华西雨屏区亮叶桦凋落叶分解对模拟氮沉降的响应

从2008年1月至2009年2月, 对华西雨屏区亮叶桦(Betula luminifera)人工林进行了模拟氮(N)沉降试验, N沉降水平分别为对照(CK, 0 g N·m^-2·a^-1)、低N (5 g N·m^-2·a^-1)、中N (15 g N·m^-2·a^-1)和高N (30 g N·m^-2·a^-1)。利用凋落袋法对亮叶桦凋落叶进行原位分解试验, 并在每月下旬定量地对各处理施N (NH₄NO₃)。结果表明, 虽然华西雨屏区大气N沉降量较高, 但模拟N沉降试验表明: 在N沉降继续增加的情况下, 凋落叶分解这一碳(C)循环和养分循环过程仍会受到显著影响。在1年的分解试验中, 模拟N沉降显著抑制了亮叶桦凋落叶的分解, N沉降处理使得凋落叶质量损失95%的时间在2.65年的基础上增加了1.14-1.96年。N沉降抑制凋落叶分解的原因在于无机N的富集对木质素和纤维素的分解造成阻碍。N沉降处理也导致C、N、磷、钾和镁元素在凋落物中的残留量增加, 但N沉降加速了钙元素的释放。凋落物基质化学特性在很大程度上决定了凋落物分解对N沉降的响应方向, 以及凋落物分解过程中各元素的动态变化。

Response of Betula luminifera leaf litter decomposition to simulated nitrogen deposition in the Rainy Area of West China

Aims Our objective was to determine the effect of simulated increased nitrogen (N) deposition on decomposition of Betula luminifera leaf litter, under a high wet-nitrogen deposition background.
Methods From January 2008 to February 2009, a field experiment of simulated N deposition was conducted in a B. luminifera plantation in the Rainy Area of West China. The levels of nitrogen deposition were control (CK), low, medium and high N (0, 5, 15 and 30 g N·m^–2·a^–1, respectively). A field experiment using the litterbag method was conducted on the decomposition of leaf litter of B. luminifera. In the end of each month, NH₄NO₃ was added into N-treated plots.
Important findings Despite the high background N deposition, there were significant effects of simulated increased N deposition on B.luminifera leaf litter. N treatments significantly slowed the decomposition of B. luminifera leaf litter through inhibiting the decay of lignin and cellulose. The time of 95% mass loss (T_95%) of B. luminifera leaf litter was increased by 1.14–1.96 a from 2.65 a (T_95% of CK) caused by simulated N deposition. Simulated N deposition significantly increased the remaining amount of carbon, N, phosphorus, potassium, and magnesium after one year of decomposition. However, calcium release rate was stimulated by simulated N deposition in all three N treatments. The initial chemical characteristics of litter determined the response direction of litter decomposition to simulated N deposition, as well as the nutrient release pattern during litter decomposition.