Biogeographic pattern of bacterioplanktonic community and potential function in the Yangtze River: Roles of abundant and rare taxa

Abstract

Bacterioplanktonic communities, consisting of a few abundant taxa (AT) and many rare taxa (RT), are essential component of riverine ecosystems. Nonetheless, the biogeographic patterns of bacterioplankton and roles of AT and RT in community structuring and functional composition remain uncertain in large rivers. Here, we employ the Yangtze River, which is the third-longest river in the world, as model system. By using high-throughput sequencing and bioinformatics tool of Tax4Fun, the geographical patterns of bacterioplanktonic taxonomic and predicted functional communities are investigated, and the relative importance of abundant and rare subcommunities in community structuring are explored. Results showed a clear spatial variation that the bacterioplanktonic communities of upper, middle and lower reaches of the river are significantly different from each other. Besides, the Three Gorges Dam exhibited impact on the bacterioplankton of upper reach whose community is relatively closer to that of the Poyang Lake. Both the abundant and rare subcommunities showed spatial variation along the river, which is similar to the total bacterioplanktonic community. The rare subcommunity comprised a majority of community diversity with 23.6% of the total sequences and 94.2% of the total OTUs. The rare subcommunity contributes a major part (56.8%) versus abundant subcommunity (16.3%) of the spatial variation of the total community. In addition, the non-RT exhibits more interactions with RT than with themselves, and all of the 33 keystone species are belonged to RT. Hence, the RT is critical for community structuring and assembling. By contrast, no obvious spatial effect was observed for the predicted functional community. The predicted functions of abundant and rare subcommunities are consistent with that of total community, despite their contrasting community composition. In summary, the rare subcommunity show significantly impact on the community structure and assembling, and play an important role in predicted function as ‘seed bank’ in the Yangtze River.