## 3 Results and Discussion
### Uncertainties and Limitations of Separation Methods  
Common observations of upper canopy eddies can provide information about ecosystem water and carbon fluxes, but in their physical meaning, they are total net fluxes, i.e., the familiar evapotranspiration and NEE, but more often, we would like to understand the flux components associated with the vegetation itself, which is difficult to address from an observational perspective. Until now, only a few studies have succeeded in partitioning the evapotranspiration of forest ecosystems using the DLEC method, with three main limitations: the determination of the coupling state of air masses between upper and lower canopy layers, the inverse gradient transport of water vapor, and the accurate measurement of canopy foliar evaporation [9]. In particular, for the determination of the coupling state, there is site-scale variability, which may be related to the homogeneity of the site substrate and the physical variability of the cover, since the three-dimensional structure of the canopy affects the state of turbulent motion. The inverse gradient transport of water vapor can be addressed by excluding negative values of water vapor flux and subcanopy above-dew-point temperature data. Under specific climatic and species conditions, surface evaporation terms can account for 10-50% of the growing season or interannual precipitation [39]. Thus, canopy surface evaporation can introduce large computational errors in the DLEC method, which can be avoided by excluding precipitation-related time series [9], but its influence on the separation of evapotranspiration components cannot be eliminated during actual observations. On the other hand, even if leaf hygrometers are used for canopy evaporation observations, they face problems of scale and representativeness, so in the future, consideration should be given to embedding a foliar evaporation simulation model in the process of separating evapotranspiration by DLEC observations [40; 41].  
The FVS, MREA, and CEC approaches establish a relatively simple and usable direction for separating studies to resolve ecosystem water-carbon flux components by considering, to varying degrees, the similarity of turbulent transport of stomatal/nonstomatal processes. FVS requires the estimation of WUE for the solution of nonlinear systems of equations, and previous studies have emphasized the importance of WUE algorithms for FVS [36; 42; 43]. Even if the optimal WUE algorithm for local sites is optimized based on leaf chamber observations, there are still many problems: the response of different vegetation types to VPD and CO\({}_{2}\) concentration may be completely different among sites, and the WUE may vary with different locations; on the other hand, it is difficult to fully consider the actual WUE under multiple weather conditions. There is also a difference between shaded and sunny leaves, as they experience completely different radiation levels [38].  
Even though we successfully obtained effective fluxes for each component using MREA, CEC, and FVS, they were all overestimated or underestimated to varying degrees relative to the DLEC methods, and the separation results of each method differed significantly in their precision on the half-hourly scale throughout the day, which may be caused by considering different assumptions rather than airflow decoupling (Figure 4a,b). Our separation process lacks independent observations of the single separation variables of transpiration or evaporation, and the fine-grained verification part of the separation results will be further improved in the future. For the similarity theory of source-sink processes and the separation method based on quadrant analysis, both face the assumption of similarity of water-carbon transport processes, i.e., having the same Schmidt number, although it is more difficult to verify this assumption, which should be taken into account as much as possible in the future to reduce the partial error between methods due to the EC observations.