Homogeneous selection dominates the microbial community assembly in the sediment of the Three Gorges Reservoir.

Deep-water reservoir sediment is a unique habitat sheltering indispensable microorganisms and facilitating their biogeochemical functions; however, the assembly processes of the microbial community therein remain elusive. This study focuses on the assembly processes in the Three Gorges Reservoir Area (TGRA). A total of 42 sediment samples were collected from the TGRA, both in the mainstream and the tributaries, and in different seasons. Metagenomic analyses of 16S rRNA using Exact Sequence Variants revealed the spatiotemporal distribution patterns of the microbial communities. Linear regressions between dissimilarity of microbial communities, geographic and environmental distance showed that environmental, rather than geographic factors, impacted the microbial community. However, the environmental differences explained little variations (14.14%) in community structure, implying the homogeneity of environmental conditions across the TGRA. From the quantification of ecological processes, homogeneous selection was shown to be a dominating factor (51.34%) in the assembly of the microbial communities. The co-occurrence network showed that keystone species were more important than prevalent abundant species in interspecies interactions. Overall, the assembly of microbial community in the deep-water reservoir sediment is mediated by both deterministic and stochastic processes, and homogeneous selection plays a leading role.