities, within a little over a hundred years, huge quantities of greenhouse gases have been released into the atmosphere, as a result of mining and combustion of fossil fuels, rampant deforestation,


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maintenance of livestock herds, and even from agricultural practices. The accumulation of the greenhouse gases in the atmosphere has warmed the planet abnormally and caused changes in the global climate systems. In 2001, the United Nations (UN) sponsored Intergovernmental Panel on Climate Change (IPCC) reported that worldwide temperatures have increased by more than 0.6°C in the past century. It is predicted that by 2100, average global temperatures may show an increase between 1.1°C and 6.6°C. The melting of the ice caps and snow cover, resulting in rising sea levels, timing and intensity of precipitation, leading to unusual floods mainly in coastal areas, and mid-term or severe drought in other regions, has been predicted. Such abnormalities arising out of climate change will adversely affect agricultural practices and productivity. The primary reasons of concerns in agriculture are,    

Geographical shifts and yield changes in agriculture, Reduction in the quantity of water available for irrigation Loss of land through sea level rise and associated salinization Changes in the behavior and incidence of major pathogens associated with important crop plants.

An estimate predicts that degradation of land, urban expansion, and conversion of crops and cropland for non-food production will cause a reduction in global cropping area between 8 – 20% by 2050 (Nellmann et al. 2009). This fact, in combination to water scarcity is already posing a formidable challenge to increase food production. Additionally because of climate change melting of glaciers, would disturb the monsoon pattern and increase flooding/drought in parts of Asia that will affect 25% of the world’s cereal production. Total food production alone does not define food security, as food must be safe, accessible, affordable, and meet the desired nutritive values. All these factors can adversely influence directly and indirectly through changes in pest and pathogen behavior because of changed climatic conditions. Soil, is a complex ecosystem comprising of different biological modules, each of which can be affected by climate change. Changes in soil ecology can affect the growth of crop plants. However, gross generalization in soil behavior cannot be solely attributed to climate change as soil types also play a vital role (Pangga et al. 2011). Water availability, another major attribute, as well as its quality are also key constraints in agriculture under present global climatic shifts. There are historical evidences that show alterations in the distribution and pattern of precipitation that affected the food production. Another aspect of water is its quality, e.g., whether it is affected by pollution or increased salinization. This directly affects crop



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productivity and food production. Another probable effect of climate change is the alterations in the behavior of pathogen and pests. Changes in temperature and precipitation play an important role in the shift in the pattern of disease incidence. Such shifts if not adequately predicted by models can lead to devastating crop losses (Elad et al. 2014).

MUNGBEAN AND FOOD SECURITY Pulses are an important protein source globally and especially for Asian and African populations many of whom depend on cereals and pulses for their daily requirement. It is a rich source of proteins, minerals, and vitamins proving the necessary nutritive requirements. It is often termed as “poor man’s protein.” The whole grain of mungbean is rich in fibers and minerals such as iron, potassium, and zinc as well as vitamins A and B. In general, mungbean seeds contain 2228% protein, 60-65% carbohydrate, 1-1.5% fat, and 3.5-4.5% fibers. Additionally it contains vitamin A (94 mg), iron (7.3 mg), calcium (124 mg), zinc (3 mg) and folate (549 mg) per 100g of seed. It is also rich in essential amino acids specially lysine, which is deficient in most of the cereal grains. Mungbean sprout is a popular vegetable since they are good and highly nutritive. Sprouted mungbeans are a rich source of vitamin C, vitamin B, folate, and thiamine (Anwar 2007). Due to such high nutritional value, they are consider as a healthy food and are often eaten raw or slightly cooked in salads and sandwiches. Mungbean vermicelli is popularly consumed in different dishes throughout Asia. Mungbean may be used in porridge, cakes, snack, sweetened bean pastes, beverage etc. The de-hulled grain of mungbean is cooked as ‘dal’ in India, Bangladesh and Pakistan (Zaid et al. 2012). Recent studies have shown that incorporation of pulses into daily diet has beneficial role in preventing cardiac diseases, cancer, hypertension, osteoporosis, and diabetes (Tharanathan & Mahadevamma, 2003). Due to such findings novel probiotic food supplements based on mungbean protein fermentation is being experimented (Wu et al. 2015). Mungbean also contains a significant amount of bioactive phytochemicals. Roots of mungbean have been traditionally used as antiinflammatory, aphrodisiac, refrigerant, and as emollient (Dongyan et al. 2015). From these facts it is clear that mungbean has an important dietary role in global food security, especially to economically weak populations. Hence, any detrimental effect on the cultivation of mungbean, arising out of global warming and climate change is a matter of concern.


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Mung Bean Production The production statistics of mungbean are a bit sketchy. The world production of mungbean is 5.5 -6 million hectares per year, out of which 90% is in Asia (Kang et al. 2014; Kaur et al. 2015). Mungbean is considered a native of India but is also cultivated in Pakistan, Bangladesh, Myanmar, Indonesia, Philippines, Sri Lanka, Nepal, China, Korea, and Japan. Although introduced late, its cultivation has also gained pace in Australia, East Africa and United States of America (Zaid et al. 2012). India stands first with respect to the total area as well as productivity of pulse crops. In 2012-13, the total area for pulse cultivation was estimated at 23.3 million hectares with an average productivity of 789 kg ha-1. The total production within the same period was pegged at 18.1 million tons (Padder et al. 2012). According to Government of India reports, India produces about 1.5 to 2.0 million tons of mungbean annually from about 3 to 4 million hectares of area with an average productivity of 500 kg ha-1 (Figure - 1 and Figure - 2). Mungbean output accounts for about 10-12% of total pulse production in the country. However, the major part of the produce is used to meet the domestic demands. Not much is exported. Next to India, China and Myanmar are the largest producers of mungbean. In Myanmar, an area of 1 million hectare with an annual production of 1410,000 metric tons has been reported (M. O. A. I. 2011). In China, production of mungbean forms 19% of its total legume production. The annual production of china is estimated at 6 million tons. In Bangladesh, mungbean cultivation occupies fifth position when compared to other pulses based on area and production and it is an annual legume (Rahim et al. 2008). In Pakistan, it is planted in 2.6 million hectares with a total production of 1.8 million tons with average yield of 723 kg ha-1 (Minfal 2009).

Effect of Climate Change on Mung Bean Cultivation Changes in earth’s climate due to global warming and increased atmospheric greenhouse gases, will significantly affect global agricultural productivity as predicted in the present millennia. Such changes in climatic factors will also affect mung bean cultivation globally. In the succeeding sections, an effort has been made to outline the broad effects of global warming and climate change on the cultivation, and yield of mungbean.



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Source: Pulses Handbook (2015). Figure 1 Global pulse production scenario. Note, Mungbean is included in dry bean production (2001-2013).

Source: Pulse Handbook (2015). Figure 2. Trends in area, production, and yield of pulses in India.

Effect of Temperature Stress on Mungbean Because of increase in greenhouse gases, worldwide temperatures are rising. Such a rise in temperature, especially in the tropical and sub-tropical regions of the world would pose serious challenge to crop plant production. Every plant species have its own specific temperature requirements, minimum and maximum, below and above which no germination occurs, and an optimum


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temperature (To) in which germination is most degraded. In the sub-optimal temperature range, the germination rate is linearly associated with temperature, allowing temperature and time to be combined into a single thermal time value (Feddes 1972; Garcia-Huidobro 1982), Ɵ = Gt50 * (T-Tb) where, Gt50 is the median germination time (d), T is temperature, Tb the minimum or base temperature at or below which no germination will occur, and Ɵ the thermal time (°Cd). Increased ambient temperature is manifested in most living organisms as heat stress. It is one of the principal stresses limiting the performance of plants worldwide (Wahid et al. 2007). The rise in temperatures is drastically affecting the growth and production potential of important crops, especially for those being grown in the tropical conditions (Hall 2001). Elevated temperatures can cause several changes at cellular and sub-cellular levels and the response of the plants depends upon the growth stage, intensity, and duration of the exposure. Increase in temperatures for plants are directly related to the denaturation of proteins and enzymes, damage to membranes while its indirect effects may include inactivation of enzymes present in the mitochondria and chloroplasts, impaired protein synthesis, degradation of proteins, and disruption of membrane integrity (Howarth 2005). Temperature is the principal environmental factor controlling not only the growth duration, but also the growth pattern, biomass partitioning and yield of mungbean crop. The critical temperatures for mungbean plant at different growth phases are shown in Table 1. Table 1. Cardinal temperatures (°C) estimated from the mungbean germination and emergence experiments Tb T0 Tc Germination 10.1 40 53 Radicle elongation 11.3 37 45 Emergence from soil 12.6 35 45 Tb: the minimum temperature at or below which no germination will occur; T0: optimum temperature for germination; Tc: the maximum temperature at or above which no germination will occur. Source: Fyfield and Gregory 1989.



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Future increases in ambient temperatures due to increased greenhouse effect (IPCC 2013) would have negative impacts on mungbean yields in Asia, especially South East Asia. In spite of the fact that mungbean is mostly cultivated in the summer ensuring high temperature tolerance in mungbean, however it’s yields are reduced significantly when growing temperatures increased from the optimum range i.e., 25 ºC - 35 ºC. High temperature can reduce the total biomass and harvest index of mung bean plant, which ultimately results in yield loss. The impact of temperature deviation on developmental stages could be observed in the alteration of durations to 50% flowering and maturity. With increasing temperatures, the flower initiation and maturity duration is also interrupted. High temperature stress is reported to have a direct negative impact on flower retention and consequently in pod formation. Flower shedding is very common in mungbean crop and the extent of flower shedding has been reported up to 79% due to excessive heat (Kumari and Varma 1983). Mungbean plants experiencing temperatures exceeding 40 ºC indicate damage as follows:       

High levels of chlorosis, Reduction of vegetative as well as reproductive growth, Abscission of buds, flowers, and pods. Yield loss, Pollen in viability, Lack of fertilization High or otherwise complete flower shedding

Mungbean plants are associated with symbiotic bacterial populations that form root nodules. Such a symbiosis is beneficial in agriculture as this helps to fix atmospheric nitrogen thereby increasing soil fertility. High root temperatures adversely affect bacterial infection along with N2 fixation in several legume species, including mungbean. The optimal temperature for nodule functioning is ranged between 25°C and 30°C. Temperature affects the legume-Rhizobium symbiosis directly, by restricting the growth of the micro symbiont and indirectly, by regulating the growth of the macro symbiont. Before nodule establishment, root zone temperature influences the rhizobial survival in soil as well as the exchange of molecular signals between the symbiotic partners (Bansal 2014). Therefore, an increase in root temperature (>35°C) can hamper the nodule formation of mungbean plant. High temperature leads to the loss of nod gene expression, which reduced the total number of bacteria that start


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nodulation with the plant. Once the nodule is established, symbiotic nitrogen fixation is dependent on the physiological state of the host plant. High soil temperatures in tropical and subtropical areas are a major problem for biological nitrogen fixation of legume crops (Michiels et al. 1994). Additionally high soil temperatures affect the root hair infection, bacteroid differentiation, nodule structure, and delay in nodulation.

Effect of Waterlogging on Mungbean Cultivation Global warming is leading to thermal expansion of seawater, together with melting of glaciers and sea-ice, the resultant effect of which is the rise in sea level. A 0.1 to 0.5m rise in sea-level by the middle of this century will pose a great threat to the livelihoods and agriculture in low-lying coastal areas of the world (Agarwala et al. 2003). Moreover, climate change has also brought about changes in the precipitation pattern. This results in excessive rain in some parts of the world while lack of rainfall hampers other parts of the world. Waterlogging takes place when water enters faster into soil than its removal by natural gravitational forces. It creates reduced oxygen partial pressure. This is important because (1) roots are particularly sensitive to anaerobic conditions, and (2) anaerobic conditions support a unique microbial community compared with aerobic conditions, and this can severely affect the nutrient relations of the soil (Nilsen and Orcutt, 1996). Waterlogging blocks the oxygen supply to the roots, inhibiting root respiration, this results in severe decline in energy status of root cells affecting important metabolic process of plants. The most common is reduction in nitrogen fixation, chlorosis and reduction in crop growth. Mungbean is particularly sensitive to waterlogging conditions. Excess water in mungbean cultivation is particularly harmful to the early stages of the plant as well as at the time of pod maturity (Tickoo et al. 2006; Singh et al. 2011). Ahmed et al. (2002) reported that waterlogging in mungbean caused a fast decline in the photosynthetic rate, transpiration rate, leaf water potential, dry matter and seed yield. The rate of photosynthesis under flooding may decrease due to increased photorespiration and reduced ribulose bisphosphate carboxylase (RuBisCO) activity. Yellowing of leaves in waterlogged conditions is a common observation in mungbean plants. Decrease in rate of photosynthesis under waterlogging may also be due to stomatal closure, decrease in leaf chlorophyll concentration, production of ethylene, reductions in sink demand, and disruption of the translocation of photosynthates. At the same time, relative



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water content (RWC) and membrane stability of mungbean plants are reduced due to severe waterlogged condition. Nodulation and biological nitrogen fixation, because of flooding has been found to be hampered in mungbean plants (Ezin et al. 2010). In addition, waterlogging results in reduced soil nitrogen through rapid volatilization and denitrification. It also produces toxic nitrites and sulphides in soil rhizosphere which are harmful for biological nitrogen fixation (Rasaei et al. 2012).

Effect of Drought on Mungbean Cultivation Lack of sufficient rainfall in certain parts of the world, because of climate change and altered precipitation patterns, have aggravated the issue of drought. Expansion of global drought stress areas threatens crop production (Postel 2000). Drought is defined as the absence of adequate moisture necessary for a plant to grow normally (Zhu, 2002). Effect of drought stress on the plant is very complex and it affects plant organization at different levels (Blum et al. 1996). Drought stress alters the water relation or water balance and at the cellular level, it affects the integrity of membranes and proteins. Such a situation leads to metabolic dysfunction mediated by general disruption of cellular compartmentation and loss in activity of membrane based enzymes. It restricts the transpiration rates and impaired active transport along with membrane permeability. As a result, nutrient uptake by roots and transport from roots to shoots is reduced severely. Common physiological responses of drought stress in plants include stomatal closure, decreased photosynthesis, reduction in internal carbon dioxide concentrations, and impair RubisCo activities (Yordanov et al. 2003, Flexas et al. 2005). These effects hamper the photosynthetic activity of the plant, which finally manifests in lower yields. Response to drought varies in plants, with the duration of stress, variety, growth stage of crop, and soil type. Mungbean is more susceptible to water deficits than many other grain legumes (Pandey et al. 1984), mostly because this crop is generally cultivated under rainfed conditions. Therefore, productivity is severely affected due to insufficient rainfall, particularly in the spring and summer grown crops. Such a situation often exposes the plant to drought conditions. The yield of mungbean plant is hampered under drought conditions largely due to impairment of the morphology and physiology of the leaves. Drought stress reduces relative leaf water content, total number of leaves, reduced plant size, root growth, and leaf area. The reduction of leaf area as well as the number is highest during the early vegetative phase of mungbean


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(Alyemeni M 2015; Baroowa and Gogoi, 2016). Further, because of drought reduced turgor pressure decreases rate of cell division and cell expansion in mungbean, which results in overall shortening of the plants. All these factors consequently reduce dry matter accumulation, number of pods per plant, and harvest index of the plant (Sadasivam 1988). In a seperate study, it was shown that water deficits at the flowering and the post-flowering stages have been found to have a greater adverse impact than that at the vegetative stage. The crop is more sensitive to drought during the flowering periods which reduces its productivity (Refiei shirvm and Asgharipu 2009). Another interesting observation in mungbean under drought stress is the elevated levels of endogenous ethylene. Such elevated endogenous ethylene reduces plant growth and is also associated with premature scenecense (Arshad et al. 2008). Increase of ethylene levels decreases stomatal conductance, proline content, increase total soluble carbohydrate in drought stresses mungbean plants (Kumari et al. 2015). Symbiotic N2 fixation of legumes is also highly sensitive to soil water deficiency. Mungbean exhibits a reduction in nitrogen fixation when subject to soil moisture deficit. Nitrogen derived from biological nitrogen fixation was found to decrease by about 26% because of water deficiency when measured by the acetylene reduction assay. Soil moisture deficiency has a pronounced effect on nitrogen fixation because nodule initiation, growth, and activity are all more sensitive to water stress than are general root and shoot metabolism (Albrecht 1994; Naz 2009). Hence, higher levels of ethylene production as a result of drought stress is also detrimental to nodulation in mungbean plants.

Effect of Increased Salinization on Mungbean Cultivation Impacts of climate change on sea-level rise would have real consequences on the livelihoods of the coastal people as it would be affected by salinity intrusion, flooding, cyclones, heavy storms and erosion of the land masses (World Bank 2000; Agarwala et al. 2003). Therefore, agriculture in low-lying areas is likely to become increasingly difficult to sustain. It is predicted by IPCC (2007) that at the end of 21st century, the sea level may rise up to about 0.60 (±0.40) cm. This would lead to widespread flooding of costal low-lying regions. Peripheral water irrigation, extreme soil fertilization, deforestation, and desertification are the major factors of soil salinization. Every year more and more arable land is falling prey to increased soil salinization. At present 800



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million hectares of land are affected by salinity worldwide (Munns and Tester 2008). Accumulation of soluble salts in soil hampers plant growth and physiology. Decreased growth in plants as a response to salt stress is attributed to osmotic effect of salinity, specific ion toxicity, nutritional and hormonal imbalance, as well as elevated cellular levels of reactive oxygen species (Ozturk et al. 2012; Raza et al. 2013). Elevated levels of reactive oxygen species could bring about damage to cell membranes, photosynthetic pigments and mutations in DNA (Ashraf 2009). Salinity drastically affects photosynthesis, nitrogen content as well as carbon metabolism and also disturbs plant mineral nutrition along with sodium accumulation in plant tissues (Hasanuzzaman et al. 2012). Mungbean is categorized as salt sensitive crop (Chakrobarti and Mukherji 2003). Therefore, salinity stress is one of the most destructive environmental factors restricting the productivity of mungbean, especially in arid and semiarid regions (Abd-Alla et al. 1998). Reduction of photosynthetic pigments (chlorophyll a, b, and carotenoids) leads to chlorosis in mungbean leaves. Reduction in germination, shoot and root length, fresh weight, vigour index, disturbances in membrane permeability, changes in osmotic potential, and specific ion toxicity results in mungbean plants because of saline stress. All these can reduce mungbean production up to 70% (Munns and Tester 2008; Saha et al. 2010; Sehrawat et al. 2013). Increasing the level of salinity gradually decreases the number of pods per plant, fresh weight of pod as well as the dry mass of mungbean plants. Dehydration, increase flower shedding, and pod-shattering during summer, due to high soil salinity, deteriorates the texture and quality of mungbean seeds (Sehrawat et al. 2015; Khan et al. 2010). High temperatures coupled with osmotic shock arising out of salinity stress severely limited mungbean growth more in summer season than in spring (Sehrawat et al, 2015). Mungbean plants experiencing salinity intrusion indicate damages, which are as follows:    

Reduction in seed germination, plant height, shoot and root length, dry matter, biomass, root, stem and leaf weights Reduced number of seeds/pod or plant and dry matter yield of individual seed Reductions in length, number of root hairs and branches, while the roots became stout, brittle and brown in color Disturbance in photosynthetic processes


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Moushree Sarkar, Sambit Datta and Sabyasachi Kundagrami 

 

Nutritional imbalances by altering the uptake of nitrogen, phosphorus, potassium, and calcium, and interferes with the cellular metabolism by causing ion toxicity and osmotic agitations Plant death Yield loss

Salinity does not affect colonization of roots by rhizobia but does delay the initiation or growth of new nodules, reduce the efficiency of fully formed nodules, which had developed earlier under non‐saline conditions. It also decreases the proportion of those nodules that are initiated in saline conditions and are able to differentiate fully into active N2‐fixing nodules. Salt stress inhibits the initial steps of rhizobium-legume symbioses by reducing the survival of rhizobia, inhibiting the infection process, affecting nodule development and function, or reducing plant growth (Elahi et al. 2004). The saltinduced distortions in nodule structure could also be responsible for the decline in the N2 fixation rate. Reduction in photosynthetic activity might also affect N2 fixation by legumes under salt stress condition.

Effect of Climate Change on Pathogens of Mungbean Plant diseases are one of the important factors that have a direct impact on global agricultural productivity and climate change will further aggravate the situation (Intergovernmental Panel on Climate Change 2007). The factors governing disease outbreaks may be summarized by a simple linear equation as: Disease (D) =Pathogen (P) × Host (H) × Pathogen environment (PE) × Host environment (HE) × Time (T) where, Climate influences pathogen (PE) and host environments (HE) separately and collectively throughout the period of crop germination, growth and reproduction (Time, T) from infection to host death. This influence will not be static and can vary throughout the lifecycles of both host and pathogen (Geoffrey RD 2012). Specific information regarding climate change and its effect on the pathogens of mung bean is greatly lacking. However, information on pathogens



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of other pulses are sparsely available. An increase in CO2 levels may encourage the production of plant biomass. Consequently, a high concentration of carbohydrates in the host tissue promotes the development of biotrophic fungi such as rust (Chakraborty et al. 2002). Rust may pose a threat to the successful cultivation of mungbean under condition favorable for rapid development of the disease. There are indications of increased aggressiveness at higher temperatures of stripe rust isolates (Puccinia striiformis), suggesting that rust fungi can adapt to and benefit from higher temperatures (Mboup et al. 2012). A change in temperature may favors the development of different dormant pathogens, which could induce an epidemic. High temperature increases the disease scenario of root rot, which has become a potential threat to the production of mungbean. Moisture can impact both host plants and pathogens in various ways. Pathogens like the powdery mildew species tend to thrive under conditions with lower moisture (Coakley 1999).

Mitigation of Climate Change and Mung Bean Production Adaptation involves some alterations to decrease the susceptibility of mungbean production to climate changes whereas mitigation emphases on reducing the emission of greenhouse gases. There are different technological options that are presently available for enhancing the mungbean production systems ability to adapt to and mitigate the effects of global climate changes. Agricultural N2O emissions are projected to increase by 35-60% up to 2030 due to increased nitrogen fertilizer use and increased animal manure (FAO, 2003). Mungbean has the distinct advantage of being a short duration pulse crop, which can grow in a wide range of soils and environments. Owing to these qualities, it has tremendous scope for horizontal expansion and can be a bonus to farmers in those agricultural lands which remain fallow for two to three months after the harvest of the main crops. However, being sensitive to thermoand photoperiods, drought, salinity and waterlogging, its widespread adoption by the farmers is not gaining ground. Therefore, there is an immediate need for the evaluation of mungbean germplasm as well as its wild relatives for identification of donors having genes for resistance to temperature, water stress, salinity, and pathogens. Mutation breeding is also a viable option for enhancement of mungbean cultivars for cultivation under changing climate conditions (Roychowdhury et al. 2012). Incorporation of genes from closely related species for resistance or tolerance to water, temperature as well as soilrelated stresses and nutrient use efficiency should be the top priority for


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mungbean breeders (Kumar et al. 2011; Baroowa and Gogoi 2016; Mahendran et al. 2014; Prasanna et al. 2014).

CONCLUSION Mungbean is one of the most important pulse crops for protein supplement in subtropical zones of the world. The world population continues to grow steadily, while land and water resources are on the decline. Studies suggest that temperature increase, rising seas and changes in patterns of rainfall and its distribution under global climate changes might lead to substantial modifications in land and water resources for mungbean production as well as the productivity of the crops grown in different parts of the world. The emission of methane and nitrous oxide gases and the deforestation in upland crop production under slash-and-burn shifting cultivation are contributors to global climate changes. Mungbean cultivation is affected by changes in climatic conditions, such as elevated temperatures, water scarcity, increased salinization etc., which positively reduces the productivity. The sustainable increase of mungbean production for food security will require efforts to enhance the capacity of mungbean production systems to adapt to global climate change as well as to mitigate the effects of mungbean production on global warming. Technical options for adaptation and mitigation are available and could be further improved. Policy support to mungbean research and development to develop and transfer appropriate and efficient technologies, however, will be vital for the realization of such measures for sustainable mungbean production.

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Chapter 6

IMPACT OF SEEDLING DIVERSITY AND THEIR SURVIVAL STRATEGY IN MODERN DAY AGRO - FORESTRY SERVICES Parasuram Kamilya and Ayan Das Laboratory of Applied Plant Systematics and Conservation, Department of Botany, Balurghat College, Balurghat, Dakshindinajpur, West Bengal, India

ABSTRACT A range of diversity is found among the seedlings of monocot and dicot species. Apart from the number of cotyledon, some other typical juvenile features vary significantly among them. Coleoptile is the tubular elongation of the cotyledonary sheath. A conspicuous collar is observed in almost all monocot seedlings, which is the transitional zone between hypocotyl and primary root. Whorls of trichomes or rhizoids are found to develop from the collar in some species. Typically branched primary root system is found in many species, which is supposed to be an ancestral condition. A derived condition of lacking the primary root system is observed in four families (Eriocaulaceae, Lemnaceae, Poaceae, Zosteraceae) of Liliopsida. The upper part of the cotyledon is a storage organ and photosynthetic in nature. The seeds of monocots lack endosperm, and the reserve is stored in the embryo, or in the cotyledon or 



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Parasuram Kamilya and Ayan Das hypocotyl during seedling stage. Both epigeal and hypogeal conditions are found among monocots. Also depending on the extension of cotyledonary axis, two types of germination can be found in monocots – adjacent and remote. In case of remote germination, the cotyledon extends profusely promoting development of plumule away from seed, whereas, embryo develops next to seed in adjacent germination.

Keywords: seedling diversity, seedling survival, agro-forestry

DEFINITION OF SEEDLING Different workers gave different definitions to denote a seedling. According to Burger (1972), seedlings are very young individuals. There are different propositions among workers considering how long a juvenile can be called seedling. Clifford (1981) defined seedling as upto the fifth post cotyledonary nodes. Tomlinson (1990) proposed that enlargement of embryo post seed maturation is the beginning of a seedling. Whether, according to others, protuberance of radical out of seed coat (Fenner and Thompson, 2005) or liberation of cotyledons from seed coat (Wardle, 1984) also detect the start of a seedling. Regarding the end of seedling stage, there is also disparity among workers. Tomlinson (1990) proposed that the emergence of the first vegetative leaf indicates the end of seedling stage, where Phillip (1992) suggested it as the loss of cotyledons. However, it is reasonable to say that when a seedling becomes independent of its maternal reserve and capable of making its own food, the individual is no more a seedling.

