Abstract: To explore the diversity of eukaryotic plankton in Nujiang River, water samples were collected from 35 locations in November 2020. The sampling area covers over 1 000 kilometers of Nujiang River. Metabarcoding technology was used to study the spatial distribution of eukaryotic plankton and its response to environmental factors based on 18S rRNA gene. Overall, 1 320 OTUs (Operational Taxonomic Unit) were obtained from the samples. The eukaryotic plankton species detected in these samples cover 34 phyla and 302 genera. According to β diversity, the eukaryotic community can be divided into three groups, namely, high altitude (above 4 000 m), middle altitude (between 1 000 m and 4 000 m), and low altitude (below 1000 m), and the difference among the groups is larger than that within the groups. The Shannon-Wiener index and Simpson index which refelct the diversity of the community, Pielou's evenness index which indicates the evenness of community, and Chao1 index which characterize the abundance of community, all decrease as altitude increases, meaning a higher altitude will affect the diversity of eukaryotic plankton. To analyze the community composition, we compared the relative abundance of different species at phylum level. The result show that Ciliophora and Chlorophyta are enriched in low altitude area, rising with the decline of altitude; Bacillariophyta, the most abundant species, are enriched in middle altitude area; Arthropoda are enriched in high altitude area, reducing with the decling of altitude. For the environmental impact, the result showed pH value and conductivity decrease as altitude decreases. Water temperature, DO (Dissolved Oxygen), FV (Flow Velocity) and Turb (Turbidity) decrease as altitude increases. Altitude, water temperature and flow velocity are the key environmental factors for the distribution of eukaryotic community in Nujiang River Basin.

Key words: eukaryotic plankton, 18s rRNA, altitude gradient, environmental factors, Nujiang River