Characteristics and assembly mechanisms of bacterial and fungal communities in soils from Chinese forests across different climatic zones

Forest soils are intricate ecosystems that harbor a diverse array of microorganisms, yet our current understanding of the characteristics and environmental implications of forest soil microbiomes remains limited. Here we present a continental-scale study on soil microbiomes of ten forests in China, spanning latitudes from 18°54′N to 50°48′N, resulting in a comprehensive catalog of bacterial and fungal operational taxonomic units (OTUs). Both bacterial and fungal communities exhibited discernible spatial variations in taxonomic and phylogenetic diversity. The composition of bacterial communities varied distinctively due to climatic zones—cold temperate, temperate, subtropical, and tropical—whereas fungal communities did not exhibit such pronounced distinctions. The co-occurrence network complexity of bacterial communities displayed a decremental trend along the cold temperate, temperate, subtropical, and tropical zones, whereas that of fungal communities displayed an incremental pattern. These results may be attributed to the facts that low temperatures sustain a high biomass of bacteria and foster increased interactions, while high temperatures and precipitation stimulate fungi-plant interactions. Furthermore, community assembly modeling revealed that forest soil microbial communities were dominated by stochastic processes. The bacterial community structure was mainly driven by homogeneous selection (26–41%) and dispersal limitation (35–44%), whereas dispersal limitation (51–56%) had the greatest impact on fungal community structure. Notably, bacterial functional genes associated with carbon fixation were more abundant in cold temperate soils compared to tropical soils. This study sheds light on spatial variations of forest soil microbiomes in China, enhancing further understanding of their response to global changes and implications for soil organic carbon cycles.