SEEDLING DIVERSITY The germination procedure of different types of plants such as dicots or monocots or even gymnosperms varies significantly. However, based on the degree of exposure of cotyledons, all the seedlings show two types of germination i.e., cryptocotyly or phanerocotyly (Duke, 1965; Wright et al., 2000). Cryptocotyly is the condition where cotyledons remain enveloped within fruit coat or testa while in case of phanerocotyly, cotyledons become entirely exposed after germination. Again, cryptocotylar and phanerocotylar seedlings have been divided into six subcategories i.e., phanero- geal, epigeal, hypogeal and crypto- geal, epigeal, hypogeal depending on the position of cotyledon with


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the surface of substratum on which germination occurs. Among these, phanerohypogeal and crypto-epigeal are of rare occurrence. Some evidences of phanerohypogeal condition have been recorded in Cleistanthus collinus of Euphorbiaceae (Paria and Kamilya, 1999) and Cojoba arborea of Mimosaceae (Ibarra-Manríquez, 2001). Similarly, occurrence of crypto-epigeal condition has been documented in Jatropha multifida of Euphorbiaceae (Kamilya and Paria, 1994) and Omphalea oleifera of the same family (Ibarra-Manríquez, 2001).Furthermore, depending on cotyledonary functional types, a different grouping of seedlings has also been recognised (Kitajima, 1996; Garwood, 1995; Ibarra-Manríquez, 2001). They suggested that cotyledon may be either reserve food storing type or photosynthetic foliaceous type and classified the seedlings into five types viz., PEF (phanerocotylar epigeal foliaceous), PER (phanerocotylar epigeal reserve), PHR (phanerocotylar hypogeal reserve), CHR (cryptocotylar hypogeal reserve) and CER (cryptocotylar epigeal reserve). Photosynthetic cotyledons are often termed as paracotyledons (Paria, 2014). Besides, the seedlings of parasitic, epiphytic, carnivorous or viviparous plants show modified germination strategies not belonging to the above categories and have been discussed later. Vogel (1980) identified the existence of three types of cotyledons – foodstoring, haustorial and photosynthetic. Food-storing and haustorial cotyledons function often in similar ways transferring nutrients from endosperm to embryo. Cotyledons may be sessile or petiolate. It has been observed that reserve type cotyledons in both phanerocotylar and cryptocotylar species show a tendency to become sessile or shortly petiolate. Also in certain phanerocotylar geal species (Nyctanthes arbor-tristis), petiole may be comaparatively longer to hold the foliaceous cotyledons above ground for photosynthesis. Usually among cryptocotylar species, cotyledons are large and nonphotosynthetic, however an evolutionary lineage can be drawn towards phanerocotylar epigeal foliaceous type. Certain species such as Shorea robusta have non photosynthetic cotyledons which come out of the seed coat, whereas, cotyledons of Pongamia pinnata often become green and free of seedc oat may be considered as intermediates. Although number of cotyledons is constant per species but sometimes variations such as trycotyly in Ipomoea sp.Has also been reported (Sampathkumar, 1982). A range of diversity is also found among the seedlings of monocot species. Apart from the number of cotyledon, some other typical juvenile features vary significantly among them. Tillich (1995) described the functional attributes of monocot seedlings such as coleoptiles, collar, primary roots, velvety root hairs, etc. Coleoptile is the tubular elongation of the cotyledonary sheath. A


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conspicuous collar is observed in almost all monocot seedlings, which is the transitional zone between hypocotyl and primary root. Whorls of trichomes or rhizoids are found to develop from the collar in some species. The upper part of the cotyledon is a storage organ and photosynthetic in nature. The seeds of monocots lack endosperm, and the reserve is stored in the embryo, or in the cotyledon or hypocotyl during seedling stage. Both epigeal and hypogeal conditions are found among monocots. Also depending on the extension of cotyledonary axis, two types of germination can be found in monocots – adjacent and remote (Tomlinson, 1990). In case of remote germination, the cotyledon extends profusely promoting development of plumule away from seed, whereas, embryo develops next to seed in adjacent germination. A range of variation may be observed in the eophylls (juvenile leaves). Juvenile leaves may be found to vary in shape, nature, number, phyllotaxy, or venation pattern than the adult ones in many species. In some species having compound leaves, heteroblastic development is not of rare occurrence. As for example, the primary leaves are simple where subsequent adult leaves become compound in Oroxylum indicum, Pongamia pinnata, Jatropha gossypifolia, etc. (Kamilya and Das, 2014). Sometimes number of leaflets increases from juvenile to adult leaves (Dalbergia sissoo). In Ziziphus mauritiana and Trema orientalis, the first two leaves are opposite while subsequent leaves are alternate (Kamilya and Das, 2014). However, in seedlings of Acacia auriculiformis,* juvenile compound leaves are replaced by simple leaves which are basically phyllodes.Some gymnosperm seedlings possess both juvenile needle like leaf and adult scale leaf (Leck et al., 2008). Tomlinson (1990) distinguished six transitional types of leaves in palms before adult leaves arise. Some modified structures such as spines or tendrils may arise at this juvenile stage. Another interesting incident is the occurrence of storage structures such as, bulbs, corms, tubers, etc. during seedling development facilitating adaptations to certain critical conditions. In Quercus oleoides, lignotuber formation occurs to transfer resources to the underground tuber before the aerial part becomes consumed by moth larva shortly after germination (Halléet al., 1978). In Ginkgo biloba, lignotubers originate from cotyledonary buds and grow downward during hostile periods (Del Tredici, 1997). Contractile roots of Lepidium pull down the shoot underground to prevent from freezing (Körner, 2003). Also hypocotyl of Asclepias tuberosa become contractile to pull the shoot meristem underground assisting tuber formation (Kummer, 1951). Occurrence of dropper roots is common in Dichopogon strictus, which protects the dormant buds from fire by burying them deep (Good et al., 1979).



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Growth pattern in seedlings varies from relatively low growth rate in cryptocotylar tree species to high growth rate in pioneer herbaceous species. Growth rate is significantly related to the amount of food reserve in seeds. Seedlings with higher amount of storage show reduced orthotrpic phase, while plagiotropism is observed in seedlings with little or no reserve. In Welwitschia mirabilis, after formation of two permanent leaf primordia and foliar appendages that persist in its lifetime, the terminal meristem dies arresting further vertical growth (Sporne, 1967). Development of seedling does not happen in a continuous way, especially in long lived tree species, it is often interrupted by regular periods of dormancy. Vogel (1980) advocated that the variation in dormancy periods may be a clue regarding seedling identification. Dormancy in growth varies among species and occurs in hypocotyl, epicotyl or even roots during different distinctive life events or seasonal changes. Thus, seedling features show a high degree of phenotypic plasticity not only among different species, but within species also depending upon the external conditions. Sometimes the area of photosynthetic zone is increased in response to low reserve nutrition or radiation in sun-loving species growing in shade. Interaction with other species in resource constraint area may induce development of primary internodes in Mimulus lutea (Lubbock, 1892). Interestingly, regeneration capacity of cotyledons may occur in Idiospermum australiense where a new offspring can be developed from each cotyledons (Edwards et al., 2001). The effect of light, water, soil nutrients, etc. on the diversity of juvenile structures has been mentioned later in this chapter. These structural plasticity due to adaptations may lead to polymorphism among species and incorporated as genetic characters*. Taraxacum hamatiforme produces two types of seeds – in case of the heavier seeds, radicles emerge first, but in case of lighter seeds, cotyledons emerge first (Mogie et al., 1990). In Amphicarpum purshii, aerial seeds produce shorter seedlings than those germinated from the subterranean ones (Cheplick, 1982). These features give such individuals selective advantage leading to better adaptations in critical conditions.


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MORPHOLOGICAL AND PHYSICAL CHANGES OF SEEDLINGS IN RESPONSE TO EXTERNAL PHYSICAL FACTORS Seedling stage is probably the most eventful time of plant life cycle beginning from the germination of seed. Lots of physiological activities go on at this time to provide the adolescent one to gain the ability to utilize its only reserve to face the unfamiliar world full of hardship. Only it has got a delicate structure with little amount of photosynthetic tissue and a cotyledon to take on the challenges in the form of nature itself and other old hand rivals. Therefore, the seedling must make the most of its maternal reserve to proliferate its primary photosynthetic organs as well as a brawny rooting system for anchorage and mining of nutrients from soil. At the same time it has to run few errands internally, like signal transduction, protein synthesis, tissue differentiation, etc. A handful of phytohormones and photoreceptors work side by side to perform the physiological activities to enable the seedling to fiddle with the neighbourhood. These fellows also help the seedling to attain its proper morphological shape. Phytohormones are low-mass polypeptide compounds that carry out regulatory functions on receiving stimulation from environment through membrane receptors. By binding with the receptors, or transporter molecules, phytohormones provoke a series of signalling pathways resulting in phenotypic responses. These events induce transcription of proteins to react with the outside stimulation. Few cellular ions (e.g., H+, Na+, Ca2+,Cl-, etc.) also take part as receptors or signals for phytohormones. There have been five types of phytohormones found to work together. These are auxin, gibberellins, cytokinins, abscisic acid and ethylene. They almost function similarly in a developing seedling as in the mature plants. All combined phytohormones act preservatively, synergistically or antagonistically (Farnsworth, 2008). Some other organic substances such as Salicylic acid or Jasmonic acid are also found to perform along with phytohormones at different stimulations. Polypeptides like systemin, phytosulfokine or CLAVATA3 (found in Arabidopsis seedlings (Clark, 1997)) also relates themselves in cell division, cell proliferation, tissue differentiation, pathogen attack, wounding response or nodule formation. Another group of polypeptide, brassinosteroids also display important role in growth and speciation (Vert et al., 2005). Polyamines such as putrescine and spermidine show similarity in function with the phytohormones during early plant growth.



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During the development of seedlings, usually four environmental factors viz., light, temperature, water and nutrients act to regulate or alter signalling pathways or responses of seedlings. These factors together determine the physiological activities and morphological features of a seedling in order to cope up with the ecosystem.

Physiological Activities in Response to Light Immediately after germination, a seedling’s first priority is to find light. It responds to light by the developing a hook like structure at the apical part. The formation of this apical hook depends on the quality and intensity of light. Apical hook forms as the cells on the abaxial side of the stem elongate more than those on the adaxial side. Apical hook helps in protection of apical meristem and thrust its way up through soil or litter. After germination, if there is total darkness or exposure to far red light, the seedling shows signs of etiolation, such as overstated upright growth of hypocotyl, lack of photosynthetic tissue, abundance of phytochrome, while in presence of high light intensity, it shows de-etiolation and proliferation (Farnsworth, 2008). Gibberellins regulate this elongation of hypocotyl as seedlings begin to deetiolate (García-Martinez and Gil, 2002). Gibberellins inactivate growth suppressor DELLA proteins allowing vertical growth (Vandenbussche et al., 2005). Cytokinins initiate gaseous hormone ethylene biosynthesis which shows ‘triple response’ during development of seedlings through proliferation of apical hook and reduction in vertical growth and increase in lateral growth of hypocotyl (Vandenbussche et al., 2005). On the other hand, auxin functions antagonistically to ethylene by inhibition of apical hook formation and vertical cell elongation in hypocotyl (Vandenbussche and Van Der Straeten, 2004). Brassinosteroids also accelerate longitudinal elongation of seedling (Vandenbussche et al., 2005). Phytochromes, a group of photoreceptors perform an important task in growing seedlings in response to light. Phytochrome A (PHYA) is highly sensitive to far-red light response and show abundance in seedlings growing in absence of abundant sun light. Phytochrome B (PHYB) on the other hand responses to high light intensity and promote de-etiolation in combination with PHYD and PHYE. Phytochromes in seedlings grown under forest canopy or deep shade converts from Pr (phytochrome absorbing red light) to Pfr (Phytochrome absorbing far-red light) which induces transcription of necessary proteins for the adaptation in shady habitat. Thus, photoreceptors assist


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seedlings in habitat preference and sensing of neighbourhood. Furthermore, this gene mediated phytochrome response leads to plasticity and adaptive divergence among seedlings in context of ecology (Schmitt et al., 2003). The morphological and physiological changes in a growing seedling is regulated by a conjugated activities of phytohormones and phytochromes. In presence of abundant light, phytochromes negatively regulate GA activity resulting in reduced stem elongation (García-Martinez and Gil, 2002). Auxin promotes positive phototropic growth and under high far-red to red light ratio, it gets reallocated in shoot promoting elongation (Vandenbussche et al., 2005). It has been observed that elongation of hypocotyls of seedlings occurs in circadian rhythm, with faster growth during dusk and sluggish growth during dawn with the peaks of amount of auxin (Jouve et al., 1999). This periodic lightdark cycle is decisive during early establishment for the growth and strengthening of seedling (Dodd et al., 2005). Similarly, the perception of blue light in seedlings is caused by another group of phytochromes– phototropins and cryptochromes. Phototropins functions in positive bending of apical part towards light, stomatal opening and chloroplast migration for better light perception. Cryptochrome promoted deetiolation and photoperiodism. KNOX homeobox genes regulates the production and activation of phytohormones. These genes are inducer for Cytokinins and suppressor for GA activities. Repression in KNOX activity initiates formation of leaf primordia around apical meristem. The spatial distribution and distance of auxin accumulation leads to the formation of leaves around the stem (Kepinski, 2006). Auxin is also supposed to manipulate the phenotype of leaves by regulating the ratio of GA and ABA. Auxin also regulates lateral gene formation through activation of NAC genes in the root apical and lateral meristem (Kepinski, 2006). Thus phytohormones and photoreceptors work synchronously in the seedlings which counters variable light environments throughout its life periods towards maturation. The physiological and morphological flexibility mediated by genes give a seedling superior adaptation in different environmental conditions better than the mature plants.

Physiological Activities in Response to Temperature Temperature of soil and environment is generally influenced by light radiated from sun and reflected by earth. An array of temperature is crucial for all physiological and biochemical cellular reactions. A seed starts to germinate



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after sensing the presence of an ideal temperature (Baskin and Baskin, 2001) which varies from species to species in different climatic conditions. If the temperature outside is not conducive for growth, abscisic acid (ABA) mediates a temporary seize in further development (Lopez-Molina et al., 2001). Physiological activities of seedlings growing in extreme climate have to regulate in such a way that the seedling must survive until favourable condition appears. In adverse conditions, seedlings go through dormancy, by arresting metabolic processes like photosynthesis, growth, water and nutrient uptake and stabilization of cell membrane against osmotic pressure fluctuation (Kozlowski and Pallardy, 2002). Before the onset of dormancy, seedlings accumulate starch and phospholipid and transfer to storage organs to use during constraining situation (Volaire and Norton, 2006). Auxin shows in a positive response to temperature in a proportional way and promotes cell proliferation and shoot elongation in seedlings similarly as in case of light (Heggie and Halliday, 2005). Seedlings show response to periodic changes of temperature in a circadian rhythm similarly as with light regulated by GA in addition to auxin (Heggie and Halliday, 2005). Temperature stress also triggers stress phytohormone ABA biosynthesis, which induces production of inositol 1,4,5-triphosphate (IP3) from the reserve phospholipid. IP3 acts as a second messenger that regulates cell sap concentration through release of Ca2+ ions (Xiong et al., 2002). ABA also mediates synthesis of dehydrin, a protective protein which protects the cell against desiccation stress (Close, 1997). ABA biosynthesis includes production of protective carotenoids– zeaxanthin and violaxanthin, which protect photosystem against extreme heat or cold environment. ABA also promotes the production of heat–shock–proteins (HSP) under extremely high temperature (Finkelstein et al., 2002). HSPs are vital for normal growth of seedlings under high temperature which can degrade other proteins. Moreover, HSPs also function in sensing increase of reactive oxygen species such as hydrogen peroxide which increase during external stresses and pathogen wounds (Miller and Mittler, 2006).

Physiological Activities in Response to Water Water is chiefly characterised by moisture content of soil. It is necessary for a seed to build a proliferating root system to seek water from the soil. The stress conditions for water or drought, flood or salinity. Auxin takes the major part in production and proliferation of root. Auxin induces positively geotropic and hydrotropic movement in roots to promote cell elongation of root primordia and


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also lateral root formation (Teale et al., 2005) to find water deep in the soil. Formation of root xylem is also mediated by auxin action. A seedling must maintain cellular osmotic balance, cell membrane integrity, reactive oxygen species and their scavengers* during water stress*. High ratio of auxin over cytokinins facilitates root production over shoot production. ABA on the other hand acts synergistically to auxin and stops the formation of root hairs (De Smet et al., 2006). ABA permits cell membrane to uptake more water by increasing membrane permeability. During water restraint, it signals for stomatal closing to prevent transpiration (Finkelstein et al., 2002). ABA independently senses temperature and prolongs dormancy of seedlings in arid environment (Volaire and Norton, 2006). ABA increases DELLA protein activity which extend the duration of juvenile period during salinity stress (Achard et al., 2006). Jasmonic acid content in seedlings is increased by impulses from drought and salinity (Creelman and Mullet, 1997) and wound caused due to herbivory. This action of jasmonic acid draws a positive correlation between salinity stress response and herbivory. Ethylene exhibits another important role during water stress, precisely flooding. Ethylene promotes programmed cell death to form aerenchyma tissue (Evans, 2004) to facilitate passive diffusion through intercellular spaces in submerged condition to counter reduced oxygen concentration around root and leaf. Ethylene also enhances stem and petiole elongation through regulation of Gas and ABA to outgrow flooding. Ethylene and GAs together promote the production of expansin proteins that promote cell expansion (Voesenek et al., 2006). Ethylene in combination with ABA helps in cell membrane stabilization during osmotic stress.

Physiological Activities in Response to Nutrients Cotyledonary reserves as the primary food source for a seedling. But as the maternal reserve is limited, the seedling has to proliferate its roots in the soil to absorb nutrients. Auxin, cytokinins and ethylene promote formation and growth of root through rapid cell division in root primordia and formation of root hair and lateral roots to increase root surface area for better access to soil nutrients (López-Bucio et al., 2003). The root system has to be extended further if soil nutrient concentration is low or localized. Seedlings growing in low-phosphate containing soil increase auxin and phosphate transport protein and produce phosphate absorbing proteoid roots (Skenel, 2001; López-Bucio et al., 2003). Similarly, deficiency of sulphate and iron in soil exhibit similar auxin activity



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(Skenel, 2001). It has been observed that in addition to auxin, ethylene also functions as the same in paucity of iron (López-Bucio et al., 2003). On the other hand, nitrate and ammonium in the soil triggers cytokinin production in phloem and root primordia (Sakakibara et al., 2006). Cytokinins then reduce nitrate uptake through negative feed back and promotes less common nutrients such as sulphate uptake (Sakakibara et al., 2006). Cytokinins also stimulate stomatal opening for transpirational uptake of nitrogen and other nutrients through mass flow. Carbon metabolism is closely related with nitrogen metabolism and the internal carbon-nitrogen ratio is crucial for seedling growth (Coruzzi and Zhou, 2001). High carbon content in seedling signals to increase nitrogen uptake whereas low carbon content triggers shutting down of nitrogen uptake. At high concentration of glucose or sucrose induces ABA production which in turn affects negatively on growth (Gibson, 2002). On the other hand, ethylene activates growth in response to sugar (Gazzarrini and McCourt, 2001). Sugar can also influence auxin-cytokinins interaction to regulate growth of seedling (Rolland et al., 2002). Thus, two major nutrient components– nitrogenand sugar interacts with phytohormone in seedling to regulate their growth and development. In specialized nutrition such as symbiosis or parasitism, phytohormones in seedlings respond to the organization of relationship with the other partner or host by producing specialized structures like nodules or haustoria. In response to flavonoids exuded by legumes, rhizobial bacteria release nodule promotion NOD factor. NOD factor induces auxin action in the root cortex to increase cell expansion and formation of primordial nodule (Farnsworth, 2008). Cytokinins function in a similar way during nodule formation, or sometimes they may substitute for Nod factors (Cooper and Long, 1994). Ethylene exhibits antagonistic action to auxin except during water logged condition, when nitrogen availability is poor (D’Haeze et al., 2003). Sucrose can suppress nodule formation by over accumulation of nitrate (Gibson, 2005). During mycorrhiza formation, IAA stimulates production of ectomycorrhizal root (Gay et al., 1994). In addition to this, mycorrhizae secret indole alkaloid hypaphorine, which inhibits root hair elongation and facilitates in mycorrhizal association (Jambois et al., 2005). In parasitic plants, haustoria formation is initiated by haustoria-inducing factor in response to host plant exudates. Haustoria initiation factors promote elongation and formation of adhesive hairs from regular root tip that binds with the host. After the contact is made, auxin and ethylene together mediate growth and radial expansion of haustorial hair (Tomilov et al., 2005). After infection, auxin is transported from


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parasite to host and elongates cells in roots. Ethylene probably mediates loss of photosynthetic tissue in the parasite.

Seedling Establishment under Special Conditions: Epiphytes, Carnivorous, Parasitic and Viviparous Species The development of seedlings of epiphytes, such as, orchids starts from protocorm germinated from embryo. Protocorm is structurally similar to the radicle (Rasmussen, 1995) and comprises of a basal part from which rhizoids develop and a meristematic apical part from which the seedling develops. The meristematic cells at the apical part give rise to the first primordial leaf. Another important event during the seedling development in orchid is establishing obligataory relationship with mycorrhizal fungi. Fungal hyphae penetrate the protocorm from which, the orchid gets its primary nutrition. In case of the bromeliad seedlings, hypocotyl emerges from the first followed by radicle and epicotyl. The radicle is next replaced by primary and secondary roots. However, in atmospheric species, roots are not produced real soon. The roots are typically used for anchorage rather than water and nutrient uptake (Benzing and Renfrow, 1974). Leaves originate eventually from the epicotyl part which functions in water and nutrient uptake for bromeliads. Interaction with mycorrhizal fungi may take place similar as orchids for better resource allocation, but it is optional for their growth. Almost all the works on the seedlings of carnivorous plants such as, Dionaea (Smith, 1931), Drosera (Crowder et al., 1990), Nepenthes (Geddes, 1893) suggest the formation of prey capturing leaves at the initial stage of development. Most of them have weakly developed root system or no roots at all (Baskin and Baskin, 1998). The initial tap root in these plants either stop growing within a short period of time after germination or soon gets replaced by adventitious roots or root hairs. For the parasitic species, it is necessary to get in touch with the host in the seedling stage. Therefore, the development of such seedling differs from nonparasitic ones. Development of haustorium is a typical feature for the parasitic plants. For these species, the radicle grows out of the seed and penetrates the soil, after which, the hypocotyl extends and raises the seed from the ground (Whigham et al., 2008). In primitive species, the radicle has a protective radicular cap. After that, the shoot starts elongating while the roots may become branched to form haustorium (Kujit, 1969). While the radicle searches for a connection with the host, and once it comes in contact with host



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surface, development of a primary haustorium occurs to its tip. Once cell to cell connection with the host is established, cotyledon emergence may occur which varies among species. Cotyledons may emerge from seed and become leaf-like in species like Gaiadendron, while in some cases, it may remain within seed functioning as absorptive organ (Whigham et al., 2008). In Cuscuta, after the initial haustorial connection is formed, a coil like structure bearing multiple haustoria is formed, from which the shoot is generated (Sampathkumar, 1982). In case of viviparous species growing in tidal swamp regions, precocious germination occurs within the fruit still attached with the mother plant. And until they are suitable for establishment, they depend on the mother plant for nutrition. To deal with the salinity stress, salt glands form during the early development. Root initiation does not take place in such seedlings until dispersal (Leck et al., 2008). In some taxa like Zostera or Saxifraga, seedlings are produced from asexual propagules like bulbils and turions, and they show morphological similarities with the sexually produced ones.

SEEDLING ECOPHYSIOLOGY – STRATEGIES FOR BUILDING UP CARBON ALLOCATION Relative Growth Rate (RGR) Relative growth rate or RGR is the enumeration of net carbon balance per unit seedling mass (Kitajima and Myers, 2008). RGR is displayed by the instant slope of the natural log of total seed mass against time (Poorter and Garnier, 2007). In a developing seedling, RGR changesinitially from negative or zero to positive following developmental of functional photosynthetic tissue. In a steady environment with continuous nutrient flow, RGR attains its optimum position for a stretch of time and then decline forming a bell shaped curve. Whereas, net assimilation rate (NAR), which quantifies net carbon balance per unit leaf area is considered only after a seedling becomes fully autotrophic. Cotyledon mass is important to evaluate RGR in species with large storage cotyledons during prolonged dependency of seedling on cotyledonary reserve and must be included within total seedling mass to understand net carbon allocation to seedling. Cotyledon mass should be considered because during development, when the reserve is transferred to seedling, larger cotyledons stop this transfer of energy after the first set of leaves become fully functional (Myers and Kitajima, 2007).


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The decline of RGR takes place with the increase of size of a seedling even in adequate supply of light and soil nutrients due to – allocation to stem elongation resulting in a decrease of the ratio of photosynthetic mass relative to nonphotosynthetic mass, and self-shading because of increase of number of leaves (Givnish, 1988). More allocation to stem and less allocation to leaf causes reduced RGR in temperate tree seedlings (Walters et al., 1993) whereas, shadetolerant evergreen tree seedlings from Chilean forest are observed to show increase in leaf area ratio to intercept more light and thus, to oppose the selfshading effect (Lusk et al., 2006). In fully photosynthetically functional seedling, RGR is the consequence of the interactions between morphology, physiology and allocation patterns of a seedling. RGR is affected suboptimal resource supplies, biotic and abiotic stresses. Inherent maximum RGR of a seedling is measured as RGR during the log linear phase under optimal condition (Kitajima and Myers, 2008). RGR displays great variation among species, from less than 0.02 g g-1 day-1 in shade tolerant tree species to more than 0.1 g g-1 day-1 in herbaceous plants and woody pioneers (Poorter and Remkes, 1990; Kitajima, 1996; Shipley and AlmeidoCortez, 2003). Studies on diverse taxa from different habitats show that RGR is negatively correlated with seed mass (Shipley and Peters, 1990). Kitajima and Myers (2008) pointed five evidences – (1) Large seeded species tend to have reserve type cotyledons (Hladik and Miquel, 1990; Kitajima 1996; Wright et al., 2000; Zanne et al., 2005) and delayed development of photosynthetic area relative to biomass, (2) Seedlings of large seeded species tend to show sluggish development in terms of time from radicle emergence to shoot extension to the first leaf expansion and to successive leaf development (Kitajima, 1992), (3) Large seeded species may store larger amounts of sugar in reserve-type cotyledons, stems and rootsand show slower deployment (Saverimuttu and Westoby, 1996; Kidson and Westoby, 2000; Green and Juniper, 2004; Myers and Kitajima, 2007), (4) Large seeded species tend to allocate more to roots and stems (Kitajima, 1994; Walters and Reich, 2000; Paz, 2003) both non-structural carbohydrates and structural mass, (5) Large seeded species tend to have leaves with low specific leaf area (SLA, the ratio of leaf area to leaf mass) and leaf area ratio (LAR). These two traits are positively correlated with interspecific differences in RGR under standardized conditions (Poorter and Remkes, 1990; Kitajima, 1994; Reich et al., 1998; Wright et al., 2000; Shipley and AlmeidaCortez, 2003; Poorter and Garnier, 2007). As seedling continues its journey towards sapling, these juvenile features like seed reserve allocation or cotyledonary functional types do not affect RGR



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anymore, rather morphological–physiological traits like biomass partitioning (such as, SLA, LAR and root allocation), photosynthetic physiology (such as, NAR) and developmental rates play more decisive role (Poorter and Garnier, 2007). Along with these, environmental condition (Poorter, 1999) and gradual difference in size of the seedling (Delagrange et al., 2004; Baraloto et al., 2005) are crucial. However seed mass related changes with these functional traits (Reich et al., 2003; Wright et al., 2007) might still influence the negative relation between RGR and seed mass when nutrients are sufficient and photosynthetic gain per unit leaf area is better. Functional correlation between cotyledonary SLA and eophyllar SLA (Kitajima, 1992) is crucial as thin photosynthetic cotyledons keep growing while true leaves are functionally acting as the main source for carbon allocation. It is also recorded that when light availability is high and growth of seedling is vigorous, the negative interrelationship between seed mass and RGR is even stronger.

