Abstract. Disentangling ecosystem evapotranspiration (ET) into evaporation (E) and transpiration (T) is of high relevance for a wide range of applications, from land surface modelling to policy making. Identifying and analysing the determinants of the ratio of T to ET (T / ET) for various land covers and uses, especially in view of climate change with increased frequency of extreme events (e.g., heatwaves and floods), is prerequisite for forecasting the hydroclimate of the future and tackling present issues, such as agricultural and irrigation practices. A powerful partitioning method consists in determining the water stable isotopic compositions of ET, E, and T (δ_ET, δ_E, and δ_T, respectively) from the water retrieved from the atmosphere, the soil, and the plant vascular tissues. The present work emphasises the challenges this particular method faces (e.g., the spatial and temporal representativeness of the T / ET estimates, the limitations of the models used and the sensitivities to their driving parameters) and the progress that needs to be made in light of the recent methodological developments. As our review is intended for a broader audience beyond the isotopic ecohydrological and micrometeorological communities, it also attempts to provide a thorough review of the ensemble of techniques used for determining δ_ET, δ_E, and δ_T, and solving the partitioning equation for T / ET. From the current state of research, we conclude that the most promising way forward to ET partitioning and capturing the sub-daily dynamics of T / ET is in making use of non-destructive online monitoring techniques of the stable isotopic composition of soil and xylem water. Effort should continue towards the application of the eddy covariance technique for high-frequency determination of δ_ET at the field scale as well as the concomitant determination of δ_ET, δ_E, and δ_T at high vertical resolution with field-deployable lift systems.

中文翻译：

---

综述与综合：利用新型同位素监测方法深入了解蒸散量

摘要。将生态系统的蒸散量（ET）分解为蒸发量（E）和蒸腾量（T）与从土地表面建模到政策​​制定的广泛应用具有高度相关性。识别和分析各种土地覆盖和用途中T与ET之比的决定因素（T / ET），尤其是考虑到气候变化以及极端事件（例如热浪和洪水）的发生频率增加，这是预测水文气候的前提条件和解决当前问题，例如农业和灌溉做法。一个功能强大的分区方法包括确定ET，E和T的水稳定的同位素组成（δ _ET，δ _È，和δ _Ť分别从大气，土壤和植物维管组织中回收的水中提取。本工作着重强调了该特定方法所面临的挑战（例如，T / ET估计的时空代表性，所用模型的局限性及其对驱动参数的敏感性）以及需要根据以下方面取得的进展最近的方法学发展。由于我们的审核是为更广泛的受众超越同位素生态水文和微气象社区，它也试图提供的用于确定δ技术合奏进行彻底审查_ET，δ _ē和δ _ŧ，并求解T / ET的分配方程。从目前的研究现状出发，我们得出结论，进行ET分区和捕获T / ET子动态的最有前途的方法是利用对土壤和木质部水的稳定同位素组成的无损在线监测技术。努力应该继续朝向涡度相关技术的应用对于δ的高频判定_ET在外地规模以及δ的伴随测定_ET，δ _È，和δ _Ť在与现场部署的电梯系统中的高的垂直分辨率。