Physiological response and ion accumulation in two grasses, one legume, and one saltbush under soil water and salinity stress

A glasshouse-pot trial using four levels of soil moisture (>100%, 90%, 75%, and 60% field capacity) and three levels of salinity (1.0dSm-1, 3.5dSm-1, and 6.0dSm-1) was done to evaluate Na+, K+, and Cl- accumulation capacity and the physiological responses (net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, quantum efficiency of PSII, and non-photochemical quenching) in Melilotus siculus, Tecticornia pergranulata, Cynodon dactylon , and Thinopyrum ponticum. Results reveal that the combined effects of soil water and salinity had a significant effect on Na+ and Cl- accumulation and not on that of K+. Concentrations of Na+ and Cl- and non-photochemical quenching increased significantly whereas, the net photosynthetic rate (Pn), stomatal conductance (gs), and intercellular CO2 concentration decreased significantly in the tested plants, because of salinity. Salinity had no significant effect on the maximum quantum yield and relative water contents in shoots. Soil moisture had a significant effect on Na+, K+, and Cl- accumulation and the physiological responses in tested plants. T.pregranulata accumulated the highest concentrations of Na+ and Cl- and had the lowest Pn. C.dactylon accumulated the lowest concentrations of Na+ and Cl-, whereas Pn was the highest. No strong positive correlation between Pn and gs was evident in tested plants. We indicate that the reduced physiological performance was because of non-stomatal activities. Na+ and Cl- accumulation capacity in the tested plants was in the following order: T.pergranulata>M.siculus>T.ponticum>C.dactylon. C.dactylon, a C4 plant, accumulated lower salt ions than the other three C3 plants.