Community assembly characteristics of abundant and rare bacterial taxa in water, sediment and riparian soil of Wujiang river, China

Bacterial communities are composed of a few abundant taxa (AT) and numerous rare taxa (RT). Rivers serve as connectors between water, sediment, and riparian soil, leading to differences in bacterial communities across these habitats. In this study, we sampled 26 sites along the Wujiang River, a major tributary of the Yangtze River in a karst region of China to systematically target the habitat-specific differences in bacterial communities. We hypothesized that (1) community composition and diversity differ among habitats; (2) AT and RT communities exhibit distinct biogeographic patterns; (3) the community assembly processes differ between AT and RT within and across habitat. Results showed significant differences in bacterial community composition between water and sediment, water and soil, but not between sediment and soil. Sediment and soil had higher species richness and diversity than water, with RT mainly contributing to diversity differences. beta-diversity was primarily driven by species turnover. A distance-decay relationship appeared only in water communities, indicating stronger spatial structuring, while sediment and soil communities were mainly shaped by environmental factors. Assembly of AT in sediment and soil was governed by undominated processes (ecological drift), whereas dispersal limitation dominated in water. for RT, homogeneous dispersal prevailed in water, while homogeneous selection was predominant in sediment and soil. these findings advance our understanding of abundant and rare bacterial community assembly across riverine habitats and provide new insights into microbial biogeography in plateau karst aquatic ecosystems.