中文摘要：

为了揭示三江源区垂穗披碱草（Elymus nutans）人工草地生态系统（100°26′-100°41′E,34°17′-34°25′N,海拔3980m）的净生态系统CO2交换（NEE）,该研究利用2006年涡度相关系统观测的数据分析了该人工草地的NEE,总初级生产力（GPP）、生态系统呼吸（Reco）以及Reco/GPP的变化特征及其影响因子。CO2日最大吸收值为6.56g CO2·m-2·d-1,最大排放值为4.87g CO2·m-2·d-1。GPP年总量为1761g CO2·m-2,其中约90%以上被生态系统呼吸所消耗,CO2的年吸收量为111g CO2·m-2。5月的Reco/GPP略高于生长季的其他月份,为90%;6月Reco/GPP比值最低,为79%。生态系统的呼吸商（Q10）为4.81,显著高于其他生态系统。该研究表明：生长季的NEE主要受光量子通量密度（PPFD）、温度和饱和水汽压差（VPD）的影响,生态系统呼吸则主要受土壤温度的控制。

英文摘要：

Aims Our objective was to understand seasonal and diurnal variations in CO_2 exchange of a grassland ecosystem by clarifying the carbon cycle and its affecting factors for a planted pasture ecosystem in the Sanjiangyuan Region of the Qinghai-Tibetan Plateau.Methods We used the eddy covariance method to measure net ecosystem CO_2 exchange （NEE） and environmental factors in the planted pasture （Elymus nutans） ecosystem in 2006.Important findings Daily maximum uptake and release of CO_2 were 6.56 and-4.87 g CO_2·m-2·d-1,respectively.Maximum rates of NEE uptake and release were-0.35 and 0.22 mg CO_2·m-2·s-1,respectively.Annual gross primary production （GPP） was 1 761 g CO_2·m-2·a-1,of which more than 90% was consumed by ecosystem respiration （Reco）.Annual NEE was-111 g CO_2·m-2.In the growing season,maximum and minimum Reco/GPP values were 90% in May and 79% in June,respectively.The Q10 was 4.81,which is higher than in other ecosystems.The NEE was mostly influenced by photosynthetic photon flux density （PPFD）,temperature and vapor pressure deficit （VPD）.The Reco was mainly affected by soil temperature at 5 cm depth （Ts）.