Microbial inoculants improve salt tolerance of Sesbania cannabina by regulating rhizosphere microbial communities and nutrient cycling genes

Soil salinization constrains plant growth and soil ecological function, microbial inoculation offers a sustainable route for saline-alkali soils. We evaluated how inoculants influence Sesbania cannabina growth and rhizosphere processes under different NaCl levels (0, 150, 300 mM). Seedlings were inoculated with either a synthetic community (Syncom; T1), a single salt-tolerant nitrogen-fixing strain (T2), or left uninoculated (CK). We measured plant growth, antioxidant enzyme activities, soil nutrient pools, rhizosphere microbial community structure, and relative abundance of nitrogen and phosphorus cycling genes. Inoculation significantly promoted plant height and fresh weight ( p < 0.05), and increased AN, TN, and OM, with Syncom (T1) providing the strongest growth response under salt stress (150 mM NaCl). Inoculation also elevated the abundance of nitrogen and phosphorus cycling genes. Path analyses integrating soil properties, microbial communities, functional genes, and plant traits supported a cascading framework in which soil nutrients and phosphorus cycling functional genes directly influence plant defense. Overall, appropriate microbial inoculants (T1) alleviate salt stress in S. cannabina by coordinating soil-microbe-plant interactions, highlighting their potential for remediation of saline-alkaline soils.