## 3 Results
### Performances of Various LUE-GPP Models
#### 3.1.2 Two-Leaf LUE-GPP Models  
The \(GPP\) simulated by the two-leaf LUE-GPP model was consistent with the changes in \(GPP_{\text{EC}}\), with a slope of 1.02 and an \(R^{2}\) of 0.721 (\(p<\) 0.01, Figure 2). The \(GPP\) values estimated by the two-leaf model in 2018-2020 growing seasons were 6.43, 5.87, and  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Models**} & \multirow{2}{*}{\(R^{2}\)} & _MAE_ & _RMSE_ & \multirow{2}{*}{\(\eta\)} & \multirow{2}{*}{\(d_{1}\)} & \multirow{2}{*}{\(GPI\)} & \multirow{2}{*}{Ranking} \\  & & & & (g C m\({}^{-2}\) d\({}^{-1}\)) & & & & \\ \hline \multirow{8}{*}{2018} & EF-LUE & 0.790 & 1.377 & 1.808 & 0.563 & 0.774 & 0.875 & 1 \\  & MODIS & 0.721 & 1.574 & 2.025 & 0.501 & 0.739 & \(-\)0.748 & 4 \\  & VPM & 0.758 & 1.465 & 1.942 & 0.535 & 0.773 & 0.240 & 3 \\  & MVPM & 0.711 & 1.563 & 2.074 & 0.504 & 0.739 & \(-\)0.870 & 5 \\  & TEC & 0.773 & 1.403 & 1.852 & 0.555 & 0.776 & 0.602 & 2 \\  & CASA & 0.742 & 2.441 & 3.038 & 0.226 & 0.607 & \(-\)2.048 & 6 \\ \cline{2-10}  & EF-LUE & 0.772 & 1.636 & 2.100 & 0.429 & 0.746 & 1.373 & 2 \\  & MODIS & 0.735 & 1.819 & 2.462 & 0.366 & 0.727 & \(-\)0.192 & 5 \\  & VPM & 0.747 & 1.869 & 2.685 & 0.348 & 0.730 & \(-\)0.062 & 4 \\  & MVPM & 0.759 & 1.511 & 2.083 & 0.473 & 0.764 & 1.451 & 1 \\  & TEC & 0.753 & 1.861 & 2.639 & 0.351 & 0.730 & 0.136 & 3 \\  & CASA & 0.759 & 2.123 & 2.511 & 0.260 & 0.665 & \(-\)1.834 & 6 \\ \cline{2-10}  & EF-LUE & 0.680 & 1.690 & 2.199 & 0.249 & 0.687 & 1.262 & 1 \\  & MODIS & 0.615 & 1.957 & 2.645 & 0.130 & 0.655 & \(-\)0.184 & 6 \\  & VPM & 0.626 & 1.895 & 2.541 & 0.158 & 0.656 & 0.062 & 3 \\  & MVPM & 0.601 & 1.726 & 2.207 & 0.233 & 0.661 & 0.066 & 2 \\  & TEC & 0.650 & 2.168 & 2.995 & 0.136 & 0.643 & \(-\)0.145 & 5 \\  & CASA & 0.668 & 2.024 & 2.327 & 0.100 & 0.623 & 0.041 & 4 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The compared performances of simulated gross primary productivity (\(GPP\)) by six big-leaf light use efficiency-based GPP models (EF-LUE, MODIS, VPM, MVPM, TEC, and CASA) against the \(GPP\) derived from the EC measurements by determination coefficients (\(R^{2}\)), mean absolute error (\(MAE\)), root mean squared errors (\(RMSE\)), fixed efficiency index (\(\eta\)), fixed sum index (\(d_{1}\)), global performance indicator (\(GPI\)), and model ranking during 2018–2020 in a humid region orchard ecosystem.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Year** & \(GPP_{\text{EC}}\) & \(GPP_{\text{EF-LUE}}\) & \(GPP_{\text{MODIS}}\) & \(GPP_{\text{PVPM}}\) & \(GPP_{\text{MVPM}}\) & \(GPP_{\text{TEC}}\) & \(GPP_{\text{CASA}}\) & \(GPP_{\text{TL}}\) \\ \hline
2018 & 6.77 & 6.27 & 7.03 & 6.99 & 6.40 & 6.99 & 7.46 & 6.43 \\ \cline{2-106.28 g C m\({}^{-2}\) d\({}^{-1}\), respectively, which were comparable to \(GPP_{\rm EC}\) values (Table 5). The \(R^{2}\) values between the \(GPP_{\rm TL}\) and \(GPP_{\rm EC}\) in 2018-2020 growing seasons were, respectively, 0.786, 0.733, and 0.621 (Table 6); _MAE_ were 1.395, 1.329, and 1.259 g C m\({}^{-2}\) d\({}^{-1}\); _RMSE_ were 1.844, 1.751, and 1.725 g C m\({}^{-2}\) d\({}^{-1}\); \(\eta\) were 0.558, 0.537, and 0.440; and \(d_{1}\) were 0.755, 0.758, and 0.714. The calculated _GPI_ values were 0.601 (3), 1.185 (3), and 1.293 (3), respectively, and the overall performance was good (the bracket number indicates the ranking compared with the six big-leaf GPP models).