Optimal Concentration of Zinc Sulfate in Foliar Spray to Alleviate Salinity Stress in Glycine soja

Zinc has previously been reported to alleviate salinity stress in plants. In this study, we monitored various biomass and chlorophyll fluorescence parameters to determine the optimum zinc sulfate concentration that can be used as foliar spray to alleviate salinity stress in Glycine soja. The plants subjected to a series of salinity levels (NaCl concentration of 0, 100, 200, and 300 mmol L-1), applied via the nutrient solution, were sprayed with different concentrations of zinc sulfate (0, 5, 10, 15, 20, 25 µmol L-1). The results showed that the biomass and chlorophyll fluorescence parameters of seedlings were significantly affected by salt stress (P < 0.05). However, zinc sulfate sprays helped the plants to cope with the stress condition. The zinc sulfate concentrations that helped G. soja to cope with the salinity stress of 100, 200, and 300 mmol L-1 were 15 to 20, 15 to 20, and 10 to 20 µmol L-1, respectively. Lower zinc concentration was ineffective in alleviating stress and higher zinc concentration inhibited plant growth because of toxicological damage to plants. The zinc sulfate spray of 15 µmol L-1 was found to be the most appropriate at all salinity stress levels. The growth measurements such as true leaves part and dry weight of total seedlings were in agreement with the chlorophyll fluorescence parameters, indicating a visible enhancement of leaf photosynthetic activity at 10-20 µmol L-1 zinc concentrations.