Structure and assembly mechanism of soil bacterial community during forest restoration process in tropical regions

Forest restoration is a critical measure for maintaining environmental quality and conserving biodiversity, providing important ecosystem services. Forest restoration process not only alters plant community composition but also affects soil microbial community structure and assembly. However, only limited studies have investigated the impacts of forest restoration process on soil bacterial communities in tropical regions. In the present study, three restoration stages of tropical secondary forests (i.e. early-recovery stage, mid-recovery stage, late-recovery stage), and old-growth forest were selected for comparison on Hainan Island. Here, we assessed soil bacterial community composition, diversity, and assembly across four restoration stages by using high-throughput sequencing. The soil bacterial diversity in the 0–10 cm soil layer peaked at the mid-recovery stage, and it reached its maximum during the late-recovery stage in the 10-20 cm layer, Proteobacteria was the dominant phyla overall. Actinobacteriota was more abundant in the 0–10 cm layer, whereas Acidobacteriota and Chloroflexi were enriched in the 10–20 cm layer. The relative abundance of Proteobacteria was consistently highest in the early-recovery stage across both soil layers. Furthermore, deterministic processes dominated bacterial assembly in mid-restoration and late-restoration stage, while stochastic processes dominated in early-restoration stage and old-growth forests. Co-occurrence networks exhibited greater complexity and stability with the forest restoration. Soil total nitrogen primarily influenced bacterial diversity and network structure, while soil water content was the key driver of community assembly. These findings highlight the critical role of restoration in shaping bacterial community assembly, providing insights for enhancing tropical forest restoration strategies and ecosystem management.