Restoration in degraded subtropical broadleaved forests induces changes in soil bacterial communities

Soil resident bacterial communities are involved in myriad key processes that facilitate ecosystem functionality. However, our understanding of their diversity and compositional dynamics following ecological restoration, and the main factors that influence them, remains inadequate. We employed a chronosequence (0–1, 5–6, 11–12, 20–24, and 28–34 years since restoration) to examine the dynamic changes in soil bacterial diversity and composition, as well as the essential factors that affected them since the cessation of anthropogenic disturbances (e.g., recurring fuelwood collection and domestic animal grazing), and used old-growth forests as a reference in the subtropical forests of Eastern China. We found that soil bacterial diversity increased with time since restoration, and community compositions shifted toward being similar to those of old-growth forests over time. However, the recovery process was prolonged since the significant difference in soil bacterial diversity between degraded and restored forests did not occur until after 24 years since restoration. Multivariate analysis using multiple-response permutation procedures indicated the soil bacterial communities were compositionally distinct between degraded, restored, and old-growth forests. An analysis of indicator species revealed that forests at the early stage of recovery times supported Rokubacteria and Actinobacteria, while old-growth forests were distinguished by Chlamydiae. Soil carbon, microbial biomass carbon, soil water content, and microbial biomass nitrogen recovered over time and became increasingly akin to those of old-growth forest soils. Soil carbon, soil water content, and soil pH could explain 84.5% of the variations in bacterial community dynamics following restoration. Overall, this study revealed a prolonged recovery process of the community structures of soil bacteria (e.g., diversity, composition, and phylum abundance) following restoration, which was coupled with changes in soil properties in subtropical forests of China.