Growth-Survival Trade off Trade off between growth rate and survival through various life stages has been in temperate trees (Reich et al., 1998), tropical trees (Dalling and Hubbell, 2002), perennial herbs (Metcalf et al., 2006), etc. From the study of tree and lianas from neotropical forest (Gilbert et al., 2006) and temperate forest trees (Pacala et al., 1996) it has been observed that growth rate is negatively correlated to survival. From such kind of trade-off, two types of growth strategies can be postulated – the opportunistic and the conservative types. Opportunistic pattern differs from conservative pattern in growth, defence and storage strategies, and shows fast growth and low survival capacity in contrast. Ahead of complete dependence on its reserve, a seedling must sustain positive net carbon balance for growth and immunity. Opportunistic species directs its carbon allocation to growth over defence. As a result, while they achieve fast growth rate in presence of nutrition continuum and absence of biotic or abiotic hazards, they have low defence, suffer from severe damage and high mortality in unfavourable situation. On the other hand, conservative species prefer defence over growth in respect to carbon allocation. And accordingly they experience less frequent or lower tissue loss and better longevity. The opportunistic strategy is morphologically characterized by thin photosynthetic cotyledons, while conservative strategy features reserve type cotyledons. From physiological point of view, species with opportunistic growth pattern have higher RGR, SLA


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and LAR than their counterparts. Seed reserves carry out influential task in determining seedling’s survival strategy as well. In pioneer species, seed size is usually smaller, hence, those seedling must adopt opportunistic strategy for better access to external nutrition. Opportunistic strategy is common among pioneer herbaceous plants that colonize gaps in vegetation. They invest a good share of carbon in reproduction producing large number of small, poor reserve seeds. They have low tissue density, low fibre content and tissue toughness due to more expenditure of carbon to growth. They are easily susceptible to herbivory and pathogen attack. But they still can survive if external resource is enough to provide the efficiency of their high growth rate. But if critical conditions such as low external resource, prolonged shade, soil infertility arise, they may not recover the damage and fail to sustain (Kitajima, 1994) resulting in high mortality and short life span. In contrast, conservative species are usually late successional (Bazzaz and Carlson, 1982), competitive (Westoby, 1998) tree species. These species overthrow the opportunistic species through resource competition and natural adversaries due to long term achievement of positive net carbon gain (Kitajima and Myers, 2008). They produce seeds in lesser amount but with greater reserves and seedlings with stout robust features and high immunity. In these species, greater proportion of carbon allocation to defence triggers survival advantage. Both physical and chemical defence are important to counter external damages. Physical defence is importantin case of burial under litter or herbivory (Clark and Clark, 1989) by molluscs to temperate forb seedlings (Hanley et al., 1995) or by soil borne pathogens to tropical tree seedlings (Augsperger, 1984). Study from Peruvian Amazon by Fine et al. (2004) also depicts survival strategy of the two categories in fertile alluvial soil and nutrient-poor white sand. They demonstrated that seedlings from alluvial soil suffered greater herbivory and achieved less net leaf area growth than the ones growing in white sand. Other studies also suggest that species that grow in nutrient rich soil can grow faster in both fertile and infertile soil than those from poor soil if protected from herbivory (Lusk et al., 1997; Schreeg et al., 2005). Species from infertile soil tend to have lower SLA and greater leaf life span (Wright et al., 2002) and low SLA species usually have thick leaves with high tissue density and thick cuticles that confer mechanical protection (Wright and Cannon, 2001). A study on neotropical tree species by Alvarez-Clare and Kitajima (2007) showed fracture toughness of stem of seedlings, which is directly influenced by tissue density and fibre contents is positively related to first year survival of seedlings. Similar survival advantage associated with high carbon allocation to tissue density and stem mechanical strength were exhibited by conservative saplings (Muller-



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Landau, 2004; Poorter and Bongers, 2006). Therefore, the growth/survival trade off also reflects natural selection.

Phenotypic Plasticity Seedlings interact to external environmental conditions through their morphological and physiological features. They have to modify their morphology and physiology in response to every alteration in the environment in order to avoid or tolerate undesirable condition or to maintain carbon gain in its optimum level (Kitajima and Myers, 2008). Study from 42 temperate herbaceous and woody species experimentally grown in non irrigated soil show considerable increase in root elongation and the species with highest plasticity in rooting depth show more notable growth of stem (Reader et al., 1993). Seedling phenotype is subjected to immense changes due to variations of light in natural condition. Phenotypic plasticity may be stimulated by both qualitative and quantitative responses. Qualitative responses are usually observed among ecological and phylogenetic groups. Light is a qualitative effector for seedling’s phenotypic responses, such as, light demanding seedlings exhibit hypocotyl elongation in response to shady condition or low red: far-red light (Kitajima, 1994). Light demanding species show such rapid growth response to escape the shade as they prefer forest gaps (Schmitt et al., 2003). On the contrary shade tolerant species do not show this response reflects that qualitative responses are genotypespecific. Soil temperature fluctuation, high temperature, flush of nitrate and smoke among other qualitative responses that stimulates the seeds to detect gaps (Pearson et al., 2002). Light quantity, water and soil nutrient availability stimulate quantitative response in seedlings. These responses are more ubiquitous than qualitative responses (Kitajima and Myers, 2008) as leaves of both sun-loving and shadetolerant species show acclimatization response to light environments in both morphological and physiological traits such as seedlings grown in higher light availability tend to have leaves with greater thickness, lower SLA, higher nitrogen and carboxylation enzyme concentration per unit area, higher chlorophyll a/b ratio and higher photosynthesis and respiration per unit area (Walters et al., 1993; Kitajima, 1994). Soil nitrogen availability also influences acclimatization response to high light (Portsmuth and Niinemets, 2007). Under low nitrogen availability, leaves must be protected against photoinjury through


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allocation of nitrogen to different photosynthetic components (Kitajima and Hogan, 2003). These intensities of phenotypic plasticity are controlled genetically. That is why variations among species such as ecotypes and genotypes are created. Generally fast growing, opportunistic, pioneer species produce more leaves per unit time (Newell et al., 1993) and exhibit higher rate in acclimation. Studies reflect these early successional species those have sun-loving seedlings with preference for gaps tend to have greater degrees of plasticity than late successional species (Kitajima, 1994; Delagrange et al., 2004). From this discussion, it can be conferred that phenotypic plasticity might allow adaptation to a broader range of environments. Likewise, the species those have greater geographical distribution should exhibit more phenotypic plasticity. Interestingly, sometimes only a particular trait show plasticity, for example only leaf traits, but not whole plant show plasticity among Acacia species from Australia (Pohlman et al., 2005). However, allocation of sugar due to phenotypic plasticity may lead to disparity among development of different parts of a seedling. Therefore, among seedlings growing in shade, stem elongation is not profitable if it is not sufficient to escape shade, and hence, seedlings minimize their response to red: far-red light. Similarly these seedlings naturally have more allocation to roots in any case of soil moisture availability (Kitajima, 1994; Delagrange et al., 2004). Greater root storage also prevent seedlings from drying during drought. Phenotypic plasticity may induce noticeable phenotypic similarity within a species in the same environmental condition as studied from two Mediterranean species of Quercus (Valladares et al., 2002).

Seedling Establishment Strategies in Critical Environments Stress conditions may be collectively defined as external constraints that reduce or stop the rate of dry mass production for all parts of an individual (Grime, 1979). Even small fluctuations in its environment may trigger abrupt changes in seedlings, both morphologically and physiologically. To avoid or reduce these external effects, seedlings have developed survival strategies. Initial strategies concern utilization of maternal reserve in the form of seeds to ensure seedling survival (Smith and Fretwell, 1974; Leishman et al., 2000) and repair damages due to stresses. Another aspect of this strategy is timing of germination to avoid germination during environmental stress or when favourable condition is too short to ensure post-germination survival (Fenner



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and Thompson, 2005; Facelli, 2008). Unfavourable environmental conditions such as drought or shade generate reduction of carbon allocation in seedlings and hence enhance mortality risk. Response to environmental stresses vary for seedlings and its mature member, but it is the seedling which incurs the adaptability for the survival of the mature one. One such adaptability concerns allocation of reserves from one part to another during stresses. Stress factors may be both biotic or abiotic; biotic stressors include herbivory, pathogen attack, allelopathy and competition from other species, while abiotic stressors comprise physical factors like, drought, extreme temperature, floods, soil salinity, pH, etc. (Grime, 1979). Biotic disturbances also include stress related to human activities like air pollution, heavy metals, salinization, sedimentation or soil erosion by overgrazing or deforestation, or in a broader aspect, desertification and climate change (Facelli, 2008). Due to their smaller size, seedlings are very susceptible to these stressors, and because of allometric constraints, there is little chance of size-dependent stress-tolerance in seedlings (Facelli, 2008).

Seedling Establishment Strategy in Deep Shade Light is one essential factor that affects from the beginning, the germination of seed to the early establishment of a seedling. Seedlings grow in different light environments, some prefer open or canopy gaps while others favour forest canopy or dense shades. They may also encounter a great variation of light situations throughout their life cycle. Stress due to light occurs when light intensity is not enough to provide positive carbon balance in seedlings. Such condition arise when photosynthetic gain is lesser than losses due to respiration or biomass destruction (Facelli, 2008). Low light intensity generates one such negative response in seedlings grown under dense canopy or shades. Seed size naturally gives an advantage to seedlings during early establishment in deep shade. Seedlings of larger seeded species tend to be more shade tolerant (Leishman and Westoby, 1994b) than the ones produced from small seeds. Larger seeds and therefore, higher seed mass serve the necessary nutrients for survival of a seedlings for longer period until they become functionally autotrophic (Walters and Reich, 2000). This is evident from several studies. Establishment of seedlings in deep shade is positively correlated with seed size in the tropical rain forests in Queensland, Australia (Osunkoya et al., 1994) and from North American Hardwood trees (Hewitt, 1998). Furthermore, as seedlings from larger seeds are larger in size, hence, they can outgrow deep


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shade and reach canopy gaps for better light accessibility (Leishman and Westoby, 1994). Negative relationship between seedling mortality in dense shade and seed size only add further support to this (Grime and Jeffrey, 1965). Larger seed mass may also enhance the survival of seedlings passively from desiccation, damage by physical and biotic factors (Metcalfe and Grubb, 1997). Allocation of reserves to different plant organs have a crucial role in seedling response to different light environments. Seedlings growing in deep shade need to allocate more carbon to leaves to capture the lower intensity of light. Interactions between resource allocationto different organs and their physiological and morphological traits are also vital for sustainability in critical environments. As the leaves should be morphologically thinner and broader and therefore physiologically have low SLA and low LAR for better access to light. Distinction in allocation of storage to different organs is also there. Under forest canopy, low irradiance invokes more allocation to leaves than roots that results in increased leaf area per unit of plant mass and lower specific root length (Reich et al., 1998).

Seedling Establishment Strategy in Burial under Litter Litter can be formed by accumulation of fallen leaves and barks from the existing vegetation or by snow. Accumulation of litter may have positive or negative effects on seedling establishment. The negative effects of burial under litter layer usually increase of amount of litter (Facelli and Pickett, 1991). Usually burial under 200 g/m2 or more litter is considered to have negative effects on seedling germination and survival (Sydes and Grime, 1981). The effects usually vary with the thickness and physical properties of litter and this may pose crucial for the selection of seedlings (Facelli and Pickett, 1991). Litter comprised of dead leaves and barks may be grasped together by hyphae to form compact mat that may exert physical impedance of growing seedlings (Facelli, 2008). Litter layer affects seed germination or seedling establishment through not only physical impedance but also changing the environment. Litter layer may reduce light and day-night temperature fluctuation. These effects may resist seed germination or seedling establishment in many species, those growing waste lands or those requiring temperature fluctuation effect to break seed dormancy (Grime, 1979; Fenner and Thompson, 2005). Position of seed during germination also interacts with litter for seedling establishment. Seedling establishment is more successful when seeds are on the soil surface. If seed germination occurs above litter, then roots may fail to reach



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soil for water and nutrients and therefore, become unsuccessful. This interaction between seed emergence and litter may depend on litter composition. Litter composed of broader leaves and barks may prevent seeds from reaching soil than litter composed of fine materials (Facelli and Kerrigan, 1996). Seed size and seed shape are also important features to determine successful establishment on soil through litter. Larger seeds can penetrate through layers of litter and reach the soil beneath due to their heavy weight. This helps in better establishment and protection from predators. Also, larger seeds allocate more reserves to seedlings that help them to outgrow the litter layer.

Seedling Establishment Strategy in Dry Environments Dry environments are characterized by high temperature and scarcity in water and other solute nutrients thus preventing seedling establishment. Plants generate different adaptations in such environments. Seeds show seasonal dormancy to avoid germination during dry hot seasons of the year. This is evident from germination pattern of North American winter annual plants which do not germinate unless the end of hot season, even in controlled environment (Baskin et al., 1993). Time of retrieval and temperature determine germination in another winter annual species from Australia (Facelli and Chesson, 2008). It has also been observed that if rainfall is sufficient or water availability is high, seeds of summer annual species (Gutterman, 1990) and desert annual species (Mott, 1972) may germinate in higher temperature. Some seeds grow high sensitivity to water availability and only germinate when water is available and continuous. In a few species, seeds remain viable through forming hygroscopic structures (Gutterman and Ginott, 1994). Adaptation in dry environments needs more allocation of reserves to root than stem. The faster rate of root elongation confirms water uptake from deep as the water level near soil surface is reduced due to dryness. When grown in standard condition, seedlings from low rainfall areas exhibited longer and thinner main root axis while seedlings from higher rainfall environments had more root tip elongation due to higher RGR (Nicotra et al., 2002). Also, species from dry environments show higher rate of root length increase in dry condition, than the species from wet environments. This plasticity of root length in different dry habitats is a crucial factor for drought tolerance. Interaction of canopy shade is also considered for seedling establishment in arid soil. Canopy shade may provide protection to seedlings from direct sunlight and thus lowering the temperature. In addition, deep shade may also contribute


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in seedling survival through alteration of soil properties and hydraulic lift in dry habitats (Nobel, 1989). Soilproperty changes under canopy due to larger accumulation of organic matters. This also increases water retention capacity of the soil and thus better seedling survival (Facelli and Brock, 2000). Seedling establishment of both annual and perennial species determines the community structure in arid regions as the traits are selected evolutionary and the external resource is scarce. For annual plants, timing of rainfall for a year may determine the community structure and year to year rainfall patterns may lead to successive vegetation (Facelli et al., 2005). Whereas, for perennial plants, the scarcity of seedling recruitment opportunities may exhibit the vegetation dynamics over years. For example, only seven favourable establishment opportunities for a particular species, Myoporum platicarpium were assessed over a time of 160 years in the arid regions of southern Australia (Westbrook, 1999).

Seedling Establishment Strategy in Saline Environments High salinity affects seedling establishment in three ways – it makes soil water potential low, for which soil water becomes unavailable for the plant. Secondly, it destroys inorganic ion balance in soil, which results in toxic ion uptake by membrane through osmosis. And thirdly, increased ion competes with nutrients for membrane transporters, causing nutritional imbalance. Plants response to salinity stress through various adaptations, which include dilution of ion through increased cell sap, separation of toxic ions from metabolically active compounds, extrusion and increased ion selectivity (Facelli, 2008). Saline environment is present in two systems – dry and wet. Dry saline systems include saltpans and saline deserts, while wet saline systems comprise salt marshes and mangroves. Plants exhibit different strategies for adaptations in both saline systems. In wet saline systems, sufficient water is present which helps in the development of ion extrusion strategies to resist salt stress. On the other hand, dry saline systems exert more stress stimulation to plants due to extreme resource constraints and accumulation of salt layer on the surface due to capillary ascent and evaporation (Facelli, 2008). Salinity at the level of 50% strongly resist seedling growth for mangrove species growing in seawater, however growth continues in slow rate still in 100% (Downton, 1982). Salinity in external environments lowers water potential around seeds through increase in ion concentration and thus preventing osmotic movement of water into seeds. Some species develop adaptive features by lowering the



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internal water potential through ion accumulation in seeds or in viviparous seedlings growing in tidal levels in mangroves (Downton, 1982). The abundance of K+ is and scantity of Cl- is observed in such seedlings which indicates selective accumulation of ions. This control of ionic balance is mediated by seed reserves. When seedlings become fully independent, they use higher Cl- and Na+ concentrations to maintain water potential 2 MPa lower than external environment (Downton, 1982). Seed size may significantly influence stress tolerance due to salinity in two ways – selective accumulation of ions which depends on seed reserve, and seedling size for survival advantage. As salt stress is volume dependent, hence seedlings from large seeds are better tolerant. In viviparous species, seeds germinate while attached with the plant, giving them better adaptation to high chloride concentration, and the more mature seedlings establish better when independent from the mother plant (Smith and Snedaker, 1995). As seedlings show higher susceptibility to salinity, seedling establishment along salinity gradients effects actively in determining species distribution and community structure in saline environments. A study on two Prosopsis species supported that differences in salinity tolerance by seedlings, rather than mature plants contribute to the differences in distribution of species in saline environments (Villagra and Cavagnaro, 2005).

Seedling Establishment Strategy in Extremely Low Temperature Due to their small size, seedlings are particularly susceptible to tissue damage and photoinhibition due to cold environment. Accumulation of frost also affects seedling growth. To avoid the damage due to cold temperature, some species prevent seed germination during late autumn or early winter. Stratification or very low temperature acts as a breaks dormancy in such cold adapted species. Seedling establishment succeeds in response to post cold condition and minimum required temperature for germination ensure emergence of seedlings after the risk of freezing has escaped (Fenner and Thompson, 2005). Cold damage arises when seedlings face abrupt chilling. Carbon scarcity in seedling due to low reserves and photosynthetic constraint coupled with low temperature injury may all contribute to reduced seedling establishment and increased mortality, causing even 80% death of seedlings during the first winter in some temperate species (Osumi and Sakurai, 2002). When seedlings subjected to frost stress are exposed to high irradiance, the photosystems are damaged temporarily or permanently due to excess energy,


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this is known as photoinhibition (Osmond, 1981). Seedlings are particularly susceptible to photoinhibition due to limitation in photosynthetic capacity and small amount of maternal reserves (Blennow and Lindkvist, 2000). It is evident that seedlings are more vulnerable to chilling stress like any other stresses than adult plants. Therefore, differential allocation of seedlings to cold environments determines altitudinal and latitudinal distribution of species (Facelli, 2008). Cold response of perennial herb, Digitalis purpurea was shown to be the main decisive factor for its altitudinal distribution in Germany (Bruelheide, 2002). A number of works support that response to cold environment determine seedling establishment and subsequently the vegetation spectrum (Germino et al., 2002). Seed size may influence seedling establishment in cold environment as well. As seed size determines the amount storage, hence, during photosynthetic limitations due to freezing stress, seedlings from larger seeds have advantage for recruitment. Work on Betula maximowicziana seedlings displayed high mortality due to small seed size (Osumi and Sakurai, 2002). Cold stress can reach so higher multitude that it can completely resist seedling establishment often. This prevents plant growth so much that most of the plants can not survive till reproductive stage and can not gather resources for seed production. Since, sexual reproduction is forbidden the only way to survive is through clonality. This is evident from the occurrence of 2000 years old clones of Carex curvula from European Alpine zone where no sexual reproduction took place for years. This type of survival strategy may also contribute to evolution of clonality as the main mechanism for recruitment in Arctic and alpine regions (Facelli, 2008).

Seedling Establishment Strategy against Physical Damage Physical damage can be caused by mechanical actions of both abiotic and biotic agents. Seedlings may be buried down or get exposed due to sand dune drifting or snow drifts. Sand dunes create an open system with loose surface particles, which can be easily accumulated or get drawn away due to wind or water activities. In such conditions, roots of the seedlings can be bared or shoots can be buried causing substantial denial to establishment. In cold regions, seedlings commonly get uprooted by dragging away of freezing soil (Goulet, 1995). In tropical rain forests, falling dead leaves or barks or epiphytes may cause potential physical damage to seedlings (Clark and Clark, 1989).



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Shifting sand can bury down seeds. This acts as a great inhibitor of seedling establishment as depth of burial affects seed germination. The more deep the seed is buried, the less chance it gets to germinate because of its limiting resource. Burial beyond a threshold imposes dormancy in seeds (Facelli, 2008). During early recruitment of seedlings, exposure of roots due to substratum drift has potential effect. Exposed roots fail to obtain water or severely desiccate. Even partially exposed secondary roots lose function. Shoots inhumed by accumulation of sand have negative effect on plant growth as well. Sand accumulation can cover the photosynthetic parts of seedling causing nutrient constriction. However, the effect is not as rigorous as in case of roots, because, growing shoots may overcome the layer of sand. If the rate of sand accumulation outmatches stem elongation, the survival of seedling depends on the degree of burial (Maun, 1998), the amount of reserve to provide emergence or if the wind exposes the seedling before all its reserve is spend off (Harris and Davy, 1987). Deep shade adaptation of a seedling or its ability to survive in darkness may provide some aid to its survival too. Although moderate accumulation of sand tends promote growth in sand-adapted species (Maun, 1998) probably due to reduction of root temperatures, accumulation of nutrient rich materials, increased soil volume for root exploration, better retention of water by roots, inhibition of pathogen or providing environment for mycorrhizal fungi (Facelli, 2008). Soil heaving in cold, wet environments have considerable effect on seedling establishment. Seedlings can be heaved out of the soil by the formation of ice crystals on the soil surface (Facelli, 2008). Soil heaving due frost results in exposure or tearing of roots causing seedling death (Legard, 1979). Species with extent lateral root system, depth of branching, mechanical resistance to tension and ability to overcome the damage exhibit better adaptability to frost heaving. In tropical rain forest, where individual density is high, seedlings often suffer casualties due to falling debris and epiphytes. It was observed in a study that death of 20% seedlings with stems less than or equal to 1 cm in diameter was caused by falling debris (Clark and Clark, 1991). This type of physical damage confirms the vegetation constitution in tropical rain forests. Walking palm species, Socratea exorrhiza exhibit adaptability to falling limbs by crawling from under it through elongating their stems, and can move up to 200 cm from their original establishment spot (Bodley and Benson, 1980). Thus, these type of stress can significantly elicit evolutionary changes for survival advantage in those species. Biotic factors such as herbivory, trampling, grazing or pathogens cause physical damage to seedlings. Seeds once dispersed are often consumed by seed


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predators before germination. These biotic stressors functions together with physical effectors in some systems and are often more effective because they can cause potential loss of biomass that is difficult to overcome under limited resource conditions. Herbivory causes severe tissue loss or defoliation which can be lethal to early seedlings. Higher amount of secondary components in plants from stressful conditions indicates a strong selective pressure of herbivores (Chapin et al., 1993). Seedlings when grown in shade are more susceptible to herbivory because of limited accumulation of biomass. Chemical defence in seedlings is also compromised in shade making them more vulnerable to herbivory. Seedlings experience similar effects by mechanical tissue loss due to trampling or grazing. Fungal pathogens cause necrosis in seedlings increasing further mortality.

SEED-SEEDLING RELATIONSHIP Seed Mass and Seedling Survival Seed size is basically characterized by the amount of maternal reserves, that is seed dry mass. Seed mass is an important intrinsic factor that induces seedling survival. In this context, size of the seed is supposed to be proportional with weight and vice versa. There is a positive relationship between seed and seedling size or weight. Usually seedlings from larger or heavier seeds are taller or larger or heavier, both intra and inter-specifically (Jurado and Westoby, 1992; Baraloto et al., 2005; Zanne et al., 2005). This larger or heavier initial size influences advantage during early establishment in many ways. Larger seedlings have better access to external resources such as, light, water, and they also enjoy competitive advantage among and across species (Leishman et al., 2000). Larger seedlings also have better proportion of reserves that is helpful during resource limitations (Kitajima, 1996; Green and Juniper, 2004; Zanne et al., 2005). Furthermore, the negative relationship between seed mass and relative growth rate (RGR) of seedlings (Kitajima, 1994; Fenner and Thompson, 2005; Paz et al., 2005) indicates slower metabolic rate in larger seedlings (Green and Juniper, 2004b) and therefore, increased longevity in those species (Moles and Leishman, 2008). Altogether, these contribute to better survival for larger seedlings both in natural systems (Moles and Westoby, 2004a; Baraloto et al., 2005) and in critical environments (Westoby et al., 2002) due to nutrient limiting, deep shade, physical damage, burial under or soil or litter and competition with other individuals.



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Seed Number/ Seedling Survival Trade off The seed number/ seedling survival trade off suggests that, large seeded species produce a few number of larger seeds while small seeded species produce much more seeds than large seeded species. But, as larger seeds produce larger seedlings, and small seeds produce comparatively small seedlings, and larger seedlings have survival advantage during early recruitment over small seedlings, then, after a given time, the survived individuals of both the large seeded and small seeded species will be equal, given the numerical advantage of small seeded species (Moles and Westoby, 2004a). However, this will be only possible, if the survival advantage of large seeded species exactly counter-balances with the seed production advantage of small seeded species. It was observed after one week of study that the survival advantage of large seeded species was not enough to counterbalance the seed production advantage of small seeded species (Moles and Westoby, 2004a). Though, as seedlings usually need more than one week for absolute establishment, hence, if the survival advantage of large seeded species continues at the same rate, then after a period of time a state should occur when the number of surviving seedlings of the large seeded species would be similar as of the small seeded species. Moles and Westoby (2004a) suggested that the time needed by large seeded species to counterbalance the above depends on the seed mass. It was also observed in the study at the small seeded end of seed mass spectrum, that after 8.8 weeks, the survival of large seeded species would be equal with 10-fold smaller seeds. However, at the large seeded end of the seed mass spectrum, the survival advantage of large seeded species would have to continue at the same rate as the first week till 4.2 years when the large seeded species had similar number of seedlings as the small seeded species (Moles and Westoby, 2004a). Although this result contrasts from the observation that seed mass has no effect in the later stages of growth (Saverimuttu and Westoby, 1996; Dalling and Hubbell, 2002; Baraloto et al., 2005) as the seed reserves is usually all deployed during late growth phases. Thus, the seed number/ seedling survival trade off is unlike to function alike shortly after the early periods. Other seed and seed ecology factors are also involved in this trade off in broader aspect.

