Combined use of AMF and chitosan improves soybean yield and soil quality in cold regions by restructuring rhizobacterial communities and network stability

Cold temperatures and seasonal freeze-thaw cycles in cold regions are key environmental factors limiting soybean growth, development, and yield improvement. These conditions frequently cause soil structure degradation, inefficient nutrient cycling, and suppressed microbial activity. Single agronomic measures are difficult to achieve systematic improvement. Arbuscular mycorrhizal fungi (AMF) and chitosan, as green regulatory materials, have been individually proven to promote crop growth and optimize rhizosphere microenvironments. However, their synergistic mechanisms in regulating rhizobacterial community structure and network stability, and simultaneously enhancing soil quality and soybean productivity in cold-region systems, remain unclear. Therefore, this study established four treatments: CK (control), FM (inoculation with Funneliformis mosseae alone), Q (chitosan application alone), and FQ (AMF + chitosan). Through cold-region field experiments, we explored their individual and combined effects on soybean growth, soil quality, and rhizosphere bacterial communities. Results showed that FQ significantly optimized soybean growth traits and yield components. The soil quality index (SQI) reached the highest level among all treatments. Soil urease, alkaline phosphatase, and β-glucosidase activities were all significantly enhanced. Microbial community analysis showed that FQ treatment significantly optimized bacterial α-diversity and composition, enriched beneficial stress-resistant groups, strengthened bacterial network properties, and shifted community assembly to stochastic-deterministic synergy dominated by stochastic dispersal. In summary, co-application of AMF and chitosan can synergistically reshape rhizobacterial community structure, enhance interspecific networks, and improve soil quality, thereby promoting the soybean-soil-microbe system in cold regions and offering a theoretical foundation and technical support for green high-yield soybean production and soil health management.