Moss crust microhabitats promote bacterial community convergence via homogeneous selection under multimetal contamination in restoring bauxite mines

Moss crusts are important ecosystem engineers in degraded mining lands, yet their role in regulating bacterial community assembly under metal contamination remains poorly understood. This study compared moss crust soil, underlying soil, and adjacent bare soil in a karst bauxite mine restoration area. Moss crusts significantly altered the distribution of multiple metals and promoted coordinated multimetal enrichment in moss-associated habitats, likely via upward capillary transport and biological adsorption. Compared with bare soils, moss crusts significantly increased bacterial richness, phylogenetic diversity, and community evenness. Moss-associated communities also showed markedly reduced spatial variability and stronger compositional consistency across sampling sites, indicating pronounced community convergence. Moss crusts selectively enriched bacterial groups associated with nutrient cycling and environmental adaptation, including Actinobacteriota, Bacteroidota, and Pseudomonadota, while maintaining clear vertical niche differentiation between crust and underlying layers. Bacterial community assembly shifted from heterogeneous selection in bare soils to homogeneous selection in moss-associated habitats. Multiple metals (Mg, Al, Mn, Zn, and Fe) were the primary factors influencing community structure and dynamics, overriding conventional soil properties (pH, EC, TP, and AP). By promoting homogeneous ecological selection under metal contamination, moss crusts stabilize microbial communities and may represent an effective nature-based strategy for restoring degraded bauxite mining ecosystems.