附着藻类对太湖水体中3种氮源的吸收作用

Uptake of Three Different Nitrogen Forms by Periphytic Algae in Taihu Lake,China

利用15N标记技术，比较了附着藻类对太湖3种氮源（尿素、NH4^＋和NO3^-）的吸收能力。附着藻类对尿素的吸收速率为1.93～5.52μmol/（g.h），对NH4^＋的吸收速率为0.89～7.67μmol/（g.h），而对NO3^-的吸收速率为0.09～0.35μmol/（g.h）。各氮源的贫化百分比在0.18 %～9.03 %。在浓度为20和50μmol/L时，尿素的贫化值分别为8.41 %和8.14 %，与NH4^＋的贫化值相当（分别为9.03 %和 7.01 %）；NO3^-的贫化值在各浓度下都低于0.29 %。附着藻类对每种氮源的吸收速率在3种氮源吸收速率总和中的相对比重：尿素平均为47.9 %，NH4^＋平均为49.6 %，NO3^-平均为2.5 %。根据Vmax与Ks比值，附着藻类对3种氮源的吸收亲和力大小顺序为：尿素＞NH4^＋＞NO3^-。研究表明，尿素是除NH4^＋外附着藻类生长可利用的又一重要氮源。

The uptake ability of periphytic algae to three different nitrogen substrates （urea, NH4^＋ and NO3^-） was examined using 15N tracer techniques in eutrophic Lake Taihu in China.The periphytic algae uptake rates of urea and NH4^＋ were 1.93～5.52μmol/（g？h） and 0.89～7.67μmol/（g？h）, respectively, accounting for 47.9 % and 49.6 % of the total N uptake rates ,which were significantly higher than that of NO3^- （0.09～0.35μmol/（g？h）） accounting for 2.5 % to the total N uptake rates.The depletion rates of each nitrogen source ranged from 0.18 % to 9.03 % in the experiment. At concentrations of 20μmol/L and 50μmol/L, the depletion rates of urea were 8.41 % and 8.14 % respectively , 9.03 % and 7.01 % for NH4^＋ , while both much lower than 0.29 % for NO3^- . According to the Vmax ： KS ratio of periphytic algal uptake kinetics, the sequence of uptake affinity was urea〉NH4^＋〉NO3^-. Our results suggested that the ability to absorb urea gives periphytic algae access to additional nitrogen source in eutrophic lakes.