Seed Mass and Seed Production Seed production is calculated as total number of seeds produced by a species annually or seed produced per unit canopy area per year (Moles and


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Leishman, 2008). Seed production is negatively correlated with seed mass for a given canopy area each year and the slope value is –1 (Henry and Westoby, 2001). Alternatively, the relationship between seed mass and lifetime seed production depends on plant life span. It is observed that there are positive relationships between plant size and seed mass (Leishman et al., 1995; Moles et al., 2005) and between seed mass and canopy area (Moles and Westoby, 2006a). This indicates, large canopy species from larger seeds might allocate more to reproduction. Therefore, the slope of the relationship between seed mass and number of seeds produced per year has less steepness (–0.29) than the relationship between seed mass and seeds produced per unit canopy area per year (Moles and Westoby, 2006a). These interactions depend substantially on the life span of the species. It is observed that small seeded plants have shorter life span than large seeded species (Moles and Westoby, 2006a). Through all these contrasting features, Moles et al. (2004) suggested that there is no relationship between seed mass and lifetime seed production. Although small seeds produce more seeds for a given amount of energy, still smaller canopy and shorter reproductive life span indicate that they do not produce more seeds than large seeded species over a lifetime.

Seed Mass and Seedling Survival to Adulthood Large seeded species exhibit better survival over small seeded species during early establishment (Moles and Westoby, 2004a). However, survival until reproductive maturity determines the evolutionary advancement of the species. A seedling’s survival to adulthood depends on two factors – probability of survival through a given amount of time and the amount of time between emergence and maturity (Moles and Leishman, 2008). Another study showed positive relationship between seed mass and duration of juvenile period (Moles and Westoby, 2006b). That means, small seeded species are supposed to reproductive maturity earlier than large seeded species (Moles et al., 2004). Because of the shorter juvenile phase, small seeded species face less chance to juvenile mortality than the large seeded species. This advantage of small seeded species counters with the higher survival advantage of large seeded species (Moles and Leishman, 2008). This indicates that there is a complex relationship between seed and seedling survival. However it is possible that there is a little negative relationship between seed mass and survival of seedling from emergence to maturity (Moles and Westoby, 2006b).



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Seed Dispersal and Seedling Survival Seed dispersal is directly related with seed mass (Leishman et al., 1995). Seeds that exhibit wind dispersal or dispersal through sticking to the outside of animals are usually smaller and lighter in weight than seeds that dispersed by water or through consumption by animals. Also seeds dispersed via ingestion by animals show variation depending on the animals involved. Seeds spread by mammals are quite larger than the ones by birds. Seed dispersal involving invertebrates are much smaller than other ones. Seed dispersal spectrum reflects on the site of seed germination or seedling habitat. Seed dispersal influences seedling establishment through interspecific and intraspecific competition (Jordano and Godoy, 2002) and formation of community structure. Seed dispersal also affects probability of surviving seed predation (Garcia-Castaño et al., 2006) and susceptibility to pathogens (Augspurger and Kelly, 1984). Selection of dispersal mechanism may also reflect on plant migration in response to climate change (Moles and Leishman, 2008).

Seed Persistence in Soil and Seedling Survival Persistence of seeds on soil subsequent to dispersal has an interesting impact on seedling establishment. Seeds once dispersed are threaten with seed predation. Usually larger seeds are prone to be consumed by seed predators. Therefore, small seeds have better chance to survive in soil. It is evident that species with small, rounded seeds from Europe (Thompson et al,, 1993) and from Argentina (Funes et al., 1999) persist better in the soil. However, studies from Australia (Leishman and Westoby, 1998) and South Africa (Holmes and Newton, 2004). Sometimes, seed mass and seed shape affect seed survival in soil independently. Studies from New Zealand (Moles et al., 2000), Iran (Thompson et al., 2001), and central Spain (Peco et al., 2003) suggest that seed persistence in soil is directly related with seed mass but not with seed shape. The benefit of small seeds to be persistent in soil coincides with the observation that species with shorter life span which produce smaller seeds tend to have more persistent seeds in soil. The seed survival advantage of small seeded species empower their frequent emergence under favourable condition for seedling establishment. Thus, seed survival in soil may determine plant life history strategy as well as population dynamics for the dispersal site environment.


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Seedling Morphology and Seedling Survival Phenotypic characters also influence seedling survival. It has been observed that seedlings from of large seeds tend to show cryptocotylar nature, that is cotyledons are hypogeal and remain within seed coat (Garwood, 1996; Wright et al., 2000; Ibarra –Manríquez et al., 2001; Zanne et al., 2005). Cryptocotyly with substantially more allocation of reserves to seedlings gives the plant for better sustainability. On the contrary, small seeded species, with minimal reserves depend more on the external resources. Therefore, those species exhibit phanerocotyly with photosynthetically competent paracotyledons. Those species are more vulnerable to stressors, especially mechanical pressures. Defoliation by herbivory is a potential cause for seedling mortality. Seedlings’ ability to resprout after defoliation depends on the correlation between seedling morphology and seed mass. Phanerocotylar seedlings with epigeal paracotyledons usually fail to resprout after removal of cotyledons and apical bud (Moles and Westoby, 2004b). Cryptocotylar species, however, sustains better after potential defoliation or tissue loss, as they have reserves and some meristematic tissue safely kept underground (Harms and Dalling, 1997). Cotyledonary photosynthetic index (CPI) which determines photosynthetic capacity of cotyledons is negatively correlated with seed mass (Zanne et al., 2005). Photosynthetic rate also depends negatively on cotyledonary thickness (Kitajima, 1992b) which justifies lower photosynthetic rate in seedlings with phanerocotylar reserve type cotyledons as they possess more maternal reserves.

Seedling Growth Strategies and Seedling Survival Seedlings of different species acquire different rate of growth to sustain better in different environments. As from the earlier discussion, it is understood that relative growth rate (RGR) is negatively correlated with seed mass (Kitajima, 1994; Wright and Westoby, 1999; Fenner and Thompson, 2005; Paz et al., 2005). Seedlings of small seeded species exhibit higher RGR as they need better exposure to external resources due to their low seed reserves. A study on Australian species showed RGR is positively correlated with specific root length and negatively correlated with leaf mass per area (Wright and Westoby, 1999). The negative relation is reflects that seedlings of small seeded species have low tissue density. This is evident from another study from Europe that seedlings with high RGR displayed low stem tissue density and broader vessels (CastroDiez et al., 1998). Seedlings with high RGR tend to maximize surface area for



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better acquisition of resources. A study on woody species from Europe displayed seedlings with higher leaf mass per area had denser but thinner leaves and had smaller cells and higher sclerified tissue density in the leaves while lower water and nitrogen concentrations than seedlings with lower leaf mass per area (Castro-Diez et al., 2000). Furthermore, positive relation between RGR and foliar nitrogen concentration was observed in seedlings from another study (Cornelissen et al., 1997).

SEEDLING MORTALITY Existence of a population usually depends on two events, seedling establishment and seedling mortality. As we discussed earlier, being the most sensitive stage of plant life cycle, seedlings exhibit the highest rate of mortality. Due to its smaller size and maternal reserve limitations, seedlings have very short supply of carbon recruitment. When all its initial carbon reserve is used up, seedlings become exposed to the mercy of nature and it has to triumph over all the odds for its survival. The natural system is full of different harsh conditions that can restrain the resource allocations of a seedling depending on external environments. When the seedling fails to overcome the external adversaries, it usually dies. The natural enemies of seedling survival are both abiotic and biotic agents. Often the natural affecters during seedling establishment reduce the carbon allotment of a seedling so minimum that they becomes easily vulnerable to mortality agents. However, after a successful establishment, those are the biotic factors that affect seedling survival the most. Moles and Westoby (2004c) categorized the causal factors for common seedling mortality cases according to their effects. The more frequent causes for seedling mortality were herbivory (38%), drought (35%) and fungal attack (20%) while the less frequent factors were physical damage (4.6%), competition with other seedlings (1.6%) and competition from existing vegetation (1.3%).

Seedling Mortality due to Herbivory Herbivory is the most lethal factor in seedling mortality. The effect of herbivory is related with the nature of the animal and the ecosystem. In forests, slug animals are responsible for mortality of an herb, Lathyrus vernus (Ehrlen, 2003). Whereas, in grasslands, herbivory is lethal by rodents, but nonlethal by molluscs though they can remove seedling tissue up to 75% (Hulme, 1994).


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Though herbivory is often lethal for seedlings, nonlethal is also quite common (Green and Juniper, 2004a). It was observed in an experiment that more than 40% seedlings could survive after removal of tissue up to 95% (Armstrong and Westoby, 1993). However, there are also sublethal effects to seedling herbivory, exhibiting reduced growth and reproduction (Hanley and May, 2006). Seed size also influences seedling herbivory quite well. Seedlings of larger seeded species generally response better to herbivory (Moles and Westoby, 2004a) because they have more reserves to counter with the carbon loss due to herbivory. Larger seedlings also have better survival than smaller ones after defoliation (Armstrong and Westoby, 1993) which may also help their better herbivory response. Although the disadvantage of larger seedlings is that they attract more herbivores is interesting in their better survival. Defence mechanism of seedlings is another important factor related to seedling herbivory. Chemical defence is an important mean in seedling defence mechanism and it was observed that seedlings with high leaf phenolic component prevent herbivores among Australian Proteaceae species (Hanley and Lamont, 2001; Rafferty et al., 2005). Leaf phenolic content is positively correlated with SLA and RGR which suggests that fast growing seedling are better adapted to this type of defence as they are more prone to herbivory (Dalling and Hubbell, 2002). Therefore, seedling herbivory may initially induce evolution of chemical defence (Eriksson and Ehrlén, 2008) in plants. Furthermore, selective grazing depending on species wise phenolic response to herbivores may establish community structure (Burt-Smith et al., 2003).

Seedling Mortality due to Pathogens Seedling mortality due to microbial pathogen especially fungal attack works in the similar manner as in case of herbivory (Eriksson and Ehrlén, 2008), only in pathogen attack causes necrosis rather than consumption of plant parts. Seedling response to pathogens was studied by the seminal tests of the JanzenConnell model for tropical tree species by Augspurger (1984), Clark and Clark (1984) and other workers. According to these studies, seedling are less vulnerable to pathogens beyond a certain distance from the mother plant due to less chance of infection. Similarly recruitment of seedlings of a tree species Prunus serotina was found successful at distance from adult plants as soil pathogens were found to be in higher amount near adult plants (Packer and Clay, 2003).



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Seedling Mortality due to Drought Draught is a severe natural cause responsible for considerable seedling mortality. Drought is generally characterised by resource shortage (Eriksson and Ehrlén, 2008). Due to limited carbon reserves, seedlings are susceptible to natural resources such as light, water, temperature and nutrients (Fenner and Thompson, 2005). Larger seeded species have survival advantage over smaller seeded species (Moles and Westoby, 2004a) through greater amount of carbon allocation and, therefore, seedlings of small seeded species show higher rate of mortality under such conditions. Also seedlings of different species respond differently to diverse stresses or sometimes to combination of more than one critical conditions. For example, effect of combinations of shade and drought (Sack and Grubb, 2002), light and water (Battaglia et al., 2000) or light and nitrogen availability (Catovsky et al., 2002) have been studied on seedling recruitment. Ontogenic shifts to combinations of resources during seedling growth has also been noted in old field annuals (Parrish and Bazzaz, 1985), ericaceous shrubs (Eriksson, 2002) or tropical trees and lianas (Gilbert et al., 2006).

Seedling Mortality due to Physical Damage Damage or tissue loss due to physical damage is often poses as a threat to seedlings. The common causes of physical damage are falling of litter (Clark and Clark, 1991), failure of seedlings to emergence through the litter layer (Dalling and Hubbell, 2002) and trampling by grazing animals. The mat of litter exerts mechanical pressure on seedlings. Due toresource limitation, it is hard for seedlings to emerge through the litter layer. Besides often seedlings die due to external resource constraint, especially lack of light under dense litter layer. Trampling often cause breakage or loss of tissue in seedlings which consequently costs more carbon allocation. Seedlings failing to do so are usually subjected to mortality. Seedlings with comparatively higher amount of mechanical tissue or greater amount of reserves are successful to avoid mortality due to physical stresses. The negative effects of litter on seedling recruitment has been discussed in details earlier, however, it has been observed that sometimes litter can promote seedling survival (Quested and Eriksson, 2006). Woody litter may promote seedling establishment and growth, evidences are found in case of ericaceous shrubs in boreal forests (Eriksson and Fröborg,


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1996), orchids in deciduous forests (Rasmussen and Whigham, 1998), and trees in Nothofagus forests (Heinemann and Kitzberger, 2006).

Seedling Mortality due to Interaction with Other Individuals During initial recruitment, seedlings experience negative effect due to competition with other recruits in the vicinity as well as due to negative pressure of the existing vegetation. In environments with limited soil nutrients, larger seedlings with profuse rooting and elongated stem acquire more resources as smaller seedlings die failing to do so. Competition within the same species is more complex and random to assess. Intraspecific density functions as a sieve where mortality agents can not affect the population much, but acts as selective agents determining the survivorship of seedlings beyond the sieve (Eriksson and Ehrlén, 2008). Existing vegetation also exerts negative pressure on seedling survival through shading, dropping of litter or attracting pathogens. However, mature plants may function as nursing plants for seedlings and may positively influence seedling recruitment (Callaway, 1995). Nursing plants protect seedlings from herbivores, for example, seedlings of Taxus baccata is protected from herbivory by neighbouring vegetation of Ilex aquifolium (Garcia and Obeso, 2003). Nursing plants may facilitate seedlings through substrate modification, a case occurs as Leymus mollis, a key species of dune succession was favoured by nurse plant Honckenya peploides (Gagne and Houle, 2001). Another mechanism for seedling survival promoted by nurse plants is recruitment modification, which occurs in Quercus forests to develop tree patches (Callaway and Davis, 1998) and to maintain woodland borders (Weltzin and McPherson, 1999). It was also observed that some invasive species such as, Pyracantha angustifolia facilitate recruitment of other invasive species (Tecco et al., 2006). This may shade light on the impact of nurse plants conservation in arid and semi-arid environments to restore vegetation (Padilla and Pugnaire, 2006). Other types of inter-specific interactions such as, interaction with microbes for mycorrhizal species (McKendrick et al., 2000) and interaction with Rhizobium for legume plants (Valladares et al., 2002) are also interesting to promote seedling recruitment.



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APPLICATION OF SEEDLING IN MODERN DAY AGRO-FORESTRY SERVICES In simpler terms, weeds are plants that interfere with healthy or normal growth and development of crops. These plants are also known to limit the yield of crops causing serious losses in output of grains, seeds, fruits, etc. (Marwat et al., 2013). A calculation that one out of every ten plants on Earth is a weed means that there are approximately 30,000 weed species globally (Duke, 1992). Although scientists and agricultural extension officers recommend eradicating them, 89% of the most widespread and aggressive weeds in the world are edible (Rapoport et al., 1995). One way to explain the use of weeds of agriculture in the diet of farmers is that of the botanical dietary paradox (Ogle and Grivetti, 1985, Price and Ogle, 2008). The paradox is that as wild edible species of the forest become more distant from the agricultural fields, farmers eat more wild species from the farming areas, and there is a tendency for farmers to eat more wild food plants. The consumption of weeds is a world-wide phenomenon that is noted as having an important role for human nutrition. Their consumption has been widely reported on the African, American and European continents. The consumption of weeds is also common in Asia, with Bicol’s weed recipes in the Philippines as one example (Marcelino et al., 2005). Other examples include the tribal people in the Indian states of Jharkhand, Orissa and West Bengal (Sinha and Lakra, 2007), the use of weeds in preparing traditional Korean and Chinese dishes (Pemberton and Lee, 1996) and, in Thailand, where 30% of weeds are reported as edible (Maneechote, 2007). Edible weeds also possess multiple additional uses besides food, such being a source of animal fodder and medicine (Pieroni, 1999). For instance, the multiplicity of uses of edible weeds has been reported in India (Datta and Banerjee, 1978), Vietnam (Van Chin, 1999), and Thailand (Maneechote, 2007). In spite of multiple uses of weeds agriculturists are following various techniques for the eradication of some weeds interacting with crops reducing yield. Farmers may eradicate few obnoxious weeds of crop field among 89% as recorded by Rapoport et al., 1995 and remaining 11% should be removed since they have no useful properties. The identification of weeds at the juvenile stage is crucial for farmers before considering them as useful or harmful. The harmful weeds of crop fields reducing the yield of crop display huge amount of seeds among the growing crops or before harvest. In the cropping seasons, the viable seeds of weeds


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produce seedlings, especially of ephemeral type. Therefore, rapid and accurate identification of these weeds and enumeration of their phenotypic traits at the seedling stage might be an important step towards the designing of successful weed management program, which could save both time and money for farmers and reduces herbicide usage (Parkinson et al., 2013). There are several advantages for weed management at seedling stage. Firstly, it is much easier, less costly, and more effective at the juvenile (e.g., rosette) stage than on mature plants. Second, controlling a weed during its early growth allows desirable crops to grow better. Finally, improper identification may lead to misapplication of management technique, such as herbicides or failure adequate control the weed species at its most vulnerable time of life (Parkinson et al., 2013). Once a species has correctly identified, an integrated weed management (IWM) program can be designed that combines the use of biological, cultural, mechanical, and chemical particles to manage the weeds. Some of the major crop field weeds of tropical Asian countries are Amaranthus spinosus, Glinus lotoides, Avena fatua, Coronopus didymus, Commelina spp., Galium aparine, Physalis spp., Stelleria media, Chenopodium album, Polygonum spp., Rumex dentatus, Paspalum spp., Echinochloa spp., Oryza punctata, Leersia spp., Eclipta alba, Lindernia spp., Sphenoclea zeylanica, Gnephalium spp., Gratiola spp., Sesbania herbacea, Aeschynomene spp., Ammania baccifera, Rotala spp., Melochia corchorifolia, Sphaeranthes indica, Grangea maderaspatana, Alternanthera spp., Croton bonplandianum, Mecardania procumbens, Scoparia dulcis, Bergia ammanoides, Trianthema portulacastrum, Hygrophila spp., Chrozophora plicata, Euphorbia spp., Eleocharis spp., Anagalis arvensis, Sagittaria spp., Scoenoplectus articulatus, Cyperus spp., Fimbristylis spp., etc. A strategy may be demonstrated to identify them at the juvenile stage for eradication supporting no time to provide the weeds for flowering or fruiting which is of very short duration for these weeds. Again weed taxa vary in response to weedicides, therefore it is important to select the correct weedicides to control particular weed species and minimize environmental damage and wastage. This approach is also must because producing an adequate quantity of healthy food without polluting environment is a formidable challenge for agriculture in future. Besides proper identification adult weeds or their seedlings because consumption of harmful weeds may create health hazards. Besides interactions with the crop, majority of weeds are important to human as food and ingradients of various ayurvedic, homoeopathic and allopathic medicines. In rural areas, some weeds are again directly used as medicine. Some of the edible weeds are Amaranthus viridis, Alternanthera



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sessilis, A. phyloxeroides, Chenopodium album, Boerhaavia diffusa, Basella rubra, Leucas aspera, Centella asiatica, Hydrocotyle spp., Coccinia grandis, Glinus oppositifolius, Ipomoea aquatica, Oenanthe benghalensis, Nymphaea pubescens, Enhydra fluctuans, Hygrophila schuli, Melilotus alba, M. indica, Trianthema portulacastrum, etc. Due to urbanisation, the population of these species is facing various kinds of threats and they are gradually disappearing. Proper identification and rehabilitation of these edible weeds in the seedling stage may restore their germplasm and sustain our food shortage in such polluted environment. Due to urbanisation, industrialization, overgrazing, overexploitation, encroachment and unsustainable practices, our forest resources having various food and food-adjunct taxa are in a state of decline. Some of such forest food and food-adjunct plants are Rauwolfia serpentina, Dioscorea spp., Asparagus racemosus, Zizyphus mauritiana, Zizyphus oenoplea, Psidium guava, Sizygium spp., Aristolchia indica, Azadirachta indica, Tamarindus indica, Spandias spp., Senna alba, Phyllanthsu acidus, Phyllanthus emblica, Paederia foetida, Wrightia antidysenterica, Bombax ceiba, Sesbania grandiflora, Andrographis paniculata, Costus speciosus, Gymnema sylvestre, Hibiscus sabdariffa, Justicia vasica, Wattakaka volubilis, Ocimum spp., Terminalia spp., Withania somnifera, Carya arborea, Neolamarckia cadamba, Streblus asper, Litsea glutinosa, Tinospora cordifolia, Tinospora sinensis, Flacourtia indica, etc. Identification at juvenile stage is crucial for rehabilitation or transfer of these germplasms from their threatened habitat to protected ex-situ conservation regions. Identification of these and many of the economically important plants has been demonstrated by many Indian workers (Balasubramanyam and Swarupanandan, 1986; Deb and Paria, 1986; Paria and Kamilya, 1999; Das et al., 2009; Singh and Sahu, 2010; Kamilya and Das, 2014; Kamilya et al., 2015, Singh, 2015). Thus, seedling morphological traits are helping for identification and restoration of germplasm in the globe partially sustain future food security in the changing environment.

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Chapter 7

MANAGEMENT OF STEM ROT OF JUTE USING PLANT GROWTH PROMOTING RHIZOBACTERIA (PGPR) AND PLANT GROWTH PROMOTING FUNGI (PGPF) CONSORTIUM: A STEP TOWARDS INTEGRATED DISEASE MANAGEMENT IN MODERN AGRICULTURE S. K. Bhattacharyya and Chandan Sengupta Microbiology Laboratory, Department of Botany, University of Kalyani, Kalyani, West Bengal, India

ABSTRACT Plant diseases caused by variety of pathogens pose a serious challenge and economic threats to various agricultural crops all around the world. It has been evidenced that despite wide use of chemical pesticides in crop production, the losses due to pests, viz. insects, diseases, nematodes, rodents are significant. These are the major groups of organisms that live in diverse habitat and continue to threat variety of agricultural crops round the globe. Since time immemorial, the major agricultural crops have been 



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S. K. Bhattacharyya and Chandan Sengupta plagued by these obnoxious organisms that feed on various plant parts viz. roots, rhizome, tubers, seedlings, stem, leaves, buds, crowns and damage worth more than 100 billion dollars annually. Stem rot of jute caused by the phyto-pathogenic fungi Macrophomina phaseolina (Tassi)Goid. {syns. M. phaseolina (Maubl.)Ashby} [= Rhizoctonia bataticola (Taub.)Butler] is a major disease occurring in almost all the jute growing areas of the world. In India, particularly in West Bengal, Assam it occurs every year in moderate or severe form, occasionally taking epidemic form based on several parameters. In this chapter, we reviewed extensively the nature of stem rot pathogen with wide hosts, particularly in jute and some sustainable management procedure using plant growth promoting rhizobacteria (PGPR) and plant growth promoting fungi (PGPF).

Keywords: stem rot of jute, Macrophomina phaseolina (Tassi)Goid., PGPR, PGPF

INTRODUCTION Plant diseases caused by variety of pathogens pose a serious challenge and economic threats to various agricultural crops all around the world. It has been evidenced that despite wide use of chemical pesticides in crop production, the losses due to pests, viz. insects, diseases, nematodes, rodents are significant. These are the major groups of organisms that live in diverse environment and continue to threat variety of agricultural crops all around the world. Since early times the major agricultural crops have been plagued by these intolerable organisms that feed on various plant parts viz. roots, rhizome, tubers, seedlings, stem, leaves, buds, crowns and damage worth more than 100 billion dollars annually. In mid-20th century chemical pesticides were the major armoury to combat with major pests, but due to their deleterious effects on the environment, human and animal health most of the effective pesticides and fumigants have been withdrawn from the world market. Though, several non-chemical management tactics for disease and pest management like fallowing, flooding, crop rotations, use of resistant crops, trap crop or cover crop, soil solarization, organic amendment etc. are available. In recent years, more efforts are directed towards the use of microbes to minimize the pest’s population as bio-control measures along with plant health and their growth promotion. In most cases, bio-control agents have been very effective under laboratory conditions, but field results, have shown varying degrees of success (Pandey et al., 2000). Microorganisms are important in agriculture in order to promote the circulation of plant nutrients, reduce the need for chemical fertilizers and


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chemical pesticides. Numerous species of soil micro-flora flourish in the rhizosphere of plants and activate or stimulate plant growth by a plethora of mechanisms. Micro organisms in soil are exposed to variety of fungal and bacterial antagonists. Bacteria are more abundantly present in soil and some of them have shown more potential for lowering the plant parasites, such as pathogens and nematodes in soil. The major objective of phyto pathogen and nematode control was to improve soil health and gain economic benefits. Soil health is the capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality and promote plant health (Doran, 1996). A healthy soil possesses high biodiversity and provides relief by pests or pathogens and most importantly, improving plant health. The management effect depends on the interaction among “Host-Plant-Target pathogen & nematode –soil-microbes-environment”. Thus phyto-pathogen and nematode management can be achieved through simultaneously promoting the growth of plant (Siddiqui and Shaukat, 2002) or beneficial organisms, facilitating the antagonistic activity or rhizosphere colonization of the microbial antagonists and thus provide induce systematic resistance in plants (Van Loon et al., 1998; Meyer and Roberts, 2002). Stem rot of jute caused by the phyto-pathogenic fungi Macrophomina phaseolina (Tassi)Goid. [syns. M. phaseolina (Maubl.)Ashby] [= Rhizoctonia bataticola (Taub.)Butler] is a major disease occurring in almost all the jute growing areas of the world. In India, particularly in West Bengal, Assam it occurs every year in moderate or severe form, occasionally taking epidemic form based on several parameters. The same fungus may attack this crop at different stages of plant growth causing ‘collar rot’; ‘seedling blight’ and ‘root rot’ (Ghosh and Mukherjee, 1970). The pycnidial stage of the fungus is responsible for ‘stem rot’ in mature plants (Ashby, 1927). Macrophomina phaseolina infects a broad range of wild and cultivated species under different climatic conditions. Although only a single species has been recognized in the genus Macrophomina, high levels of variation in pathogenecity have been found (Su et al., 2001).

