摘要：
Nitrogen is the essential element for phytoplankton. Its concentration and form affect the biomass and community composition of phytoplankton directly or indirectly. In order to discover the restriction of different forms of nitrogen on phytoplankton growth in Lake Taihu, and supply scientific ground for further study of cyanobacteria blooms and eutrophication control, the especial uptake rates of ammonium, nitrate and urea by phytoplankton using 15N-tracer technology as well as physicochemical parameters, urea concentration and phytoplankton community in Mailiang Bay were determined in the middle of January, April, July and October. The result showed that the uptake of ammonium, nitrate and urea, except the uptake of ammonium in August, exhibited the classic hyperbolic Michaelis-Menten kinetic curves. The maximum uptake speed rates (Vmax) of three forms of nitrogen were:ammonium＞ nitrate＞ urea in winter and spring while ammonium＞urea＞ nitrate in summer. The differences of Vmax between seasons and forms were owing to the different phytoplankton community compositions and ammonium concentration in water. According to the Ks, the growth of phytoplankton community was more likely to be limited by nitrate and not prone to be limited by urea in winter and spring, while more likely to be limited by ammonium in summer. In autumn, it was prone to be limited by urea other than nitrate. In a word, the growth of phytoplankton community was limited by different forms of nitrogen in different seasons.%浮游植物对氮的吸收与其生长繁殖密切相关, 太湖梅梁湾湖区蓝藻水华频频暴发, 对该水域浮游植物氮吸收进行研究具有重要意义.本文分别在冬、春、夏、秋4个季节于梅梁湾采样, 对水体常规理化指标和浮游植物群落结构进行分析, 并利用15N稳定同位素示踪技术研究了浮游植物对铵态氮 (NH4+-N) 、硝态氮 (NO3--N) 和尿素态氮 (Urea-N) 吸收的动力学特征.结果表明, 太湖梅梁湾浮游植物群落除了秋季对NH4+-N的吸收不符合米氏方程外, 其余均符合.冬季和春季3种形态氮最大吸收速率 (Vmax) 的大小依次为:NH4+-N＞ NO3--N＞Urea-N, 而夏季为:NH4+-N＞Urea-N＞NO3--N. 3种形态氮Vmax的季节变化规律为夏季>秋季>春季>冬季. Vmax在不同季节以及不同形态氮之间的差异性可能与浮游植物群落组成以及水体中NH4+-N浓度不同有关.浮游植物对NH4+-N吸收的KS值在冬、春季高于夏季, 对Urea-N吸收的Ks值则在夏、秋季高于冬、春季, 而对NO3--N吸收的Ks值则在夏季显著高于其他3个季节.冬季和春季梅梁湾浮游植物群落最容易受到NO3--N限制, 而最不容易受到Urea-N的限制;而夏季, 则最容易受到NO3--N限制, 而最不容易受到NH4+-N的限制, 且浮游植物群落对NH4+-N的亲和力最高.与NO3--N相比, 秋季浮游植物更容易受到Urea-N的限制.不同季节, 容易对浮游植物产生限制作用的氮的形态不同.
