Photosynthesis, Transpiration, Stomatal Conductance ...

Photosynthesis, Transpiration, Stomatal Conductance Potential and Water uptake in selected Rice cultivars (Oryza sativa.) under Various Saline Conditions 1

Abida Kausar, Anam khurshid2, Yasin Ashraf 3, Rehmana Ghafoor4, * 5Munazza Gull

1

Department of Botany, GC women University, Faisalabad, Pakistan

2,3 4

Nuclear Institute of Agriculture and Biology, Faisalabad, Pakistan

Department of Botany, GC University, Faisalabad, Pakistan

5*

Biochemistry department, Faculty of science, King Abdulaziz University, 42805, Jeddah, Kingdom of Saudi Arabia *

Corresponding author: Munazza Gull e-mail ([email protected])

Key Words: Rice, Plant growth, NaCl, Gas exchange, water potential, saline soil

Abstract: Objectives: The main objectives of the present study were the evaluation of two rice cultivars for salinity tolerance potential through the analysis of different gas exchange characteristics and growth water relations in salt stress.

Methods: Basmati 515 and Super Basmati were analyzed using various levels of sodium chloride stress. The completely randomized design with three replications was used for the experiment. The salinity treatments of 40, 80 and 120 mM of NaCl were given in split form with three replications. Soil and water were analyzed for various biochemical characteristics. The differences among means were calculated by STATISTICA Computer Program and analysis of variance technique was used.

Results: The sodium chloride levels negatively reduced the water potential of both rice cultivars. The different levels of salinity negatively decreased the plant osmotic potential. The maximum negative value of osmotic potential (2.8417 MPa) was measured under the salinity level of 120 mM. The rate of transpiration (E) reduced for both rice cultivars under the salinity stress. Under saline conditions the highest reduction in transpiration rate was measured at the salinity level of 120mM (43 %) followed by 80mM (27 %) and 40mM (19 %) for both rice cultivars. The uptake of toxic was more evident in the presence of salt stress than non stressed plants which reduced the uptake of essential nutrients for plants e.g., potassium and chloride.

Conclusion: Addition of NaCl in the growth medium cause adverse effect on the plant dry biomass of both cultivars of rice. It was recommended that, Basmati 515 showed better growth than Super basmati under saline and non saline conditions. So, Basmati 515 could be used in future plan to obtain the best yield in saline environments.

1. Introduction Salt stress is one of the abiotic threats disturbing the plant growth, development and productivity, especially in rice crops in all over the world (Kosova et al., 2013). Under saline environments, the plant cells are not only confronted by osmotic stress but also ionic toxicity and nutritional imbalance (Ashraf et al., 2013). About 10% of arable lands and 24% of irrigated soils through out the world are spoiled by salt stress (Pessarakli and Szabolcs, 2000). The total salt affected area is about 953 M ha which occupied almost 8 % of the surface of land (Singh, 2009). The saline lands cover 6.9 million ha area (Khan et al., 2007) in Pakistan which cause annually a loss of 22 billion rupees due to fall in crop productivity ( Ali et al., 2012) that is the main reason in reduction in progress because about 67% of the population depends on agriculture in Pakistan (Economic survey of Pakistan, 2006). Saline conditions are responsible for reduced and

[SYLWAN., 159(3)]. ISI Indexed

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exhibited growth of plants (Ghoulam et al., 2005). Salinity has caused ample of influences onvarious plants. The accumulation of toxic ions like sodium and chlorides in the water disturb the osmotic imbalance because of the lowering of water potential in plants (Ashraf et al., 2003). The major reason of reduction in plant growth and productivity may be due to salt stress which disturbs the potential of water in the soil and as a result there is less availability of water to plants which ultimately upset all the physiological and biochemical metabolic process in plants (Kausar and Gull 2014). The lowering of water potential caused the reduction in conductance of root that decreases the level of water in upper part of canopy as a result the water stress builds up in leaves (Ghoulam et al., 2005; Kausar and Gull 2014). Growth and development of Plants depends the uptake of essential nutrients from the soil and also the rate of photosynthesis. However the salt stress, influence negative effect on photosynthesis and uptake of these nutrients, which suppressed the rate of photosynthesis which leads directly towards the reduction in growth under saline conditions (Ashraf, 2006). Rice is the staple food and traditional diet for Bruneians. It is main monocot crop because it has an important position in the global food technology. More than half of the peoples of the world use rice in diet (Dobberman, 2005). The world rice production rose up to 8.9 billion in 2030 (Datta, 2004). The rice is major crop and occupied third position after the wheat and cotton in Pakistan (Nawaz et al., 2006). The Pakistani rice varieties especially 'Basmati' is well-eminent for grain length and fragrance in all over the world (Rashid et al., 2001). Water shortage conditions, salt stress and shortage of labor in the country decreases the overall yield of rice (Aslam et al., 2008; Kausar et al 2014). Different techniques are being utilized to increase the production of rice in the saline conditions. The most important techniques is balancing of the nutrients resources and cultivation of salt tolerant varieties on salt affected soils. Keeping in view the importance of rice and salinity the current research project was planned to examine the effect of salt stress. The purpose of the present study was to evaluate the effect of salinity on physiological and biochemical parameters in rice.

