中文摘要：

硝氮（NO3--N）和氨氮（NH4＋-N）是水体中无机氮的主要形态。利用15N稳定同位素技术研究了斜生栅藻（Scendesmus obliquus）对NO3--N和NH4＋-N的吸收特征。结果显示,在相同浓度条件下,斜生栅藻对NH4＋-N的吸收速率显著高于对NO3--N的吸收率,在180min的试验中,对15NH4＋-N的吸收速率为0.62～1.15μmol/（g·min）;对15NO3--N的吸收速率为0.08～0.15μmol/（g·min）。在NO3--N和NH4＋-N2种形态氮源同时存在的混合组中,斜生栅藻对NO3--N的吸收速率[0.12～1.00μmol/（g·min）]显著低于NO3--N作为唯一氮源的单一组[0.78～1.23μmol/（g·min）],表明NH4＋-N的存在对藻类吸收NO3--N有抑制作用。在14NO3--N和15NO3--N同时存在时,斜生栅藻优先吸收14NO3--N,产生同位素分馏效应,但不同形态氮对藻类氮吸收的影响远远大于同位素的影响。

英文摘要：

Nitrate （NO-3-N） and ammonium （NH＋4-N） nitrogen are the main forms of inorganic nitrogen in waters.This paper studied the uptake characteristics of NO-3-N and NH＋4-N by Scendesmus obliquus based on 15N stable isotope technique. The result showed that the NH＋4-N uptake rate was significantly higher than NO-3-N uptake rate at the same nitrogen concentration,15NH＋4-N uptake rate was 0.62-1.15 μmol/（g·min） while 15NO-3-N uptake rate was 0.08-0.15 μmol/（g·min） in this 3 h experiment.The NO-3-N uptake rate in the mixed nitrogen group [0.12-1.00 μmol/（g·min）]in which both NO-3-N and NH＋4-N presented was significantly lower than that in the single nitrogen group [0.78-1.23 μmol/（g·min）] in which only NO-3-N presented, indicating that the presence of NH＋4-N inhibits the uptake of NO-3-N.The result also showed that when 15NO-3-N and 14NO-3-N existed simultaneously,Scendesmus obliquus took up 14NO-3-N preferentially which produces isotope fractionation.However,the effect of different forms of nitrogen source is far greater than the effect of isotope fractionation.