Riverine microbial community assembly with watercourse distance-decay patterns in the north-south transitional zone of China

Deciphering the spatiotemporal patterns and ecological processes of microbiota is a key challenge in community assembly research. The microbial patterns in complex mountain rivers and the ecological processes influencing community assembly remain poorly understood. In the present study, water samples were collected from Weihe and Hanjiang Rivers, including their tributaries, in the transitional zone between North and South China in autumn 2017 and spring 2018. We analyzed watercourse and geographic distance-based patterns of riverine microbiota through sequencing of 16S rRNA genes and multivariate statistical analyses. The distance-decay patterns in water quality factors based on geographic and watercourse distances were similar across seasons. However, the distance-decay patterns in riverine microbiota based on watercourse distance were stronger than those based on geographic distance in both seasons. Deterministic processes were predominantly responsible for community assembly in different seasons, with homogeneous selection making the highest contribution: 89.40 % in autumn and 83.33 % in spring. Autumn precipitation facilitated microbial dispersal, as indicated by the dispersal limitation of 5.01 % and 10.25 % in autumn and spring, respectively. Dispersal and environmental selection synergistically drove microbial community assembly in autumn. The results could enable a broader understanding of microbial community assembly with watercourse distance-decay patterns in complex mountain rivers.