Environmental Issues Surrounding Human

Environmental Issues Surrounding Human Overpopulation Rajeev Pratap Singh Banaras Hindu University, India Anita Singh University of Allahabad, India Vaibhav Srivastava Banaras Hindu University, India

A volume in the Advances in Environmental Engineering and Green Technologies (AEEGT) Book Series

Published in the United States of America by IGI Global Information Science Reference (an imprint of IGI Global) 701 E. Chocolate Avenue Hershey PA, USA 17033 Tel: 717-533-8845 Fax: 717-533-8661 E-mail: [email protected] Web site: http://www.igi-global.com Copyright © 2017 by IGI Global. All rights reserved. No part of this publication may be reproduced, stored or distributed in any form or by any means, electronic or mechanical, including photocopying, without written permission from the publisher. Product or company names used in this set are for identification purposes only. Inclusion of the names of the products or companies does not indicate a claim of ownership by IGI Global of the trademark or registered trademark. Library of Congress Cataloging-in-Publication Data Names: Singh, Rajeev Pratap, editor. | Singh, Anita, 1981- editor. | Srivastava, Vaibhav, 1988- editor. Title: Environmental issues surrounding human overpopulation / Rajeev Pratap Singh, Anita Singh, and Vaibhav Srivastava, editors. Description: Hershey : Information Science Reference, [2017] | Series: Advances in environmental engineering and green technologies | Includes bibliographical references and index. Identifiers: LCCN 2016041793| ISBN 9781522516835 (hardcover : alk. paper) | ISBN 9781522516842 (ebook : alk. paper) Subjects: LCSH: Overpopulation--Environmental aspects. | Overpopulation--Economic aspects. | Sustainable development. Classification: LCC HB871 .E648 2017 | DDC 363.7--dc23 LC record available at https://lccn.loc.gov/2016041793 This book is published in the IGI Global book series Advances in Environmental Engineering and Green Technologies (AEEGT) (ISSN: 2326-9162; eISSN: 2326-9170)

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Chapter 14

Tropospheric Ozone Pollution, Agriculture, and Food Security Abhijit Sarkar University of Gour Banga, India Sambit Datta University of Calcutta, India Pooja Singh Banaras Hindu University, India

ABSTRACT Increasing population and unsustainable exploitation of nature and natural resources have made “food security” a burning issue in the 21st century. During the last 50 years, the global population has more than doubled, from 3 billion in 1959 to 6.7 billion in 2009. It is predicted that the human population will reach 8.7 - 11.3 billion by the year 2050. Growth in the global livestock industry has also been continuous over the last two decades. An almost 82% increase in future livestock is expected in developing countries within 2020, due to an expanding requirement for food of animal origin. Hence, the future demand of this increased human and livestock population will put enormous pressure on the agricultural sectors for providing sufficient food and fodder as well as income, employment and other essential ecosystem services. Therefore, a normal approach for any nation / region is to strengthen its agricultural production for meeting future demands and provide food security. Tropospheric ozone (O3), a secondary air pollutant and a major greenhouse gas, has already been recognized as a major component of predicted global climate change. Numerous studies have confirmed the negative impact of O3 on agricultural productivity throughout the world. The present chapter reviews the available literature, and catalogue the impact of this important gas pollutant on modern day agricultural production worldwide.

INTRODUCTION Ozone (O3) whether in stratosphere or troposphere has been a major talking issue for scientists, policy makers, and even the common man since last couple of decades. In stratosphere this tri-oxygen provides a crucial barrier against incoming solar ultraviolet radiation and protects life on earth; so depletion of O3 DOI: 10.4018/978-1-5225-1683-5.ch014

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Tropospheric Ozone Pollution, Agriculture, and Food Security

layer in stratosphere is a problem. However, in troposphere it is a gaseous pollutant with negative impact on human and animal respiration as well as causing severe damage to both natural and cultivated plant populations (Cho et al, 2011); so, rising of O3 level in troposphere is again a major crisis. Now, which one is more serious problem – might be a million-dollar question; but, this present section mainly focuses to review the available scientific literatures which specifically deal with the O3 formed in the troposphere and its further consequences mainly on plant’s health and productivity. Although, some O3 is believed to be transferred from the stratosphere to the troposphere too; but the amount is debatable (Jaffe, 2003).

THE ATMOSPHERIC O3: GOOD UP HIGH, BAD NEARBY Ozone is generally present as a trace gas in our atmosphere, averaging about three molecules for every 10 million air molecules. In spite of this very small quantity, O3 plays a vital function in controlling the atmospheric chemistry. This trace gas is mainly found in two different regions of Earth’s atmosphere. The major amount of the total atmospheric O3 (approximately 90%) exist in a layer that begins between 10 and 17 kilometers above the Earth’s surface and extends up to about 50 kilometers. This region of the atmosphere is called ‘stratosphere’ and the stratospheric O3 is commonly known as the ‘ozone layer’. The remaining O3 is present in the lower region of the atmosphere, which is commonly called ‘troposphere’. Though the O3 molecules at upper atmosphere, i.e. stratosphere, and lower atmosphere, i.e. troposphere, are chemically identical but they perform very different roles in atmosphere as well as show very different effects on the living world too. The stratospheric O3 (sometimes referred as ‘good ozone’) plays a valuable role for living world by absorbing most of the biologically damaging ultraviolet sunlight (UV-B), allowing only a small amount to reach the Earth’s surface. The absorption of ultraviolet radiation by O3 creates a source of heat, which actually forms the stratosphere itself (a region in which the temperature rises as one goes to higher altitudes). Ozone thus plays a key role in the temperature structure of the Earth’s atmosphere. Without the filtering action of the O3 layer, more of the Sun’s UV – B radiation would penetrate the atmosphere and would reach the Earth’s surface. Many experimental studies of plants and animals and clinical studies of humans have shown the harmful effects of excessive exposure to UV-B radiation. However, in the troposphere, O3 acts as a harmful gaseous pollutant which itself affects the health and productivity of all the living forms.

