Combined Effects of Native AMF Inoculation and Straw Incorporation on Maize (Zea mays L.) Growth and Soil Biological Functions in Coastal Saline Soil

Soil salinization severely threatens global agricultural productivity. Arbuscular mycorrhizal fungi (AMF) and straw incorporation are promising biological amendments for salt-affected soils, but their interactive effects on crop growth and soil biological processes remain poorly understood. In this study, a sterilized-soil pot experiment was conducted to evaluate the individual and interactive effects of a native AMF strain (Claroideoglomus sp., AM5) inoculation and straw incorporation (SI) on maize performance traits, soil properties, and bacterial communities in saline soil. Four treatments were established, including control (CK), AM5, SI, and AM5 + SI. The combined treatment exerted significant synergistic effects. AM5 successfully colonized maize roots with a 72% mycorrhizal infection rate (MIR) and 106% mycorrhizal dependence, and SI further enhanced colonization (80% MIR, 127% MD). Compared with CK, AM5 + SI increased aboveground fresh and dry weights by 61.5% and 48.7%, and Chlorophyll a and net photosynthetic rate by 35.4% and 147.3%, respectively. Soil physicochemical and biological conditions were improved, as evidenced by reduced topsoil and subsoil electrical conductivity (55.2% and 40.6%, respectively), increased nutrient availability (e.g., available phosphorus and potassium contents), and enhanced soil hydrolase activities (sucrase, urease, and alkaline phosphatase), particularly in subsoil. The combined treatment also restructured the soil bacterial community in both layers, increasing microbial diversity and selectively enriching beneficial phyla (e.g., Pseudomonadota, Actinomycetota), whose abundances were closely correlated with improvements in soil properties. These results confirm our hypothesis that the co-application of native AM5 and straw incorporation exerts synergistic effects on soil biological functions, leading to enhanced maize growth and soil fertility in saline soil. Random forest and PLS-SEM revealed that these soil-microbe changes were accompanied by greater maize biomass accumulation, photosynthetic capacity, and antioxidant defense, with distinct regulatory pathways between topsoil and subsoil. These findings indicate that co-application of native AMF and straw incorporation may effectively improve soil biological functions and maize performance in coastal saline soil, providing mechanistic insights for biological remediation using native AMF and organic residues.