中文摘要：

以三江平原沼泽湿地典型湿地植物小叶章枯落物（Calamagrostisangustifolia）为研究对象，采用分解袋法研究了不同外源氮输入（N1、N2分别为6、12g·m^-2a^-1）对小叶章枯落物分解过程酶活性的影响，并设置对照区（NO，0g·m^-2a^-1）进行比较．研究结果表明，在枯落物最初分解的2个月里，氮输入会抑制蔗糖酶活性，尤其是低氮输人（NI）抑制作用显著（p〈0．05），2个月后，氮输入显著促进了该酶活性（p〈0．05）；氮输入除在160d时抑制了淀粉酶活性，其它时期均促进了该酶活性，且高氮输入（N2）促进作用显著；氮输入提高了枯落物分解前2个月的脲酶活性，而在分解后期，低氮输入抑制脲酶活性，高氮输入则主要表现为促进脲酶活性；低氮输入提高了小叶章枯落物分解前2个月的酸性磷酸酶活性，随后表现为抑制，高氮输人则只在分解后期（160d）抑制酸性磷酸酶活性，其它时期均表现为促进．总体而言，氮输入促进了蔗糖酶、淀粉酶活性，而对于脲酶及酸性磷酸酶活性来说，低氮输入抑制了酶活性，而高氮输入则表现为促进酶活性．

英文摘要：

To explore the effects of exogenous nitrogen input on the enzyme activity of Calamagrostis angustifolia during litter decomposition in a freshwater marsh, we supplied dissolved N H4 NO3 （NO ：0; N1：6 g·m^-2a^-1;N2：12 g·m^-2a^-1） to field plots on the Sanjiang Plain and determined the enzyme activities of litter decomposition within 160 d using litter bags. The results showed that nitrogen addition suppressed the invcrtase activity in the first two months of the decomposition period and low-nitrogen addition （N1） had significant suppression （p 〈 0.05）, but the enzyme activity was obviously increased by nitrogen input（p 〈0.05）after 60 d. Nitrogen input promoted amylase activity, except at a decomposition time of 160 d. Nitrogen addition increased the activities of urease and acid phosphatase in the first two months of litter decomposition, but after that different nitrogen treatments had different effects. Nitrogen input at all concentrations increased the activities of invertase and amylase. Although low-nitrogen addition inhibited acid phosphatase and urease activity, high-nitrogen addition promoted their activity.