Assembly Characteristics and Influencing Factors of the Soil Microbial Community in the Typical Forest of Funiu Mountain

Assessing the relationship between litter characteristics and soil microbial community traits across different forest types can enhance our understanding of the synergistic interactions among litter, soil, and microorganisms. This study focused on three representative forest types in the Funiu Mountains-<i>Larix gmelinii</i> (LG), <i>Quercus aliena</i> var. <i>acutiserrata</i> (QA), and <i>Quercus aliena</i> var. <i>acutiserrata</i> + <i>Pinus armandii</i> (QAPA). The findings indicated no significant differences in Chao1 among the three forests; however, the Shannon index exhibited an initial increase followed by a decline. NMDS and ANOSIM analyses revealed significant structural differences across these forest types. Network topological metrics (nodes, edges, average degree, and average path distance) for bacterial taxa were higher in LG and QA compared with QAPA. Additionally, LG and QA demonstrated significantly greater average niche breadth than QAPA. The results from the null models (the proportion occupied by dispersal limitation is 62.2%, 82.2%, and 64.4% in LG, QA, and QAPA), modified stochasticity ratio (LG: 0.708, QA: 0.664, and QAPA: 0.801), and neutral community models (LG: R² = 0.665, QA: R² = 0.630, and QAPA: R² = 0.665) suggested that stochastic processes predominantly govern the assembly of soil bacterial communities. Random forest analysis alongside Mantel tests highlighted LTP (litter total phosphorus), STN (soil total nitrogen), MCP (carbon-to-phosphorus ratio of microbial biomass), and SCN (soil carbon-to-nitrogen ratio) as critical factors affecting bacterial niche width; conversely LCN (litter carbon-to-nitrogen ratio), RCP (ratio of dissolved carbon to phosphorus), MCP, and SCN emerged as key determinants influencing community assembly processes. Furthermore, the PLS-SEM results underscored how both litter characteristics along with soil properties-and their associated alpha diversity-impact variations in niche breadth while also shaping community assembly dynamics overall. This research provides vital insights into understanding synergistic relationships between litter quality, soil characteristics, and microbial community across diverse forest ecosystems.