CROP- AN OVERVIEW Jute is the most eco-friendly fibre in India; sown and harvested annually (the White jute crop is usually mature in July, the Tossa crop slightly later). It is produced in Eastern and North Eastern States comprising of West Bengal, Bihar, Orissa, Assam, Meghalaya and the Tarai areas of Uttar Pradesh. It grows


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best in monsoon climates, as the cultivation requires plentiful rainfall - essential not only for the good growth of the plant, but also to provide fresh water for retting (the plant is cut and immersed in clean pond-water or slow-running streams, to clean and soften the fibre and to enable it to be stripped from the stem). Too little rainfall can reduce the size of the crop and also affect the quality of the fibre and to remove impurities. Too much rain before the plants reach maturity may also reduce the size of the crop by flooding. One of the constraints in increasing productivity is due to different pests and diseases. It is one of the cheapest natural fibers and is second only to cotton in amount produced and variety of uses. Jute fibres are composed primarily of the plant materials, cellulose (major component of plant fibre) and lignin (major components wood fibre). It is thus a ligno-cellulosic fibre that is partially a textile fibre and partially wood. It falls into the bast fibre category (fibre collected from bast or skin of the plant) along with kenaf, industrial hemp, flax (linen), ramie, etc. White jute (Corchorus capsularis L.) is known to have been cultivated in India more than four hundred years ago, to be spun into cloth by artisans, and also used in ropes and twines. Jute is a natural long, soft, shiny vegetable fibre that can be spun into coarse, strong threads. The fibres are off-white to brown, and 1–4 meters (3–12 feet) long. Jute fibre is often called hessian, jute fabrics are also called hessian cloth and jute sacks are called gunny bags in some European countries. Tossa Jute (Corchorus olitorius L.) which is silkier and stronger than White jute (Corchorus capsularis L.) has traditionally been grown around the area of the Ganges Delta and was already in such large-scale production two hundred years ago to allow export of raw fibre to a nascent Jute-spinning industry in Dundee. Tossa jute (Corchorus olitorius L.) is known as the “Golden Fibre”, from the lustrous appearance of the threads, although tossa can range in colour from dark to reddish, depending upon the area of cultivation. Tossa jute (Corchorus olitorius L.) is an Afro-Arabian variety and a member of the Mallow Plant family (same family of Marshmallow). Bangladesh (formerly East Bengal until the Partition of India, and East Pakistan until independence), together with the Indian state of West Bengal, produces most of the world's jute fibre.

PATHOGENIC OCCURRENCE AND IMPORTANCE M. phaseolina (Tassi.)Goid. is an important pathogen in jute (Corchorus olitorius L. and C. capsularis L.), having nearly 500 host range and this particular necrotic fungus causes seedling blight, damping off, collar rot, stem



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rot and root rot disease complex in jute throughout the growing stages from seedling till harvest (Bandopadhyay et al., 2004). It causes serious economic levels ranging from 20-30% under dry warm conditions. Macrophomina phaseolina (Tassi.)Goid. is an omnipresent pathogen initiating a number of diseases in jute which are wide spread in nature. The pathogen is both seed and soil borne. Disease is spread secondarily through pycnidiospores which are airborne in nature. Pycnidia are initially immersed in host tissue, then erumpent at maturity. The facultative parasite attacks the jute plant causing seedling blight, damping off, collar rot, stem rot and root rot at any part of the plant at any stage of growth from seedling stage to until harvest (Anonymous, 1998). Plant debris provides the primary source of infection every summer. Rootknot nematode also play significant role for disease initiation. Besides Jute M. phaseolina infects over 500 plant species including C. capsularis L. and C. olitorius L. (Butler and Bishby, 1931) and has a wide geographic distribution. Major cultivated hosts include: Arachis hypogaea (Peanut), Brassica oleracea (Cabbage), Capsicum annuum (Pepper), Cicer arietinum (Chick pea), Citrus spp. Cucumis spp., Fargaria sp., Glycine Max (Soybean), Gossypium sp., Helianthus annuus (Sunflower), Ipomoea batatas (Sweet potato), Medicago sativa (Alfa alfa), Phaseolus spp., Pinus spp., Prunus spp., Sesamum indicum (Sesame), Solanum tuberosum (Potato), Sorghum bicolor (Sorghum), Vigna unguiculata (Bean), and Zea mays (Corn). Report of M. phaseolina infecting Psidium guajava L. from West Bengal was also made by Chattopadhyay and Sengupta (1955).

CAUSAL ORGANISM AND NOMENCLATURE Macrophomina phaseolina (Tassi.)Goidanich. {syns. M. phaseolina (Maubl.)Ashby} [=Rhizoctonia bataticola (Taubenhaus)Butler] Rhizoctonia bataticola (Taub.)Butler (Britton-Jones, 1925)]. Rhizoctonia bataticola (Taub.)Butler [=Sclerotium bataticola (Taub.1913)] and Botryodiplodia phaseoli (Maubl.)Thriumis, a soil borne plant pathogen belonging to the phylum Deuteromycetes (Fungi imperfecti) and class Coelomycetes which is highly variable with isolates differing in micro-sclerotial size and presence or absence of pycnidia. The fungus was reported earlier by several authors. However, Ashby (1927) showed that the fungus produced pycnidial stage corresponding to Macrophomina philippinensis Petrak, the type species of the genus Macrophomina. It was shown that Macrophoma phaseoli Maubl. was an earlier name, hence the combination was Macrophomina phaseoli (Maubl.) Ashby.


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Goidanich suggested an earlier name, Macrophoma phaseolina Tassi and proposed the combination Macrophomina phaseolina (Tassi.)Goid. for the same fungus (Subramanian, 1971). Sub-phases: One, the mycelial phase named Rhizoctonia bataticola (Taub.)Butler and the other a pycnidial phase called M. phaseolina (Dhingra and Sinclair, 1978). Mihail (1992) indicated that there is an unconfirmed report of a teleomorph named Orbilia obscura of M. phaseolina. M. phaseolina infects a broad range of wild and cultivated species under different climatic conditions. Although only a single species has been recognized in the genus Macrophomina, high levels of variation in pathogen city have been found (Mayek-Perez et al. 2001). The genetic diversity of M. phaseolina could favour its survival and adaptation to variable environments because significant morphological, physiological (Mihail and Taylor, 1995) and genetic (Babu, K.B et al. 2007) diversity has been reported. However, no clear evidence to suggest formae specialis, sub-species or physiological races has been reported, although Su et al., 2001 suggested host specialization in the genus. Significant advances in molecular detection and differentiation of M. phaseolina isolates on the basis of Pathogenicity, host and/or geographical origin have been reported, because specific Random Amplified Polymorphic DNA (RAPD), Simple-sequence repeats (SSR) or Universal Rice Primers (URP)-polymerase chain reaction (PCR) primers have been generated and then applied for the genetic analysis of M. phaseolina isolates (Jana et al. 2005 a, b).

SYMPTOMATOLOGY IN DIFFERENT STAGES OF HOST Seedling Blight The disease is prevalent in sandy loam soil. Observed mainly in the districts North and South 24 paraganas, Malda, Nadia, West Dinajpur, Coohbehar in West Bengal, Purnea district in Bihar, Cuttack district in Orissa and at locations on the north bank of river Brahmaputra in Assam. The disease is both externally and internally seed-borne. Very young seedlings are attacked. Plants grown from infected seeds may have reduced growth. Infection is seen in cotyledons, seed coat of the affected seeds and also on fresh leaves which turn brown to black and droop off. The disease may spread to the stem and roots under favourable conditions. When soil temperature are on and around 40oC, soil pH between 5.4 to 6.0, soil moisture 8-16% and presence of low soil organic matter are conducive conditions then spread disease spreads.



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Damping-off It is a fungal disease covers several soil borne diseases of plants and seed borne fungi. Infection occurs in warm to hot temperatures and moderate moisture levels. The fungus is found in all natural soils and can survive indefinitely. Infected plants often have slightly sunken lesions on the stem at or below the soil line. When severe, the lower portion of the stem can become slimy and black. It does not occur in strongly acid soils with a pH of 4.5 to 5.5. Seeds may be infected as soon as moisture penetrates the seed coat or a bit later as the radical begins to extend, all of which rot immediately under the soil surface (pre-emergence damping-off). This condition results in a poor, uneven stand of seedlings, often confused with low seed viability. Cotyledons may break the soil surface only to wither and die or healthy looking seedlings may suddenly fall over (post-emergence damping-off).Healthy roots are fibrous appearing and are usually white or tan in color. These symptoms are easily confused with severe mite, aphid, scale infestations, or root-feeding by nematodes or insect larvae. Environmental factors such as accumulated salts in the soil, insufficient light or nitrogen, pot bound roots, cold drafts, etc. can be eliminated only by examination of the roots. The seedling will discolor or wilt suddenly, or simply collapse and die. Weak seedlings are especially susceptible to attack by one or more fungi when growing conditions are only slightly unfavorable.

Collar Rot The presence of black sclerotia was observed on the rotted portion. The mycelium was initially hyaline and later became grey in colour; Sclerotia were minute, black, round to oblong or irregular in shape with mycelial attachment. The pathogen was found to cause rot in collar region of Jute and root rot in many legumes, cereals, oilseeds and medicinal coleus plants including fiber crop also. Typical symptoms include root and basal stem rot with a large number of minute, fungal sclerotia visible under the bark. Plants dry prematurely, particularly when they face drought stress. Infection of seedlings and leaf infection has been reported from India. Disease incidence severe in off-season, irrigated, summer crops in several parts of India, and it is a minor one in the normal season crop. The pathogen is both soil and seed-borne.


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Stem Rot Finally, after seed and soil-borne, secondary spread through air-borne pycnospores causing infections into the nodal parts of stem and spreads gradually which turns stem break and fall on the ground. The predisposing factors are low pH of the soil, the lack of adequate potash, water-logging, high temperature, humidity with high rainfall and excessive application of nitrogenous fertilizer pause the problem (Ghosh and Basak, 1965). The pycnidial stage of the fungus is responsible for ‘stem rot’ in mature plants (Ashby, 1927). Characteristics symptoms of the disease are the formation of lesions on the stem as blackish-brown depression which increase in size and several such lesions may coalesce and finally girdle the stem, where streaks run along the length of the stem and cortex becomes shredded exposing fibres. In case of severe infection pycnidia and sclerotia are formed on capsule and seed (De and Kaiser, 1991). Within a few days the disease spreads drastically and cause serious loss in Yields. It is the major disease caused by the pathogen Macrophomina phaseolina. The disease is favored in lateritic and alluvial soil with low pH (5.66.5) and acidic soil of North Bengal, Assam and Tarai region. Therefore, soil amendment with lime @2-5 ton/ha one month ahead of sowing depending on soil pH can reduce the disease. Macrophomina stem rot of jute is especially severe when the plants are mature and almost ready for harvest. However, the significance of environmental impact in relation to disease severity on jute is not clear.

Root Rot This disease was characterized by browning of the roots and conducting tissues of the stem, followed by collapse and withering of the plant, and the formation of black sclerotia in August. Infection began in late June and reached a peak in late July- August, developing rapidly with a rise in soil temp, to 30°C, and 70 mm. rain every 10 days. Sclerotia lost their viability after 15 months when buried at 10-20 cm. in sandy loam and after 11 months in clay loam, but survived more than 3 year on the soil surface. Weak or abnormal plants were most susceptible. Besides jute; groundnut, lucerne, cotton, and broad bean were also attacked. Plant debris provides the primary source of infection every summer. Root-knot nematode also play significant role for disease initiation.



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PERPETUATION AND SPREAD The pathogen is soil and seed-borne. The mycelium and conidia are carried over from season to season on the seed and diseased crop debris left in the field. Macrophomina phaseolina (Tassi.)Goid. is an ubiquitous pathogen initiating a number of diseases in jute which are wide spread in nature. Disease is spread secondarily through pycnidiospores which are air-borne in nature. Pycnidia are initially immersed in host tissue, then erumpent at maturity. The facultative parasite attacks the jute plant causing seedling blight, damping off, collar rot, stem rot and root rot at any part of the plant at any stage of growth from seedling to until harvest. Primary infection through diseased seed is probably most common. Disease is spread secondarily through pycnidiospores which are airborne in nature, although the main source of infection is seed and soil. The pathogen survives in soil for long. Secondary infection is caused by the first formed spores on seedlings, which become wind or air borne and spread from one plant to another in the field. Studies on aerial dispersal of conidia revealed that maximum flight of conidia takes place at a wind velocity of 4.0-8.8 km/hr. Minimum temperature and relative humidity are also important but their effect is masked by the effect of wind velocity. Minimum temperature of 26.50C28.50C, relative humidity 70-90 per cent, wind velocity of 4.0-8.0 km/hr and presence of low soil organic matter with minimum to moderate rainfall of 1.0 to 14.0 mm were found most conducive factors for dispersal of conidial spores in atmosphere.

PRE-DISPOSING FACTORS The disease development is favoured by certain predisposing factors which may be soil related, crop related or weather related and more over by seed borne. The pre-disposing factors are low pH of the soil, lacking of adequate potash, water-logging, high temperature, humidity with high rainfall and excess application of nitrogenous fertilizer pause the problem. Primary infection through diseased seed is probably most common, although diseased seeds do not necessarily always give rise to infected seedlings. Nutritional deficiencies, primarily those of nitrogen and potash predispose jute to infection of Macrophomina phaseolina (Tassi.)Goid. Leaching of nutrients from soil, low potassium status, upsetting of Fe/Mn ratio, low as well as excess of nitrogen, excessive soil moisture as well as dry and extreme temperature (around 3545ºC) with humid condition (80% __ 90%) are the important predisposing factors


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for disease development. Plant debris provides the primary source of infection every summer. The disease is prevalent in sandy loam soil, observed mainly in the districts North and South 24 parganas, Nadia etc. Effect of sowing date also play significant role for disease initiation (De, R. K., 2013).

CONVENTIONAL MANAGEMENT OPTIONS The conventional management options are lies mainly within the use of selective fungicides, others are infrequent within limited spheres which include cultural practices, chemical control, biological control with few common parasites and predators and use of resistant varieties. More over their study in the crop health and impact on environment was very limited. The difficulty of controlling the disease lies in the ability of the pathogen to form sclerotia which overwinters for long time in its wide host range and lack of resistant in jute. Foliar application of fungicides may control this disease but it is not eco-friendly and cost effective for the jute growers who are most marginal farmers. Under the above circumstances, it becomes inevitable to develop a biobased eco-friendly, biodegradable, plant derived or microbial derived method in order to control plant pathogens. An attempt was made to evaluate some biocontrol bacterial and fungal strains against Macrophomina phaseolina singly and in compatible combinations.

RHIZOBACTERIA AND FUNGI IN THE MANAGEMENT OF PLANT DISEASES Many rhizobacteria and fungi triggering ISR can also inhibit growth of a pathogen directly; their capacity to suppress disease may involve more than one mechanism. Biological control of plant pathogens is an attractive preposition as it mimics the natural, cheapest way of balancing population of living organisms and helps to increase the yield by the suppression of pathogen inoculum, protect plants against infection or increase the ability of plants to resist pathogen and also to attain a safe and clean environment. Therefore, as an alternative to fungicide, it is desirable to exploit environmentally safe means. Integrated disease management is an acceptable approach and biocontrol has become one of the basic components in disease management practices. Plant growth promoting rhizobacteria or fungi



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(PGPR/PGPF) are a group of root associated bacteria/fungi which intimately interact with plant roots and consequently influence plant health and soil fertility (Kloepper and Schroth, 1978).

ROLE OF PLANT GROWTH PROMOTING BACTERIA AND FUNGI Plant growth in agricultural soils is influenced by a myriad of abiotic and biotic factors. While growers routinely use physical and chemical approaches to manage the soil environment to improve crop yields, the application of microbial products for this purpose is less common. An exception to this is the use of rhizobial inoculants for legumes to ensure efficient nitrogen fixation; a practice that has been occurring in North America for over 100 years. Root colonizing bacteria (rhizobacteria) that exert beneficial effects on plant development via direct or indirect mechanisms have been defined as plant growth promoting rhizobacteria (PGPR). Although significant control of plant pathogens or direct enhancement of plant development by plant rhizosphere bacteria or fungi has been demonstrated as PGPR/PGPF. There are many ways and variety of mechanisms in which PGPR and PGPF may improve the growth or health of plants. A detailed discussion of each of these mechanisms is followed by Buchenauer (1998), Glick (1995) and Whipps (2001) for more information. Recent progress in our understanding of their diversity, colonization ability, mechanisms of action, formulation and application should facilitate their development as reliable components in the management of sustainable agricultural systems. The prospect of manipulating crop rhizosphere microbial populations by inoculation of beneficial bacteria to increase plant growth has shown considerable promise in laboratory and greenhouse studies, but responses have been variable in the field (Bhattacharyya et al. 2014).

SCREENING AND SELECTION OF PGPR AND PGPF STRAINS Some Plant growth promoting rhizobacteria (PGPR) and Plant growth promoting fungi (PGPF) viz. Pseudomonas fluorescens, Phosphobacter (Pseudomonas striata), Bacillus sp., Trichoderma stimulate plant growth while repress the pathogen producing plant hormone and siderophores in the


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rhizosphere (Kloepper et al., 1980). These beneficial bio agents when applied locally, found to have potentiality for inhibiting pathogenic fungi in the rhizosphere of the plant through diverse mechanisms. Pathogen control by PGPF may also occur via niche exclusion, antibiosis, predation, mycoparasitism and ISR induction (Whipps and Davies, 2000). The mechanisms by which PGPR/PGPF promote plant growth are not fully understood, but are thought to include: the ability to produce phytohormones (Egamberdiyeva, 2007), asymbiotic N2 fixation against phyto pathogenic microorganisms by production of siderophores, the synthesis of antibiotics, enzymes and/or fungicidal compounds (Bharathi et al. 2004) and also solubilization of mineral phosphates and other nutrients (Cattelan et al., 1999). Biochemical and molecular approaches may provide new insight into the genetic basis of these traits: the biosynthetic pathways involved, their regulation and expression are important for biological control in laboratory and field studies. Various “classical” inducers of ISR have been reported, including pathogens, attenuated pathogens, synthetic chemicals, and metabolic products of hosts or infectious agents (Liu et al. 1995c and references therein); however reports of induced resistance in the field by classical inducing agents have been infrequent.

USE OF ANTAGONISTIC MICRO-ORGANISMS/ BIO-CONTROL AGENTS Antagonistic micro-organisms are generally used in direct control of plant pathogens by virtue of their capacity of hyper parasitism, inhibition, antibiosis, etc., and the phenomenon is called biological control. However, some biocontrol agents are also known to induce resistance upon pre-inoculation. Fawcett (1931) for the first time published the historical review of microbiological antagonism and biological control. Tveit and Wood (1955) reported inhibition of Fusarium and other plant pathogenic fungi by Bacillus megatharium antagonists. Tu (1980), Upadhyay and Mukhopadhyay (1983) and Bhatia et al., (2003) shown non-volatile and volatile antibiotics produced by Gliocladium virens, Trichoderma harzianum and Pseudomonas fluorescens respectively had immense potential for inhibiting the growth of pathogens like Sclerotinia sclerotiorum, Sclerotium rolfsii and Macrophomina phaseolina accordingly. Biocontrol microbes, almost by definition, must contain a large number of genes that encode products that permit biocontrol to occur. Several genes have



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been cloned from Trichoderma spp. that offer great promise as trans-genes to produce crops that are resistant to plant diseases. No such genes are yet commercially available, but a number are in development. These genes, which are contained in Trichoderma spp. and many other beneficial microbes, are the basis for much of “natural” organic crop protection and production (Kubicek et al., 1998). During the last couple of decades the negative environmental impact given by the chemical fertilizers and their increasing costs, the use of soil microorganisms with the traits like PGP for sustainable agriculture has increased in various parts of the world and their research has brought together the scientists from multiple disciplines, who have addressed a wide range of topics including: discovery of novel PGPR strains and traits; performance in greenhouse and field trials; production, formulation and delivery of inoculums; registration and commercialization; mechanisms of growth promotion, biocontrol of pathogens based on their molecular and biochemical traits; root colonization and rhizosphere competence traits; role of PGPR in suppressive soils; plant pathogen and rhizosphere community responses to PGPR and PGPF; and recombinant Plant Growth Promoting microbes and their risk assessment (Chet, 1987). Thus safer, eco-friendly approach to biological management of the soil borne/air borne disease with antagonistic fungi and rhizobacteria seems to hold great promise to that effect (Bandopadhyay and Bandopadhyay, 2004).

CONCLUSION From the study, it was revealed that rhizobacteria and fungi showed variation according to abilities in their different PGP traits via biocontrol characteristics. The results are tallied in case of observations made under different forms of study, but ultimately significantly expressed as per objectives/minutes of the study. Single and compatible co-inoculation with PGPR like Bacillus amyloliquefaeciens (AB909000), PGPB i.e., Alcaligenes faecalis (AB901364) and PGPF viz. Trichoderma aureoviridae (AB916337) sufficiently support and accorded with early observations made by Zaidi and Khan, 2005; Rajendran et al., 2008 in case of wheat and pigeon pea. The synergistic effects of plant growth-promoting rhizobacteria and fungi on plant growth, yield and nutrient uptake of jute were determined both in green house and field conditions. The co-inoculation significantly increased the dry matter above the control. These are most efficient isolates regardless of crop seeds and


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form of inoculants used at green house and field studies even when it was applied with other bio-agents, agro-chemicals (Carbendazim 50 WP), commercial growth regulator (Indole 3 acetic acid) and herbicides (Quizalofop ethyl) for post emergence effect in an integrated manner. The results proved that the newly isolated bio agents have the synergistic effects with each other and potentially compatible when applied as mixture with different agrochemicals without any adverse effect to the plant. Further research should be carried out with such efficient PGPR and PGPF isolates. Formulation of consortium for better management of plant health viz. plant growth promotion profile, biocontrol of plant pathogens or diseases as well as abiotic stress management. Therefore, biological and integrated management of diseases are the most important facets in this perspective. The relevance of this microbial based approach in the context of a reclamation strategy addressed to environmental sustainability purposes may be of great importance.

ACKNOWLEDGMENTS The authors are grateful to the Director of Central Research Institute for Jute and Allied Fibres, Barrackpore for his active scientific support and also grateful to Director, Directorate of Research; BCKV, Kalyani for providing facilities to execute the present investigation along with the financial help provided by DST purse programme of KU during the tenure of which this work was carried out is gratefully acknowledged.

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fungal antagonist and PGPR – A success story. In: Proc. International Conference on Emerging Technologies in Agricultural and Food Engineering and Management and Agro-Environmental Engineering. Book Eds. Manish Sejwal: Anamaya Publishers, New Delhi, pp. 385-390. Bandopadhyay, Anuradha and Bandopadhyay, A. K. 2004. Beneficial traits of Plant Growth Promoting Rhizobacteria and fungal antagonist consortium for biological disease management in bast fibre crop. Ind. Phytopathology, 57(3): 356-357. Bharathi, R., Vivekananthan, R., Harish, S., Ramanathan, A. and Samiyappan, R. 2004. Rhizobacteria-based bio-formulations for the management of fruit rot infection in chillies. Crop Prot., 23: 835-843. Bhatia, Shweta, Bhatia, S., Dubey, R. C. and Maheswari, D. K. 2003. Antagonistic effect of fluorescent pseudomonas against Macrophomina phaseolina that causes Charcoal rot of Ground nut. IJEB. 4:1442-1446. Bhattacharyya, S. K., Sengupta, C., Adhikary, N and Tarafdar, J. 2014. Bacillus amyloliquefaciens – A novel PGPR strain isolated from jute based cropping system. The Bioscan 9(3): 1263-1268. Buchenauer, H. 1998. Biological control of soil-borne diseases by rhizobacteria. Journal of Plant Disease and Protection, 105: 329- 348. Butler, E. J. and Bishby, G. R. 1931. The fungi of India, Imp. Coun. Agric. Res. (India) Sci. Monograph, I. Cattelan, A. J., Hartel, P. G. and Fuhrmann, J. J. 1999. Screening for plant growth-promoting rhizobacteria to promote early soybean growth.Soil Sci. Soc. Am. J., 63: 1670-1680. Chattopadhyay, S. B. and Sengupta, S. K. 1955. Studies on wilt of Psidium guajava L. in West Bengal. Indian J. Hort., 12: 76–79. Chet, I. 1987. Trichoderma - application, mode of action, and potential as a biocontrol agent of soil borne plant pathogenic fungi. In: I. Chet (ed.), Innovative Approaches to Plant Disease Control, pp. 137-160. John Wiley & Sons: New York. De, D. K. and Kaiser, S. A. K. M. 1991. Genetic analysis of resistance to stem rot pathogen (Macrophomina phaseolina) infecting jute. Pesquisa Agropecuaria Brasileira, 26: 1017- 1022. De, R. K. 2013. Effect of date of sowing on the incidence of stem rot of jute caused by Macrophomina phaseolina Tassi (Goid.). J. Mycopathol. Res. 51(2): 252-258. Dhingra, O. D. and Sinclair, J. B., 1978. Biology and Pathology of Macrophomina phaseolina. Universidade Federal de Vicosa, Vicosa, Brazil.


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Doran, J. W. 1996. Soil quality & health: The Intl. situation & criteria for indicators. Proc. Workshop on soil quality indicators for New Zealand Agriculture. 8-9th Feb.1996, Lincoln. Univ., Christchurch, New Zealand. Egamberdiyeva, D. 2007. The effect of plant growth promoting bacteria on growth and nutrient uptake of maize in two different soils. Applied Soil Ecol., 36: 184-189. Fawcett, H.S. 1931. The importance of investigation on the effects of known mixtures of organisms. Phytopath. 21: 545-550. Ghosh, T. and Basak, M. N. 1965. Possibility of controlling stem rot of Jute. Indian J. Agric. Sci., 35: 90-100. Ghosh, T. and Mukherjee, N. 1970. Macrophomina phaseoli (Maubl.)Ashby of jute. Plant disease problems. Proc. 1st Int. Symp.on Plant path. Indian Phytopath.Soc. pp.369-70. Glick, B. R., 1995. The enhancement of plant growth by free-living bacteria. Canadian J. Microbiol. 41: 107-117. Jana, T. K., Singh, N. K., Koundal, K. R., Sharma, T. R. 2005a. Genetic differentiations of charcoal rot pathogen, Macrophomina phaseolina, in to specific groups using URP-PCR. Can. J. Microbiol., 51: 159–164. Jana, T. K., Singh, N. K., Koundal, K. R., Sharma, T. R., Singh, N. K. 2005b. SSR based detection of genetic variability in the charcoal root rot pathogen Macrophomina phaseolina. Mycol. Res., 109: 81–86. Kloepper, J. W. and Schroth, M. N. 1978. Plant Growth Promoting Rhizobacteria in radishes. In: Proc. of IV International Conference on Plant Pathogenic bacteria. 2: 879-882. Kloepper, J. W., Leong, J., Teintze, M. and Schroth, M. N. 1980. Enhanced plant growth by siderophores produced by plant growth-promoting rhizobacteria. Nature, 286: 885-886. Kubicek, C. P. and Harman, G. E. 1998. Trichoderma and Gliocladium. Vol. 1. Basic Biology, Taxonomy and Genetics, Taylor & Francis, London, p.278. Liu, L., Kloepper, J. W. and Tuzun, S. 1995c. Induction of systemic resistance in cucumber by plant growth-promoting rhizobacteria: Duration of protection and effect of host resistance on protection and root colonization. Phytopathology, 85: 1064-1068. Mayek-Perez, N., Lopez-Castaneda, C., Gonzalez-Chavira, M., GarciaEspinosa, R., Acosta-Gallegos, J. A., Martinez-Dela-Vega, O., Simpson J., 2001. Variability of Mexican isolates of Macrophomina phaseolina on basis of pathogenesis and AFLP genotype. Physiological and Molecular Plant Pathology, 59: 257-264.



