Changes in soil bacterial and fungal community composition and functional groups during the succession of boreal forests

Clarifying the response of soil microbial communities and their potential functions during succession is of great significance for understanding the biogeochemical processes and the sustainability of forest development. However, the study of microbial community dynamics during the process of succession remains poorly understood in boreal forest ecosystems. Thus, in order to study the dynamics of microbial diversity caused by succession, we adopted the "space instead of time" method and selected four habitats in a national natural reserve (including grassland, birch forest, mixed forest and larch forest) to represent the primary successional sequence of the boreal forest. We used 16S and ITS rRNA gene sequencing to detect bacterial and fungal communities and used FAPROTAX and FUNGuild database to predict bacterial and fungal functional groups. The results showed that forest succession significantly changed the community composition of bacteria and fungi, among which the fungal community was more sensitive to the changes with successional stage. The relative abundance of ectomycorrhizal fungi significantly increased with succession, while the relative abundance of bacterial functional groups involved in the nitrogen cycle did not change significantly, indicating that fungi might play a major regulatory role in the nutrient cycling process during the successional process. In this study, the soil total carbon and total nitrogen were the dominating factors affecting the soil microbial community and the structure of fungal functional groups. Our results suggest that the shifts in fungal community structure and functional groups may play a key role in soil nutrient cycling during boreal ecosystems succession.