Salt reponses of lettuce to salinity. II. Effect of calcium on growth and mineral status

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Abstract
The effect of Ca2+ on the salt tolerance of two lettuce cultivars (Lactuca sativa L. cv. Calmar and cv. Climax), differing in their salt tolerance, was investigated. The plants were grown in a 0.5 modified Hoagland solution. Treatments of NaCl or NaCl plus CaSO4 (final Na+:Ca2+ ratio approximately 7:1 on a mol m–3 basis) were added to the nutrient solution when the second leaf above the cotyledons appeared. The plants were harvested 20 days after the treatments began. Plant growth was reduced by salinity (0 to 120 mol m–3 NaCl), but addition of supplemental Ca2+ did not affect salt tolerance. The mineral status of the plant, however, was affected by the Ca2+ treatments. The Ca concentrations in both root and shoot, and the Mg concentrations in the shoot were higher than those in the low Ca2+ treatment. High external Ca2+ decreased the absorption of Na. The high Ca2+ treatments did not affect Cl–1 tissue concentrations, nor shoot or root growth. The effect of high Ca2+ concentration on K tissue concentrations remained equivocal. The differential responses of these elements to high Ca2+ suggested that selective ion transport was affected by salinity and Ca2+ treatments.