水浮莲(Pistia stratiotes L．)对NH_4~+-N和NO_3~--N吸收动力学研究

水体中的营养元素过多（特别是氮、磷）所导致的富营养化现象已是全球性的环境问题。近来利用大型维管束植物对富营养化水体的修复已备受关注。然而，水体中氮的去除受到包括氮的离子形态及其在水体中浓度等各种因素的影响。研究通过Michaelis—Menten动力学方程来研究植物根系表面氮的浓度与植物吸收氮的相互关系。该方程包括2个参数：吸收最大速率（Vmox）和米氏常数（Km），其分别表示植物吸收不同氮形态的最大速率和对不同氮形态亲和力的高低。利用加权回归分析结果表明，生长在不同浓度营养液水浮莲（Pistia stratiotes L．）吸收速率拟和Michaelis—Menten方程。水浮莲对NH4^＋LN的Km很高。表明其对NH4^＋-LN亲和力高；在NO3^--N单一氮源提供下，水浮莲对NO3^--N的吸收动力学与NH4^＋-N相似。然而，在营养液中同时存在NH4^＋-N和N03^--N时，NO3^--N吸收的最大速率明显降低，但对其Km的影响不大，这种抑制作用看来属于非竞争性的。在NH4^＋-LNN和NO3^--N的同时存在下，由于植物吸收NO3^--N能力的降低可能导致植物对氮的利用率下降。

The Kinetic of Ammonium and Nitrate Uptake by Water Lettuce (Pistia stratiotes L.)

Eutrophication, which overenrich with nutrients (principally nitrogens and phosphorus) in water bodies, has been recognized as a global problem. Macrophytes play a major role in nutrient removal. However, nitrogen removal is affected by many factors including the N-ion species and its concentration in water bodies. In the present study, the relation between N concentration at the root surface and N uptake was characterized using Michaelis-Menten kinetics. The equation involves two parameters, Vmax and Km, which are measures of the maximum rate of uptake and the affinity of the uptake sites for the nutrient, respectively. Uptake rates of water lettuce (Pistia stratiotes L.) growing in a different concentration nutrient solution system were fitted to the Michaelis-Menten model using a weighted regression analysis. For NH4 -N the Km values for Pistia stratiotes L. indicated a high affinity for the ammonium ions, and the kinetics of NO3--N uptake was similar to that of NH4 -N when NO3--N was the only N source. However, if NH4 -N and NO3--N were coexistent in the solution, the Vmax for the uptake of NO3--N was obviously reduced, while the Km was influenced very little. The inhibition seems to be noncompetitive. The coexistence of NH4 -N and NO3--N at the root surface may also result in inefficient N recovery because of decreased uptake of NO3--N.