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

Abstract

AbstractCalcium (Ca2+) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca2+ 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 Ca2+ was examined using plants grown in 25% modified Hoagland solution at different Na+ : Ca2+ ratios. In control plants (1 mM Ca2+; 1 mM Na+) surplus Ca2+ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K+ and leaf Mg2+ concentrations, and inhibition of CO2 assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca2+ effect was not cation‐specific since similar results were found in plants supplied with high external Mg2+ or with a combination of Ca2+ and Mg2+. Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg2+ activity, and inhibition of stomatal opening and CO2 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 Ca2+ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO2‐assimilation rate in plants exposed to the highest Ca2+ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca2+, supplemental Mg2+, 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 Ca2+‐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.