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Meyer, S. L. F and Roberts, D. P. 2002. Combinations of biocontrol agents for management of plant-parasitic nematode and soil borne plant-pathogenic fungi. J. Nematol., 34: 1–8. Mihail, J. D. 1992. Macrophomina. In: Methods for Research on Soil-borne Phyto pathogenic Fungi. Ed. Larry L. Singleton, Jeanne D. Mihail, Charles M. Rush. pp 134-136. APS Press. The American Phytopathological Society, 2nd edition 1993. St. Paul Minnesota. Mihail, J. D. and Taylor, S. J. 1995. Interpreting of variability among isolates of Macrophomina phaseolina in pathogenicity, pycnidium production and chlorate utilization. Canadian Journal of Botany, 73: 1596-1603. Pandey, C., Soccol, R. and Mitchell, D. 2000. New developments in solid state fermentation, Process. Biochem, 35: 1153-1169. Siddiqui, I. A. and Shaukat, S. S., 2002. Rhizobacteria-mediated induction of systemic resistance in tomato against Meloidogyne javanica. J. Phytopath., 150: 469-472. Su, G., Suh, S. O., Schneider, R. W. and Russin, J. S. 2001.Host specialization in the charcoal rot fungus, Macrophomina phaseolina. Phytopathology, 91: 120-126. Subramanian, C.V., 1971. Hyphomycetes- An account of Indian species except Cercosporae. ICAR, New Delhi. Tu, J. C. 1980. Gliocladium virens: A destructive mycoparasite of Sclerotinia sclerotiorum. Phytopathology, 70: 670-674. Tveit, M. and Wood, R. K. S. 1955. The control of Fusarium blight in Oat seedlings with antagonistic species of Chaetomium. Ann. Appl. Biol., 43: 538-552. Upadhyay, J. P. and Mukhopadhyay, A. N. 1983. Effect of non-volatile and volatile antibiotics of Trichoderma harzianum on growth of Sclerotium rolfsii. Indian J.Myco.PI. Pathol.,13: 232-233. Van loon, L. C., Bakker, P. A. H. M and Pieterse, C. M. J. 1998. Systemic resistance induced rhizosphere bacteria. Annu. Rev. Phytopathol. 1998. 36: 453–83. Whipps, J. M. 2001. Microbial interactions and biocontrol in the rhizosphere. Journal of Experimental Botany, 52: 487-511. Whipps, J. M. and Davies, K.G. 2000. Success in biological control of plant pathogens and nematodes by microorganisms. In: Gurr, G., Wratten, S. D., eds. Measures of success in biological control. Dordrecht: The Netherlands: Kluwer Academic Publishers, 231–269.




Chapter 8

IMPACT OF RISING CARBON DIOXIDE (CO2) ON PLANT HEALTH AND EFFICACY: AN INSIGHT TO CELL METABOLISM Pratika Singh and Amrita Srivastava Life Science Programme, Centre for Biological Science, Central University of South Bihar, Patna, India

ABSTRACT A better way of understanding of the symbiotic and integrated mechanisms associated with plant growth and productivity is needed subsequent to the alarming rise in the global atmospheric concentration of greenhouse gases. This review sums up the current understanding of components that determine the response of plants to high carbon dioxide concentration CO2. Many research efforts have been initiated to understand the response of plants and ecosystems to rising CO2. Plants acknowledge and respond to increasing carbon dioxide concentration CO2 through increased photosynthesis (A) and reduced stomatal conductance (gs). These two fundamental responses help in the derivation of all other effects of increased CO2 on plants and ecosystems. Supplement to being a greenhouse gas, atmospheric carbon dioxide is also the source of carbon for most of the plant species. Its rapid increase is likely to affect the quantity and quality of a number of agriculturally relevant crop species and earthy plant species including those with C3, C4 and crassulacean acid 



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Pratika Singh and Amrita Srivastava metabolic (CAM) pathways. The lenience of horticultural commodities to CO2 is also restricted.

INTRODUCTION The level of carbon in the atmosphere rose from 285 μmol l–1 (600gigatonnes (Gt) in preindustrial times to the present level of 384 μmol l–1 (800 Gt; Inter-governmental Panel on Climate Change, IPCC), and a rise in the atmospheric CO2 up to 1000 Gt by the year 2050 is further predicted which would ultimately result in global climate changes both directly and indirectly. Due to anthropogenic intensification, there would be an increase in CO2 concentrations together with other greenhouse gases which would increase the global average temperatures. It would further result in severe shifts in the annual precipitation. Plant growth and progress is primarily affected by climate change due to changes in photosynthetic carbon reception patterns. Past two decades have visualized rapidly modifying environment and co-evolving acclimatory responses of plants to them. Major attention has been diverted to understanding the impacts of multiple collaborating factors such as water availability, temperature, soil nutrition, etc. on crop physiology and productivity various contradictory reports have been made. Differences in experimental technologies, plant species used for the experiments, age of the plant as well as span of the treatment could be assumed as the possible reasons for differing reports on plant responses to high CO2, and many such different photosynthetic responses. The effects of climate change, both direct and indirect, on plants have been important sources of uncertainty in the impact valuation and parameterization which are very important for modelling plant growth and productivity. Furthermore, the perceptiveness of photosynthesis to each of the environmental variables which includes high temperature, low water availability, shortage in vapour pressure and soil salinity, associated with the certain increase in atmospheric CO2 is of major concern in addressing the food crisis in the upcoming climate change scenario.

RESPONSE OF PHOTOSYNTHESIS TO ELEVATED CO2 It has been observed that elevated CO2 improves photosynthesis by increasing the carboxylation rate of Rubisco and competitively inhibiting the oxygenation of Ribulose-1,5-bisphosphate (RubP) (Drake et al., 1997).


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Aranjuelo et al. (2009) suggest that plants with small sink size decrease their capacity for photosynthesis and thus acclimate to elevated CO2. Likewise, plants with higher sink size will reap higher benefits of CO2 mediated enhancement in photosynthesis in contrast to those with smaller sink size. Photosynthesis in C3 plants is affected by RuBP (ribulose bisphosphate) carboxylase–oxygenase (Rubisco) (EC 4.1.1.39) and by carbohydrate accumulation during carbon assimilation. This activity of the enzyme would result in the union of CO2 with RuBP proceeded by dismutation into two molecules of 3-PGA, which is known as the first committed step in the Calvin– Benson– Bassham cycle. As rubisco is substrate which is limited by the present atmospheric CO2 levels, this enzyme can respond to increases in CO2 concentration and can have a metabolic control to alter the CO2 flux during carbon assimilation. C3 photosynthesis is believed to operate at a lower CO2 level than the optimal one and can show sudden increase in carbon assimilation, growth and yields. Kimball has shown a biomass increase of 10–143% in many C3 crops in response to doubling of the atmospheric CO2. According to a literature survey on the impact of elevated CO2 among certain C3, C4 and crassulacean acid metabolism (CAM) species, majority of the C3 plants showed a significant positive response to photosynthetic acclimation. The boon of efficient CO2 assimilation in C3 plants has been due to the increased substrate in the atmosphere and the fact that they do not have to spend on metabolic costs of CO2 concentrating mechanism at the site of carboxylation. Elevated CO2 enhances the velocity of carboxylation and on the other hand it competitively inhibits the oxygenase reaction. Experiments performed in open top chambers (OTCs) and free atmospheric CO2 enrichment (FACE) environment have indicated significant increases in light-saturated rates of photosynthesis in several C3 plants grown at elevated CO2. The photosynthesis response pattern is slightly different in C4 plants. C4 plants have received very less attention as compared to C3 plants because of the assumption that the inherent CO2 concentrating mechanism in C4 plants makes these plants lesser sensitive or slightly insensitive to elevated CO2. Significantly higher CO2 level saturates the carboxylase reaction and annihilates photorespiration. Photosynthesis in C4 plants gets easily saturated eve at the normal concentration of atmospheric CO2. As the main enzyme, PEP Case lacks binding of O2 to its catalytic site, differences in CO2:O2 ratio have little impact on photosynthetic variation. However, increased photosynthesis through increased carbon uptake in response to elevated CO2 has been reported in several C4 plants. Ghannoum et al. reported that light intensity played a significant role in CO2 governed photosynthesis enhancement in C4 plants as the


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plants grown under high irradiance in addition to increased CO2, showed positive response under high CO2 conditions. It is also well known that the growth stimulation of C4 crops is much lesser compared to that of C4 weeds. Although certain C4 plants showed positive response to high CO2, the underlying mechanisms for the enhanced growth responses are still not clear. In addition to improved photosynthetic rates under elevated CO2, C3 plants exhibited reduced mitochondrial respiratory rates, which could contribute to increased biomass yield. However, little is known about the impact of increased CO2 on the respiratory rates of C4 plants. The positive responses of certain C4 plants to elevated CO2 were believed to be due to differences in bundle sheath leakiness, biochemical subtype, and direct CO2 fixation in the bundle sheath cells as well as C3-like photosynthesis in young and developing leaves of C4 species. Further, the lack of photosynthetic acclimation in C4 plants (in contrast to several C3 plants) could be attributed to relatively less rubisco protein and more active carbonic anhydrase and PEPcase. Although there are many studies on the interactive effects of increased air temperature, nutrients, water availability and elevated CO2, very little is known about such interactive influence of elevated CO2 with the environmental variables during growth of C4 plants. Based on the studies conducted in C3 species, an increase in plant growth and grain yield was proposed due to an increased photosynthesis in enhanced CO2 scenario (Aben et al., 1999; Kimball et al., 2002; Seneweera et al., 2002). Many workers have reported that this initial increase in photosynthesis is only transient until the photosynthesis rate steadies at a much lower level (Ainsworth et al., 2003; Gutierrez et al., 2009; Leakey et al., 2009; Seneweera et al., 2002). This process of stabilizing initially increased rate of photosynthesis is known as ‘acclimation’ and is observed in most of the cases. There may be several reasons behind acclimation. Two of the most important factors contributing to the latter are reduction in the leaf nitrogen content and the concentration of Ribulose 1,5bisphosphate carboxylase/oxygenase, the chief enzymatic component for photosynthesis (Drake et al., 1997; Bloom et al., 2002). Synthesis of Rubisco occurs through transcription of rbcL and rbcS genes. It has been observed in few cases that elevated CO2 leads to repressed transcription of rbcL and rbcS genes due to accumulation of carbohydrates in leaves (Cheng et al., 1998; Moore et al., 1999). However, this relationship to acclimation is still not very certain. Seneweera and Conroy (2005) experimented with young expanding leaves of wheat and concluded that while leaf nitrogen content showed a decline, carbohydrate accumulation played no significant role. Nitrogen partitioning is yet another important factor that might lead to changed Rubisco levels. Nitrogen



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plays different roles depending on the site of its presence. At the site of cell division, nitrogen is needed as a component of rapidly synthesizing protein for newly formed cells and in the cell expansion zone, nitrogen is mostly allocated for the formation of photosynthetic proteins (Gastral and Nelson, 1994; Skinner and Nelson, 1994). Therefore, acclimation in response to elevated CO2 may be attributed to variations of nitrogen allocation at these two major sites of function in the leaf. Even the changed CO2 environment around mature leaves can alter the nitrogen content of expanding leaves (Miyazawa et al., 2011). Total number of leaves present under any circumstances is yet another important factor that governs the photosynthesis rate. Limiting the rate photosynthesis can thus be channelized by regulating leaf number. Accordingly, incremented leaf senescence is another factor that contributes to photosynthetic acclimation (Zhu et al., 2009). Leaf senescence is also a part of nitrogen re-allocation whereby the leaf proteins are broken down, including Rubisco degradation, and channelized elsewhere. The loss of Rubisco brings down the initially increased photosynthesis rate. Apart from its effect on functional aspects of leaf physiology, reduced nitrogen alters the patterns of insectivory and herbivory with major impact on the ecological food web balance (Whittaker, 1999).

EFFECT ON CRASSULACEAN ACID METABOLISM There are approximately 7% of the vascular plants in which CAM photosynthesis is known to occur. In CAM plants, CO2 is fixed into malate in the dark and stored in vacuoles until daylight, when the stomata are closed (minimizing water loss) and malate serves as a source of CO2 for Rubisco. Of the three types of photosynthesis used by vascular plants, CAM is one in which nocturnal CO2 fixation results in the formation of malate, which is decarboxylated during day time releasing CO2, which in turn is absorbed into carbohydrates. Very little is known about the response of CAM plants to rising atmospheric CO2 concentrations when compared to the studies on the effects of elevated CO2 in C3 and C4 plants. CAM plants are recognised for their large inherent photosynthetic ductility associated with environmental conditions during different developmental stages. The generalization of the response of nocturnal CO2 fixation is more complex than those of C3 and C4 plants. It is due to their characteristic features in CAM plants and variation in responses of carboxylating enzymes (both rubisco and PEPCase). Although certain CAM plants show motivated rates of photosynthesis and 20–40% increase in biomass production, under elevated atmospheric CO2 concentrations, with no


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acclimation during growth, a contradictory range of responses of certain CAM plants to elevated CO2 have been reported, which include increase and/or decrease in nocturnal CO2 ingestion, daytime CO2 fixation patterns as well as in water use efficiency. Succulence which could be a diffusional constraint to CO2 as well as to accommodate large amount of photosynthate to avoid feedback hindrance has been assumed to be a possibility for the lack of acclimation in CAM plants under elevated CO2. The biomass production in CAM plants under elevated CO2 atmosphere, on small arid and semi-arid lands, has shown a significant rise which suggests that CAM plants could also be employed for terrestrial sequestration of atmospheric CO2 in the changing global environment. Further, the exceptional degree of stress tolerance in CAM plants to water-lacking regimes, high temperatures and high light intensities should deliver these plants robust to the predicted severe impacts of the future global climate change. The importance of several economically important CAM plants worldwide in improving the photosynthetic productivity could be enhanced by the lack of acclimation of CAM species under high atmospheric CO2 concentrations.

IMPACT ON TOTAL NITROGEN STATUS Decrease in the dry mass concentration of nitrogen has been observed in leaves of woody plants, gymnosperms, angiosperms, seeds, edible parts of food crops although more variable results have been obtained on account of several interacting factors (Curtis and Wang, 1998; Norby et al., 1999; Jablonski et al., 2002; Taub et al., 2008). Taub and Wang have put forward several hypotheses for decrement of dry mass concentration of nitrogen (Nm) which are being discussed here. Declined Nm might be a result of ‘dilution’ – either biomass dilution or functional dilution. Former occurs when the total biomass of plant increases manifold as compared to increase in the amount of nitrogen under increased CO2 influence. On the contrary, functional dilution is the decline in Nm due to increased shoot specific activity i.e., accumulation of photosynthetic end products in the shoots. Nm may also be influenced due to altered rate of nitrogen uptake by the roots. Nitrogen along with other important nutrients such as S, Mg and Ca are taken up by roots through mass flow (Barber, 1984; Marschner, 1995). This is driven mainly by transpiration pull. In almost all the cases of increased CO2 exposure, stomatal conductance is negatively affected which causes decreased transpiration and a consequent decline in nitrogen uptake (Ainsworth and Rogers, 2007). This holds equally true for rice the major



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nitrogen source is ammonium available in waterlogged condition (Funayama et al., 2013). Same hypotheses was supported by Polly et al. (1999) and Del Pozo et al. (2007) working on wheat and C3 perennials respectively. Contradictory to this, crops where nitrate is the major nitrogen source, suppression of photorespiration is the chief reason for reduced nitrogen assimilation under the influence of elevated CO2 (Bloom et al., 2010). CO2 induced alteration in the overall pattern of root structure differentiation also affects nitrogen uptake. Elevated CO2 promotes the growth of lateral roots as compared to primary roots leading to less efficient uptake of nutrients (Berntson, 1994; Pritchard & Rogers, 2000). Conroy (1992) stated a much lower critical foliar nitrogen concentration in plants grown at elevated CO2 than the ones growing at ambient CO2 concentration. This implies that under the influence of increased CO2 plants can easily thrive at much lower nitrogen content. This phenomenon occurs due to increased photosynthetic nitrogen use efficiency (PNUE). Thus, the demand supply chain ensures a lower nitrogen uptake in response to decreased demand of cellular nitrogen. Higher efficiency is ensured partly by better carboxylation of RUBP and decresed formation of photosynthetic nad photorespiratory enzymes (Davey et al., 1999; Stitt and Crapp, 1999; Gifford et al., 2000). Finally, loss of nitrogen in the form of ammonia from dead and decaying plant matter and through root exudation as organic nitrogen also contributes to decreased Nm. in confirmation with all the above mentioned factors, Tsutsumi et al. (2014) did not observe any significant decline in leaf soluble protein when rice plants were subjected to enhanced CO2 levels in presence of sufficient nitrogen.

EFFECT ON STOMATAL CLOSURE AND CONDUCTIVITY Guard cells respond to the intercellular CO2 rather than CO2 at the surface of the leaf thus exhibiting an essential property of CO2 sensing (Mott 1988). Metabolism and signalling of guard cells have therefore been thoroughly examined (Assmann 1999; Hetherington 2001; Hetherington & Woodward 2003; Vavasseur & Raghavendra 2005). The turgor pressure in the guard cells that decides stomatal aperture arises due to ion and organic solute concentration. Stomatal closure occurs due to depolarization of the guard cell membrane potential (Assmann 1999). Reduced stomatal density i.e., the number of stomata per leaf area is also reduced along with the reduction in stomatal conductance. Changes in leaf size and anatomy include increase in single leaf area, total leaf area of each plant and overall leaf thickness (Pritchard et al., 1999). Reduced


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stomatal conductance of mature leaves is known to regulate the development of stomata in newly expanding leaves. Same results have been documented in Arabidopsis thaliana and poplar (Lake et al., 2001; Miyazawa et al., 2006). Rising CO2 levels lower the activity of inward rectifying K+ channels, add to the activity of outward rectifying K+ channels, enhances S type anion channel activities, activates Cl- release from guard cells and intensify guard cell Ca2+ concentration (Webb et al. 1996; Brearley, Venis & Blatt 1997; Hanstein & Felle 2002; Raschke, Shabahang & Wolf 2003). Together these forces make the guard cell membrane less negative and cause stomatal closure due to membrane potential depolarization (Assmann 1993). As a result, with increase in depolarization at elevated CO2 there is a reduction in stomatal aperture. The exact signal transduction pathways that operate upstream of the ion channel activities are not well recognized (Assmann 1999; Schroeder et al. 2001), but it has been debated that stomatal closure is a result of intricate guard cell signalling network (Hetherington &Woodward 2003). Cytosolic free calcium concentration Ca2+, apoplastic and cytoplasmic pH gradients, ion channels and membrane potential, chloroplastic zeaxanthin levels, photosynthetically derived ATP and protein phosphorylation/dephosphorylation are several potential carriers in the stomatal CO2 response (Assmann 1999; Hetherington & Woodward 2003; Vavasseur & Raghavendra 2005; Hashimoto et al. 2006; Messinger, Buckley & Mott 2006; Young et al. 2006). In addition, guard cells demonstrate photosynthetic electron transport-dependent and independent mechanisms of response to CO2 (Messinger et al. 2006), and calcium sensitive and -insensitive phases of the response to CO2 (Young et al. 2006). Apparently, abscisic acid and light offer similar impact on stomatal closure, indicating an overlapping CO2 -sensing mechanisms of guard cells (Hetherington & Woodward 2003; Roelfsema et al. 2006). Mutant studies on Arabidopsis with impaired guard cell responses to CO2 have supported some of the underlying mechanisms of CO2 sensing (Hashimoto et al. 2006; Young et al. 2006). Insensitivity to high CO2 in gca2 mutant depicts deteriorated ROS activation of guard cell Ca2+-permeable channels (Pei et al. 2000). The mutant is believed to lack the normal priming of Ca2+ sensors on exposure to elevated CO2 needed for closing of stomata due to decrease in cytosolic Ca2+ transients that should operate in guard cells (Young et al. 2006). The Free-Air CO2 Enrichment (FACE) experiments keeps the plants exposed to elevated CO2 under natural and fully open-air conditions. FACE technology doesn’t use any confinement structures. In place of that, an array of vertical or horizontal vent pipes are used to deliver jets of CO2 enriched air or pure CO2 gas at the periphery of vegetation plots. In all the experiments,



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reduction of stomatal conduction has been reported invaribly (Long et al. 2004; Ainsworth & Long 2005). As compared to C3 and C4 grasses and herbaceous crops, trees, shrubs and forbs indicated a lower percentage reduction in stomatal conductivity. A similar trend was reported previously for herbaceous and woody species (Saxe et al., 1998; Nowak et al. 2004). Although, there exist certain exceptions to the general rule that stomatal conductivity declines at elevated CO2. It has been observed that in particular, Pinus taeda guard cells seems to be insensitive to elevated CO2 (Ellsworth, 1999). There is a decrease in stomatal density in a wide variety of species and in many Arabidopsis thaliana ecotypes due to growing elevated CO2 (Woodward et al., 2002; Hetherington &Woodward, 2003). However, in some of the cases the reduction in stomatal conductivity at elevated CO2 in FACE experiment does not seem to be caused by a significant change in stomatal density (Estiarte et al. 1994; Bryant, Taylor & Frehner 1998; Reid et al. 2003; Marchi et al. 2004; Tricker et al. 2005). Reid et al. (2003) reported higher stomatal density in FACE experiments, although the results were not statistically significant.

EFFECTS OF CO2 ON METABOLISM Information about the effects of high CO2 is largely restricted to fruit and vegetables after harvest at the metabolic level. There are many similarities between the effects of low O2 and high CO2 on metabolism, with most effects being suppression of various metabolic processes (Beaudry, 1999; Kader, 1997). The following exceptions are obvious

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Respiration can be inhibited, unaffected or stimulated by high CO2 in the storage environment even though it is usually inhibited by low O2 (Mathooko, 1996a). The stimulation of respiration may represent stress responses by the tissue. Both low O2 and high CO2 inhibit 1-Aminocyclopropane-1-carboxylic acid (ACC) synthase activity. However, while ACC oxidase activity is inhibited by low O2, it is stimulated and inhibited by low and high CO2concentrations, respectively (Mathooko, 1996b). Activity of phenylalanine ammonia lyase (PAL), an enzyme involved in phenolic metabolism, is inhibited by low O2 but is enhanced by high CO2 in some (Prusky et al., 1996), but not all, tissues (Holcroft et al., 1998).


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High CO2 is a hostile inhibitor of ethylene action (Burg and Burg, 1967). High CO2 appears to do the following-Increase carbon flux through glycolysis and maintain energy levels in the cell. Activation of glycolysis may not involve the same enzymes as those affected by low O2, especially the phosphofructokinases, PPi-PFK and ATP-PFK (Kerbel et al., 1990). Also, low O2 and high CO2affect directly the pyruvate kinase and pyruvate decarboxylase activities (Silva, 1998). Increase carbon flux through the fermentation pathway, although activation of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) is less evident in high CO2 than in low O2 treatments (Ke et al., 1995). Result in accumulation of the TCA cycle intermediate, succinate, in CO2, but not in O2-treated tissues. This accumulation, which is thought to be toxic to plant cells (Hulme, 1956), may be related to the inhibition of succinate dehydrogenase (SDH) activity (Frenkel and Patterson, 1973; Ke et al., 1993). Succinate accumulation could also result, however, from activation of the glyoxylate cycle (Yang et al., 1998), the γ-aminobutyrate shunt (Satya Narayan and Nair, 1986), and/or phosphoenolpyruvate carboxylase activity (Bisbis et al., 1997). Enhance the alternative pathway by induction and/or activation of the alternative oxidase, and inhibition of the cytochrome pathway by suppression of cytochrome oxidase activity, although treatment effects can be diverse according to physiological state of the tissue, harvest season, temperature, and CO2 concentration (Lange and Kader, 1997a).

CONCLUSION As differential rise in the concentration of atmospheric CO2 has been noticed since pre-industrial period, photosynthesis and plant water relations are affected in a large noticeable portion by the increasing atmospheric CO2 (Thomas and Harvey 1983). The impact of rise in CO2 on photosynthesis in different group of higher plants has both negative and positive effect as illustrated by the extensive literature. Photosynthesis is a major procedure of remoteness and turnover of the total carbon on the earth. Reduced stomatal conductance and increased photosynthesis are the two processes that will impact plants and ecosystem due to increasing CO2. However, in guard cells, the CO2 sensing mechanism that is responsible for the short-term sensitivity of gs to eloquent CO2 is still not known. According to the results obtained from FACE



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studies show that neither stomatal density change significantly nor does stomatal conductance acclimate to elated CO2 independently of photosynthesis but stomatal conductance is consistently decreased in both C3 and C4 species. The exact after-effect startling rise in atmospheric CO2 concentrations are hard to anticipate. Hence, the associated effects of various environmental factors on plant responses to rising CO2 require accurate and attentive study.

REFERENCES Aranjuelo, I., Irigoyen, J. J., Nogués, S. and Sánchez-Díaz, M. (2009). Elevated CO2 and water-availability effect on gas exchange and nodule development in N2-fixing alfalfa plants. Environ. Exp. Bot., 65, 18–26. Attipalli, R., Reddy, Girish K., Rasineni, Agepati. and Raghvendra, S. (2010). The impact of global elevated CO2 concentration on photosynthesis and plant productivity. Current Science, vol 99, NO. 1. Assmann, S. M. (1999). The cellular basis of guard cell sensing of rising CO2. Plant, Cell & Environment, 22, 629–637. Bassow, S. L., McConnaughay, K. D. M. and Bazzaz, F. A. (1994). The response of temperate tree seedlings grown in elevated CO2 to extreme temperature events. Ecol. Appl., 4, 593–603. Beaudry, R. M. (1999). Effect of O2 and CO2 partial pressure on selected phenomena affecting fruit and vegetable quality. Postharvest Biol. Technol., 15, 293–303. Bisbis, B., Kevers, C. and Gaspar, T. (1997). A typical TCA cycle and replenishment in nonphotosynthetic fully habituated sugarbeet callus overproducing polyamines. Plant Physiol. Biochem., 35, 363–368. Brearley, J., Venis, M. A. and Blatt, M. R. (1997). The effect of elevated CO2 concentrations on K+ and anion channels of Vicia faba L. guard cells. Planta, 203, 145–154. Cao, B., Dang, Q. L., Yü, X. and Zhang, S. (2008). Effects of (CO2) and nitrogen on morphological and biomass traits of white birch (Betula papyrifera) seedlings. For. Ecol. Manag., 254, 217–224. Christopher, B. Watkins. (2000). Response of horticulture commodities to high carbondioxide as related to modified atmosphere packaging. Hortechnology, 10(3). Cominelli, E., Galbiati, M., Vavasseur, A., Conti, L., Sala, T., Vuylsteke, M., Leonhardt, N., Dellaporta, S. L. and Tonelli, C. (2005). A guard-cell-


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specific MYB transcription factor regulates stomatal movements and plant drought tolerance. Current Biology, 15, 1196–1200. Crous, K. Y., Walters, M. B. and Ellsworth, D. S. (2008). Elevated CO2 concentration affects leaf photosynthesis–nitrogen relationships in Pinus taeda over nine years in FACE. Tree Physiol., 28, 607–614. Uprety, D. C., Dwivedi, N., jain, V. and Mohan, R. (2002). Effect of elevated carbon dioxide concentration on the stomatal parameters of rice cultivators. Photosynthetica, 40(2), 315-319. Elizabeth, A. and Ainsworth, Alistair Rogers. (2007). The response of photosynthesis and stomatal conductance to rising [CO2]: mechanism and environmental interactions. Plant, Cell and Environment, 30, 258–270. Elizabeth, A., Ainsworth, Stephen. and Long, P. (2005). What we have learned from 15 years of free-air CO2 enrichment (FACE). A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to risisng CO2. New phytologist, 165, 351-372. Fleisher, D. H., Timlin, D. J. and Reddy, V. R. (2008). Elevated carbon dioxide and water stress effects on potato canopy gas exchange, water use, and productivity. Agr. For. Meteorol., 148, 1109–1122. Frenkel, C. and Patterson, M. E. (1973). Effects of carbon dioxide on activity of succinic dehydrogenase in ‘Bartlett’ pears during cold storage. HortScience, 8, 395–396. Ghannoum, O., von Caemmerer, S., Barlow, E. W. R. and Conroy, J. P. (1997). The effect of CO2 enrichment and irradiance on the growth, morphology and gas exchange of a C3 (Panicum laxum) and a C4 (Panicum antodotale) grass. Aust. J. Plant Physiol., 24, 227–237. Gray, J. (2005). Guard cells: transcription factors regulate stomatal movements. Current Biology, 15, R593–R595. Gunn, S., Bailey, S. J. and Farrar, J. F. (1999). Partitioning of dry mass and leaf area within plants of three species grown at elevated CO2. Funct. Ecol., 13, 3–11. Hanstein, S. M. and Felle, H. H. (2002). CO2-triggered chloride release from guard cells in intact fava bean leaves. Kinetics of the onset of stomatal closure. Plant Physiology, 130, 940–950. Hashimoto, M., Negi, J., Young, J., Israelsson, M., Schroeder, J. I. and Iba, K. (2006). Arabidopsis HT1 kinase controls stomatal movements in response to CO2. Nature Cell Biology, 8, 391–398. Hetherington, A. M. (2001). Guard cell signaling. Cell, 107, 711–714. Hetherington, A. M. and Woodward, F. I. (2003). The role of stomata in sensing and driving environmental change. Nature, 424, 901–908.



