中文摘要：

植被和大气之间CO2通量的观测有助于理解陆地生态系统的碳循环及其控制机理。以中国北方典型草原克氏针茅草原为研究对象，以涡度相关法为主要技术手段，探讨了2008年生长季内克氏针茅草原净生态系统碳交换（NEE）的变化特征。结果表明，克氏针茅草原生态系统CO2通量的日变化进程可以依据高峰出现的时间分为两种，一种具有一个吸收高峰，出现在11：00左右，另一种则具有两个吸收高峰，在正午前后出现碳释放现象。2008年克氏针茅草原生态系统最大的CO2吸收速率为-0．4mg·m^-2·s^-1。克氏针茅草原在4月和10月的NEE昼夜变化比较平缓，在5—9月日间CO2吸收量和夜间CO2排放量都开始增大，出现了明显的CO2日吸收峰值，但各月的日动态格局差异较大。2008年生长季中7—9月白天碳吸收活动最强，6—9月夜间CO2释放量较大。克氏针茅草原碳通量日累积量在2008年出现了3个明显的碳吸收峰；NEE的日最大累积吸收量和最大累积释放量分别为-2．38和1．47gC·m^-2·d^-1，并且出现在植被生长最旺盛的7、8月份。研究表明，温度和水分是影响克氏针茅草原生态系统碳通量变化的重要因子。

英文摘要：

Long-term measurement of the CO2 fluxes between the vegetation and the atmosphere has facilitated the research on carbon cycte in terrestrial ecosystems and its controlling mechanism. Based on the eddy covariance measured CO2 fluxes at the Stipa krylovii ecosystem in northern China, the variation of net ecosystem CO2 exchange（NEE） in growing season in 2008 was discussed. The results indicated that there had two different CO2 flux daily patterns at the Stipa krylovii ecosystem. One had a single uptake peak with the maximum CO2 uptake peak around 11 ： 00, and the other had a dual peak in daily course of CO2 fluxes with CO2 emission before and after noon. The maximum CO2 uptake rate was -0.4 mg·m^-2·s^-1 in 2008, which was in the low level contrasted with the values of other grasslands. The variation of NEE in April and October had small ranges, and the uptake and emission values of CO2 began to increase from May to September with obvious CO2 uptake peak. In 2008, there had the strongest daytime uptake from July to September and the strongest nighttime emission happened from June to September. With the rise of the temperature and the more rainfall, the Stipa krylovii ecosystem shows the characteristic of carbon sink. There have three obvious uptake peak of daily integrated NEE for Stipa krylovii ecosystem in 2008. Daily integrated NEE reached its uptake and emission peak magnitude of-2.38 g C ·m^-2·d^-1 and 1.47 g C ·m^-2·d^-1 respectively in July and August when the plant was in vigorous growth period. The research shows that the temperature and the moisture, but not limited to, are the most important factors to impact the variation of net ecosystem carbon flux exchange over Stipa krylovii steppe.