Abstract: In a sinus of Lake Yezhi localized in the southern suburb of Wuhan City,the sediments with high biomass of Potamogeton crispus showed significantly higher P sorption index,maximum sorption capacity and sorption bonding energy,calculated by the Langmuir equation :C/X=C/X_m+K×1/X_m,a common result derived from the samples in different times and at different depths.Therefore,increasing the P sorption ability is an important mechanism for P.crispus to maintain the low nutrient level in water body.Since iron bonding P dominated in P pool in sediments,the improvement of P sorption ability could be partially explained by the role of organic matter and its interaction with iron.The sediments with high biomass of P.crispus collected in different times exhibited significantly lower activity and maximum reaction rate of alkaline phosphatase,which meant that the decomposition rate of organic matter mediated by alkaline phosphatase decreased,providing an additional mechanism for P.crispus to maintain the low nutrient level in water level.