Abstract: In an outdoor controllable experiment, the effects of different TN∶TP ratios (12.5∶1, 25∶1, and 50∶1) in eutrophic water on the growth of Vallisneria spiralis were investigated. When the TN∶TP ratio was 25∶1,V. spiralis had the best growth, with a biomass increment being 54% and 31% higher than that when the TN∶TP ratio was 12.5∶1 and 50∶1, respectively, while the growth of periphyton, especially of epiphytic algae, was the worst, giving the least dverse effects on V. spiralis, indicating that a 25∶1 of TN∶TP ratio in eutrophic water was optimal for the growth of V. spiralis. However, such an optimal TN∶TP ratio only worked when the nutrients concentration in eutrophic water was below the limited level, otherwise, it could be failed to be applicable.

Key words: Qilian Mountains, Moss-Picea crassifolia forestry, Shrub-Picea crassifolia forestry, Soil water