华西雨屏区亮叶桦凋落叶分解对模拟氮沉降的响应

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

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,0gN·m-2·a-1)、低N(5gN·m-2·a-1)、中N(15gN·m-2·a-1)和高N(30gN·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。

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 ofB. 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 ofB. luminifera leaf litter through inhibiting the decay of lignin and cellulose. The time of 95% mass loss （T95%） ofB. lumi- nifera leaf litter was increased by 1.14-1.96 a from 2.65 a （T95% 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.