TROPOSPHERIC OZONE CYCLE: FORMATION, DEPOSITION AND TRANSPORT OF OZONE IN TROPOSPHERE Being a secondary pollutant in nature tropospheric O3 is generally formed by the photo-chemical reactions between oxides of nitrogen (NOX) and volatile organic compounds (VOCs) in the presence of bright sunlight. Even, O3 also formed from the methane emitted from swamps and wetlands and some other primary pollutants through similar reactions; and through long range transport O3 travels huge distances and spreads over larger areas (Kondratyev & Varotsos, 2001; Varotsos et al., 2004). VOCs emission has not contributed significantly to increasing tropospheric O3 concentrations (Fiore et al., 2002). The chemical reactions involved in tropospheric O3 formation are a series of complex cycles in which carbon-monoxide and VOCs are oxidized to water vapor and carbon dioxide. The oxidation occurs in

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carbon monoxide due to hydroxyl radical (OH·). The resultant hydrogen atom reacts rapidly with oxygen to give a per-oxy radical (HO2·). OH· + CO → H + CO2 H + O2 → HO2· Peroxy radicals react with NO to give NO2, which is photolyzed to give atomic oxygen and by reacting with oxygen, a molecule of O3 is formed. HO2·+ NO → OH· + NO2 NOx + radiations (>380 nm) → NO + O O + O2 → O3 Besides, O3 formation also depends upon reaction of methane (CH4), carbon monoxide (CO) and non-methane hydrocarbons (NMHCs) with O2. Formation of O3 from carbon monoxide CO + 2O2 + hv → CO2 + O3 Formation of O3 from methane CH4 + 4O2 + 2hv → HCHO + H2O + 2O3 HCHO + hv → H + HCO (λ < 330nm) HCO + hv → H + CO (λ < 360nm) CO + 2O2 + hv → CO2 + O3 Formation of O3 from non-methane hydrocarbons RH + 4O2 + 2hv → RCHO + H2O + 2O3. So, it is quite clear that formation of O3 in troposphere is long process which involves a number of primary pollutants. Ozone in upper layer of troposphere can have a lifetime of many days or even a week or two. This is because the major loss processes, scavenging by nitric oxide and dry deposition occur at or very close to the surface of the Earth. This means that O3 produced in one region can, if lifted to higher levels, travel to another region, increasing the background O3 concentrations of that region, even if the sources of O3 precursors are absent (Reid, 2007). A number of studies in U.K., Europe and U.S.A., have examined surface O3 concentrations in relation to other regional air movements (Van Dop et al., 1987; Comrie & Yarnal, 1992). Ozone concentrations also varied due to different atmospheric physical factors like simple air circulation index involving anticyclonic and cyclonic air movement has been demonstrated at Sibton, U. K. (Davies et al., 1987). Davies et al. (1992) indicated a positive surface ozone/wind speed relationship in winter and a negative relationship in summer at Bottesford, U.K. and other European stations, which are strongly influenced by westerly winds. It has been shown by Fiore et al. (2002) and Jaffe et al. (2003)

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that western North America receives a background O3 contribution from Asia and Europe, Europe receives O3 transported from both North America and Asia (Auvray & Bey, 2005). High levels of O3 are recorded from remote rural areas hundreds or thousands of miles away from the original sources (Prather et al., 2003). Ozone along with the precursors are found to be transported over the Pacific Ocean and occasionally reaching North America from East Asian countries (Hoell et al., 1997; Mauzerall et al., 2000; Derwent et al., 2004).

TRENDS IN TROPOSPHERIC O3 CONCENTRATIONS: PAST, PRESENT AND FUTURE As a secondary air pollutant, the regional mapping of O3 concentration throughout the globe is a quite critical thing. However, researchers found that the amount of tropspheric O3 is constantly increasing worldwide (Mittal et al., 2007; Cho et al., 2011; Rai et al, 2012). Ozone occurs naturally at low concentrations ranging from 5 to 15 ppb (Marenco et al., 1994). The earliest O3 measurements began in mid-1800s when more than 300 stations recorded O3 concentrations in different parts of Europe and USA. However, the continuity of O3 monitoring was maintained only at a few stations and hence long term data are limited. These data indicated towards a general indication of what the natural background levels of O3 would be in the absence of significant anthropogenic influences.

Ozone Concentration Around the Globe Ozone concentrations around the globe showed a diverse picture. Evaluation of daily O3 concentrations over Athens over a period of 1901- 1940 gives a range of about 20 ppb (Varotsos & Cartalis, 1991). Measurements from Great Lakes area of North America yielded an average daily maximum of approximately 19 ppb in the late 19th century (Bojkov, 1986). European measurements between 1850s and 1900 were found to be in the range of 17 -23 ppb approximately (Bojkov, 1986). Using O3 data collected at Montsouris, France, between 1876 and 1910, Volz and Kley (1988) reported an annual average range between 5- 16 ppb over a period of 11 ppb. Background O3 concentrations have more than doubled in the last century (Meehl et al., 2007) and there are also evidences of increase in annual mean values ranging from 0.1 to 1 ppb per year (Coyle et al., 2003). In UK, O3 concentrations are predicted to reach 30- 40 ppb in rural areas resulting in doubling of AOT40 values by 2030 (Coyle et al., 2003). Clean Air Status and Trends Network (CASTNet, 2004) recorded O3 concentrations from 11 National Parks in USA (designated as protected areas) and showed that annual medians at US parks ranged from 13 to 47 ppb, while maxima ranged from 49 to 109 ppb (CASTNet, 2004). In Canada, Canadian Air and Precipitation Network (CAPMoN) has recorded annual median O3 concentrations at Canadian background sites ranging between 23 to 34 ppb, while annual maxima ranged from 63 to 108 ppb (Vingarzan, 2004). A Community Multiscale Air Quality Model has calculated highest O3 concentrations ranging from 55 to 70 ppb during May and June in the boundary layer over East China and Japan (Yamaji et al., 2006). Rate of increase of tropospheric O3 concentrations over East Asia is larger than in any other area of Northern mid latitudes (Akimoto et al., 1994; Kaneyasu et al., 2000). This unusual increase can be attributed to increased anthropogenic emissions of O3 precursors released from rapidly emerging industrialized Asian continent (Hoell et al., 1997). O3, along with the precursors are transported over the Pacific Ocean and occasionally reaching North America (Hoell et al., 1997; Mauzerall et al., 2000; Derwent et al., 2004). 236


