Effects of Ectomycorrhizal Fungi on the Physiological and Ecological Characteristics of Larix gmelinii under Salt Stress

Soil salinization has become a major constraint on afforestation and forest regeneration in Northeast China, limiting the growth and development of Larix gmelinii . Enhancing the salt tolerance of L. gmelinii is therefore of considerable importance, and ectomycorrhizal fungi (ECMF) inoculation has been shown to improve plant stress resistance. However, the mechanisms by which ECMF enhance salt tolerance in L. gmelinii remain poorly understood. In this study, L. gmelinii seedlings inoculated with an ECMF consortium consisting of Boletus edulis and Gomphidius rutulus were subjected to 120 mM NaCl stress. Photosynthetic characteristics, antioxidant enzyme activities, osmotic adjustment substances, ion contents, and metabolite profiles were analyzed to elucidate the physiological mechanisms underlying ECMF-mediated salt tolerance. The results showed that ECMF inoculation promoted the growth of L. gmelinii under salt stress. ECMF alleviated the decline in net photosynthetic rate caused by stomatal limitation and maintained photosynthetic performance. Under salt stress, L. gmelinii primarily scavenged reactive oxygen species through increased peroxidase activity, activation of ascorbate and aldarate metabolism, and enhanced flavonoid biosynthesis. Furthermore, ECMF inoculation enhanced galactose metabolism and amino acid biosynthesis, resulting in increased soluble sugar and soluble protein contents and improved osmotic adjustment capacity. In addition, ECMF improved ion homeostasis by promoting K⁺ translocation to shoots while restricting Na⁺ transport and enhancing Na⁺ retention in roots. These findings demonstrate that ECMF enhance salt tolerance in L. gmelinii through coordinated regulation of photosynthesis, antioxidant defense, osmotic adjustment, and ion homeostasis, providing a theoretical basis for the application of ECMF in saline-alkali land afforestation.