Biogeographic patterns and co-occurrence networks of diazotrophic and arbuscular mycorrhizal fungal communities in the acidic soil ecosystem of southern China

Low soil nutrient availability severely constrains plant growth and productivity in acidic soil ecosystems. Diazotrophs and arbuscular mycorrhizal fungi (AMF) are the important microbial groups that improve the bioavailability of soil nitrogen (N) and phosphorus (P), respectively. Therefore, the objective was to investigate the biogeographic patterns and co-occurrence networks of the diazotrophic and AMF communities in the acidic soil ecosystem. We collected 52 soil samples from four long-term field observation stations with spatial distances of 961.3 km in the acidic soil region of southern China, and analyzed the community composition and biogeographic distributions of the diazotrophs and AMF using high-throughput sequencing of the functional gene amplicons. The variation partition analysis indicated that soil physicochemical factors provided more contributions than geographic distance, sampling stations and land-use types in the assembly of the diazotrophic and AMF community communities. Distance-decay relationships and Mantel tests showed that soil physicochemical factors had remarkable effects on both microbial community structures, whereas geographic distance only significantly affected the diazotrophic community variations. Co-occurrence network analysis revealed that AMF network was more complex and stable than the diazotrophic network. Furthermore, the dominant genera Bradyrhizbium and Glomus might be the more important keystone taxa in the diazotrophic and AMF networks, respectively. These findings suggest that the diazotrophic and AMF communities exhibit different assembly mechanisms and co-occurrence ecological networks in the acidic soil region of southern China, and both community assemblies were mainly driven by soil physicochemical factors.