在全球氮、磷化肥污染加剧、大气氮沉降增加的背景下，河岸带森林生态系统将如何响应氮磷输入的增加已成为学术界关注的焦点。本项目以秦岭南坡重要水源地（金水河流域）的典型河岸带森林生态系统为研究对象，在前期研究基础之上，开展野外添加氮磷的控制实验、凋落物输入调控实验、稳定同位素示踪实验。通过改变氮、磷及凋落物的输入以研究河岸带森林生态系统的土壤碳氮循环关键过程（凋落物分解、碳氮矿化作用、硝化作用、固氮作用、反硝化作用、CO2、CH4及N2O排放）及其耦合关系，揭示土壤碳氮库组分及碳氮循环关键过程对氮磷输入增加的响应。在此基础上，结合土壤微生物宏基因组学技术(Metagenomics)及碳氮循环关键功能基因分析，揭示土壤碳氮循环关键耦合过程响应氮磷输入增加的微生物学机制。本研究的结果将丰富和发展对河岸带森林生态系统碳氮循环的认识，为南水北调中线工程水源地生态系统管理提供重要信息。

The increasing nitrogen (N) and phosphorus (P) fertilizer inputs and atmospheric N deposition have brought about serious pollution problems and significantly influenced the natural ecosystems. Naturally, riparian forest ecosystems are important barriers preventing the N & P pollutants from agricultures to aquatic ecosystems. Thus, the response of riparian forest ecosystems to the increased N & P inputs has received extensive attention in ecology and global change research. However, the responses of soil C and N cycling processes in riparian forest to the increased N & P inputs are poorly understood. This research project will be built upon our previous studies on ecosystems in the Jinshui River watershed, an important water resources conservation region for the middle line of the South-to-North Water Transfer Project (SNWTP), located in the south aspect of the Qinling Mts. We will conduct N & P addition experiment, litter manipulating (double & remove) experiment, and 13C & 15N labeled-litter decomposition experiment in typical riparian forest ecosystems in Jinshui watershed in order to reveal the response of soil important C & N cycling processes and their coupled relationships to the increased N & P inputs. The important soil C & N cycling processes, i.e., litter decomposition, mineralization, N fixation, nitrification, denitrification, CO2, N2O, and CH4 fluxes, will be measured, and their coupled relationships will be analyzed based on results of the N, P & litter manipulating experiments. Moreover, the soil microbial community composition and the occurrence of genes encoding carbohydrate and lignin decomposition will be revealed by metagenomic analysis and the abundance of key soil microbial functional genes associated with C & N cycling will be quantified by quantitative PCR, including cbhI gene (encoding for cellobiohydrolase), chiA gene (mineralization/ammonification), mcrA gene (the methyl coenzyme M reducreductase subunit A gene), pmoA gene (the particulate methane monooxygenase gene), nifH gene (N fixatioin), amoA gene (nitrification), narG, nirK, nirS and nosZ genes (denitrification). The mechanisms and the regulations mediated by soil microbes for the response of important soil C & N cycling processes to the increased N & P inputs will be revealed by synthesizing all the data obtained in our experiments. The results of this project will fill some knowledge gaps on soil C & N cycling in riparian forest ecosystems and provide useful information for ecosystem management in SNWTP.