Spatiotemporal distribution of protists in the Yarlung Zangbo River, Tibetan Plateau

Protists, which include eukaryotic algae and protozoa, are crucially important for biogeochemical cycling and the aquatic food web but are sensitive to environmental fluctuations. Despite investigations in the 1970s, protist diversity and biogeographic characteristics in the Tibetan Plateau are poorly understood. Within the framework of a regional survey of protist diversity, we used high-throughput amplicon sequencing to investigate the compo-sition and spatiotemporal turnover of protist communities along the Yarlung Zangbo River, a representative aquatic habitat of the Tibetan Plateau. In total, we detected 9,959 amplicon sequence variants in protist com-munities along the river and associated lakes and wetlands. The alpha diversity of protists was highest in spring and declined in the autumn. Moreover, alpha diversity was much higher in the middle and upstream reaches and tributaries than in the connected lakes and wetlands. We discovered spatiotemporal heterogeneity in the composition of protist communities across the seasons. Bacillariophyta predominated in protist communities in cold seasons (spring and autumn) and colder (high-altitude) areas, whereas Ciliophora and Cercozoa species predominated in the warm season (summer) and warmer (low-altitude) areas. Of the environmental factors, altitude, turbidity and salinity correlated with spatiotemporal dissimilarities among protist communities. The breadth of the habitat niche was restricted by turbidity and altitude in river areas and by salinity in lake and wetland areas. Co-occurrence network analysis suggested that protist communities in the Yarlung Zangbo River were substantially more complex in the warm season than in the cold seasons, and that amplicon sequence variants belonging to Ochrophyta, Chlorophyta, and Ciliophora contributed greatly to the stability of the co -occurrence network. In summary, this study provides a comprehensive overview of the spatiotemporal dy-namics of protist diversity in the Yarlung Zangbo River and improves our understanding of the environmental adaptation of protists living in aquatic habitats of the Tibetan Plateau.