River networks serve as critical pathways for the conveyance of substances and nutrients, with bacterial communities acting as pivotal agents in the biogeochemical cycle. Unraveling the diversity and assembly mechanisms of these bacterial communities within intricate riverine networks, from a multi-scale perspective, bears profound implications for the safeguarding and prognostication of aquatic ecosystem functionalities.

The Ili River system is divided into different basins by the Tianshan Mountain system, forming a complex river network. The abundant water supply sustains the residents of the Ili River basin in Xinjiang. The Kashi (KS), Kunes (KN), and Tekes River (TK) are three important tributries that originate from diverse terrestrial habitats and sequentially confluence into the Ili River (IL).

The Environmental Genomic Group of Wuhan Botanical Garden, in cooperation with Xinjiang Institute of Ecology and Geography, employed 16S ribosomal ribonucleic acid (rRNA) gene amplicon sequence variation (ASVs) to examine the heterogeneity of bacterial communities in the Ili River network, analyzing underlying mechanisms at regional and local scales.

Contrary to expectation, the bacterial community composition of IL exhibited distinct characteristics, with significantly reduced diversity compared to three tributaries. With the change of community composition, the functional redundancy of the mainstream was greatly reduced compared with that of the tributaries. It suggested that strong dispersal limitation significantly influenced community structure at the regional scale, with distance and altitude variations intensifying the distance decay pattern. Locally, the complex process of community coalescence significantly influenced the formation of the mainstream bacterial community. The increased influence of drift processes due to multi-flow perturbations underscored the contribution of undominated processes in community assembly.

This research uncovers the diversity, biogeographic patterns, and potential mechanisms of bacterial communities within the Ili River network. This study serves as a crucial reference for multi-scale investigations into the assembly mechanisms of bacterial communities in natural river networks. It further emphasizes the importance of source protection and community coalescence at confluences.

This work was supported by the West Light Foundation of Chinese Academy of Sciences, the Starting Research Fund from the Key Laboratory of Aquatic Botany and Watershed Ecology, Chinese Academy of Sciences. The relevant results have been published in Water Research entitled “Linking ecosystem multifunctionality to microbial community features in rivers along a latitudinal gradient”.