India: A Future O3 Hot Spot Very few systematic data of O3 monitoring are available in spite of the favourable climatic conditions for O3 formation in the country. At Varanasi, situated in northern India, mean O3 concentrations were 34.68 ppb during 1989 - 1991 (Pandey et al., 1992), 45 to 48 ppb during 1999 - 2001 (Agrawal et al., 2003), 45.18 to 62.35 ppb during summer and 28.55 to 44.25 ppb during winter from 2002 to 2006 (Tiwari et al., 2008), and 41.65 to 54.2 ppb during 2006 - 2007 (Singh et al., 2009). Daytime O3 concentration at an urban site in Delhi varied between 9.4 to 128.3 ppb in 1991 (Varshney & Aggarwal, 1992) and between 34 to 126 ppb during winter in 1993 (Singh et al., 1997). An annual average daytime O3 concentration of 27 ppb was reported at Pune, an urban site situated in western India between August 1991 to July 1992 (Khemani et al., 1995). Lal et al. (2000) reported that daytime mean O3 concentration rarely exceeded 80 ppb at an urban site at Ahemedabad situated in western India from 1991 to 1995. Ozone concentrations varying from 40 - 50 ppb were recorded from an urban and rural site in Maharashtra, India during 2001- 2005 (Debaye & Kakade, 2009). Using chemical transport model named HANK, Mittal et al. (2007) calculated that 8 h daily average O3 concentration varied between 33 - 40 ppb in Varanasi during February to April, 2000. Roy et al. (2009) used a REMO - CTM model to study the distribution of AOT40 (accumulated exposure to ozone above a threshold of 40 ppb) over the Indian region and observed high AOT40 values, exceeding the threshold set by WHO (3 ppm.h for 3 months) for agricultural crops over most of the fertile Indo Gangetic Plains. Elevated monthly AOT40 values for O3 were found between November and May, while highest value was recorded in March over Pune (Roy et al., 2009). Regular measurements over a period of 6 months (November to April, 2003) have also shown that AOT40 values for O3 exceeded up to 36 ppm.h, which is almost 3.6 times the critical level set for the protection of forests (Roy et al., 2009). In India, the number of measurement centers performing valid and long term representative measurements of surface O3 and their precursors is too small. Recently a new grided emission inventory of O3 precursors over Indian geographical region has been prepared by Roy et al. (2008).

TROPOSPHERIC OZONE AND PLANT LIFE Since O3 entry through the leaf cuticle is negligible, stomata play a fundamental role in determining the flux of O3 in to the apoplastic region of the plants (Kerstein & Lendzian, 1989; Leitao et al., 2003). The flux of O3 from troposphere into the plants depends on different resistances at various levels, i.e.- aerodynamic resistance depending on atmospheric resistance boundary layer resistance caused by a layer of laminar air adjacent to the leaves, the stomatal resistance exerted by the stomatal pores and an internal resistance of the plants (Guderian, 1985). The sensitivity of plants to O3 depends upon their stomatal response. Since O3 exposure generally results in decline in stomatal aperture, plants that show more rapid stomatal closure are reported to be more resistant in population level studies (Winner et al., 1997). However, O3 induced declines in stomatal apertures may be of limited protective value, since stomatal closure is generally a consequence of damage to photosynthetic apparatus (Farage & Long, 1995). Martin et al. (2000) modelled the data from earlier literature and showed that in most of the cases, stomatal aperture caused by acute O3 exposure can be predicted by changes occurring in the mesophyll photosynthesis. After entering through stomata, O3 can directly react with the plasma membrane through ‘ozonolysis’ or it can be converted into reactive oxygen species (ROS) and hydrogen peroxide (H2O2), which can alter 237


cellular functions causing cell death, premature senescence, and the up- or down-regulation of specific genes (Long et al., 2002; Fiscus et al., 2005). In the chloroplast, O3-induced responses could directly or indirectly impair the light and dark reactions of photosynthesis (Fiscus et al., 2005). Different studies indicate that O3 damages the photosynthetic machinery leading to a progressive loss in the amount as well as activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) (Agrawal et al., 2002; Cho et al., 2008). Miller et al. (1999) reported that O3 specifically induced 12 senescence-related genes in Arabidopsis thaliana (ecotype Lansberg erecta) leading to premature senescence. It should be noted that the O3-induced early senescence involves many genes associated with natural senescence in Arabidopsis. Therefore, the harmful effects of O3 on the plant have normally been attributed to foliar injuries leading to early senescence; decreases in light interception and photosynthesis, consequent reductions in assimilate availability and alterations at the gene and protein levels.

