Biogeography of eukaryotic plankton communities along the upper Yangtze River: The potential impact of cascade dams and reservoirs

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The effects of large cascade dams on eukaryotic plankton communities in freshwater river-reservoir ecosystems are probably uncharted in previous studies. The purpose of this research was to investigate the large-scale genetic diversity and biogeography patterns within large cascade dams and to reveal the key drivers shaping eukaryotic plankton community. Eukaryotic plankton communities of 24 sampling sites along the upper Yangtze River were assessed based on Illumina Miseq sequencing. Generally, the mainly dominant eukaryotic plankton communities were Cryptophyta, Fungi and Alveolata, with these three clades encompassing 52.36%, 24.34% and 15.26% of all sequences. Generally, the Shannon diversity was higher in the dry season than that in the flood season, varying from 0.60 to 3.83 in the flood season and 1.41–4.53 in the dry season. Moreover, the α-diversity index decreased significantly from the upstream to the downstream. Principal coordinate analysis of the eukaryotic plankton taxa yielded a distinct biogeographical distribution pattern between different seasons and locations. Redundancy analysis results suggested that total organic carbon, DO, Chl a and PC have significant influence on the community compositions. Variation partitioning analysis indicated that the purely environmental variables, pure spatial variables, pure hydrological variables explained 17.5%, 5.1% and 10.0% of the community. The distance decay analysis (eukaryotic plankton community dissimilarity and site location) also suggests that geographical distance was important in structuring the eukaryotic plankton community and determining the spatial dissimilarity in the river network. Our findings show that eukaryotic plankton community across the upper Yangtze River exhibit an ecological succession along the river continuum, and this is primarily driven by the combination of environmental, spatial and hydrological variables in the river-reservoir system.