Year-round eddy covariance flux measurements were made in a semiarid grassland in Mongolia during 20092014 to examine the interannual variability in net ecosystem CO2 exchange (NEE) and its climatic controls. Annual cumulative NEE ranged from -20.9 to 8.1 g C m yr, indicating that the semiarid grassland ecosystem can be a carbon source or a carbon sink, depending on climatic conditions. A correlation analysis showed that interannual variability in NEE was significantly related to precipitation and soil water content at 10 cm depth (SWC10) in June and to the vapor pressure deficit (VPD) in July. In addition, the variation in gross primary production (GPP) in July contributed most to the interannual variation in NEE; and GPP in July was significantly related to June precipitation, June SWC10, and July VPD. From these results, we concluded that precipitation during the early growing season and air dryness during the middle growing season were essential climatic factors regulating the interannual variation in NEE in this semiarid grassland.

中文翻译：

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蒙古半干旱草原净生态系统CO ₂交换的年际变化及其气候控制

20092014 年期间在蒙古的半干旱草原进行了全年涡流协方差通量测量，以检查净生态系统二氧化碳交换 (NEE) 的年际变化及其气候控制。年累积 NEE 范围为 -20.9 至 8.1 g C m yr，表明半干旱草原生态系统可以是碳源或碳汇，这取决于气候条件。相关性分析表明，NEE的年际变化与6月份10 cm深度的降水和土壤含水量（SWC10）以及7月份的水汽压亏缺（VPD）显着相关。此外，7月份初级生产总值（GPP）的变化对NEE的年际变化贡献最大；7 月 GPP 与 6 月降水、6 月 SWC10、7 月 VPD 显着相关。从这些结果来看，