2. Materials and Methods The present research work was designed to investigate the effect of various conditions of salt stress on the biochemical and physiological processes of two cultivars of rice. Two cultivars of rice i.e., Basmati 515 and Super Basmati, were used in the experiment. The Nursery of both two cultivars was grown. About 40 days after sowing of seeds the young plants were subjected into plastic pots. Each pot was containing about 8 kg of clay loamy soils. Both the cultivars of rice i.e., Basmati 515 and Super Basmati were analyzed using various levels of sodium chloride stress. The completely randomized design with three replications was used for the experiment. The treatment of salt stress was applied after 15 days of young plants transplantation. The four levels of salinity i.e., 0, 40, 80 and 120 mM of NaCl were used in the experimentation. The salinity treatments of 40, 80 and 120 mM of NaCl were given in split form with three replications. The soil analysis was done using 300 g sample of soil in a plastic beaker. A paste of soil was formed with distilled water by continuously stirring. The extract was obtained from the homogenized paste form soil extractor. Physiochemical characteristics of soil revealed following observations i.e, soil texture clay loam, EC( dS m-1) 0.9-1.3, pH 7.5, Ca (m eqL-1) 5, Mg (m eq L-1) 4, K+ (mg kg-1 ) 20-47, Cl- (m eq L-1) 5-7.5, HCO3 (m eq L-1) 4-6.5.The observations of physiochemical characteristics of water were EC(μS/cm)684, PH7.6,Mg(meqL-1)5,Ca(meqL-1)5,HCO3(meqL-1) 6,Na+(mg kg-1) 62, Cl- (meq L-1) 4-5, K+(mg kg-1) 3-4. The plants of both cultivars were subjected for 0, 40, 80 and 120mm NaCl stress for 120 days after transplantation. After fifteen days of treatments the data ere recorded for water, osmotic and turgor potential of leaves. The data were also analyzed for total rate of carbon dioxide assimilation, rate of transpiration and stomatal conductance. After 120 days of transplantation the experiment was terminated and plants were oven dried at 65 °C for dry weights. The dry weights were determined and their means were calculated.


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2.1 Physiological Parameters The third leaf from top (fully expanded youngest leaf) of two plants from each treatment was used to determine the leaf water potential. The measurements were made during 8.00 to 10.00 a.m. with Scholander type pressure chamber. The same leaf, as used for water potential, was frozen in a freezer below -20oC for seven days, then the frozen leaf material was thawed and cell sap extracted with the help of a disposable syringe. The sap so extracted was directly used for the determination of osmotic potential using an osmometer (Wescor 5500). Turgor potential was calculated as the difference between osmotic potential (s) and water potential (w) values. (p) = (w) - (s) Total rate of carbon dioxide assimilation (A), stomata conductance (gs), and rate of transpiration (E) were estimated by using infrared gas analyzer (Model Cl-340; Analytical development company, Hoddesdon, England). The measurements were recorded from 10.00 a.m. to 01.00 p.m. during that time the leaves were entirely expended and the second leaf of each plant was analyzed for study. The data for the mechanism of gas exchange was measured by the following method. The molar flow of air per unit leaf area 403.3 m mol m-2s-1, Pressure of the atmosphere 99.9 KPa, water vapor pressure into chamber lies from 6.0 to 8.9 m bar, PAR at leaf surface was highest up to 1711 mol m-2s-1, temperature of arranged leaf was from 28.4 to 32.40C, ambient temperature ranged from 22.4 to 27.9 0C and ambient concentration of CO2 was 352 mol mol-1.

2.2 Statistical Analysis The Statistical software COSTAT (v. 6.3, Cohort software, California) was use to calculate the analysis of variance (ANOVA) of data.

