申请人从事森林生态系统氮循环、氮沉降、稳定同位素生态学研究。主要学术成绩：1）研究了氮沉降对森林生态系统氮循环的影响，发现氮沉降快速加剧南亚热带森林氮流失和土壤酸化、增加土壤无机向可溶性有机氮（DON）转化和流失。发现我国森林整体上氮流失率相对欧洲森林较低；2）量化了森林氮沉降速率、组成、空间分布和历史变化，发现氮污染环境下DON是氮沉降的重要组分；3）探讨了叶片15N自然丰度对森林氮饱和程度的指示作用，揭示了氮污染城市硝酸盐氮来源和形成过程，揭示了森林土壤硝酸盐氧来源，建立了硝酸盐氮氧同位素技术量化集水区尺度反硝化作用速率技术。研究成果丰富了森林生态系统氮生物地球化学循环的理论，为制定氮管理政策提供依据。发表SCI论文35篇，其中第一作者和通讯作者15篇。论文在SCI他引291次，单篇被SCI引用最高65次。申请项目拟运用15N示踪法研究热带和温带典型森林土壤氮气损失及其对氮沉降的响应。

I have been involved for more than 10 years in the research on nitrogen cycling in forest ecosystems, atmospheric nitrogen deposition, and applications of stable isotopes in N cycling. Main achievements include: 1) using N-addition experiments and along an N deposition gradient, we have systemically investigated N cycling processes, e.g., N leaching, N retention and N transformations and their responses to N deposition in subtropical forests in southern China. We found that N addition immediately and drastically increased inorganic N leaching in all study forests. N addition also increased dissolved organic N leaching, suggesting that inorganic N added can be converted into organic N in N-saturated forest soils. Increased N leaching induced by N addition had led to further soil acidification and our results provide an explanation for constant acidification observed in the last three decades in the study forests. 2) We have quantified the rates and compositions of atmospheric N deposition in southern China. We also explored N sources and formation pathways of atmospheric nitrate using nitrate dual isotopes, and examined three-decade changes in N deposition in Guangzhou city. We found that organic N is important component at air N pollution conditions, accounting for 20-30% of total N deposition. In addition, we have reviewed current status of N deposition into forest ecosystems and N leaching in China, so that we can discuss the contribution of elevated N deposition to carbon sequestration in Chinese forest ecosystems. 3) We have explored ecosystem N availability at a global scale since 1850 and changes with increased N deposition at regional scales (in southern China and across East Asia), using plant 15N natural abundance. We also determined N and O isotopes for nitrate produced from soil nitrification in 9 temperate forests, and pointed to that δ18O can not be calculated based on a theoretical ratio of 2:1 using δ18O of soil H2O and O2 and that many of previous studies have underestimated the contribution of atmospheric nitrate into terrestrial ecosystems. In addition, we have developed a novel method, using nitrate triple isotopes, to quantified denitrification loss at a forested catchment scale and found N loss via denitrification was much larger than that previously appreciated in three tropical and three temperate forests. Our results listed above have been published by some high quality journals such as Global Change Biology, Atmospheric Physics and Chemistry, Environmental Science & Technology. In total, I have co-authored 35 peer-review SCI journal papers, among which 15 I was leading and/or corresponding authors. All publications have been cited by 291 times by other researchers, with the highest record of 65 times for a single publication. The proposed project is designed to quantify N2 losses in both tropical and temperate typical forests and their responses to elevated nitrogen deposition, using 15N tracer technique.

森林土壤是陆地生态系统中重要的氮库，在调节区域及全球氮素平衡中发挥着重要的作用。氮损失途径包括淋溶损失和气态氮损失，然而目前对于气态氮损失，特别是氮气损失量及途径还不清楚。在全球氮沉降格局改变的背景下，如果过多的氮输入以氮气形式返回大气则一定程度上可以减缓氮沉降造成的环境负效应。为此本项目在我国首次建立和优化氮气同位素分析方法，量化了中国热带森林、温带森林土壤氮气排放速率及其微生物过程贡献。研究主要发现：1）野外原位条件下N2释放远高于N2O，达25倍多，二者释放速率随土壤湿度的增加而增加，而N2O/(N2 + N2O)比值出现下降趋势。基于该比值和年均N2O释放通量，估测出清原温带森林生态系统水平上土壤N2释放通量为3.2 kg N ha-1 yr-1。2）清原混交林N2排放高于落叶松人工林。反硝化作用依然是这两个森林土壤N2产生的主要途径。厌氧氨氧化过程主要发生在表层土壤，与共反硝化作用对N2贡献能达到12%。3）清原森林土壤N2O和N2释放速率的温度敏感性Q10为1.0~1.4和1.2~1.9，无显著差异。4）随着氮添加量的增加，热带次生林表现出土壤N2O排放速率降低和N2排放速率增加的趋势，原始林中并没有发现类似的现象。氮添加同时降低了反硝化作用对N2O的排放贡献而增加了共反硝化和异养硝化作用的贡献。反硝化作用是氮气产生的主要途径（98-100%），并且不受氮添加的影响。5）反硝化作用产生N2O的氮氧同位素分馏作用（15ε和18ε）分别为31-65‰和11-23‰，15ε的分馏作用远高于以往研究（5-30‰），而15ε和18ε比值（0.22-0.60）小于以往研究（0.5-1）。硝化作用产生NO的氮同位素分馏系数（-65‰）较反硝化作用（-30‰）偏负，这与土壤产生N2O的氮15ε相关研究结果相似。本项目的实施能够加深我们对森林土壤气态氮损失及其对氮沉降的响应的认识，增强对森林生态系统氮循环及其对全球变化的预测能力，丰富对陆地生态系统生物地球化学循环的理解。项目执行期间共发表相关SCI论文7篇于Ecological Monograph，Applied and Environmental Microbiology，Soil Biology Biogeochemistry等国际主流刊物上，超额完成既定研究任务和目标。