## 5 Conclusions  
In this paper, we evaluated the SCOPE model's performance for \(\mathrm{SIF_{A}}\), \(\mathrm{SIF_{B}}\), and \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) simulations using high-accuracy spectral and flux observations in ten diurnal experiments on winter wheat. The SIF simulation accuracy with both fixed and variable FQE values was quantitatively assessed by comparison with the SIF retrieved from measurements using the 3 FLD method with a QE pro spectrometer.  
If simulated with fixed FQE values, the SCOPE model can reliably interpret SIF diurnal cycles and provide acceptable results for \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\) simulations. The RRMSEs of \(\mathrm{SIF_{A}}\) and \(\mathrm{SIF_{B}}\) for all 106 spectral measurements in the ten diurnal experiments were 24.35% and 23.67%, respectively. Nevertheless, the fixed FQE values were not suitable for wheat at all growth stages. At wheat's erecting period and at its booting or flowering period, the systematical deviations in \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) simulations were noteworthy, and the seasonal cycles of \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) cannot be credibly reproduced, with a low determination coefficient (\(R^{2}\)) of 0.0286.  
When the SIF simulation was conducted with variable FQE values, which vary with the growth of wheat, its accuracy was improved greatly. Specifically, the SCOPE model can accurately simulate the \(\mathrm{SIF_{B}}\) and \(\mathrm{SIF_{A}}\) with RRMSEs of 18.27% and 19.25%, respectively, and the SCOPE simulations track well with the seasonal \(\mathrm{SIF_{A}}\)/\(\mathrm{SIF_{B}}\) values with an RRMSE of 20.63% and a determination coefficient (\(R^{2}\)) of 0.48. The results indicated a clear seasonal pattern of suitable FQE values. When the growth stage changed from the erecting to the flowering stage, the fqe1/fqe2 increased from approximately 0.05-0.1 to approximately 0.3-0.5, while the fqe2 decreased from 0.013 to 0.07.  
Therefore, although the SCOPE model can credibly simulate canopy SIF, the input FQE values should be carefully determined. Seasonal changes of the FQE values or the FQE values' dependence on plant physiological status cannot be ignored for accurate simulations of canopy SIF. Our quantitative results of the model assessment and FQE adjustment can serve as a significant reference for future application of the SCOPE model. However, the study is preliminary; more experiments are needed to determine FQE values in the SCOPE model.  
This research was supported by the National Key Research and Development Program of China (2017 YFA0603001), and the National Natural Science Foundation of China (41701396). The authors are thankful to [PERSON] for providing the SCOPE model. We thank the anonymous reviewers for providing comments that helped to improve the quality of the original manuscript.  
[PERSON] was primarily responsible for mathematical modeling and experimental design. [PERSON] improved the experimental analysis and revised the paper. [PERSON] contributed to the original idea for the research and to the experimental design. [PERSON] provided support regarding the application of Diurnal flux and meteorological observations.  
The authors declare no conflict of interest.