摘 要 ：了解三江源人工草地净生态系统CO2交换(Net ecosystem CO2 exchange, NEE)的季节变化规律和主要生物因子及环境因子对这些过程的影响将有助于认识青藏高原人工草地生态系统碳循环、生态价值、功能，以及对三江源区的生态安全的重要意义。该研究利用涡度相关技术，于2005年9月1日至2006年8月31日对位于青海腹地的垂穗披碱草（Elymus nutans）人工草地的NEE及生物和环境因子进行观测， 阐明NEE及其组分的动态变化特征和影响因子。三江源区人工草地生态系统的日最大吸收量为2.38 g C·m－2·d－1，出 现在7月30日。日间最大吸收率和最大排放率都出现在8月，分别为-6.82和2.95μmol CO2·m－2·s－1。在生长季， 白天的NEE主要受光合有效辐射(Photosynthe tically active rad iation, PAR)变化控制，同时又与叶面积指数和群落多样性交互作用，共同调节光合速率和光合效率的强度。最大光合同化速率为2.46～10.39μmol CO2·m－2·s－1，表观初始光能利用率为0.013～0.070μmol CO2·μmol－1 PAR。 在碳交换日过程中，NEE并不完全随着 PAR的增加而增大，当PAR超过某一值（>1 200μmol ·m－2·s－1）时，NEE随PAR的增加而降低。受温度的影响，生长季的生态系统的呼吸商Q10（1.8）小于非生长季节的 2.6）。 生态系统呼吸主要受温度的控制，同时也受到叶面积指数的显著影响。生长季昼夜温差大并不利于生态系统的碳获取。 三江源区人工草地生态系统是一个较强的碳汇，为-49.35 g C·m－2·a－1。
Abstract:Aims It is important to the study of the carbon cycle and ecological issues to understand seasonal variation in CO2 flux and the influence of environ mental factors on the artificial grassland in the source region of the three rivers on the Qinghai-Tibetan Plateau. Methods We utilized the eddy covariance method to observe net ecosystem CO2 exchange (NEE) and biological and environmental factors and their variation at the Elymus nutans artificial grassland from September 1, 2005 to August 31, 2006. Important findings The daily maximum uptake of CO2 was 2.38 g C·m－2·d－1 on July 30. The ratio of daily uptake and emission in August were observed, -6.82 and 2.95μmol CO2·m－2·s－1, respectively. In the growing seasons, daily NEE was dominated by the variation of photosynthetically active radiation (PAR). At the same time, daily NEE combined with leaf area and community diversity to control photosynthetic rate and photosynthetic efficiency. Maximum photosynthetic rate was 2.46-10.39μmol CO2·m－2·s－1, and the apparent quantum yield (denoting the maximum efficiency of light utilization in photosynthesis) was 0.013-0.070μmol CO2·μmol－1 PAR. The influence of temperature, Q10 (1.8) in the growing season was less than in the non-growing season. The respiration of the ecosystem was mainly dominated by temperature and leaf area. Carbon absorption was not dominated by the larger temperature difference of the day and night in the growing season. Our study proved that the artificial grassland ecosystem was a carbon sink with a carbon absorption of -49.35 g C·m－2·a－1. Our study also proved that the source and sink function of carbon was influenced by the amount, intensity and seasonal allocation of annual precipitation, as well as by plant community diversity.