Abstract
To elucidate the comparative effect of chloride and sulfate salinities on photosynthesis and yield components in rice, plants of Oryza sativa (cv. I Kong Pao (salt-sensitive)) were exposed in nutrient solutions to 20 mM Na2SO4 or 40 mM NaCl (electrical conductivity of c.a. 4.30 dS m−1 for both solutions) from seedlings to maturity stage. Both types of salt induced a strong decrease in net photosynthesis (AN) at the seedling and tillering stages, while the intercellular CO2 concentrations (Ci) remained unaffected. Instantaneous transpiration (E) and stomatal conductance (gs) decreased at the tillering and seedling stages, respectively, only in plants exposed to NaCl. Chloride salinity also strongly decreased photosynthetic pigments, while no impact was detected in response to Na2SO4. All yield-related parameters were affected by salinities, but NaCl was significantly more deleterious than Na2SO4 for the mean number of tillers produced per plant, spikelets sterility and non-viable pollen percentage. In contrast, both types of salinity similarly impacted the percentage of fertile tillers and 1000-grain weight. At the grain level, more than 90% of toxic ions (Na+, excess of Cl− and S6+) accumulated in the hulls, thus preserving the internal part of the caryopses from toxic ion injuries.
Highlights
Soil salinity is a major environmental constraint to crop production, affecting millions of hectares of land throughout the world, and costing billions of dollars every year
Instantaneous transpiration decreased at the tillering stage for plants exposed to NaCl salinity, but not for control or plants exposed to Na2 SO4
Stomatal conductance was reduced in response to NaCl only, while both types of salinity reduced gs at the tillering stage
Summary
Soil salinity is a major environmental constraint to crop production, affecting millions of hectares of land throughout the world, and costing billions of dollars every year. High contents of soluble salts in the soil are reported in numerous areas of the world. Rice (Oryza sativa L.) is extremely sensitive to salinity and yield decreases by more than 10% for every unit (dS/m) increase in electrical conductivity of root-zone saturated soil extract above 3 dS/m [3]. Salt sensitivity depends on the plant developmental stage. Numerous authors reported that salinity delays flowering in rice and has a negative impact on several yield components, including the number of panicles, fertile tillers and spikelets per plant, floret fertility and grain size [7,9,10,11,12,13]. Differential sensitivity during developmental stage is a major issue in the management of saline water for irrigation
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