Abstract: To clarify the community structure and spatial distribution of planktonic bacteria in natural river without the influence of dam, five sampling sites were monitored along the upstream of Qingjiang River in Lichuan City, Hubei Province. The results showed that 35 phyla of planktonic bacteria were recorded in the research area, with Proteobacteria being the dominant phylum. At genus level, there were 447 genera, with Ainetobacterbeing the dominant genus in the headwater of Qingjiang (Site 1) and Limnohabitanbeing dominant in the other sites. ACE index, Shannon index, and specific OTU in Site 1 were much higher than those in other sites, indicating that planktonic bacterial diversity and abundance were the highest in the upstream. Total phosphorus, dissolved oxygen and water temperature were the main factors affecting planktonic bacterial community structure. The abundance of Proteobacteria was significantly positively correlated with total phosphorus and water temperature, but negatively with dissolved oxygen. Bacteroidetes and Verrucomicrobia were significantly positively correlated with dissolved oxygen. At the genus level, water temperature was the main factor driving the spatial distribution of dominant bacterial genera.

Key words: Qingjiang headwater, planktonic bacterial community, high-throughput sequencing, diversity, environmental factor.