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Holcroft, D. M., Gil, M. I. and Kader, A. A. (1998). Effect of carbon dioxide on anthocyanins, phenylalanine ammonia lyase and glucosyltransferase in the arils of stored pomegranates. J. Amer. Soc. Hort. Sci., 123, 136–140. Hulme, A. C. (1956). Carbon dioxide injury and presence of succinic acid in apples. Nature, 178, 218–219. Kader, A. A. (1997a). Biological bases of O2 and CO2 effects on postharvest life of horticultural perishables, p. 160–163. In: M. E. Saltveit (ed.). Proc. 7th Intl. Controlled Atmosphere Res. Conf., vol. 4. Vegetables and ornamentals. Univ. Calif. Postharvest Hort. Ser. 18. Ke, D., Yahia, E., Hess, B., Zhou, L. and Kader, A. A. (1995). Regulation of fermentative metabolism in avocado fruit under oxygen and carbon dioxide stresses. J. Amer. Soc. Hort. Sci., 120, 481–490. Kerbel, E. L., Kader, A. A. and Romani, R. J. (1990). Respiratory and glycolytic response of suspension-cultured ‘Passe Crassane’ pear fruit cells to elevated CO2 concentrations. J. Amer. Soc. Hort. Sci., 115, 111–114. Korner, C., et al. (2005). Carbon flux and growth in mature deciduous forest trees exposed to elevated CO2. Science, 309, 1360– 1362. Lange, D. L. and Kader, A. A. (1997a). Changes in alternative pathway and mitochondrial respiration in avocado in response to elevated carbon dioxide levels. J. Amer. Soc. Hort. Sci., 122, 245– 252. Long, S. P., Ainsworth, E. A., Rogers, A. and Ort, D. R. (2004). Rising atmospheric carbon dioxide: Plants FACE the future. Annu. Rev. Plant Biol., 55, 591–628. Mathooko, F. M. (1996a). Regulation of respiratory metabolism in fruits and vegetables by carbon dioxide. Postharvest Biol. Technol., 7, 1–26. Mathooko, F. M. (1996b). Regulation of ethylene biosynthesis in higher plants by carbon dioxide. Postharvest Biol. Technol., 9, 247–264. Messinger, S. M., Buckley, T. N. and Mott, K. A. (2006). Evidence for the involvement of photosynthetic processes in the stomatal response to CO2. Plant Physiology, 140, 771–778. Mitz, M. A. (1979). CO2 biodynamics: A new concept of cellular control. J. Theor. Biol., 80, 537–551. Nowak, R. S., Ellsworth, D. S. and Smith, S. D. (2004). Functional responses of plants to elevated atmospheric CO2 – do photosynthetic and productivity data from FACE experiments support early predictions? New Phytologist, 162, 253–280. Pei, Z. M., Murata, Y., Benning, G., Thomine, S., Klusener, B., Allen, G. J., Grill, E. and Schroeder, J. I. (2000). Calcium channels activated by


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hydrogen peroxide mediate abscisic acid signaling in guard cells. Nature, 406, 731–734. Polle, I. A. and McKee, L. B. (2001). Altered physiological and growth responses to elevated (CO2) in offspring from holm oak (Quercus ilex L.) mother trees with lifetime exposure to naturally elevated (CO2). Plant Cell Environ., 24, 1075–1083. Prusky, D., Hamdan, H., Ardi, R. and Keen, N. T. (1996). Induction of biosynthesis of epicatechin in avocado suspension cells treated with an enriched CO2 atmosphere. Physiol. Mol. Plant Pathol., 48, 171–178. Qaderi, M. M., Kurepin, L. V. and Reid, D. M. (2006). Growth and physiological responses of canola (Brassica napus) to three components of global climate change: temperature, carbon dioxide and drought. Physiol. Plant., 128, 710–72. Raschke, K., Shabahang, M. and Wolf, R. (2003). The slow and the quick anion conductance in whole guard cells: their voltage dependent alternation, and the modulation of their activities by abscisic acid and CO2. Planta, 217, 639–650. Roelfsema M. R. G., Konrad, K. R., Marten, H., Psaras, G. K., Hartung, W. and Hedrich, R. (2006). Guard cell sinalbino leaf patches do not respond to photosynthetically active radiation, but are sensitive to blue light, CO2 and abscisic acid. Plant, Cell & Environment, 29, 1595–1605. Satya Narayan, V. and Nair, P. M. (1986). The 4aminobutyrate shunt in Solanum tuberosum. Phytochemistry, 25, 997–1001. Saxe, H., Ellsworth, D. S. and Heath, J. (1998). Tree and forest functioning in an enriched CO2 atmosphere. New Phytologist, 139, 395– 436. Seneweera., et al. (2011). New insight into photosynthetic acclimation of elevated CO2: the role of leaf nitrogen and ribulose 1,5-bisphosphate carboxylase/oxygenase content in rice leaves. Environmental and Experimental Botany, 71, 128–136. Shimono, H., Okada, M., Yamakawa, Y., Nakamura, H., Kobayashi, K. and Hasegawa, T. (2008). Genotypic variation in rice yield enhancement by elevated CO2 relates to growth before heading, and not to maturity group. J. Exp. Bot., 60, 523– 532. Silva, S. (1998). Regulation of glycolytic metabolism in asparagus spears (Asparagus officinalis L.). PhD thesis. Mich. State Univ., E. Lansing. Srivastava, A. C., Tiku, A. K. and Pal, M. (2006). Nitrogen and carbon partitioning in soybean under variable nitrogen supplies and acclimation to the prolonged action of elevated CO2. Acta Physiol. Plant., 28, 181–188.



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Stephen, A., Prior, G. and Brett, Runion. (2011). A review of elevated atmospheric CO2 effects on plant growth and water relations: implications for horticulture. Hortscience, 46(2). Vavasseur, A. and Raghavendra, A. S. (2005). Guard cell metabolism and CO2 sensing. New Phytologist, 165, 665–682. Webb, A. A. R., McAinsh, M. R., Mansfield, T. A. and Hetherington, A. M. (1996). Carbondioxide induces increases in guard cell cytosolic free calcium. Plant Journal, 9, 297–304. Widodo, W., Vu, J. C. V., Boote, K. J., Baker, J. T. and Allen, Jr. L. H. (2003). Elevated growth CO2 delays drought stress and accelerates recovery of rice leaf photosynthesis. Environ. Exp. Bot., 49, 259–272. Woodward, F. I., Lake, J. A. and Quick, W. P. (2002). Stomatal development and CO2: ecological consequences. New Phytologist, 153, 477–484. Yang, Y., Murayama, H. and Fukushima, T. (1998). Activation of glyoxylate enzymes in cucumber fruits exposed to CO2. Plant Cell Physiol., 39, 533– 539. Young, J. J., Mehta, S., Israelsson, M., Godoski, J., Grill, E. and Schroeder, J. I. (2006). CO2 signaling in guard cells: calcium sensitivity response modulation, a Ca2+-independent phase, and CO2 insensitivity of the gca2 mutant. Proceedings of the National Academy of Sciences USA, 103, 7506– 7511.




Chapter 9

TOXICOLOGICAL STUDY OF ORGANOPHOSPOHOROUS PESTICIDE AND PROPOSED DETOXIFICATION METHODOLOGY Md Shabbir1,2, Samar K. Saha2 and Mukesh Singh1, 1

Department of Biotechnology, Haldia Institute of Technology, HIT Campus, Hatiberia, Purba Medinipur, Haldia, India 2 Department of Zoology, Visva Bharati, Bolpur, West Bengal, India

ABSTRACT Pesticides and insecticides application has become a regular practice in agriculture to protect crops from pathogens and insects attack. Most of these chemicals are toxic to human and non-target species. Among these compounds, Organo-phoshates have become most popular and have wide application during cropping seasons and postharvest period. Chlorpyrifos is one of the most used broad spectrum chlorinated organo-phosphorous insecticide. Chloropyrifos is extensively used in agricultural field to control various types of pest and insects. But its extreme toxicity on the non-target species of all groups including human has raised serious criticisms. It causes cytotoxicity, genotoxicity, mutagenicity, carcinogenicity, immune-toxicity and physiological disorder in all groups of organism. It has potentiality to persist in environment for long time, due to its long half-life period. Regular use of this pesticide has become a major 



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Md Shabbir, Samar K. Saha and Mukesh Singh health issue owing to the above ill effects and slow degradation rate. Simultaneously, researchers around the globe started working on bioremediation of chloropyrifos using eco-friendly techniques. Many countries banned the use of such insecticides. In rural areas of many countries including India, uses of this pesticide are still in practises. Bioremediation is an ecological approach which has several advantages over other remediation process, being inexpensive, effective, and environmentally safe technology to clean chlorpyrifos contaminated environment. Extensive researches are going on at several research stations in exploiting soil microbes and optimizing bioreactor for degradation of chlorpyrfos. The present report highlights the toxicological aspects as well as the bioremediation of chloropyrifos.

Keywords: organo-phosphorous pesticides, chloropyrifos, bioremediation, toxicity, soil microbes

INTRODUCTION In our ecosystem, several toxic compounds can be found. These toxic chemicals enter our environment through both natural as well as anthropogenic activity. They are mostly discharged to the environment by industrial or agricultural practices. Pesticides and insecticides are one such type of class of chemicals which needs urgent removal from the environment owing to high toxicological effects, although these are useful to destroy or inhibit growth of pathogenic microorganisms, insects that are responsible for the reduction or lower the quality of the food and/or crop production. Different pesticides are available in the market to prevent these kinds of losses. Pesticide applications to the field and during the storage have greatly improved agricultural yield, although cytogenetic studies have shown that many insecticides affect cell division and induce mitotic and chromosomal abnormalities in crop plants. Our principle sources of food are various plants, since primary consumers totally depend on autotrophs. World population is increasing in an exponential way so we need to produce more and more food in a limited agricultural area. In spite of increase in usage of farm machinery, the challenges due to species of plant pathogens causing disease and insects which reduce the quantity and degrade the quality of the product obtained per unit area are not under control (Kumar et al. 1995, Ashour et al. 1990, Kligerman et al. 2000). Therefore, to prevent the losses in yield due to such damage, the use of pesticides and insecticides has become outmost necessity. However, even though this greatly


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contributes to the agricultural yield as a strong positive advantage, it has strong negative perspectives too. It not only affects the target organism but sometimes it is found to affect non-target organisms too, including humans (Chantelli-forti et al. 1993, Chaudhuri et al. 1999). Primary effects on animals including humans are of mutagenic and carcinogenic nature. Such evidence has been well established experimentally in animals even on low dose exposure (Bull et al. 2006; Karabay and Oguz 2005). Additional factors such as lack of information, low literacy of the rural population, poor and inappropriate working conditions, inadequate protection during pesticide application, and faulty spraying technology have also been shown to play important roles in the environmental degradation. One of the major groups of insecticides is organo-phosphorus compounds. These insecticides are easily transported to the aquatic environment due to application on paddy fields or other usages. However, the possible translocation and transformation of organo-phosphorus compounds in the aquatic environment has not been extensively investigated as compared with more persistent organo-chlorine compounds. Chlorpyrifos is an emulsifiable organophosphate that causes stomach poisoning. It has a long residual action for the control of flies, mosquitoes, cockroaches, bedbugs and ants for household purpose and used on a wide variety of crop types (EPA, 1984) in agriculture. The acute systemic toxicity of chloropyrifos is due to its inhibitory effect on cholinesterase which is produced by its active metabolite of chlorpyrifos (Gennady et al. 2001). Still it is not validated whether chlorpyrifos causes cancer in humans. Animal studies have also not confirmed that chlorpyrifos causes cancer (Yano et al. 2000). Although chloropyrifos lacks carcinogenic potential, its ill effect cannot be ignored. The present study highlights the toxic effects of chloropyrifos and proposed bioremediation.

Toxicological Aspects of Organo-Phosphorous Compounds Chlorpyrifos is one of the widely used organophosphate pesticides applied on a variety of crop and non-crop plants. It can persist in aquatic ecosystem under anaerobic conditions. It has a long range transport potential and is even found in Arctic regions in ice, snow, fog, air, seawater, lake sediment, fish and vegetation, etc. Even in very low dose, it is very active as a neurotoxin by inhibiting cholinesterase. Chlorpyrifos is an endocrine disrupter with antiandrogenic and oestrogenic properties and reduces serum levels of cortisol and thyroid hormone T4. It can cause behavioural anomalies in adolescence and


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adulthood and also cause reduced IQ. Chlorpyrifos has been detected in human breast milk, cervical fluid, sperm-fluid, cord blood and the meconium of newborn infants. Chlorpyrifos has genotoxic as well as mutagenic effects on both acute and chronic exposure. Chloropyrifos exposure to rat causes significant damage in liver, brain, kidney and spleen (Ojha et al. 2013). Damages in DNA occur in Channa punctatus (Ali et al. 2008) and Drosophila melanogaster (Gupta et al. 2010). Chlorpyrifos induces formation of micronucleus and chromosome aberrations in various living systems (Ali et al. 2008, Cui et al. 2011, Shabbir et al. 2015). Figure 1 demonstrates chromosome aberrations in root tip cells of Allium cepa treated with chloropyrifos. Reports also suggest various types of cancer which can be developed due to ingestion/bioaccumulation of chlorpyrifos (Ventura et al. 2012, Engel et al. 2005, Lee et al. 2004, Alavanja et al. 2005). Immune toxicity in rat is reported by Blakely and co-worker 1999. Human liver cytochrome P450-dependent (CYP450) is inhibited by chloropyrifos and thus acts as an inhibitor molecules (Hodgson and Rose 2008). Chloropyrifos is also reported by many authors as potent anti-androgenic compounds (Viswanath et al. 2010). It is also reported that sex can be altered in tadpoles when exposed to chloropyrifos contaminated water (Bernabo et al. 2011).

Figure 1. Different chromosomal aberration of treated Allium cepa root tips with chloropyrifos for 24 hours (Shabbir et al. 2015).



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Figure 2. Paddy fields adjacent to a water body in Mahisadal district of Purba Medinipur, West Bengal, India. Pesticides applied to this field can percolate easily through the soil and make its way into the nearby water body.

Chlorpyrifos is exposed directly to the environment when it is applied as a pesticide. Chlorpyrifos can move far from its source of application and therefore, individual countries or regions cannot protect themselves or culmination the chemical effects. Pesticides applied to the crop plants can make ways to the nearby ponds and accumulation may hamper aquatic lives (Figure 2). Chlorpyrifos causes various disorders in freshwater and marine fauna such as ataxia, delayed maturation, growth and reproduction impairment, deformities and depressed populations (Jarvinen et al. 1983, Odenkirchen and Eisler 1988; NMFS 2008).

Bioremediation of Organo-Phosphorous Compounds Environmental chemical pollutants can be remediated generally by two approaches; viz. engineering approach and ecological approach. Usually engineering approaches involves external methods for restoration of soil, while the ecological approach involves the manipulation of inherent natural process to remove, immobilize, transform or degrade contaminants. Bioremediation is the usage of living microorganisms (bacteria and fungi) to degrade environmental pollutant. It is a process where microorganisms like bacteria convert organic compounds of various chemical complexities into nontoxic metabolites. All natural microorganisms are not capable of degrading


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all toxic chemicals. Trichloropyrinol (TCP), a metabolite of degraded chloropyrifos is very much persistent in the soil (Figure 3). This problem can be solved by engineering microbes by the process of genetic engineering. Bioremediation is recognised as inexpensive, effective, and environmentally safe technology for the degradation of the pollutants and cleanup of the environment. The main aim of bioremediation is to reduce pollutant load to minimum, nontoxic or acceptable levels i.e., within limits set by regulatory agency or ideally completely mineralize organo-pollutants to carbon dioxide. Total mineralization is desirable in protecting the environment, as it represents complete detoxification. Due to high mammalian toxicity of organophosphate pesticides such chlorpyrifos and their wide spread use, the microbial degradation is of particular interest. Several review on microbial mineralization of chloropyrifos have been reported by several workers (Getzin 1981, Singh et al. 1999, Singh and Walker 2006) Chlorpyrifos degrading bacteria cannot be isolated easily from soil or sewage by repeated treatments or enrichment of soil microbes with chlorpyrifos. Flavobacteria sp. and Escherichia coli have been engineered to degrade chlorpyrifos in broth by cloning opd gene in them. Arthrobacter species capable of degrading chlorpyrifos in mineral salt medium was initially isolated from methyl parathion-enriched soil. Chlorpyrifos pesticide was mineralized in minimal medium in which the pesticide was the only source of carbon.

Figure 3. Chloropyrifos and its metabolites. Trichlropyridinol (TCP) is very much persistent metabolite which cannot degrade easily within the soil.



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The study of organophosphate degradation at molecular level has been done extensively. The gene which is responsible for organophosphate degrading is widely distributed and isolated from temporally, geographically and biologically different species. The opd gene is usually present on plasmid but in Agrobacterium radiobacter it is reported to be present on chromosome. Genetic constituent of this gene is quite similar both on plasmid and chromosome. There are a number of genes reported to metabolites different types of pesticides and insecticides. The nuclei acid sequences of different pesticide degrading genes are not similar they are quite differ. Methyl parathion-degrading Plesiomonas species has different gene sequence than opd gene. Similarly, Nocardioes simplex NRRLB-24074 degrading the pesticide coumaphos have normal organophosphate-degrading enzyme systems. Alcaligenes faecalis DSP3, is able to degrade both chloryprifos and TCP (3,5,6-trichloro-2-pyridinol). TCP is a hyrolysed product of chlorpyrifos. The opd gene synthesises organophosphorous hyrolase (OPH), which has broad spectrum substrate specificity and hydrolytic activity against oganophosphates.

CONCLUSION From the above discussion it is clear that chlorpyrifos is one of the most potent toxic chemical affecting non-target organisms including human. Nature itself contains various soil microbes which can degrade and mineralize these chemicals. Mineralization process will help in detoxifying of these chemicals. Development of bacterial consortium capable of degradation of pesticides in either soil or water will helps in minimizing these toxic compounds from nature. We have isolated three bacteria which can degrade chlorpyrifos individually and in combination synergistically. These may be used in future for in situ bioremediation.

REFERENCES Alavanja, M. C., Samanic, C., Dosemeci, M., Lubin, J., Tarone, R., Lynch, C. F., Blair, A. (2003): Use of agricultural pesticides and prostate cancer risk in the Agricultural Health Study cohort. American Journal of Epidemiology, 157(9), 800-814.


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Ali, D., Nagpure, N. S., Kumar, S., Kumar, R., and Kushwaha, B. (2008): Genotoxicity assessment of acute exposure of chlorpyrifos to freshwater fish Channa punctatus (Bloch) using micronucleus assay and alkaline single-cell electrophoresis. Chemosphere, 7, 1823-31. Ashour, S., A., Abdou, R., F. (1990): Effect of weed control treatments on weeds, seed yield, yield components and nodulation in winter lentil. Fabis Newsltter, 26:10. Bernabò, I., Gallo, L., Sperone, E., Tripepi, S., Brunelli, E. (2011): Survival, development, and gonadal differentiation in Rana dalmatina chronically exposed to chlorpyrifos. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 315(5), 314-327. Blakley, B. R., Yole M. J., Brousseau, P., Boermans, H., Fournier, M. (1999): Effect of chlorpyrifos on immune function in rats. Vet. Hum. Toxicol. 41(3): 140-144. Bull, S., Fletcher, K., Boobis, A. R., Battershill J., M. (2006): Evidence for genotoxicity of pesticides in pesticide applicators: a review. Mutagenesis, 21(2), 93-103. Cantelli-Forti, G., Paolini, M., Hrelia, P. (1993): Multiple end point procedure to evaluate risk from pesticides. Environmental Health Perspectives, 101 (Suppl 3), 15. Chaudhuri, K., Selvaraj, S., Pal, A. K. (1999): Studies on the genotoxicity of endosulfan in bacterial systems. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 439(1), 63-67. Cui, Y., Guo, J., Xu, B., Chen, Z. (2011): Genotoxicity of chlorpyrifos and cypermethrin to ICR mouse hepatocytes. Toxicology Mechanisms and Methods, 21(1), 70-74. Engel, L., S., Hill, D., A., Hoppin, J. A., Lubin, J. H., Lynch, C. F., Pierce, J., and Alavanja, M. C. (2005): Pesticide use and breast cancer risk among farmers’ wives in the agricultural health study. American Journal of Epidemiology, 161 (2), 121-135. Environmental Protection Agency (EPA US) (1984). Pesticide Fact Sheet, chlorpyrifos. Gennady, A., Lyudmila, A., Vladimir, V., Bezuglov, J., Stephanie, P., Theodore, A. (2001): Effects of chlorpyrifos and Dieldrin in sea Urchin Embroys and larvae. Journal of National Institute of Environmental Health Science, 109 (7): 651-658. Getzin, L. W. (1981): Degradation of chlorpyrifos in soil: influence of autoclaving, soil moisture, and temperature, Journal of Economic Entomology, 74:158-162.



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Gupta, S., C., Mishra, M., Sharma, A., Balaji, T. D., Kumar, R., Mishra, R. K., Chowdhuri, D. K. (2010): Chlorpyrifos induces apoptosis and DNA damage in Drosophila through generation of reactive oxygen species. Ecotoxicology and Environmental Safety, 73(6), 1415-1423. Hodgson, E., Rose, R. L. (2008). Metabolic interactions of agrochemicals in humans. Pest Management Science, 64(6):617-21. Karabay, N. U., Oguz, M. G. (2005): Cytogenetic and genotoxic effects of the insecticides, imidacloprid and methamidophos. Genetics and Molecular Research, 4(4), 653-662. Kligerman, A. D., Doerr, C. L., Tennant, A. H., Peng, B. (2000): Cytogenetic studies of three triazine herbicides: II. In vivo micronucleus studies in mouse bone marrow. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 471(1), 107-112. Kumar, M., Prasad, M., Kumar, H. (1995): Cytotoxic effects of two herbicides on meiosis. Maize Genetics Cooperation Newsletter, 69:25. Lee, W., J., Blair, A., Hoppin, J. A., Lubin, J. H., Rusiecki, J. A., Sandler, D. P., Alavanja, M. C. (2004): Cancer incidence among pesticide applicators exposed to chlorpyrifos in the Agricultural Health Study. Journal of the National Cancer Institute, 96(23), 1781-1789. Ojha, A., Yaduvanshi, S. K., Pant, S. C., Lomash, V., Srivastava, N. (2013): Evaluation of DNA damage and cytotoxicity induced by three commonly used organophosphate pesticides individually and in mixture, in rat tissues. Environmental Toxicology, 28(10), 543-552. Shabbir MD, Singh, D., Maiti, S., Singh, M. (2015): Toxicological analysis and bioremediation study of chlorpyrifos. National Seminar on New Horizon in Biotechnology, DST sponsored on 14-15, October at Haldia Institute of Tech., Haldia. Singh, B, A; Kuhad, R, C, Singh, A, Lal, R and Tripathi, K, K (1999): Biochemical and molecular basis for pesticide degradation by microorganisms. Critical Review Biotechnology, 19 (3), 197-225. Singh, B, K; Walker, A (2006): Microbial degradation of organophosphorus compounds. FEMS Microbiology Letter, 30: 428-471. Ventura, C., Núñez, M., Miret, N., Lamas, D. M., Randi, A., Venturino, A., Cocca, C. (2012): Differential mechanisms of action are involved in chlorpyrifos effects in estrogen-dependent or-independent breast cancer cells exposed to low or high concentrations of the pesticide. Toxicology letters, 213(2), 184-193.


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Viswanath, G., Chatterjee, S., Dabral, S, Nanguneri, S. R, Divya, G., Roy, P. (2010): Anti-androgenic endocrine disrupting activities of chlorpyrifos and piperophos. The Journal of steroid biochemistry and molecular biology, 120(1), 22-29. Yano, B. L., Young, J. T., Mattsson, J. L. (2000): Lack of carcinogenicity of chlorpyrifos insecticide in a high-dose, 2-year dietary toxicity study in Fischer 344 rats. Toxicological Sciences, 53(1), 135-144.



Chapter 10

FOOD SECURITY IN THE CHANGING ENVIRONMENT: CHALLENGES AND SOLUTIONS Divya Pandey1, and Abhijit Sarkar2 1

Stockholm Environment Institute at York, University of York, York, UK 2 Laboratory of Applied Stress Biology, Department of Botany, University of Gour Banga, West Bengal, India

ABSTRACT Agriculture is a pivotal system to human sustenance. Population growth demands for continued increase in food production and supply, however, finite availability of land and water resources limit agricultural expansion. Moreover, environmental changes like global warming, climate change, land and water contamination and some air pollutants are negatively affecting agricultural productivity. Agricultural practices also play important role in environmental degradation. It is a major contributor to anthropogenic greenhouse gas emissions and a significant cause of water pollution. Therefore, to ensure food security, adaptation of agriculture to environmental changes along with making agriculture optimally resource efficient while reducing its environmental footprints is essential. Here we discuss some of the major challenges agriculture is currently facing and the solutions available for sustaining food production systems in near and long 



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Divya Pandey and Abhijit Sarkar term future. There is a consensus that increasing productivity of available farmlands is achievable by identifying the key limiting factors that create yields gaps while reducing the overuse of resources. Climate change and global warming will create unfavorable conditions to crop growth and fisheries in many parts of the world, hence adaptation actions are urgently needed. Through suitable management, agricultural practices can cut down their own emissions and possibly also support carbon sequestration in soils, thus offering greenhouse gas mitigation potential.

