Secondary forest succession drives differential responses of bacterial communities and interactions rather than bacterial functional groups in the rhizosphere and bulk soils in a subalpine region

Background and aims Community dynamics, functions and driving factors of rhizosphere and bulk soil bacteria during secondary forest succession remain poorly understood in subalpine regions. Methods Three typical successional stages (grassland, shrubland and secondary forest) were selected to analyse bacterial communities, functions and interactions in the rhizosphere and bulk soils using high-throughput sequencing technology. Results The results showed no significant difference in the bacterial α- diversity in the rhizosphere soil, whereas the bacterial α- diversity in the bulk soil of the grassland was significantly lower than that of the shrubland and secondary forest. Bacterial β- diversity in the rhizosphere soil differed significantly among the three succession stages, while the bacterial β- diversity in the bulk soil in the shrubland and secondary forest was significantly different from that in the grassland. However, the potential bacterial functions of the carbon, nitrogen and sulfate cycles revealed a consistent response in the rhizosphere and bulk soils to secondary forest succession. The soil total phosphorus, ammonium nitrogen, ratio of carbon to phosphorus and pH were the main factors affecting bacterial communities and potential functional groups. Bacterial network complexity was highest in the secondary forest rhizosphere soil and the shrubland bulk soil. Different keystone bacteria were detected in the rhizosphere and bulk soils among the three successional stages; they play major role in maintaining ecosystem function and community structure. Conclusion Our results demonstrate that the bacterial communities and interactions in the rhizosphere and bulk soils respond differently to secondary forest succession, while the bacterial functional groups revealed a consistent response.