Effect of O3 on Lower Group of Plants Most of the studies in present days were mainly concerned with the higher plants. Though, O3 can cause severe harm to lower group of plants also. Frederick and Heath (1970), exposed photosynthetic green algae Chlorella sorokiniana var pacificensis to a controlled O3 exposure (2.6 µ moles min -1 O3 was supplied to the medium) and observed an exponential decline in its viability. They also observed that, this decline in cell viability was highly correlated with the production of malondialdehyde, arising from the oxidative break down of unsaturated fatty acid material. Paralkar and Edzwald (1996), observed that, lower dose of O3 generally increased the release of extra-cellular organic matter (EOM) in algae but the same O3 in higher concentration affects the structure of EOM (by lowering the molecular size) which may hinder in subsequent coagulation. Plummer and Edzwald (2001), in their experiment with two different algae (Scenedesmus sp. and Cyclotella sp.), found that ozone exposure in the culture of respective algae increased the production of chloroform and chlorinated haloacetic acid (HAA). According to them, a pre-ozonation with 1mgL-1 O3 has increased chloroform formation from Scenedesmus sp. by 17 – 44% and from Cyclotella sp. by 5 – 26%. Chlorinated HAA also increased by 38 – 78% for Cyclotella sp. 3mg L-1 pre-ozonation. In their study, they also reported that SEM studies revealed severe cell alterations in Scenedesmus sp. after O3 exposure. Plummer and Edzwald (2002), in another report, showed that O3 improved the coagulation of Scenedesmus sp. Chen et al. (2009) also found the same type of results in their study and concluded that, O3 not only improved the coagulation but it also increased the cell lyses in algae.

Effect of O3 on Higher Group of Plants: Mainly Agricultural Crops Physiological Responses Tropospheric O3 and their generated ROS are known to alter membrane properties and membrane bound organelles like chloroplast, which may lead to destruction of photosynthetic pigments, and thus ultimately affect photosynthetic activity. Accelerated chlorophyll destruction is reported due to induced metabolic changes within the plant cells caused by oxidative force of O3 (Rai et al., 2011). Several studies have suggested chlorophyll content of leaves as an indicator of stress under O3 exposure (Sarkar & Agrawal, 2010; Leitao et al., 2007). Total chlorophyll content decreased significantly by 14, 32, 52 and 47% at elevated levels of O3 i.e 74, 86, 100 and 124 ppb, respectively in maize plants (Leitao et al., 2007). In 238


a study with 20 cultivars of wheat, Biswas et al. (2008) found 24-35% reductions in total chlorophyll content in recent cultivars and 3- 12% in older cultivars of wheat exposed to 82 ppb O3 for 7 h day-1 over 21 days in OTCs suggesting that recent cultivars are more sensitive than older ones. Similar finding was also reported by Pleijel et al. (2006) with two wheat cultivars, one modern cultivar “Dragon” and another 100-year-old “Lantvete” when exposed to 57 ppb of O3 (non-filtered chamber receiving elevated O3) compared to 9 ppb O3 (filtered chamber). It was found that O3 induced decline in flag leaf chlorophyll content tended to proceed at a faster rate in “Dragon” compared with Lantvete. Reduction in chlorophyll content is known to reflect the activation of leaf senescence. The degradation of chloroplastic absorbing pigments might be an adaptive response to limit the production of ROS mainly driven in chloroplasts by excess absorption in photosynthetic apparatus (Herbinger et al., 2002). Carotenoids are vital photoprotective agents, which prevent photoxidative chlorophyll destruction (Singh et al., 2009). Carotenoid content also reduced due to oxidative destruction under O3 stress, leading to a decreased capacity to protect photosystems against photo oxidation (Singh et al., 2009). Hence, the loss of chlorophyll and carotenoids can produce a decrease in the light absorbing capacity to develop thermal dissipation energy under O3 exposures (Singh et al., 2009). Several studies have indicated that an early or primary response to O3 in leaves is an interference with photosynthesis, carbohydrate metabolism, partitioning of photosynthetic products between mobile and stored pools in the leaf, and/or the translocation of photosynthate within the plants. Reductions in Ps have been widely reported under ambient field conditions at higher concentrations of air pollutants (Feng et al., 2011; Akhtar et al., 2011; Rai et al., 2011) Meta data analyses of heat, soybean and rice varieties (Feng & Kobayashi, 2009) showed varying degrees of negative response of photosynthesis under O3 exposure. Tropospheric ozone also reduces assimilation by decreasing leaf longevity and increasing senescence in wheat plants grown in NFCs compared to FCs (Rai et al., 2011). Loss of assimilation capacity was attributed to reduced carboxylation efficiency, which can be directly related to loss of Rubisco activity. Ozone affects the synthesis as well as leads to the degradation of Rubisco due to its oxidation (Agrawal et al., 2002). Non denatured Rubisco has a large number of free- sulphydryl (-SH) residues and these groups are responsible for maintaining the correct structural conformation of Rubisco. Ozone induced oxidation of SH groups in Rubisco could alter the structural conformation of this enzyme, resulting in reduced catalytic activity and increased vulnerability (Agrawal et al., 2002). Ozone caused reduction in the level of RNA transcript for the small subunit (rbcS) of Rubisco and also decreased the expression of photosynthetic genes for Rubisco and Rubisco activase (Feng et al., 2008). Ozone led to reductions in m RNA levels of both small (rbcS) and large (rbcL) subunits of Rubisco in wheat (Sarkar et al., 2010). In a proteomic analysis conducted under in- vivo condition on rice seedlings exposed to O3 (40, 80, 120 ppb for 6 h d-1 for 9 d), reductions in expression of Rubisco large subunit (LSU) and small subunit (SSU) were reported (Feng et al., 2008). Agrawal et al. (2002) found that O3 imposes a negative effect on energy metabolism by altering gene expression of enzymes involved in energy metabolism i.e. fructose bisphosphate aldolasechloroplast P and ATP synthase beta subunit. This leads to reduction in ATP production through photophosphorylation and thus affects the Calvin cycle in photosynthesis. Similar findings of reductions in expression of large subunit (LSU) and small subunit (SSU) of Rubisco were observed in rice cultivars Shivani and Malviya dhan 36 grown in NFCs at a rural site of Varanasi at 20 ppb above ambient O3 level (51ppb) under natural field conditions (Sarkar and Agrawal, 2010). Sarkar et al. (2010) reported more reductions in Ps in sensitive cultivar of wheat than tolerant cultivar, which also showed higher reduction in gs suggesting more stomatal closure to avoid O3 uptake. Response 239