3. Results The salinity stress concentrations (40, 80 and 120mm NaCl) reduced the plant dry biomass of both cultivars of rice. The various concentrations of sodium chloride affect differently. The maximum plant dry weight (16.827 g) was calculated under non saline environment of both rice cultivars. In distinction, in saline environment the maximum reduction was estimated at the sodium chloride level of 120mM (61 %) followed by 80mM (53 %) and 40mM (20 %) in both rice cultivars (Fig 1a). The difference of plant dry weight at the saline and non-saline environments was significant (Table1). Table 1: Mean squares analysis of variance (ANOVA) of data for dry weights, water potential, osmotic potential and turgor potential of two rice cultivars at different saline conditions Degree of freedom

Dry weight

Water potential (MPa)

Osmotic potential(MPa)

Turgor Potential(MPa)

Genotypes (G)

1

0.5954 ns

0.01170 **

0.06417ns

0.02106 ns

NaCl treatments (S)

3

17.5544***

0.70208 ***

4.57512 ***

1.71434***

GxS

3

0.0539 ns

0.00063 ns

0.00303 ns

0.00494 ns

Error

16

0.2122

0.00155

0.01911

0.02214

Total

23

*, **, ***= significant at 0.05, 0.01 and 0.001 levels, respectively. ns=non-significant The greatest fresh weight observed in Basmati 515 was (4.5092 g) and smallest measured in Super Basmati was (4.1942 g) over all. The difference between the plant dry weights of both rice cultivars was non-


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significant. Sodium chloride levels negatively reduced the water potential of both rice cultivars. The varietal response against sodium chloride stress of both rice cultivars was non-significant (Table1). The greatest value of water potential observed in Super Basmati was (1.0658 MPa) and smallest observed in Basmati 515 was (1.0417 MPa) over all. The interaction of treatments and varieties was non-significant, indicated that the rice cultivars responded similarly to the sodium chloride stress. The different levels of sodium chloride influenced differently. The highest value of water potential (1.50 MPa) was estimated under the sodium chloride level of 120 mM. In distinction, the maximum reduction under non- saline environment was estimated followed by 40mM (13.040 %) and 80mM (14.647 %) in both rice cultivars (Fig 1b). The different levels of salinity negatively decreased the plant osmotic potential of both the cultivars of rice. The maximum negative value of osmotic potential (2.8417 MPa) was measured under the salinity level of 120 mM. In contrast, the minimum negative value of osmotic potential found under non- saline conditions (0.8402 MPa) followed by 40mM (1.3383 MPa) and 80mM (2.0417 MPa) in both rice cultivars (Fig 1c).The various salinity concentrations decreased the value of turgor potential in both rice cultivars. The various levels of salt stress adversely affect the rate of turgor potential differently. The highest rate of turgor potential (1.4700 MPa) was recorded under saline conditions of 120mM of both rice cultivars. In opposition, maximum decrease in the rate of turgor potential was observed under non saline conditions (0.1302 MPa) followed by 40 mM (0.4467 MPa) and 80 mM (0.9333 MPa) of both cultivars of rice (Fig 1d). The all levels of sodium chloride stress decreased the rate of photosynthesis of both the rice cultivars. The various sodium chloride levels affect differently. The maximum rate of photosynthesis (18.533 m mol/m 2 /s) was determined under the non saline environment in both cultivars of rice. Whereas, under the saline environments the maximum reduction was estimated at the level of 120mM (68 %) followed by 80mM (47 %) and 40mM (26 %) in both rice cultivars (Fig 2a). The difference of rate of photosynthesis under the saline and non-saline environments was significant (Table 2). The varietal response of both rice cultivars against sodium chloride stress was significant (Table 2). The highest rate of photosynthesis evaluated in Basmati 515 was (13.400 m mol/m2/s) and smallest observed in Super Basmati was (11.938 m mol/m 2/s) over all. The difference between the rates of photosynthesis of both rice cultivars was significant. The interaction of treatments as well as the varieties of both cultivars of rice was non- significant which exhibited that both rice cultivars showed similar performance towards the sodium chloride stress. It was approved that the rice cultivars exhibited maximum value of rate of photosynthesis under non saline conditions as compared to the stressed conditions (Table 2). Table 2: Mean squares analysis of variance (ANOVA) of data for net rate of photosynthesis, rate of transpiration and stomatal conductance of two rice cultivars at different saline conditions Degree of freedom

Net rate of photosynthesis

Rate of transpiration

Stomatal conductance

(μ mol CO2 m-2 S-1)

m mol H2O m-2 S-1

12.819 ***

4.82407 ***

5.9203

151.255***

8.35401 ***

10.0556 ***

(C) (m mol H2O m-2 S-1)

