Water use efficiency (WUE, the ratio of gross primary productivity (GPP) to evapotranspiration (ET)) reflects the coupled relationship between water loss and carbon gain in the process of plant photosynthetic carbon assimilation. As a dominant tree species in arid area, Populus euphratica plays an important ecological role in slowing desertification. Here, continuous observations of carbon, water, and energy fluxes were carried out in Populus euphratica forest with eddy covariance (EC) technique in 2018. We systematically explained the variation characteristics of energy fluxes and WUE at different time scales, and explored the main controlling factors of WUE in drought-stressed environment based on the synchronous meteorological data. Results showed that the carbon exchange of the Populus euphratica forest ecosystem occurred mainly during the growing seasons (April–October). During this period, the entire ecosystem appeared as a carbon sink with the potential to sequester atmospheric carbon dioxide. The average daily WUE was 2.2 g C/kg H₂O, which was lower than other temperate forests (2.57–6.07 g C/kg H₂O) but higher than grassland, wetland, and cropland. We also concluded that an increase in carbon dioxide concentration (CCO₂) and air relative humidity (RH) could promote the increase of WUE. Nevertheless, WUE was negatively correlated with air temperature (Ta), photosynthetically active radiation (PAR), and normalized difference vegetation index (NDVI). Additionally, WUE increased under moderate soil water content (SWC), but decreased due to the continuously rising SWC. WUE was more strongly affected by factors affecting water consumption than carbon uptake. Under the conditions of high temperature, strong radiation and low humidity in the summer, the growth rate of ET was much larger than that of GPP. This study not only contributes to our understanding of the carbon, water, and energy dynamics of the Populus euphratica forest ecosystem but also provides an important reference for ecological conservation and ecological restoration in arid regions.

水分利用效率（WUE，总初级生产力（GPP）与蒸散量（ET）之比）反映了植物光合碳同化过程中水分流失与碳增加之间的耦合关系。胡杨作为干旱地区的优势树种，在减缓荒漠化方面起着重要的生态作用。在这里，利用涡度协方差（EC）技术对胡杨林中的碳，水和能量通量进行了连续观测（2018年）。我们系统地解释了不同时间尺度上能量通量和WUE的变化特征，并探讨了主要的控制措施。同步气象资料的干旱胁迫环境中水分利用效率的影响因素 结果表明，碳交换胡杨林生态系统主要发生在生长季节（4-10月）。在此期间，整个生态系统似乎是一个碳汇，有可能封存大气中的二氧化碳。平均每日WUE为2.2 g C / kg H ₂ O，低于其他温带森林（2.57–6.07 g C / kg H ₂ O），但高于草地，湿地和农田。我们还得出结论，二氧化碳浓度（CCO ₂）和空气相对湿度（RH）可以促进WUE的增加。然而，WUE与气温（Ta），光合有效辐射（PAR）和归一化植被指数（NDVI）呈负相关。此外，在中等土壤含水量（SWC）下WUE有所增加，但由于SWC持续升高，WUE有所降低。WUE受影响水消耗的因素比吸收碳的影响更大。在夏季高温，强辐射，低湿的条件下，ET的生长速率远大于GPP。这项研究不仅有助于我们了解胡杨的碳，水和能量动力学 森林生态系统，也为干旱地区的生态保护和生态恢复提供重要参考。