Interactive effect of salinity and supplemental calcium application on growth and ionic concentration of soybean and cucumber plants

Effects of the application of supplemental Ca on the growth and mineral content and on the ion concentration of the sap of individual plant parts were investigated in soybean and cucumber plants that were treated with 50 mM NaCl. Treatment with NaCl reduced the growth of both kinds of plants and also the photosynthetic rate of the first cucumber leaf and the first soybean trifoliolate leaf at 7 d after the treatment. Increase of the Ca concentration in the medium alleviated the reduction of growth and photosynthetic rate, and its effect was more conspicuous in cucumber than in soybean. In the plant parts that contained high amounts of Na and Cl but a low amount of K with the NaCl treatment, the application of supplemental Ca decreased the Na content, increased the K content but did not affect appreciably the uptake and translocation of Cl. Because increasing Ca concentrations in the medium affected the contents of cations such as Na and K, the ameliorative effect of Ca was considered to be remarkable in cucumber plants where a high Na content resulted in growth inhibition due to salinity. On the contrary, the effect of supplemental Ca application appeared to be weak in soybean plants because in these plants, Cl might induce growth inhibition due to salinity and the application of supplemental Ca did not affect substantially the Cl status. In the NaCl treatment, the decrease in the concentrations of anions other than Cl(-) was more conspicuous in soybean plants than in cucumber plants. Hence anion imbalance due to excess Cl(-) might induce growth inhibition in soybean. In cucumber plants, the total cation concentration was slightly changed whereas the Na(+) concentration increased with the decrease in the K(+) concentration by the NaCl treatment. Cation imbalance that was caused by increased Na(+) concentration and decreased K(+) and Mg(2+) concentrations might be responsible for the growth inhibition in cucumber plants. Increase of the Ca concentration in the medium affected only slightly the occurrence of such imbalance of cations or anions in both kinds of plants.