Linking microbial community coalescence to ecological diversity, community assembly and species coexistence in a typical subhumid river catchment in northern China.

ABSTRACT

Community coalescence denotes the amalgamation of biotic and abiotic factors across multiple intact ecological communities. Despite the growing attention given to the phenomenon of coalescence, there remains limited investigation into community coalescence in single and multiple source habitats and its impact on microbial community assemblages in sinks. This study focused on a major river catchment in northern China. We investigated microbial community coalescence across different habitats (i.e., water, sediment, biofilm, and riparian soil) and seasons (i.e., summer and winter). Using 16S rRNA gene amplicon sequence variants, we examined the relationship between community coalescence and microbial diversity, assembly processes, and species coexistence. The results showed that the intensity of microbial community coalescence was higher in the same habitat pairs compared to disparate habitat pairs in both summer and winter. During the occurrence of microbial community coalescence, the assembly processes regulated the intensity of coalescence. When the microbial community exhibited strong heterogeneous selection (heterogeneous environmental conditions leading to more dissimilar community structures), the intensity of community coalescence was low. With the assembly process shifted towards stochasticity, coalescence intensity increased gradually. However, when homogeneous selection (homogeneous environmental conditions leading to more similar community structures) predominantly shaped microbial communities, coalescence intensity exceeded the threshold of 0.25-0.30. Moreover, the enhanced intensity of community coalescence could increase the complexity of microbial networks, thereby enhancing species coexistence. Furthermore, the assembly processes mediated the relationship between community coalescence and species coexistence, underscoring the pivotal role of intermediate intensity of community coalescence in maintaining efficient species coexistence. In conclusion, this study highlights the crucial role of community coalescence originating from single and multiple source habitats in shaping microbial communities in sinks, thus emphasizing its central importance in watershed ecosystems.