Adjustment, growth, photosynthesis and transpiration of sugar beet plants exposed to saline conditions

Abstract

Abstract Salinity adjustment and its relation to growth, photosynthesis and transpiration of sugar beet plants was investigated. Plants were exposed to salinity (90, 180, 270, 360 mM NaCl) in the growth media for different durations up to 14 days, and various growth parameters, photosynthesis and transpiration rates were determined during this period. Complete osmotic adjustment was obtained after 14 days of plant exposure to 90–270 mM NaCl, as suggested by the constant difference between leaf Ψw and solution Ψo on the one hand, and between leaf Ψw and leaf sap Ψo on the other hand. Concentrations of inorganic ions in total leaf water, calculated from the contents of Cl−, Na+, K+, Ca2+ and Mg2+ after 3 days of exposure to salinity, could account for 40% of the required adjustment. After 7 days of exposure it accounted for over 80% of this requirement. Dry matter accumulation rates were significantly reduced in leaves during the initial 3 days following salinization at all NaCl concentrations. A recovery was then found at NaCl concentration up to 180 mM, and leaf dry matter growth rates reached the control values. No such relief was found at high concentrations. Recovery of fresh weight accumulation (as evaluated by total leaf water content) was slower and not complete within 7 days. Roots were more sensitive to salinity than leaves; dry weight accumulation in roots was inhibited even at 90 mM NaCl and no relief in accumulation was found. Leaf expansion was more sensitive to salinity than was dry weight accumulation, leading to an increase in leaf dry weight per unit area. Leaf protein content was also increased even more under salinity, while chlorophyll concentration was not affected. Transpiration rate, as well as leaf diffusive conductance to water vapor, was reduced by salinity.