Stand Density Drives Soil Microbial Community Structure in Response to Nutrient Availability in Larix gmelinii var. principis-rupprechtii (Mayr) Pilger Plantations

Sustainable forest management requires a comprehensive understanding of how stand density regulates soil ecological processes. We examined a <i>Larix principis-rupprechtii</i> plantation under three thinning retention densities (High-HD; Medium-MD; Low-LD) and an unthinned control (CK), with soil samples collected from four depth layers (0-10, 10-20, 20-30, and 30-40 cm). This study investigated the effects of stand density on soil properties and microbial communities in a <i>Larix principis-rupprechtii</i> plantation by combining high-throughput sequencing with soil physicochemical analysis to identify the optimal density regime for maintaining soil health. Results demonstrated the following: (1) Moderate-density (MD) management best balanced the stability of soil ecosystem structure, showing superior water retention, organic carbon content, and microbial diversity in the 0-30 cm soil layer. The mechanism underlying these improvements can be attributed to the moderately open canopy structure in MD stands, which facilitated efficient litter decomposition and drove functional complementarity between <i>Basidiomycota</i> (enhancing cellulose degradation capacity) and <i>Acidobacteriota</i> (adapted to oligotrophic conditions). (2) Redundancy analysis revealed that soil pH and available nutrients (AK, AP) were key environmental factors driving microbial community restructuring: <i>Actinobacteriota</i> dominated in neutral, phosphorus-rich environments, while <i>Acidobacteriota</i> thrived under acidic, phosphorus-limited conditions. Fungal communities showed high sensitivity to management intensity, with significant shifts between <i>Ascomycota</i> and <i>Basidiomycota</i>, whereas bacterial communities remained relatively stable due to functional redundancy. We recommend the adoption of moderate-density management as a sustainable practice to enhance soil nutrient cycling and maintain microbial diversity, thereby providing scientific support for sustainable plantation management.