Influence of calcium silicate on growth, physiological parameters and mineral nutrition in two legume species under salt stress

Cowpea and kidney bean plants were grown in a hydroponic system, and the effect of calcium silicate supplied to the nutrient solution under salt stress was investigated. The plants were subjected to four different treatments: (1) nutrient solution alone (C), (2) nutrient solution + 40 mmol l(-1) NaCl (NaCl), (3) nutrient solution + 40 mmol l(-1) NaCl + 0.5 mmol l(-1) CaSiO3 (NaCl + Si-1) and (4) nutrient solution + 40 mmol l(-1) NaCl+1 mmol l(-1) CaSiO3 (NaCl + Si-2). The results showed that, in both species, salinity reduced all growth variables but silicate supplementation however partly overcame this growth reduction. Addition of silicate in NaCl-stressed plants maintained membrane permeability. Net photosynthesis, chlorophyll content, stomatal conductance and transpiration were higher in plants under control treatment, and the inclusion of silicate in the nutrient solution resulted in a slight increase in these plant parameters. Intercellular CO2 was slightly higher in plants under silicate treatment than in plants under control or NaCl treatment. Calcium concentration in shoots and roots in both species was slightly higher in the treatments where silicate was added. Potassium concentration for salt treatment was reduced in shoot and root of both species in the absence of silicate. Sodium and chloride concentration in shoots and roots in both species were slightly higher in the presence of NaCl and were slightly reduced in the plants under silicate treatments. The results suggest that, in hydroponically grown plants, the inclusion of silicate in the nutrient solution is beneficial because it improves growth, physiological parameters and may contribute to a more balanced nutrition by enhancing nutrient uptake under NaCl-stressed conditions. Added calcium silicate may ameliorate the parameters affected by high salinity, may reduce sodium and chloride, and can slightly increase calcium and potassium concentrations in shoots and roots of salt-stressed cowpea and kidney bean.