Rhizosphere effects on soil microbial community structure and enzyme activity in a successional subtropical forest

Forest succession is a central ecological topic due to the importance of its dynamic process for terrestrial ecosystems. However, we have limited knowledge of the relationship between forest succession and belowground microbiota, particularly regarding interactions in the rhizosphere. Here, we determined microbial community structure and biomass using phospholipid fatty acid (PLFA) biomarkers and microbial activity using extracellular enzyme activity in bulk and rhizosphere soils from three successional stages of subtropical forests in eastern China. Principal component analysis of PLFAs indicated distinct soil microbial communities among different successional stages and habitat locations. Specifically for the topsoil, we found the total microbial biomass, bacterial biomass and enzyme activities showed higher levels in the late than early stage, with a significant succession-induced accentuated rhizosphere effect. The increase in total microbial biomass and activity coincided with a net growth in bacterial rather than fungal biomass, indicating a model in which microbial biomass carrying capacity and activity could be affected by the creation or expansion of niches for certain functional group rather than by a rebalancing of competitive interactions among these groups. Furthermore, we demonstrated that forest succession significantly influenced enzyme activity via the changes in microbial biomass, as driven by edaphic factors. Overall, our study deepens the mechanistic understanding of forest recovery by linking soil microbial community and activity along successional chronosequences.