To characterize the nitrogen uptake by phytoplankton and its relationships with phytoplankton community structure and enviromental factors,we measureed the uptake of ammonium,nitrate and urea by phytoplankton community from different areas of Lake Taihu in mid-May, 2010,using the ¹⁵N-tracer technology.The results showed that:Uptake rate of ammonium was highest for all lake areas,accounting for 62.8% of the total nitrogen uptake.The uptake rates were 0.181-1.575, 0.004-0.118 and 0.043-1.116μmol/(L·h) for ammonium,nitrate and urea,respectively.Phytoplankton communities preferred uptaking ammonium in Meiliang Bay,Lake Center and Wuli Bay and the uptake rates of the three forms of nitrogen were arranged as follows:ρ(NH₄) >ρ(UREA) >ρ(NO₃).However, phytoplankton community in Xukou Bay preferred urea to ammonium and the uptake rate of urea was the highest,the uptake rate of nitrate was the lowest.When concentrations of nitrogen are high,phytoplankton abundance and com-munity structure are likely important factors determining the nitrogen uptake by phytoplankton community in Lake Taihu.