中文摘要：

利用千烟洲人工林基于涡度相关技术的碳水通量数据,同时借助基于生理生态学过程EALCO模型的冠层导度（Gc）模拟值,分别从生态系统水分利用效率（WUE）、内在水分利用效率（WUEi）及固有水分利用效率（IWUE）等方面探讨季节性干旱对我国中亚热带人工林水分利用效率的影响。结果表明：短期干旱期间WUE下降;干旱对全年WUE的影响不明显,全年WUE与太阳辐射存在显著的负相关关系（r=-0.903,P=0.014）。WUEi和IWUE在短期干旱状况下表现为升高,根据它们的物理意义,这表明在大气CO2浓度不变的情况下,干旱发生时通量贡献区内森林冠层的胞间CO2浓度权重平均值减小。当相对土壤含水量（REW）〈0.4时,WUEi迅速升高,因此可以将REW=0.4作为WUEi受到干旱胁迫的阈值。与WUE相比,WUEi和IWUE能够更好地表征环境改变后植物的生理响应。

英文摘要：

Data from the eddy covariance measurements in Qianyanzhou plantation forest in ChinaFLUX （2003 -2008） and a process-based model （EALCO） were applied to estimate of gross primary production （GPP）, evapotranspiration （ET） and canopy stomatal conductance at the ecosystem level. In terms of water use efficiency （WUE）, intrinsic water use efficiency （WUEi） and inherent water use efficiency （ IWUE）, the effects of seasonal drought on the coupling of carbon and water were investigated. The results showed that for the short-term response to drought, WUE decreased during drought. There were no obvious effects of drought on annual WUE. However, annual WUE was significantly correlated with solar radiation （r = -0. 903,P = 0. 014）. In response to the short-term drought, the WUEi and IWUE increased, which suggested that the weighted average concentration of intercellular carbon dioxide through the canopy and within the tower footprint reduced in drought occurrence with a constant atmospheric CO2 concentration. WUEi increased sharply when REW（relative extractable soil water） dropped below 0.4, thus REW = 0.4 might be taken as a threshold to identify WUEi under drought stress. Compared to WUE, IWUE and WUEi are more appropriate for describing the biochemical functions of vascular plants and should be applied more in the future research.