Response of Bean Plants to Sodium Chloride and Sodium Sulphate Salinization12

Bean plants were grown under constant levels of sodium chloride and sodium sulphate salinity, and under changing levels of sodium sulphate salinity. Although growth was suppressed similarly by the two types of salinity when expressed on an osmotic basis, other parameters showed different responses according to salinity type. Chloride-salinated plants have thicker leaves with higher water content than the sulphate and control plants. The relative water content of the sulphate plants was somewhat lower. Transpiration rates were suppressed more by chloride salinity. Osmotic adjustment seems to be faster under chloride salinity and was of a different nature. Chloride accumulated to much higher levels than sulphate. Increase in potassium ion concentration and decrease in calcium ion concentration was more pronounced under sulphate salinity, but the total cation concentration in the sap was similar for all treatments. As a result, the inorganic ions' electrical balance was more negative under chloride salinity. Leaf expansion in the changing-level treatment reflected rapidly the variation m substrate salinity. However, total yield was suppressed by the changing treatments to a similar extent as by constant salinity. According to other parameters the changing regime may be considered as a shorter period of exposure to salinity.