Genotypes (G)

1

NaCl treatments (S)

3

GxS

3

0.633 ns

0.10888 ns

0.4355

Error

16

0.328

0.12817

0.0460

Total

23

***

***

*, **, ***= significant at 0.05, 0.01 and 0.001 levels, respectively. ns= non-significant


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The rate of transpiration (E) reduced of the both rice cultivars under the salinity stress. The different concentrations of salinity stress influenced the rate of transpiration differently. The highest rate of transpiration measured was (5.8650 m mol/m 2/s) in non saline conditions of both cultivars of rice. In contrast, under saline conditions the highest reduction was measured at the salinity stress level of 120mM (43 %) followed by 80mM (27 %) and 40mM (19 %) of both cultivars of rice (Fig 2b). The difference of rate of transpiration under the saline and non-saline conditions was significant (Table 2).The response of varieties of both the rice cultivars towards salinity stress was non-significant (Table 2). The maximum rate of transpiration estimated in Basmati 515 was (4.8850 m mol/m 2/s) and minimum rate evaluated in Super Basmati was (4.2117 m mol/m 2/s) over all. The difference in between the rate of transpiration of both rice cultivars was non- significant. It was concluded that the cultivars of rice explore the highest value of rate of transpiration in non saline environments in contrast to the stressed environments (Table 2). The various levels of salt stress adversely affects on the rate of stomatal conductance. The maximum rate of stomatal conductance (6.6750 m mol/m 2 /s) was recorded under the non saline or control conditions of both rice cultivars. In opposition, maximum decrease in the rate of stomatal conductance was observed under saline conditions of 120mM (37 %) followed by 80mM (23 %) and 40mM (16 %) of both cultivars of rice (Fig 2c). The interaction of varieties versus treatment was non – significant of both rice cultivars and they both similarly performed under salt stress. It was showed that the rice cultivars exhibited the maximum value of the rate of stomatal conductance under non- saline environments in contradiction to the stressed conditions (Table 2).

(a)

(c)

(b)

(d)

Fig. 1 Plant dry weight (a), water potential (b), osmotic potential (c), turgor potential (d) of two cultivars of rice under different saline conditions


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(a)

(b)

(c)

Fig 2. Net rate of photosynthesis (a) rate of transpiration (b) stomatal conductance (c) of two cultivars of rice under different saline conditions

4. Discussion Various abiotic stresses are accountable for the decline of growth and development of a variety of crops. Present research work depicted that salt stress badly inhibited the plant growth and development by hindering various physiological and biochemical parameters in both rice cultivars. The deterioration of growth, physiological and biochemical parameters of different crops by salinity has been reported previously (Tavallali et al., 2009). Similar findings were also observed at higher salinity levels which cause reduction in water contents, rate of photosynthesis and negative effects on biomass production (Ashraf et al. 2003; Ashraf et al., 2013; Kausar et al. 2014). Salinity stress adversely affected the gas exchange characteristics of both rice varieties i.e. rate of transpiration, fixation rate of carbon dioxide and stomatal conductance which may be as a result of chlorophyll degradation and closing of stomata in stressed environments (Ashraf et al., 2013). Parallel findings get supported by Akhtar et al. (2001) and Ashraf et al. (2006). Under the salinity stress a decrease in the physiological attributes like water potential, osmotic potential and turgor potential was determined by Wahid et al., 2004; Almodares et al. 2007; Abogadallah et al., 2010. The current investigation exhibited a decrease in dry biomass production and physiological parameters i.e., water potential, osmotic potential, turgor potential, carbon dioxide fixation rate, photosynthetic rate and stomatal conductance were also severely affected by the salt stress. Salt stress inhibited the growth of different crops as observed in both rice cultivars that salinity stress decreased the growth of different parameters as reported by (Khan et al., 2007) in grasses that salt stress reduced the growth and other attributes. Similar mechanism of salinity was explored by (Rezaei et al., 2012) on different growing stages of rice and concluded that salinity reduced all morphological, physiological and biochemical parameters of plants.

Conclusion and recommendations The study was conducted to find the effect of salinity stress on plant biomass production, gas exchange characteristics and water potential ability in two rice cultivars. It is concluded that addition of NaCl in the growth medium causes adverse effect on the plant dry biomass and water potential ability of both rice cultivars. It was recommended that, Basmati 515 showed better growth than Super basmati under saline and


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non saline conditions. So, Basmati 515 could be used in future plan to obtain the best yield in saline environments.

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