Vegetation restoration increases the diversity of bacterial communities in deep soils

Soil microbial communities are engineers of key biogeochemical processes and mediate the functioning of vegetation restoration ecosystems following cropland abandonment. However, how microbial communities in the deep soil profile, especially the complexity and stability of their interactions, respond to vegetation restoration remains unclear. Here, we explored the soil properties and bacterial community diversity, structure, and network interactions and attempted to identify the keystone taxa along the 0–500 cm soil profile under different land use types (cropland, restored woodland, restored grassland). The results showed soil bacterial alpha diversity, indicated by phylotype richness and Shannon diversity index, was higher in deeper soil layers under restored lands (woodland and grassland) compared to long-term cultivated cropland. The dominant phyla of bacterial communities included Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, and GAL15. Using the molecular ecological network approach, we confirmed bacterial ecological networks were more complex in restored woodland and grassland, compared to cropland, indicating the bacterial species have greater niche-sharing and more interactions over the whole 0–500 cm profile under restored ecosystems. Moreover, relatively large and intricate bacterial interactions persisted in the soil deep layer (380–400 cm). Soil available phosphorus (P), organic carbon, and total P contents, fine root length density, and soil moisture conditions strongly affected microbial communities after vegetation restoration. In general, our findings have implications for understanding the potential of restored ecosystems to withstand disturbances under global climate change scenarios.