Effects of Exogenous Calcium on Adaptive Growth, Photosynthesis, Ion Homeostasis and Phenolics of Gleditsia sinensis Lam. Plants under Salt Stress

Salinity is the main environmental factor responsible for limited plant growth in many areas of the world. Gleditsia sinensis Lam. is a shelter forest tree species that does not require high-quality soil and can even grow in mild saline soil. This study mainly explored the tolerance of G. sinensis to salt and the effect of exogenous calcium addition on the growth of G. sinensis in a salinized soil. The concentrations of NaCl were set as 0 mmol/L, 100 mmol/L, and 200 mmol/L. Compared with the control, under the NaCl treatment of 200 mmol/L, it was observed that the leaves of G. sinensis turned yellow, the electrical conductivity significantly increased, and the water content and the chlorophyll content significantly decreased, which is probably unfavorable for growth. Our study showed that the addition of 10 mmol/L exogenous calcium chloride under salt stress had a positive effect on the growth and photosynthetic characteristics of G. sinensis. Moreover, the addition of exogenous calcium attenuated the cytotoxicity caused by Na + under salt stress and promoted the equilibrium of ion homeostasis. More importantly, the addition of exogenous calcium ions was beneficial for the survival of G. sinensis plants on salinized land and the increase of effective active ingredient content including phenolic compounds, which is of direct significance for improving environmental problems such as desertification of saline-alkali land. In conclusion, we investigated the effect of salt treatment on G. sinensis , as well as the positive effects of exogenous calcium on the survival and growth of G. sinensis in salt environment, which provided a scientific basis for the targeted cultivation of G. sinensis in salinized land and the effective utilization of salinized and alkaline land.