of rice cultivars showed a contrasting trend as sensitive cultivar NDR 97 showed higher Ps rate and more reductions in gs compared to Saurabh 950, a tolerant cultivar (Rai and Agrawal, 2008). Biswas et al. (2008) and Pleijel et al. (2006) found that modern or cultivated species demonstrated higher O3 flux as shown by increased gs resulting in higher relative reduction in Ps than wild/old species of wheat. Two cultivars of clover exposed to 150 ppb for 3 h showed 37% reduction in Ps and 38% in gs in Trifolium repens, a sensitive cultivar while tolerant cultivar T. pretense did not show any change in Ps and gs suggesting that tolerant cultivar performed better due to better ability of photosynthetically active mesophyll cells to cope up with photo oxidative stress (Degl’ Innocenti et al., 2003). Similar findings were also recorded in two tomato genotypes 93.1033/1 and Cuor di Bue exposed to O3 (150 ppb for 3.5 h) (Degl’Innocenti et al., 2007). Among bush bean cultivars, exposed with 160 ppb O3 for 3 h, higher reduction in Ps was recorded in sensitive cultivar (36%) while no change was recorded in tolerant cultivar (Guidi et al., 2009). Rice cultivars (Sufi and Bijoy) of Bangladesh ozone at 60 and 100 ppb concentrations reduced Ps rate by 27.6- 39.9% in Sufi and Bijoy cultivar suggesting no variation in sensitivity. Feng et al. (2011) exposed wheat cultivars at 27% higher ambient O3 (52.1 ppb for 7 h) on wheat cultivars Yanmai 16 (Y 16) and Yangfumai 2 (Y 2) after flag leaf development and found significant reductions in Ps rate and stomatal conductance in Y2. The reduction in photosynthesis may also occur due to structural damage of thylakoids, which affects the photosynthetic transport of electron, indicated as reduction in Fv/Fm ratio. Reduction of Fv/Fm ratio indicates an alteration of PS II photochemistry associated with a sign of photoinhibition, making plants more sensitive to light. Lowering of Fv/Fm ratio is observed in lettuce cv Vallaolid (2.5%) and Morella (2.6%) at mean O3 concentration of 60 ppb (Calatayud and Barreno, 2004). Fv/Fm ratio reduced by: • • •

12% in white clover sensitive clone (NC-S) at 200 ppb O3 for 5 h d-1 (Francini et al., 2007), by 9.3% in snap bean cv S 156 at 60 ppb O3 (Flowers et al., 2009), and by 5.4% in wheat cv M 234 at mean O3 concentration of 42.4 ppb (Rai et al., 2007).

Ishii et al. (2005) also found lowering of Fv/Fm ratio in rice cv. MR 84 and MR 185, at low, medium and high O3 doses of 27, 55 and 87 ppb. The reduction in Fm under ambient O3 levels is ascribed to decline in the ability to reduce the primary acceptor QA and associated increase in non- photochemical quenching. Reductions recorded in variable fluorescence (Fv) are more strongly correlated with lowering of Fm, suggesting impairment of an electron transport, which involves a recombination reaction between P 680 and reduced phaeophytin (Phaeo-) within photosystem II (PS II) or directly affecting a PS II antenna system (Ishii et al., 2005). Degl Innocenti et al. (2003) exposed T. repens and T. pretense to 150 ppb O3 for 3 h and maximum reductions in Fm and Fo was recorded in sensitive cultivar T. pretense (28 and 13.2%). But, after post fumigation recovery in Fv/Fm ratio was observed in T. repense and no recovery in T. pretense. Under O3 exposure, there are several reports for increase in Fo and a parallel decrease in Fm on wheat (Rai et al., 2007) and rice (Rai and Agrawal, 2008) suggesting impairment of PS II activity due to the inability of the reduced plastoquinone acceptor QA to oxidize completely because of retardation of the electron flow through PS II or to the separation of light harvesting chl a/b protein complexes. This effect may be due to the inhibition of Calvin cycle activity as indicated by the reduction in CO2 assimilation rates, signifying that O3 increased excitation pressure on PS II reaction centres and thus decreased the possibility of e- transport from PS II to PS I (Sarkar et al., 2010).

