NaCl and Na2SO4 Salinities Have Different Impact on Photosynthesis and Yield-Related Parameters in Rice (Oryza sativa L.)

To elucidate the comparative effect of chloride and sulfate salinities on photosynthesis and yield components in rice, plants ofOryza sativa(cv. I Kong Pao (salt-sensitive)) were exposed in nutrient solutions to 20 mM Na(2)SO(4)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 (A(N)) at the seedling and tillering stages, while the intercellular CO(2)concentrations (Ci) remained unaffected. Instantaneous transpiration (E) and stomatal conductance (g(s)) 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 Na(2)SO(4)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.