Cl− More Detrimental Than Na+ in Rice Under Long-Term Saline Conditions

Rice is considered sensitive to salinity and hence, improving the salinity tolerance of rice is desired to increase productivity. Most research on salinity tolerance for the growth and grain yield of rice focuses on the toxicity of sodium (Na+) and not chloride (Cl−); the information on the negative effects of Cl− on rice is still limited. To learn the difference in the long-term effects of Na+ and Cl− on the whole plant and grain productivities, three rice varieties differing in salinity tolerance were grown in pots irrigated by water with NaCl and KCl in the same molar concentration. The whole plant dry weight and grain yield in all varieties decreased to the same extent after NaCl and KCl treatments compared to the control during the full heading and maturity stages. However, Na+ content in shoots of all varieties under NaCl treatment were higher at all stages than that under KCl treatment and the control. In the most cases, the Cl− content in plants was similar in the NaCl and KCl treatment groups. There was a negative significant correlation between the relative dry weight and grain yield (treated/control) and the Cl− content in the plants. From these results, it was suggested that plant dry weight and grain yield under long-term salinity conditions was reduced by Cl− toxicity rather than Na+ toxicity.