Integrated biogeography and assembly process of planktonic and sedimentary bacterial communities in the Yangtze River

Bacterial communities are essential to the biogeochemical cycle in riverine ecosystems. However, the integrated biogeography and assembly process of planktonic and sedimentary bacterial communities in large rivers is still poorly understood. Here, the study provided the spatiotemporal pattern of bacterial communities in the Yangtze River of 4300 km continuum, which is the largest river in Asia. We found that the taxa in sediments are the main contributors to the bacterial diversity of the river ecosystem since sediments sub-group took 98.8% of the total 38, 904 Operational Taxonomic Units (OTUs) observed in 280 samples. Seasonal differences in bacterial communities were statistically significant in water, whereas bacterial communities in both water and sediment were geographically clustered according to five types of landforms: mountain, foothill, basin, foothill-mountain, and plain. Interestingly, the presence of two huge dams resulted in a drastic fall of bacterial taxa in sediment immediately downstream due to severe riverbed scouring. The integrity of the biogeography was satisfactorily interpreted by the combination of neutral and species sorting perspectives in meta-community theory for bacterial communities in flowing water and sediment. Although deterministic process had dominant influence on assembly processes in water and sediment communities, homogeneous selection was the main contributor in water, while combination of homogeneous selection and variable selection contributed selection process in sediment. In addition, homogenizing dispersal played more important role in community assembly process in sediment than water. Our study fills a gap in understanding of biogeography and assembly process of bacterial communities in one of the world’s largest river and highlights the importance of both planktonic and sedimentary communities to the integrity of bacterial biogeographic patterns in a river subject to varying natural and anthropogenic impacts.