模拟氮沉降对华西雨屏区苦竹林凋落物基质质量的影响

凋凋落物基质质量是影响凋落物分解速率的决定性因子之一，本研究旨在探究模拟氮沉降对苦竹林凋落物基质质量的影响。2007年11月至2010年12月每月一次连续对华西雨屏区苦竹人工林进行了模拟氮沉降试验，施氮水平分别为：低氮（5 g N?m–2?a–1），中氮（15 g N?m–2?a–1）和高氮（30 g N?m–2?a–1）。在施氮2 a后，于2010年1月开始收集各样方的凋落物样品，连续收集12个月，分析测定凋落物基质质量。结果表明：施氮显著增加了凋落叶中N、P元素含量，中氮处理显著增加了凋落枝中N元素含量，中氮和高氮处理均显著增加了凋落枝中P元素含量；施氮对凋落物中C元素含量影响很微弱，显著降低了凋落叶中的C/N，中氮处理显著降低了凋落枝中的C/N，对木质素和纤维素含量均未造成显著影响。由于模拟氮沉降增加了苦竹凋落物的N、P含量，降低了其C/N，因此氮沉降可能会促进苦竹凋落物的初期分解速率。

Effects of simulated nitrogen deposition on substrate quality of litterfall in a Pleioblastus amarus plantation in Rainy Area of West China

Forest litter is an important part of forest ecosystem and its chemical property is called substrate quality, which is defined as the relative decomposability of litter and depends on the easy decomposition components of the organization. A number of studies have found that the substrate quality of litter is the main factor affecting the litter decomposition process, which is the key process of biological chemical cycle of forest ecological system. In order to investigate the effects of N deposition on the substrate quality of bamboo forest litter, a simulated N deposition experiment was conducted in a P. amarus plantation in Rainy Area of West China, from November 2007 to December 2010. Four treatments was installed, i.e., control (0 g N·m^-2·a^-1), low nitrogen (5 g N·m^-2·a^-1), medium nitrogen (15 g N·m^-2·a^-1) and high nitrogen (30 g N·m^-2·a^-1). From January to December in 2010, litter samples were collected each half month and the basic properties of litter quality (concentration of C, N, P, lignin and cellulose) were measured. The results indicate that simulated N deposition significantly increased the concentration of N and P in leaf litter and medium nitrogen treatment increased the N content of twig litter, meanwhile medium and high nitrogen treatments increased the P content of twig litter; The effects of simulated N deposition on concentration of C, lignin and cellulose were not significant. The C/N ratio of leaf litter and twig litter were decreased significantly. Results suggest that the litter decomposition rate in early stage of decomposition may be stimulated by simulated N deposition because of increasing N (decreased C/N ratio) and P in fresh fallen litter.