Arbuscular mycorrhizal fungi enhanced salt tolerance of Gleditsia sinensis by modulating antioxidant activity, ion balance and P/N ratio

Gleditsia sinensis is a valuable tree species with important pharmaceutical uses. However, high soil NaCl concentration limits its growth in saline soil, including coastal areas. This study aimed to investigate the effects of arbuscular mycorrhizal fungi (AMF) on G. sinensis salinity tolerance and reveal its underlying physiological mechanism. A greenhouse experiment was performed. G. sinensis seedlings with and without AMF inoculation were subjected to four salinity levels: 0- (control), 50-, 100-, and 150-mM NaCl. After 2 months, the seedlings were harvested and analyzed for growth and biochemical parameters (antioxidant enzyme activity, superoxide anion content, malondialdehyde content, nutrient concentration, ion concentration, etc.). High AMF colonization rates (over 95%) and high mycorrhizal dependencies (over 75%) were observed across all NaCl levels. AMF effectively enhanced the salinity tolerance of G. sinensis seedlings by enhancing leaf stomatal conductance inducing higher net photosynthetic rates; improving peroxidase, catalase, and superoxide dismutase activities resulting in higher membrane stability indexes, lower superoxide anion and malondialdehyde contents in leaves and roots; increasing P/N ratio to mitigate P-limited biomass products; selectively absorbing less Na + and more Ca 2+ in their tissues to alleviate ion toxicity and maintain more favorable ion balances (e.g., K + /Na + ) in their tissues. The results suggested AMF could effectively improve the salinity tolerance of G. sinensis , owning the great potential for afforestation and rehabilitation of G. sinensis in coastal areas.