Effects of salinity on ionic content, water relations and gas exchange parameters in some citrus scion—Rootstock combinations

Abstract

The effect of the scion on Cl − and Na + accumulation properties of rootstocks was investigated using grafted plants treated with 0 or 75 mM Cl − for 11 weeks. The grafted plants were ‘Valencia’ orange, ‘Taylor’ lemon and ‘Ellendale’ tangor scions on ‘Cleopatra’ mandarin rootstock, and ‘Valencia’ orange scion on rough lemon rootstock, abbreviated V/C, T/C, E/C and V/R, respectively. Own-rooted rough lemon (R) was also included in the study. During or after the period of salt treatment, measurements were made of gas exchange rates, chlorophyll concentration, water and osmotic potentials of single leaves and Cl −, Na + and K + contents of leaves, stems and roots. There was a limit to loading of Cl − in roots of both rootstocks under all scions. Scions on ‘Cleopatra’ mandarin accumulated less Cl − in their stems and leaves than V/R and R, demonstrating that Cl − accumulation in shoots was rootstock-dependent. Sodium accumulation in shoots seemed to be more scion-dependent. Salinity caused a decrease in K + concentrations in all roots and in most shoots. Salt treatment increased turgor pressure in leaves of all combinations. All salt-treated scions had lower chlorophyll levels except for V/C, and the changes were significant for V/R and R. Control plants (not receiving salt) had significantly lower rates of photosynthesis at the end of the experiment, probably due to the aging of leaves. Stomatal closure was one reason for the decrease in rates of photosynthesis and transpiration in salt-treated plants. Photo- and dark-respiration also decreased in these plants. Stomatal closure in salt-treated plants was not related to changes in leaf water potential because osmotic adjustment occurred in all cases. Regression analysis showed that Na + exerted a greater effect on reductions of photosynthesis and transpiration than did Cl −. A significant correlation also existed between chlorophyll content and rate of photosynthesis.