[Underlying Mechanisms of Fertilization-mode-driven Microbial Community Reconstruction in Non-grain Reclaimed...

Non-grain cropland reclamation is a critical initiative in China to ensure food security. However, the degradation of soil microbial functions caused by long-term cash crop cultivation severely restricts soil fertility restoration. This study focused on soil fertility improvement in bamboo forests, a typical non-grain land use in Dongwu Town, Ningbo City, Zhejiang Province. A fertilization regime involving maize-faba bean rotation combined with 50% replacement of chemical fertilizers by organic fertilizer and biochar was implemented. High-throughput sequencing, network topology analysis, and multifactor correlation models were employed to systematically elucidate the mechanisms by which different fertilization modes drive the reconstruction of soil microbial communities. The results revealed that fertilization significantly altered the spatiotemporal patterns of soil microbial diversity. During the maize maturation stage, soil diversity was less affected, whereas bacterial diversity in faba bean maturation-stage soil decreased significantly, with fungi exhibiting an inverse response. For microbial community structure, fertilization markedly reshaped bacterial community configurations in the faba bean season. Pure chemical fertilization in the maize season formed highly complex networks but had the lowest modularity index, indicating that excessive nutrient inputs reduced system stability. In the faba bean season, 50% organic fertilizer substitution fostered a highly mutualistic network dominated by Acidobacteriota, with clustering coefficients significantly higher than those in other treatments. Correlation analysis demonstrated that bacterial diversity in the maize season was positively correlated with TC, TN, and TP, and fungal richness was closely linked to ACP enzyme activity, while microbial communities in the faba bean season were significantly associated with pH and AK. This study clarifies the biological mechanisms by which organic amendments enhance the ecological functions of reclaimed lands through remodeling microbial interaction networks, providing a theoretical foundation for precision fertility management in degraded croplands.