作者：J. Li, L. Wang, B. Wu, J. Wang, Y. Yu, Y. Kuzyakov, et al.

Microbiota within interconnected river-lake systems define cycles of carbon and nutrients, yet the mechanisms underlying the assembly of microbial communities during their transition from tributaries to lake remains to be deciphered. This study examined the communities of protists, fungi and bacteria in sediments of Qinghai Lake - a saline lake on the Tibetan Plateau, China - and its connected upstream freshwater tributaries, using highthroughput amplicon sequencing targeting the 18S, ITS2 and 16S rDNA regions. Our findings reveal divergent assembly mechanisms across microbial groups: communities of microeukaryotes (protists and fungi) in tributaries were predominantly shaped by stochastic processes (similar to 85% contribution), shifting to environmental selection dominance in the lake (similar to 55%). In contrast, bacterial community assembly in tributaries was primarily deterministic (similar to 60% environmental selection), shifting to stochastic dominance (similar to 70%) in the lake. Despite the differences, all groups exhibited congruent biogeographic patterns in terms of diversity and network complexity. The tributary-to-lake transition enhanced the complexity of microbial co-occurrence network but resulted in significant species loss, with alpha-diversity reduced by 56%-62%. beta-diversity increased from tributaries to the estuary but decreased within the lake. Microbial alpha- and beta-diversity correlated positively with sediment C: N ratio but negatively with total sediment C content. Notably, only 1% to 13% of microbial taxa in lake sediments originated from tributaries, suggesting alternative pathways that warrant further geological investigation. This study provides new insights into the convergent biogeographical patterns of diversity and network complexity, coupled with divergent assembly mechanisms, among protist, fungal, and bacterial communities along the riverQinghai Lake sediment continuum.

（来源：Water Research 2025 Vol. 282   DOI: 10.1016/j.watres.2025.123757）