Abstract: To explore the characteristics and key driving factors of phytoplankton functional groups in Xiaowan Reservoir area of Lancang River, a survey was conducted in August during 2017 to 2019. Data were analyzed by using functional groups classification, redundancy analysis and Pearson correlation analysis. A total of 71 species of phytoplankton from 7 phyla were identified, among which chlorophyta were the most phytoplankton species (34 species, accounting for 47.89%). The 71 species were classified into 23 functional groups according to functional group classification. The top 5 important functional groups were identified according to the dominance index(>0.2). The identities of important functional groups showed interannual variations. Results of the correlation analysis between functional groups and environmental factors showed that nitrate and ammonium were the main limiting factors in Xiaowan Reservoir, and the reservoir area was limited by nitrogen from 2017 to 2019. Results of comprehensive analysis showed that the characteristics of phytoplankton functional groups were consistent with the changes of water environmental factors. Xiaowan Reservoir was generally at the state of moderate eutrophication to eutrophication. The habitat characteristics of Xiaowan Reservoir area could be well indicated by phytoplankton functional groups.

Key words: Xiaowan Reservoir, phytoplankton functional group, water environmental factor, redundancy analysis.