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Biochemical Response After O3 exposure there is a need to tune the level of ROS produced to achieve a positive cell reaction through the signaling cascade without inducing uncontrolled cell death. As ROS are physiologically generated from various sources during cell metabolism, plants have evolved very efficient enzymatic and non- enzymatic antioxidant defense system, capable of detoxifying substantial amount of these reactive oxygen species. The antioxidant defence system plays a fundamental role in determining the cell fate, not only by keeping ROS level under control, but also acting as a central component of the cell redox balance and of the signaling modulation. The first line of defence against O3 derived ROS is the apoplast, where ascorbate (ASC) is believed to provide important protection from the oxidative injury. The O3 induced changes in apoplast ascorbate and redox state was first reported in 1996 (Ranieri et al., 2000). Ranieri et al. (1996) showed that enhanced apoplast ascorbate level, while intracellular concentration did not vary markedly, supporting the hypothesis of an O3 induced stimulation of ASC synthesis followed by active export to the apoplast in young asymptomatic and mature symptomatic leaves of pumpkin exposed to 150 ppb O3 (5 h d-1, 5 days). The protective role of ASC as ROS scavenger is also supported by the enhanced O3- sensitivity shown by mutant deficient in ASC (Conklin et al., 1996). The importance of ascorbic acid is demonstrated in the VTC 1 mutant of Arabidopsis where low ascorbic acid (AA) content in leaf tissue was associated with increased O3 sensitivity. There is also evidence that O3 tolerant genotypes have elevated AA content (Burkey et al., 2000, Robinson and Britz, 2000). Burkey and Eason (2002) exposed three cultivars i.e. Tendrette and Provider (O3 tolerant) and Oregon-91 (O3 sensitive) and four experimental lines R 123, R 142, S 144 and S 156 of snap bean (Phaseolus vulgaris L.) to 75 ppb O3 for 12 h and found higher levels of leaf apoplast ASC in O3 tolerant genotypes relative to sensitive lines. Higher apoplast AA/ASCT ratio was found in O3 tolerant cultivars than sensitive lines suggesting greater capacity for transport of DHA (dehydroascorbate) from the apoplast into the cytoplasm. Leaf ascorbic acid content and redox status were compared in O3 tolerant (Provider) and O3 sensitive (S 156) genotypes of snap bean exposed to 71 ppb O3 in open top chambers (OTCs) for 10 days in mature leaves early in the morning (06:00- 08:00 h) or in the afternoon (13:00- 15:00 h) (Burkey et al., 2003). Results showed that total ascorbate content [AA+ DHA] of leaf tissue was 28% higher in tolerant genotype compared to sensitive ones, exhibiting that tolerant cultivar (Provider) maintains total ascorbate content under O3 stress and level of apoplastic ascorbate were significantly higher in the afternoon than early morning for both genotypes. Rai and Agrawal (2008) found higher ascorbic acid content in sensitive cultivar of rice NDR- 97 compared to tolerant cultivar Saurabh 950 exposed to ambient O3 concentration of 35.5 ppb grown in OTCs. Higher ascorbic acid content was observed in tolerant soybean cultivar PK 472 compared to sensitive cultivar Bragg at 70 and 100 ppb O3 for 4 h from germination to maturity. Feng et al. (2010) showed that leaf apoplastic ascorbate content was 33.5% higher in tolerant wheat cultivar Y2 exposed to elevated O3 concentration (83.8 ppb) which was 27% higher than the ambient O3 concentration (66 ppb). Since, ASC is synthesized inside the cells and the oxidized form must be transported back into symplast to be re- reduced, the transport rate across the plasma membrane must be taken into account when discussing the antioxidative capacity of apoplastic ASC in the detoxification of O3. Burkey and Eason (2002) showed that transport of DHA from the apoplast into the cytoplasm was higher in tolerant genotypes of snapbean than sensitive lines. The antioxidant role played by ASC depends mainly on the cell ability to maintain it in a reduced state and it occurs at the cost of reduced glutathione (GSH) by monodehydroascorbate reductase (MDHAR) 241


or dehydroascorbate reductase (DHAR). Glutathione is generated by glutathione reductase (GR) at the expense of NADPH oxidation in Halliwell- Asada cycle. Among the tobacco cvs Bel B and Bel W3 known for their differential sensitivity to O3, reductions in the chloroplastic GR mRNA was recorded in Bel W3 at exposure of 150 ppb to O3 for 5 h (Pasqualini et al., 2001). Ascorbate may act as reducing substrate for ascorbate peroxidase (APX), which is one of the most efficient ROS scavenging systems. In sunflower, increased level of extracellular APX activity may contribute to avoid the buildup of toxic H2O2 concentrations (Ranieri et al., 2003). The higher constitutive APX activity measured in a resistant white clover clone with respect to a sensitive clone was further enhanced following long term exposure to O3 (60 ppb for 5 h d-1 for 56 days). Sarkar et al. (2010) reported increase in APX and GR activities in wheat cultivars exposed to elevated O3

Genome and Proteome Response Over the years, many integrated and individual studies on O3 stress responses have been reported in several plant species, and such studies have used typical research approaches. Although the demonstration of complicated mechanisms of O3 response in plants has been attempted, much work still remains to be done in this area. In recent years, analyses have been performed to obtain information on O3-triggered responses in plants; to this end, many high-throughput ‘omics’ approaches were performed in: • • • • • •

Arabidopsis (Mahalingam et al. 2006; Tamaoki et al. 2003), Bean (Torres et al. 2007), Maize (Torres et al. 2007), Pepper (Lee and Yun 2006), Rice (Agrawal et al. 2002; Cho et al. 2008), and Wheat (Sarkar et al., 2010).

However, as the present chapter mainly deals with the agricultural crops; in following section we will discuss about the ‘-omics’ responses of some important crops under O3 stress. Among all the major crops, rice (Oryza sativa L.) has been studied most for its response to O3-stress (Agrawal et al., 2002; Cho et al., 2008, Feng et al., 2008; Frei et al., 2010). Agrawal et al. (2002) first reported a detailed combined trancriptomics and proteiomics response of rice plants under elevated O3-exposure. Two weeks old rice (cv. Nipponbare) seedlings were exposed to 200 ppb of O3 for three days in a controlled fumigation chambers. A drastic visible necrotic damage in O3-exposed leaves and consequent increase in ascorbate peroxidase protein(s) accompanied by rapid changes in the immuneblotting analysis and 2-DE protein profiles were observed. They also reported nearly 52 differentially expressed proteins; among which, O3 caused drastic reductions in the major leaf photosynthetic proteins, including the abundantly present ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and induction of various defense/stress related proteins. Most prominent change in the rice leaves, within 24 h post-treatment with O3, was: • • • • • • 242

The induced accumulation of a pathogenesis related (PR) class 5 protein, Three PR 10 class proteins, ascorbate peroxidase(s), Superoxide dismutase, Calcium-binding protein, Calreticulin, a novel ATP-dependent CLP protease, and An unknown protein.


