Abstract: In summer， we selected a dominant Hippuris vulgaris in Jiuzhaigou to examine biomass， leaf area， diurnal rapid light curves （RLCs） and water quality in three lakes， namely Grass Lake （GL）， Arrow Bamboo Lake （ABL） and Five Colored Lake （FCL）， in order to investigate the effects of water quality on its growth and photosynthetic characteristics. The results showed that there were significant differences in plant height， leaf area and biomass under different lake conditions， and the value of ecological characteristics of ABL were the largest. Submerged Hippuris vulgaris in GL showed a significant diurnal variation in maximum relative electron transport rate （rETRmax） and saturating photon flux （Ek）， but in ABL and FCL， diurnal variation of submerged Hippuris vulgaris appeared to be a marked doublepeak. The daily averages of rETRmax， Ek of submerged Hippuris vulgaris in FCL was significantly greater than that of other two lakes， therefore submerged Hippuris vulgaris in FCL was a plant with a strong photosynthetic capacity for acclimation to high light intensity. By the path analysis between the biomass and water quality and rETRmax， the results showed that biomass was determined by water nitrate （NO-3） content， which was the most important factor， while conductivity was the limiting factor. The determined factor for rETRmax was water temperature， while total hardness was the limiting factor.

Key words: water quality, Hippuris vulgaris, biomass