## 4 Discussion
### Evaluation of Estimating Tr from SIF and Environmental Factors  
The results of the random forest importance analysis indicate that there are differences in the environmental factors affecting Tr at different temporal scales. Overall, an increase in temporal scale tends to diminish the contribution of PAR and VPD to Tr, while enhancing the contribution of Ta and SM to Tr, which is consistent with the results of the correlation analysis. The long-term changes in vegetation Tr are usually determined by Ta and SM, which control or influence biological rhythms and hydraulic properties [70]. During the day, radiation is the switch that induces stomatal opening for water and carbon exchange [71], making micrometeorological factors the main regulatory variables for stomatal conductance. Ws primarily affects SIF by altering canopy structure through leaf rolling and displacement [72], and influences Tr by changing leaf temperature and vapor movement. The significant contribution of Ws to arborvitae Tr may be due to the location on the southern hillside, where Ws is higher. The complexity of the influence of environmental factors on SIF, Tr, and the SIF-Tr relationship makes it impossible to ensure the accuracy of a single linear model [73]. Incorporating environmental factors into the model can enhance the ability of SIF to simulate Tr to varying extents.  
Based on SIF, appropriately incorporating environmental factors into the model leads to a reduction in RMSE, an increase in R\({}^{2}\), and k\({}_{0}\) will more closely approach 1. The number of variables and the selection of variables can affect the accuracy of the simulation. When choosing environmental factors, the impact of tree species and temporal scales should be considered. The results of the model may be species-specific. Deciduous species may require more factors than evergreen species, and higher resolution temporal scales may require more factors. The model performance ranking across the three plantations is as follows: poplar > Chinese cork oak > arborvitae, and [PERSON] et al. [16] also found that the correlation between SIF and Tr in deciduous forests is higher than in evergreen broadleaved forests. Overestimation at low SIF and underestimation at high SIF may be the main reasons for the smaller k\({}_{0}\). This study assumes ET to be Tr during the full leaf period; however, in reality, soil evaporation is not zero. This study is based on the analysis of a period with relatively stable canopy structure and excludes the effects of canopy structure changes. In fact, canopy structural characteristics such as LAI, leaf inclination angle, and clumping index can affect the direct and diffuse radiation received by leaves within the canopy, as well as the scattering and reabsorption processes of emitted fluorescence within the canopy. Therefore, when studying canopies with drastic structural changes, the influence of canopy parameters must be taken into account. This study mainly considered the impact of environmental factors; however, throughout the growing season, growth stage, canopy structure, and other physiological factors also affect the ability of SIF to estimate Tr. In future research, to improve the reliability of SIF in estimating Tr, the impact of soil evaporation and plant physiology should be taken into account.