Feng et al. (2008) also followed similar experimental model with two weeks old rice seedlings exposed at 0, 40, 80 and 120 ppb O3 for nine days. A drastic damage in the photosynthetic proteins, mainly – large and small sub units of RuBisCO, and primary metabolism related proteins; but an induced expression of some major antioxidant, like - glutathione S transferase and Mn superoxide dismutase, and defense / stress related proteins, like - pathogenesis-related (PR) class 5 protein (PR5) and two PR10 proteins OsPR10/PBZ1 and RSOsPR10 were reported. Feng et al. (2008) also confirmed that the damage in rice proteome is strictly O3-dose dependent. In another independent study, Cho et al (2008) also checked the expression profiles of genes in leaves of two weeks old rice seedlings exposed to 200 ppb O3 for 1, 12 and 24 h using a 22K rice DNA microarray chip. A total of 1535 genes were differentially expressed more than fivefold over the control. Their functional categories suggested that genes involved in transcription, pentose phosphate pathway and signal transduction at 1h, and genes related to antioxidant enzymes, ribosomal protein, post-translational modification (PTM), signal transduction, jasmonate, ethylene and secondary metabolism at 12 and 24h play a crucial role in O3- response (Cho et al., 2008). Recently, Frei et al. (2010) have tried to identify the possible mechanism of O3-response in rice seedlings by characterizing two important quantitative trait loci (QTL), in two different chromosome segment substitution lines (SL15 and SL41); and demonstrated that the activity of some major antioxidant genes might contribute significantly in the response strategy of rice plant under higher O3-stress. In contrast with the above laboratory based experimental models, Sarkar and Agrawal (2010b) had applied ‘field based integrated –omics’ approach to understand the background of O3 response in two high yielding cultivars (Malviya dhan 36 and Shivani) of mature rice plants under natural conditions; and, found dependable phenotypical response, in the form of foliar injury, followed by definite changes in leaf proteome. Major damage in the photosynthetic, like – large and small sub units of Rubisco, and primary metabolism related proteins; but an induced expression of some antioxidant and defense / stress related proteins in rice leaf proteome were reported. Wheat (Triticum aestivum L.) is the third most important crop around the globe, and nearly two third of the world population depends on this crop for their primary nutrition supplement. Sarkar et al. (2010) recently employed ‘field based integrated –omics’ approach to understand the background of O3 response in two wheat cultivars (cvs Sonalika and HUW 510) against elevated O3 concentrations (ambient + 10 and 20 ppb) under near natural conditions using OTCs. Results of their study showed drastic reductions in the abundantly present Rubisco large and small subunits. Western blot analysis confirmed induced accumulation of antioxidative enzymes like superoxide dismutase and ascorbate peroxidase protein(s) and common defense/stress-related thaumatin-like protein(s). 2-DGE analysis revealed a total of 38 differentially expressed protein spots, common in both the wheat cultivars. Among those, some major leaf photosynthetic proteins (including Rubisco and Rubisco activase) and important energy metabolism proteins (including ATP synthase, aldolase, and phosphoglycerate kinase) were drastically reduced, whereas some stress/defense-related proteins (such as harpin-binding protein and germin-like protein) were induced. Maize (Zea mays L.) is another important crop at global context. Being a C4 crop, its response to climate change has been always bit different from the others. Torres et al. (2007) have done detailed investigation of O3 response in maize (cv. Guarare 8128) plants through gel based ‘omics’ approaches. In that experiment, 16-day-old maize plants (grown in controlled environment at green house) were exposed to 200 ppb O3 for 72 h., and then the response was compared with a controlled plant (grown under filtered pollutant-free air). Results showed that nearly 12 protein spots were differentially expressed under O3 exposure, and can be exploited as marker proteins. Expression levels of catalase (increased), SOD 243


(decreased), and APX (increased) were drastically changed by O3 depending on the leaf stage, whereas cross-reacting heat-shock proteins (HSPs; 24 and 30 kDa) and naringenin-7-O-methyltransferase (NOMT; 41 kDa) proteins were strongly increased in O3-stressed younger leaves. The study also enumerated leaf injury as bio-marker under O3 stress in maize leaves. Torres et al. (2007) also conducted a study on response of cultivated bean (Phaseolus vulgaris L. cv. IDIAP R-3) against O3 stress using the same experimental protocol, and the effects were evaluated through integrated ‘omics’ approach using gel-based proteomics followed by MS and immunoblotting. Results showed that in bean leaves two SOD proteins (19 and 20 kDa) were dramatically decreased, while APX (25 kDa), small HSP (33 kDa) and a NOMT (41 kDa) were increased after O3 fumigation. Lee and Yun (2006) applied cDNA microarrays to monitor the transcriptome of ozone stress-regulated genes (ORGs) in two pepper cultivars [Capsicum annuum cv. Dabotop (O3-sensitive) and cv. Buchon (O3-tolerant)]. Ozone stress up- or down-regulated 180 genes more than three-fold with respect to their controls. Transcripts of 84 ORGs increased, transcripts of 88 others diminished, and those of eight either accumulated or diminished at different time points in the two cultivars or changed in only one of the cultivars. 67% (120) of the ORGs were regulated differently in O3-sensitive and ozone-tolerant pepper cultivars, most being specifically up-regulated in the O3-sensitive cultivar. Tripathi et al. (2010) analyzed the response of linseed plants under elevated O3-stress through combined genomics and proteomics approaches. The results showed that 10 ppb elevation over ambient O3 concentration can cause 50% damage in the genome stability of linseed plants. In line to the genome response, leaf proteome also got severely affected under O3-stress, and the damages were mainly found on the photosynthetic and primary metabolism related proteins.

