Functional and taxonomic biogeographical patterns of carbon-cycling microbial communities in farmland ecosystems of Shaanxi Province, China

Despite the critical role of microorganisms in soil carbon cycling, studies on the biogeography and assembly of carbon cycling functional traits and taxonomic groups in farmland ecosystems remain limited. Here, we collected soil from typical crop-growing areas in Shaanxi Province, China, including rapeseed (southern Shaanxi), wheat (Guanzhong area), and potato (northern Shaanxi) fields, to explore the distribution, assembly, and influencing factors of soil carbon-cycling microbial communities in farmland ecosystems. Distance-decay relationships were observed for both functional traits and taxonomic groups. Latitudinal diversity gradients were prominent for taxonomic groups but scarce for functional traits. The effects of environmental variables on functional and taxonomic community composition were slightly more influential than those of geographic distance. Functional traits and taxonomic groups are shaped by the same set of environmental factors, primarily mean annual temperature and precipitation, and soil pH. Neutral community and null model analyses demonstrated that stochastic processes predominantly governed the assembly of functional and taxonomic communities. Mean annual precipitation, functional trait composition, and microbial community composition also prominently affected the assembly of functional and taxonomic communities. Untargeted metabolomics identified strong associations between key carbon-cycling microbial taxa (e.g., Acidobacteria, Verrucomicrobia, and Gemmatimonadetes) and soil metabolite accumulation, including positive correlations with lipids, saccharides, and alcohols. The results broaden our understanding of microbially-driven soil carbon cycling. The findings underscore the need to consider both functional and taxonomic dimensions when managing soil microbiome-mediated carbon sequestration in agroecosystems.