Investigating the response of riparian vegetation to water quality is crucial for maintaining the structural integrity and function of riparian ecosystems. This study focused on riparian zones within the Songhua Lake watershed reservoir and its tributaries. We established 86 herbaceous plots to investigate plant community characteristics, with measurements taken for water quality indicators and altitude factors. Partial Least Squares Regression (PLSR), Pearson correlation analysis, and Mantel tests were used to analyze plant species diversity, community composition, and their responses to water quality. Results showed that there were 189 plant species from 51 families and 129 genera within the watershed. Dominant families were Asteraceae (27%), Brassicaceae (11%), and Poaceae (8%). There were significant differences in species diversity between Songhua Lake and tributaries. Clonal plant species constituted 46.5% of riparian vegetation in tributaries and 39% in the reservoir riparian zone. Total dissolved particulate matter was significantly positively correlated with salinity, total phosphorus, and total nitrogen (P<0.001), forming a ‘turbidity-nutrients-salinity’ synergistic stress. Dissolved oxygen showed significant positive correlations with total phosphorus, salinity, and total dissolved particulate matter, while altitude exhibited significantly negative correlation with total nitrogen (P<0.001). Plant species richness exhibited regional differentiation. Both total phosphorus and total nitrogen promoted species richness in reservoir and tributary zones. The effects of water pH on species richness were zone-specific, inhibiting reservoir riparian species richness while promoting tributary riparian species diversity. Salinity enhanced tributary riparian plant species richness. This study provides scientific evidence for analyzing riparian vegetation adaptation strategies to water quality.

riparian zone, clonal plant, water quality factor, plant diversity