Growth and Yield Response Tropospheric O3 was found to adversely affect the growth and yield of a variety of agricultural plants. Tropospheric O3 reduced the marketable yield of a range of crop species even in the absence of visible injury, primarily through its effects in reducing photosynthetic rates and accelerating leaf senescence (Ashmore, 2005). Cultivar sensitivity was evaluated on the basis of experiments conducted in open top chambers (Sarkar et al., 2010) and FACE experiments (Zhu et al., 2011). In Pakistan, 29- 47% yield reductions were reported for 6 varieties of wheat (Maggs et al., 1995; Wahid et al., 1995), 28- 42% for two varieties of rice (Wahid et al., 1995) and 37- 46% for 2 varieties of soybean (Wahid, 2006) due to different pollutants in the ambient air. Exposure of O3 at 80 ppb concentration for 1.5 h daily for 30 days showed yield reductions of: • • •

29.5% in Vicia faba, 20.6% in Oryza sativa, 13% in Panicum miliaceum, and 9.7% in Cicer arietinum (Agrawal, 2005).

Differential responses were recorded among different crops and their cultivars. Maximum reductions were found in soybean (40- 60%) followed by wheat (20- 40%), rice (10- 20%) and minimum in barley (Feng & Kobayashi, 2009). Studies by Emberson et al. (2009), Feng and Kobayashi (2009) and Mills et al. (2007) found same trend of sensitivity, reporting legumes to be most sensitive and barley to be most resistant under O3 exposure.

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In open top chamber studies, wheat and soybean cultivars were studied extensively. Ozone exposure 70 and 100 ppb for 4 h d-1 for 70 days led to reductions in yield by 13.9 and 10% and 33.5 and 25% in soybean cv PK 472 and Bragg (Singh et al., 2010). The yield reductions in wheat cv HP 1209 and M 234 at O3 concentration of 70 and 100 ppb for 4 h daily for 70 days were 8 and 4.7 and 17 and 15.5%, respectively (Agrawal, 2005). Rai et al. (2007) found 20.7% reductions in yield of wheat cv M 234 grown in chambers ventilated with ambient air (40.6 ppb) as compared to filtered chamber. Analysing the cultivar sensitivity response, Sarkar and Agrawal (2010) found reductions of 7, 16.7 and 22% in wheat cv. Sonalika and 8.4, 18.5 and 25% in cultivar HUW 510 grown in NFCs (45.3 ppb), NFCLOs (50.4 ppb) and NFCHOs (55.6 ppb) compared to FCs. Rai and Agrawal (2008) reported yield reductions of 10 and 14% in rice cultivars Saurabh 950 and NDR 97 at ambient O3 concentration of 35.5 ppb grown in open top chambers. Among soybean cultivars, highest reduction in yield was recorded in Forrest under O3 exposure as compared to Essex (Robinson and Britz, 2000). In SoyFACE experiment, 10 soybean cultivars were exposed to ambient (46.3 and 37.9 ppb) and elevated (46.3 and 37.9) O3 concentrations in 2007- 2008. Yield reductions varied from 11.3- 36.8% in 2007 and 7.5- 16% in 2008 in ambient and elevated O3 levels and the yield response relationships also indicated that Loda and Pana were tolerant and IA 3010 was sensitive (Betzbergler). Zhu et al. (2011) exposed four winter wheat cultivars (Yannog 19, Yangmai 16, Yangmain 15 and Yangfumai 2) under elevated O3 with a FACE system from 2007 to 2009 with mean O3 levels of 56.9 ppb for 7 h in 2006- 2007, 57.6 ppb in 2007- 2008 and 57.3 ppb for 2008- 2009. The grain yield reductions recorded were 18.7, 34.7 and10.1% in Y 19 in three consecutive years of O3 exposure from 2006 to 2009. Morgan et al. (2003) showed that a 23% increase in O3 from an average daytime ambient level of 56 ppb to 69 ppb, will lead to 20% more reduction in soybean yield. Feng and Kobayashi (2009) calculated that at projected O3 concentration (51- 75 ppb), the yield losses would be 10% more for soybean, wheat and rice and 20% more for bean than at present ambient level of O3 (41- 40 ppb), thus predicting that future rise in O3 is a significant threat to food production in the world.

CONCLUSION On the basis of different studies conducted worldwide using different study approaches such as open top chambers (OTCs) and FACE experiments showed economic losses varies from Rs.1972- 77,055 in major crops. Rai et al. (2011) reported economic loss of Rs 1,208- 30,550 ha-1 for major agricultural crops wheat, rice, mustard, urd, soybean, pea and mungbean grown at ambient O3 using different studies approach like and field transect study (FTS) in India. Even, globally Van Dingenen (2009) using a global chemistry transport model a global economic loss of approximately US $ 14- 26 billion has been calculated at world market prices for the year 2000. Emberson et al. (2009) conducted modeling based studies to assess the extent and magnitude of O3 risk to agriculture suggest that yield losses of 5- 20% for important crops may be common in areas experiencing elevated O3 concentrations and also concluded Asian grown wheat and rice cultivars are more sensitive to O3 than the North American cultivars. The economic loss for 23 horticultural and agricultural crops due to O3 was estimated to be 3% (€ 6.7 billion) for the base year 2000 (Holland et al., 2006). But with the scenario of implementation of current legislation, the overall loss of all crop species is estimated to be 2% (€ 4.5 billion) for 2020 (Holland et al., 2006). The scenario is however, entirely different for Asia due to tremendous increase in anthropogenic activities and rapid expansion of economy, leading an increased emission of O3 precursors. 245


ACKNOWLEDGMENT AS acknowledges the financial assistance from University Grant Commission, New Delhi, GoI, and University of Gour Banga, Malda, India.

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