氮沉降对城市森林凋落物养分元素含量及其耦合性的影响

目前，氮沉降增加呈现全球化趋势，影响森林生态系统生物地球化学循环过程，已成为生态和环境研究的热点内容之一。为探讨氮沉降增加对城市森林凋落物养分含量的影响，进一步认识城市森林养分循环过程，为区域城市化进程的生态风险评估提供科学依据，本研究以安徽省合肥市蜀山国家森林公园凋落物为研究对象，在连续3年模拟氮沉降实验后（氮添加设置3种水平，分别为对照组：0 kg·hm^-2·a^-1、CK；低氮：50 kg·hm^-2·a^-1、LN；高氮：100 kg·hm^-2·a^-1、HN），研究氮沉降对城市森林凋落物（枝叶果碎）养分元素含量及其耦合性的影响。结果表明：（1）不同施氮水平下，凋落果内CK与HN中C元素含量，凋落叶中CK与LN、碎中LN与HN两组中N元素含量差异显著（P＜0.05）。（2）凋落物不同组分间，N沉降显著影响Ca元素含量（P＜0.05），对C元素含量无显著影响；凋落枝组分间K含量差异显著（P＜0.05），凋落叶与其他各组间N含量差异显著（P＜0.05），凋落果与其他各组间P含量差异显著（P＜0.05）；凋落叶与凋落果间Mg元素差异显著。（3）N沉降对各组分间的C/N、C/P、N/P等生态化学计量比无显著性影响，但对凋落叶、凋落果中C/N值有显著抑制作用（P＜0.05）。（4）N沉降显著影响C、N间相关性及Ca、Mg间相关性，且均表现为LN显著增强相关性，HN显著抑制相关性；N沉降显著增强了P、K间的相关性，而显著降低了K与Ca、Mg的相关性。（5）N沉降对C/N与N/P、C/P与N/P间的耦合性有显著影响，且均表现为LN显著增强生态化学计量比间的耦合性，HN显著降低二者耦合性。研究结果为城市森林凋落物养分循环过程对N 沉降的响应提供了理论依据。

Effects of nitrogen deposition on nutrient elements and coupling coordination in urban forest litter

At present, the increase of nitrogen deposition presents a global trend, affecting the biogeochemical cycle of forest ecosystem, and has become one of the hot topics in the international ecological and environmental research. To explore the effects of increased nitrogen deposition on the nutrient content of urban forest litter and further understand the nutrient cycling process in urban forests, so as to provide a scientific basis for the ecological risk assessment of regional urbanization processes, the litter of Shushan National Forest Park in Hefei, Anhui Province, China were selected to study after conducting a simulated nitrogen deposition experiment for three consecutive years (with three nitrogen addition levels: control group: 0 kg·hm^-2·a^-1, CK; low nitrogen: 50 kg·hm^-2·a^-1, LN; high nitrogen: 100 kg·hm^-2·a^-1, HN), for the purpose of examining the effects of nitrogen deposition on the nutrient element content and coupling of the urban forest litter (branches, leaves and fruits).The results showed that: (1) Under different nitrogen application levels, there were significant differences (P<0.05) in the carbon (C) content between CK and HN in the fruit litter, as well as in the nitrogen (N) content between CK and LN, and LN and HN in the leaf and fragment litter. (2) Among different litter components, nitrogen deposition significantly influenced the calcium (Ca) content (P<0.05), but it had no significant effect on the carbon content. There were significant differences (P<0.05) in