中文摘要：

目前,高寒草甸对全球温室效应的贡献仍具有不确定性,而随着N沉降的增加,该系统温室体气排放也必将发生变化。为揭示高寒草甸对N沉降的响应机制,探讨其对全球变化的反馈作用,利用人工添加氮素的方法,于2014年生长季（6-9月）在那曲地区那曲县设置不同水平N添加梯度（0、7、20kg hm^-2a^-1和40 kg hm^-2a^-1）,模拟氮沉降增加对藏北高寒草甸温室气体排放的影响。经过1a的研究结果表明：1）施氮显著促进了CO2排放但对CH4的吸收和N2O的排放无显著影响。总体而言,添加氮素明显增加了温室气体排放总量,其中N2O处理下高寒草甸温室气体排放总量最高。2）回归分析结果表明,CO2与NPP（总生物量）和TOC（土壤有机碳）线性相关（P〈0.05）,而与TN（总氮）、NH4^＋-N和NO3^--N均无显著相关关系（P〉0.05）,CH4与TN/NPP/TOC/NH4^＋-N/NO3^--N均不相关（P〉0.05）,N2O与NPP/TOC/NO3^--N均显著线性相关（P〈0.05）,而与TN/NH4^＋-N不相关。综合初步研究结果,未来氮沉降增加条件下,藏北高寒草甸温室气体排放通量将有可能明显增加,从而对气候变化产生重要的反馈作用。

英文摘要：

The alpine meadow is the largest and most important ecosystem in northern Tibet. Recently, nitrogen deposition in Tibet has had a profound impact on carbon and nitrogen cycles in grassland ecosystems. To assess the impact of nitrogen deposition on greenhouse gas emissions from alpine meadows in northern Tibet, we conducted a nitrogen fertilizing experiment, using four fertilizing levels of 0, 7, 20, and 40 kg hm^-2 a^-1, in Nagqu County in the growing season in 2014. Our results showed that the impact on greenhouse gas emission varied with different levels of nitrogen deposition. Regarding daily variation, nitrogen significantly enhanced CO2 emission but had no effect on the absorption of CH4, or the emission of N2O. Overall, nitrogen deposition significantly increased greenhouse gas emissions. The highest emission occurred with the N20 treatment, and there was a positive correlation among CO2, net primary productivity （NPP）, and total organic carbon （TOC） （P 〈 0.05）. The total nitrogen （TN）, NH4^＋-N, and NO3^--N were not correlated with CO2 （P 〉 0.05）, and the same pattern was observed in the relationship between CH4 and TN/NPP/TOC/NH4^＋-N/NO3-N （P 〉 0.05）. N2O levels showed a significant linear correlation with NPP/TOC/NO3-N （P 〈 0.05）, but were not correlated with TN/NH4^＋-N （P 〉 0.05）. With additional nitrogen deposition expected in the future, greenhouse gas emissions would increase significantly and have a positive or negative feedback on climate change in Northern Tibet.