Sodium‐calcium interactions with growth, water, and photosynthetic parameters in salt‐treated beans

Calcium (Ca 2+ ) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca 2+ did not improve growth in Phaseolus vulgaris L. cv. Contender under high‐saline conditions and negatively affected several physiological parameters in nonsalinized plants. The response to supplemental Ca 2+ was examined using plants grown in 25% modified Hoagland solution at different Na + : Ca 2+ ratios. In control plants (1 mM Ca 2+ ; 1 mM Na + ) surplus Ca 2+ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K + and leaf Mg 2+ concentrations, and inhibition of CO 2 assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca 2+ effect was not cation‐specific since similar results were found in plants supplied with high external Mg 2+ or with a combination of Ca 2+ and Mg 2+ . Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg 2+ activity, and inhibition of stomatal opening and CO 2 assimilation. However, NaCl (50 and 100 mM NaCl) enhanced leaf K + concentration and water‐use efficiency. At 100 mM NaCl, leaf water content also significantly increased. Supplemental Ca 2+ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO 2 ‐assimilation rate in plants exposed to the highest Ca 2+ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca 2+ , supplemental Mg 2+ , and NaCl salinity suggest that P. vulgaris cv. Contender has a high non‐ion‐specific salt sensitivity. On the other hand, the improvement in gas‐exchange parameters in Ca 2+ ‐supplemented plants by high NaCl could be the result of specific Na + ‐triggered responses, such as an increase in the concentration of K + in the leaves.