Keywords: agriculture, food security, climate change

INTRODUCTION Nutrition is the most fundamental requirement of all organisms. In 2000, a Millenium Development Goal was set to reduce hungry population by 2015. Serious efforts were undertaken and the goal was achieved well in time, however in the world today, with human population of over 7.4 billion, over 800 million people still suffer from hunger and 1 billion are chronically malnourished (FAO, 2015; Foley et al., 2011). Predictions say that 650 billion people will still suffer by 2030 (FAO, 2015). As the population continues to grow, the food production also needs to be increased in sustainable way (FAO, 2015). Scientific development has helped the world overcoming food shortages in past, and with expansion of irrigation systems and advancements in plant breeding, fertilizers, pest management; agriculture has been able to produce food for the expanding world. In the present scenario, increasing food production is challenged by limited land available for conversion and degrading arable lands. Changing environmental conditions are in general further limiting the productivity. Agriculture is inherently sensitive to environment and over the past few years, environmental changes have become a dominant stress factor to crop production. Rising temperatures, altered precipitation patterns, extreme climatic events such as severe draughts and floods have increased over the past few years that have led to incidences of crop losses. Air and water pollution are significantly affecting the productivity and safety of food in croplands and fisheries in some regions. In this chapter, we discuss some of these challenges. We collate and present the scientific analysis of the issue and its proposed solutions. Solutions are optimistic and motivate to integrate food production and distribution with pro poor development and environmental conservation.


Food Security in the Changing Environment

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FOOD DEMAND, ACCESSIBILITY AND CHALLENGES By 2050, human population is expected to reach 9 billion thereby creating a demand to double the food production. Even in the present context, about one third of children in developing countries have been observed to have retarded growth, and lack of nutrition is an important cause of child mortality in some parts of the world. For future food security, being able to produce enough for everyone is the main key, followed by its logical and justified distribution. In this section, we discuss the major points concerning our current and future food production systems.

Limited Scope of Agricultural Expansion Agriculture is already the largest land use. Croplands and pastures together occupy more than one third of the earth’s available terrestrial area (Ramakutty et al., 2008, Monfreda et al., 2008). These croplands have more or less already occupied the potential arable area on earth. In the recent years, most of the agricultural expansion has occurred into the tropics, nearly by 2.7% in Asia and 1.4% in Africa during 1985 to 2005. In most other parts of the world, net area under agriculture decreased due to conversion of croplands to other land uses. Overall, global agriculture area increased by 3% (Foley et al., 2011).

Competing Land Uses With increasing population and economic growth, especially in developing countries, city expansion takes place usually taking share from agricultural lands. Moreover, not all croplands are used to grow food crops. Cash crops and biofuels compete with the food crops, choice of allocation of fertile land to these alternate uses depends on the economic returns, climatic conditions, available resources and markets. In some parts of the world, bioenergy crops are taking over the food crops, while animal feed and other cash crops like cotton, sugarcane etc. compete almost worldwide with food crops. Because farmers prefer to grow produce for the available market, the distribution of croplands to food and non-food crops also varies in different parts of the world. In Asia and Africa, nearly 80% of the cropland is devoted to food crops whereas in Europe


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and North America, only 40%. At global level, about 62% of crop production comprises of direct human food, 35% to animal feed and 3% for bioenergy, seed and other industrial products (Foley et al., 2011).

How Long Can Crop Yields Increase? The last decades have been very important in bringing out major reforms to agriculture sector worldwide. Development of new varieties, mechanization of farming, fertilizer and pest control methods and development of irrigation facilities in different parts of the world led to remarkable increase in food production, and in some sensitive regions, it defied the Malthusian predictions that starvation would eradicate large populations. Green revolution of India is one such example that turned once starving country into self-reliant for most food grains. Between 1985 and 2005, worldwide production of common crops such as cereals, oilseeds, fruits and vegetables increased by 47%. However, the increase in yields is disproportionately much higher than the cropland area expansion during the same period. This happened due to improved farming practices. Shorter duration high yielding varieties, fertilizers, time saving techniques and irrigation facilities have enabled farmers to use the same space and time for multiple crops. Between 1987 and 1997, global production of farmed fish and shellfish also more than doubled due to advancement and expansion of aquaculture (Naylor et al., 2000). However, it is important to note that increase in yields is now slowing down in some of the highly productive areas. In a majority of the intensively cultivated lands a plateau has been achieved, and in some regions, yields are even showing a slight declining trend. For example, in some intensively cultivated regions of the Indo-Gangetic plains of India, yields of cereals are reported to not respond further to fertilizer inputs, and in many cases, continuous intensive cultivation with over irrigation has caused decrease in soil fertility (Gupta and Seth, 2007). Sustainability of aquaculture is also at stake in many regions due to potential damage to ocean and coastal resources through habitat destruction, pollution and unsustainable harvests for high demand for secondary products such as fish oil (Naylor et al., 1998).



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Environmental Change: Agriculture is Vulnerable Pollution, global warming and climate change are some of the major factors to which agriculture sector is highly vulnerable. Here we talk about them in detail.

Global Warming and Climate Change Agriculture is one of the most vulnerable sectors to rising temperatures and climate change. Mitigation of climate change and adapting agriculture is a crucial component of food security in immediate and long term future (FAO, 2015). While rising CO2 levels may have fertilization effect on most crops, the final effect is actually predicted to cause yield declines (Ainsworth and Long 2005). Countries that are currently reeling with malnutrition are also more vulnerable to climate change effects. Most of these are in the tropical region where extreme warming would hit the first. Their low ability to invest into adaptation worsens the situation (Parry et al., 2004). Increased frequency of extreme climatic conditions such as heat stress, draught, salinity and flooding will pose threats of crop productivity. Sea level rise will directly lead to loss of coastal agricultural lands due to their flooding, intrusion of salt water and change the coastal fisheries. Coral reefs, which are productive aquaculture systems, face risk from rising ocean temperatures and acidification. For populous countries like India and China, agricultural losses due to climate change will have far-reaching implications. In countries where rivers are glacier fed, such as in India, warming will cause substantially increased water flow, flooding downstream regions in the short term followed by prolonged drought conditions that will take toll on even the most irrigation-facilitated regions in indo-gangetic plains. In temperate countries, melting permafrost will create arable lands and better growing conditions in the regions where low temperatures are major limitation to crop growth. However, the current level of understanding of overall implications of future climatic conditions is still poor. It is however a concern that all components of ecosystems may not be able to adapt to the fast rate of changes, adding to unpredictable negative consequences in the long run. Studies are being conducted to predict the possible impacts of climate change on agriculture worldwide, and marked changes have already been recorded. As an example, drier parts of China are getting drier while some of the wet and agriculturally important regions are getting wetter. Moreover, the frequency of heatwaves in


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central China has significantly increased over the last 50 years, which call for taking immediate adaptive actions to maintain food production in the populous country (Piao et al., 2010).

Environmental Pollution and Its Impact on Food Production Systems Air, water and soil pollution also challenge the food production. With stringent air quality regulations, most of these pollutants have been substantially controlled in developed countries. In developing countries however, these pollutants are still a problem especially in the industrial areas. In rural areas, an important air pollutant, tropospheric ozone has increased to levels that can cause significant losses in forests and crops (Anvery et al., 2013). It is a secondary air pollutant, which forms in the atmosphere during sunny days. With stringent air quality control measures, peak ozone concentrations have been controlled in developed countries but with rising temperatures, average ozone concentrations may increase in future. Increase in nighttime ozone is being observed in many parts of Europe. However, in developing countries, mainly India and China, ozone levels high and it will continue to increase given the plenty of its precursors and favorable environmental conditions for its formation in these regions. According to an estimate, ozone is responsible for loss of approximately 60 Mt cereals annually in India (Ghude et al., 2014). Croplands also suffer from land pollution, mainly from industrial discharges that contaminate the soil with toxic chemicals. In many cases, the shortsighted agricultural practices such as sewage sludge and fly ash application on agricultural soils tend to increase heavy metals in soils. These amendments are often applied to improve soils physical conditions but the increased metal contents can contaminate the food chain and pose threat to human health. Water resources have attracted much attention from scientific community and it is observed that contamination of water bodies have serious implications on aquaculture. Discharge of industrial and domestic sewage to waterbodies is a common observation worldwide. This leads to wide range of issues ranging from nutrient pollution to toxicity caused by chemicals and metals. The conditions often become alarming in shallow and (or) confined water bodies. Nitrogen and phosphorous runoff from agricultural areas or sewage sludge discharge create anoxic conditions in water bodies leading to fish kills (Hargreaves, 1998). Toxicants also may pollute the food chain. The famous Minamatta case is one example where mercury compounds entered human



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bodies via fishes harvested from Minamata bay which received industrial discharge containing mercury.

ENVIRONMENTAL COSTS OF AGRICULTURE Even though agriculture suffers from environmental changes, ironically, it itself is one of the significant sources of environmental contaminants. The relationships between environmental changes and agriculture often form a feedback loop. The environmental impacts of agriculture span from direct (from immediate farm activities) to indirect as discussed below.

GHG Emissions Associated with Agriculture Agriculture is the major cause of deforestation thus making it an important contributor to GHG emissions (Gilbert, 2013). These land use conversions not only take away the natural carbon reserves but also disrupt ecosystems, affecting the biodiversity and important ecosystem functions that regulate water supply, local climate and soil stabilization. Approximately 70% of the grassland, 50% of the savanna, 45% of the temperate deciduous forest, and 27% of the tropical forests have already been converted for agricultural uses (Ramakutty and Foley, 1999). Given that, most new conversions will take place in tropics, mainly at cost of tropical forests, they pose a danger of causing loss of a significant natural carbon sequestration process on the earth. This will release around 1.1 × 1015 grams of carbon per year (Friedlingstein et al., 2010). Agriculture is also a major source of direct GHG emissions, mainly methane and nitrous dioxide. Rice cultivation and livestock are the biggest anthropogenic methane sources. N2O is emitted mainly from N fertilized croplands. Rice fields alone emit 32 to 44 Tg CH4 yr–1 (Le Mer and Roger, 2001). Asia contributes to 90% of these emissions with more than 50% coming from China and India alone (Yan et al., 2009). Regarding CO2, soil respiration is an important source, but farm operations and inputs like fertilizers, pesticides and energy also bear embodied CO2 content. Table 1 presents emissions of CH4, N2O and CO2 from agricultural soils assessed in different studies. Due to intensive farming practices, world’s croplands have also lost the soil carbon, an important carbon store.


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Divya Pandey and Abhijit Sarkar Table 1. Emissions of greenhouse gases from different agricultural systems and their global warming potentials

Emissions (kg ha-1) CH4 N2O CO2 Rice 286.81 1.62 19652.00 Wheat 9.88 14.22 26510.00 Rice 126.70 0.18 Rice 85.00 0.06 Rice 69.00 Rice 440.90 0.587 7630.00 Maize 0.20 0.2 Maize 4.14 5.71 *Global warming potential -Not estimated/available Crop

GWP (kg CO2-e ha-1) 20142.00 30794.00 3252.00 2142.88 1725.00 18827.43 62.50 1775.00

Reference Ma et al., 2013 Ma et al., 2013 Qin et al., 2010 Zou et al., 2005 Ma et al., 2008 Ahmad et al., 2009 Gauder et al. 2012 Ussiri et al., 2009

Agriculture consumes approximately 70% of freshwater withdrawals (Gleick et al., 2009). Withdrawal of groundwater for irrigation has caused water table to fall in many regions whereas over irrigation with ground water in many has caused salinization of soil in several regions. Therefore water saving technologies and sustainable irrigation solutions are inevitable to save existing croplands. Nitrogen and phosphorus fertilizers, manure and cultivation of nitrogen fixing crops have disrupted the natural nitrogen and phosphorus cycles (Bennett et al., 2001; Canfield et al., 2010). The excess of these run off to nearby streams, lakes and groundwater thus negatively affecting aquatic ecosystems (Canfield et al., 2010). These excess nutrients cause eutrophication of water bodies that may finally lead to its disappearance. Since 80% of the N2O emissions is related with agriculture, mitigation of this gas without halting food production is a challenge. Due to very slow removal processes, N2O is long lived with mean residence time of ~120 years (Hsu and Prather, 2010).

CAN AGRICULTURE PRODUCTION BE SUSTAINED Experts have constantly been analyzing this crucial question and it is identified that ensuring food security for everyone in future is attainable with strategic global action. Different group of experts have analyzed the question and a common set of suggested solution are discussed here briefly.



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Increasing Yields and Closing the Yield Gaps without Further Cropland Expansion A consensus has been attained that clarify that expanding the agricultural land will not offer a sustainable solution for producing more food. Instead, the focus should be on increasing the yields on existing farmlands by identifying and acting on the factors that create the gap between potential and observed yields (Tilman, 2002). Scientific analyses have identified significant opportunities to increase yields in currently yield limited areas, mainly in Africa, Latin America and Eastern Europe, where adoption of appropriate management systems promise higher yields by overcoming the nutrient and water limitations (Foley et al., 2011). Development of varieties that perform better in environmental stress and future climatic conditions are key components. Even though most challenged areas lie in underdeveloped countries, food should be considered as a shared resource and hence investment is expected from developed countries as a priority for common global future. Analysis of global food production and current limitations to it by Foley et al. (2011) showed that existing yield gaps for important food crops be closed by up to 95%.

Improving Resource Use Efficiency for Agriculture As discussed, agriculture consumes a major share of freshwater, and fertilizers and pesticides lead to direct and indirect chain of environmental problems, which ultimately affect agriculture itself. Future will be more water constraint, hence the water use efficiency of cultivation process must be increased. With intelligent management of land and water saving technologies (including drip and sprinkling systems), careful variety selection and crop rotations; crop production per unit water consumption can significantly be enhanced. Even for more water intensive crops such as rice, some management practices that reduce water use such as intermittent flooding are found effective without compromising yields. Common water saving techniques involve mulching, cover crops, monitored irrigation timing and amount, and proper land levelling. Similarly, nitrogen use efficiency is crucial. By cutting nitrogen use in agriculture, the N2O emissions can be controlled substantially. Use of nitrification inhibitors, agronomic practices and manure management are also being evaluated. Soil borne N2O emissions are also sensitive to temperature, moisture and land use changes (Skiba and Smith, 2000). Reducing N fertilizer


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doesn’t necessarily means compromising the yields. There exists a wide parity in production per unit of fertilizer application in the world. The hotspots of low fertilizer efficiency regions can be helped with adoption of suitable crop and soil management practices (Foley et al., 2011). No tillage, agroforestry, crop covers, mulching and crop rotations are the suggested practices to maintain physical condition, prevent erosion and degradation of soil. Scientific assistance through regular monitoring of soil quality is essential so that farmers can maintain the quality of their lands.

Promoting Soil Carbon Sequestration Soil is the largest terrestrial carbon store holding about 2.50 Pg carbon of which ~1.55 Pg is organic. Through proper management, agricultural soils offer an attainable recovery of historic carbon loss that amount to 55 to 78 Pg carbon by 50% (Lal, 2004). Although, soil carbon sequestration is regarded as a ‘winwin strategy’, there are certain controversies over quantification and assessment of sink capacity reliably (Lehman, 2009). Table 2. Carbon sequestration reported in some agricultural systems Region

System

practices

India

Wheatmaize Wheatcotton Barley

India Canada Brazil Scotland

Germany

Australia

NT vs. CT

Time (years) 20

C Sequestration (kg C ha-1 y-1) 206

NT vs. CT

20

182-206

NT vs. CT

10

901

OatMaize Barley

NT vs. CT

9

511.11

NT vs. CT

24

1207

MaizeMaizewheat Wheat

NT vs. CT

17

62.94

NT vs. CT

10

262

CT: conventional tillage, NT: no tillage.


Reference Grace et al., 2012 Grace et al., 2012 Arshad et al., 1990 Bayer et al., 2000 Soane and Ball, 2012; Ball et al., 1997 Tebrügge and Dürong, 1999 Dalal et al., 1995;


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Minimization of soil disturbance and increasing inputs of organic matter are the two fundamental keys to support carbon sequestration. Cover crops, mulching, no tillage, organic manure and decreasing the fallow period are some of the recommended management practices (Lal, 2004). Impact of similar practices on carbon stock in soil is presented in Table 2. It is also observed that improvement in nutrient status particularly, N and P also strengthens carbon sequestration. Therefore, intercropping with legumes is found to be effective. Lal (2000) calculated that adoption of suitable practices will let the world’s soil to sequester 0.6-2.0 Pg carbon every year. Agricultural soils in European Union and UK can offset 0.09-0.12 and 0.010 Pg carbon annually (Smith et al., 2005).

Behavioral Change and Investment in Agriculture While it is clear that feeding the future population of the world is possible but it can only be achieved through a joint action. Goal to eliminate hunger does not only rely on more food production but also its distribution and assess to everyone. This requires a massive behavioral change towards how the food is being viewed, minimizing food losses and promoting governments to take action to mobilize surplus food to the needy areas. This can be complicated by international relations and economic policies. Investing into agriculture and connecting it to the pro-poor development is nevertheless inevitable.

CONCLUSION Agriculture is facing multiple challenges. While the food production must grow at a pace to be able to keep producing enough for growing population, the limited natural resources and environmental changes mainly climate change, global warming and pollution are limiting the production systems. However, critical scientific analysis suggests that adapting to climate change and minimizing agriculture’s own environmental implications must integrate into agricultural development. Due to large disparity in productivity, conflicting socioeconomic demands and abilities to adapt to sustainable agriculture, a global action is required considering food and the nature a common shared resource.


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INDEX A

B

abscisic acid (ABA), v, ix, 81, 82, 84, 85, 86, 87, 88, 89, 91, 92, 93, 94, 95, 96, 97, 126, 128, 129, 130, 131, 160, 163, 167, 202, 208 agricultural productivity, ix, xi, 62, 99, 104, 112, 221 agriculture, vii, xi, 6, 42, 56, 59, 62, 73, 74, 82, 100, 102, 107, 108, 110, 155, 156, 178, 189, 211, 213, 221, 222, 223, 224, 225, 227, 228, 229, 231, 232, 234 Agrobacterium radiobacter, 217 agro-forestry, 122 air pollution, viii, 19, 20, 21, 38, 43, 44, 47, 48, 49, 51, 52, 53, 54, 56, 57, 58, 59, 139 Alcaligenes faecalis DSP3, 217 Allium cepa, 214 aquatic ecosystem, 1, 3, 213, 228 aquatic floral bioresources, 3, 5 aquatic plants, 2 aquatic vegetations, 9, 10, 14 Arthrobacter, 216 Asia, ix, 16, 17, 30, 64, 70, 100, 102, 103, 104, 107, 155, 159, 170, 223, 227 atmospheric carbon di-oxide, 62 Azolla, 6, 16 Azolla (Azolla pinnata), 6, 16 Azollaceae, viii, 1

bacteria, 40, 71, 107, 131, 187, 192, 193, 215, 217 Bangladesh, ix, 15, 100, 103, 104, 114, 119, 180 bioremediation, xi, 2, 14, 212, 213, 215, 217, 219 bioresources, viii, 1, 2, 3, 9, 16

C C3 crops, 62, 64, 197 C4 crops, 62, 64, 198 cadmium, 82, 83, 91, 92, 93, 95, 96 carbon dioxide (CO2), v, vi, viii, x, 28, 29, 50, 55, 57, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 109, 112, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 216, 225, 227, 228, 232 carcinogenicity, xi, 211, 220 China, ix, 17, 30, 37, 45, 47, 59, 60, 100, 104, 225, 226, 227, 234, 235 chloropyrifos, xi, 212, 213, 214, 216 chlorpyrifos, xi, 211, 213, 215, 216, 219 chloryprifos, 217


238

Index

climate change, viii, ix, xi, 2, 3, 20, 44, 61, 62, 64, 73, 74, 79, 80, 82, 96, 99, 100, 101, 102, 103, 104, 108, 109, 110, 112, 113, 114, 115, 116, 139, 149, 196, 221, 222, 225, 231, 234 collar rot, 179, 180, 185 conventional tillage, 230 convolvulaceae, viii, 1, 10, 171 cotyledonary nodes, 122 cytotoxicity, xi, 211, 219

global climate change, v, ix, 62, 77, 99, 100, 101, 113, 114, 196, 200, 208, 233 growth, vi, x, 177, 178, 187, 188, 189

H heavy metal, 31, 33, 34, 37, 40, 54, 58, 82, 83, 87, 96, 139, 226 Hydrocharitaceae, viii, 1

D

I

damping, 183 Drosophila, 214 Drosophila melanogaster, 214 drought stress, 65, 67, 70, 80, 100, 109, 110, 115, 119, 183, 209 dry deposition, 33, 35, 47, 52, 54

immune-toxicity, xi, 211 India, v, vii, ix, x, xi, xii, 1, 2, 4, 8, 10, 15, 16, 17, 19, 30, 37, 38, 45, 47, 49, 55, 56, 58, 61, 63, 66, 68, 69, 70, 81, 99, 100, 101, 103, 104, 105, 121, 155, 169, 172, 177, 178, 179, 180, 183, 191, 195, 211, 212, 215, 221, 224, 225, 226, 227, 230, 232 indo-gangetic plains, 225 Ipomoea (Ipomoea aquatica), 5, 10, 12, 16, 123, 157, 181

E e[CO2], viii, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71 ecosystem, viii, 2, 3, 14, 20, 31, 39, 40, 44, 49, 53, 54, 57, 58, 59, 65, 101, 102, 126, 151, 179, 204, 212, 227 Escherichia coli, 216

F fishes, 2, 4, 6, 9, 13, 14, 16, 17, 83, 213, 218, 224, 226, 234 Flavobacteria sp., 216 food security, vi, vii, ix, xi, 20, 40, 41, 42, 62, 81, 99, 100, 102, 103, 114, 157, 221, 222, 223, 225, 228, 233 fungi, x, 40, 113, 132, 145, 178, 179, 183, 186, 187, 188, 189, 191, 193, 215

G

L Lemnaceae, viii, ix, 1, 121 Liliopsida, ix, 121 Eriocaulaceae, ix, 121 Lemnaceae, viii, ix, 1, 121 Poaceae, ix, 121 Zosteraceae, ix, 121 Lotus (Nelumbo nucifera), 4, 16, 17

M Macrophomina phaseolina (Tassi)Goid., 178, 179 maize, 41, 62, 64, 65, 69, 70, 75, 76, 79, 192, 230 Makhana (Euryale ferox), 4, 5, 17

genotoxicity, xi, 211, 218


Index

239

mungbean, ix, 100, 101, 103, 104, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119 mutagenicity, xi, 211 Myanmar, ix, 100, 104

pre-emergence damping-off, 183 promoting rhizobacteria (PGPR), vi, x, 177, 178, 186, 187, 188, 189, 191, 192

N

ribulose bisphosphate (RuBP), 64, 79, 108, 197 Ribulose bisphosphate carboxylaseoxygenase (Rubisco), 64, 66, 67, 79, 196, 197, 198, 199 rice, 2, 31, 41, 43, 47, 59, 64, 65, 66, 67, 68, 69, 71, 72, 73, 75, 76, 77, 78, 79, 80, 84, 85, 101, 160, 200, 201, 206, 208, 209, 229, 233, 234, 235 rural development, 2, 3

no tillage, 230, 231 Nocardioes simplex NRRLB-24074, 217 non-toxic metabolites, 215 Nymphaeceae, viii, 1

O occult deposition, 35, 36 opd gene, 216, 217 organo-phosphorous compounds, 213, 215 organophosphorous hyrolase (OPH), 217 organo-phosphorous pesticides, 212

P Pakistan, ix, 30, 59, 100, 103, 104, 167, 180 Papillionaceae, viii, 1 particulate matter, viii, 19, 20, 21, 31, 32, 33, 34, 35, 36, 38, 39, 41, 42, 45, 46, 49, 54, 56, 57, 58 Pati Bet (Schumannianthus dichotomus), 8 pesticides, x, 177, 178, 179, 211, 212, 213, 215, 216, 217, 218, 219, 227, 229 PGPF, vi, x, 177, 178, 187, 188, 189 PGPR, vi, x, 177, 178, 186, 187, 188, 189, 191, 192 physiological disorder, xi, 63, 211 phytotoxicity, 20, 83 plant growth promoting fungi (PGPF), vi, x, 177, 178, 187, 188, 189 plant health, ix, 19, 20, 21, 25, 178, 179, 187, 190 plant response, 38, 40, 52, 62, 96, 157, 196, 205 Plesiomonas, 217 post-emergence damping-off, 183

R

S salinity stress, 100, 111, 117, 119, 130, 133, 142 seedling blight, 179, 180, 185 seedling diversity, 122 seedling survival, 122, 138, 141, 146, 147, 148, 150, 151, 153, 154, 158, 168, 174 Shola (Aeschynomene aspera), 7, 16 soil microbes, xi, 212, 216, 217 sorghum, 64, 65, 70, 73, 75, 77, 78, 79 stem rot, 178, 179, 181, 183, 184, 185, 191, 192 stem rot of jute, 178, 184, 191 stress, 21, 24, 39, 46, 50, 54, 66, 69, 70, 71, 73, 82, 84, 86, 87, 91, 92, 93, 95, 96, 106, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 129, 130, 138, 139, 142, 143, 144, 145, 159, 168, 175, 190, 200, 203, 206, 222, 225, 229

T temperature stress, 67, 75, 84, 91, 100, 107, 117 tolerance, ix, 25, 44, 45, 46, 48, 69, 75, 82, 84, 86, 87, 91, 93, 94, 96, 107, 113, 115,


240

Index

116, 117, 118, 119, 139, 141, 143, 164, 165, 168, 169, 170, 171, 200, 205 toxicity, xi, 23, 42, 55, 92, 111, 112, 211, 212, 213, 214, 216, 220, 226 toxicological effects, 212 Trapaceae, viii, 1 Trichlropyridinol (TCP)/TCP (3,5,6trichloro-2-pyridinol), 216, 217 troposphere, 21, 22, 23, 119 tropospheric ozone, viii, 19, 20, 21, 22, 40, 42, 53, 60, 226

V Vigna radiata (L.) Wilczek, 100, 101, 117, 119

W Water chestnut (Trapa bispinosa), 5 Water lily (Nymphaea odorata), 4 wet deposition, 22, 35, 36 wheat, 30, 31, 38, 41, 43, 47, 48, 51, 55, 56, 59, 62, 64, 65, 68, 69, 72, 73, 74, 76, 77, 78, 79, 80, 84, 101, 117, 167, 189, 198, 201, 230, 233 wild leafy vegetables, 12
