Shifts in Abiotic and Biotic Factors Correlate with Changes in Bacterial and Fungal Network Assembly Under Straw Incorporation Across Three Soil Depths

Crop residue management strongly influences soil microbial communities, yet the mechanisms by which it regulates microbial co-occurrence network assembly across soil profiles remain poorly understood. Here, we investigated the effects of three straw management practices—no straw return (CK), straw burning (BS), and deep plowing with straw incorporation (DPS)—on soil physicochemical properties, microbial diversity, and co-occurrence network structure across multiple soil depths in a Mollisol of Northeast China. By integrating high-throughput sequencing, network analysis, and structural equation modeling (SEM), we explored the correlative relationships associated with microbial network assembly. DPS significantly correlates with higher soil organic carbon content, nutrient availability, and moisture content, particularly in subsoil layers. Under DPS, we obtained more complex and robust microbial networks characterized by higher connectivity and clustering. In contrast, under BS, we found reduced network complexity and stability. SEM may suggest the presence of distinct assembly mechanisms between microbial groups: bacterial network structure models responded to soil physicochemical properties, suggesting strong environmental filtering, whereas shifts in fungal network structures correlate with alpha diversity, highlighting the importance of biotic regulation. Notably, under the evaluated conditions, beta diversity was positively associated with network structural attributes across both groups, indicating potential links between community compositional variation and microbial co-occurrence patterns. These findings suggest that straw incorporation may be associated with shifts in microbial co-occurrence network attributes under the evaluated field conditions. However, the observed relationships are primarily correlative and based on statistical modeling approaches. The underlying ecological mechanisms linking soil properties, microbial diversity, and network structure require further validation through controlled biochemical, physiological, and experimental studies. This study provides additional ecological insights into soil microbial responses to residue management and highlights the potential role of residue management in shaping microbial network stability under the evaluated field conditions.