Water use efficiency (WUE) represents a crucial parameter and a major source of error influencing the accuracy of evapotranspiration separation through flux variance similarity (FVS). However, there is a paucity of studies investigating the application of FVS for the separation of evapotranspiration across multiple plantations, thereby constraining our understanding of water use strategies in plantation forests. This study assessed the outcomes of four intercellular carbon dioxide models and an optimization model (Opt) within the FVS framework, utilizing Eddy Covariance (EC) data gathered from two broad-leaf plantations and four coniferous plantations. Additionally, we examined the relationship between WUE and solution rate, as well as the responsiveness of the proportion of transpiration to evapotranspiration (T:ET) to soil moisture. The results showed that the solution rate of the Sqrt model differed by only 1 % - 2 % from the constant Ci value (Ci) and the constant Ci/Ca ratio (K) model in plantations, excluding Pinus tabuliformis. Moreover, the Sqrt model exhibited an average overestimation of T:ET by 8 % compared to the Opt model. The solution rate of Ci, K, and Sqrt models were decreased with an increase in WUE. At a half-hour scale and daily scale, the plantation's solution rate was ranged from 39 % to 67 %, and 29 % to 76 %, respectively. Except for the Linear model, all other models effectively tracked the dynamic changes in soil moisture. This study enhanced our understanding about the distinctions and consistencies in FVS separation among five WUE models in plantations, providing a foundation for the selection of WUE models to elucidate water use strategies in plantations.

中文翻译：

---

高频涡流相关数据蒸散分配中水分利用效率模型的评价 - 人工林地点间的比较

水分利用效率 （WUE） 是一个关键参数，也是通过通量方差相似性 （FVS） 影响蒸散分离准确性的主要误差来源。然而，缺乏调查 FVS 在多个人工林之间分离蒸散作用中的应用的研究，从而限制了我们对人工林水分利用策略的理解。本研究利用从两个阔叶种植园和四个针叶林收集的涡度相关 （EC） 数据，评估了 FVS 框架内四个细胞间二氧化碳模型和一个优化模型 （Opt） 的结果。此外，我们还研究了 WUE 与溶出率之间的关系，以及蒸腾与蒸散比 （T：ET） 对土壤水分的响应性。结果表明，Sqrt 模型的溶出率与人工林中恒定的 Ci 值 （Ci） 和恒定的 Ci/Ca 比值 （K） 模型仅相差 1 % - 2 %，不包括油松 。此外，与 Opt 模型相比，Sqrt 模型对 T：ET 的平均高估了 8%。Ci 、 K 和 Sqrt 模型的求解率随着 WUE 的增加而降低。在半小时尺度和日尺度上，人工林的溶出率分别为 39 % 至 67 % 和 29 % 至 76 %。除线性模型外，所有其他模型都有效地跟踪了土壤水分的动态变化。本研究增强了我们对人工林 5 种 WUE 模型之间 FVS 分离的区别和一致性的理解，为选择 WUE 模型阐明人工林用水策略提供了基础。