## 3 Results
### Comparisons among Multiple Annual GPP Estimates  
As shown in Figure 4, the relationships between annual GPP\({}_{\text{MTL-LUE}}\) and GPP\({}_{\text{MOD17}}\) (\(R^{2}\) = 0.77, \(RMSE\) = 368 gC m\({}^{-2}\)yr\({}^{-1}\), \(rRMSE\) = 35%), GPP\({}_{\text{MTL-LUE}}\) and GPP\({}_{\text{TL-LUE}}\) (\(R^{2}\) = 0.65, \(RMSE\) = 165 gC m\({}^{-2}\)yr\({}^{-1}\), \(rRMSE\) = 16%), and GPP\({}_{\text{MTG}}\) and GPP\({}_{\text{TG}}\) (\(R^{2}\) = 0.78, \(RMSE\) = 141 gC m\({}^{-2}\)yr\({}^{-1}\), \(rRMSE\) = 48%) were all closer than that between annual GPP\({}_{\text{BEPS}}\) and GPP\({}_{\text{BTL}}\) (\(R^{2}\) = 0.33, \(RMSE\) = 465 gC m\({}^{-2}\)yr\({}^{-1}\), \(rRMSE\) = 48%). The GPP\({}_{\text{MOD17}}\) of almost all the pixels had a higher annual value than the GPP\({}_{\text{MTL-LUE}}\), and the GPP\({}_{\text{TL-LUE}}\) of most pixels also had a higher annual value than the GPP\({}_{\text{MTL-LUE}}\). The difference between annual GPP\({}_{\text{MTL-LUE}}\) and GPP\({}_{\text{MOD17}}\) in forest pixels was lower than that in shrub and grass pixels, with the  
Figure 3: Spatial distributions of annual GPP\({}_{\text{MTL-LUE}}\) (**a**), GPP\({}_{\text{TL-LUE}}\) (**b**), GPP\({}_{\text{MOD17}}\) (**c**), GPP\({}_{\text{MTG}}\) (**d**), GPP\({}_{\text{TG}}\) (**e**), GPP\({}_{\text{BTL}}\) (**f**), and GPP\({}_{\text{BEPS}}\) (**g**) over Wanglang Reserve. The annual values were summed from those daily (i.e., MOD17, TL-LUE, MTL-LUE, BEPS, and BTL) or 8-day (i.e., TG and MTG) estimates during DOY 1–273 in 2020. _rRMSE_ decreasing by 16% and 19%, respectively. The _rRMSE_ between annual \(\text{GPP}_{\text{MTL-LUE}}\) and \(\text{GPP}_{\text{TL-LUE}}\) presented a similar value in the forest (15%), shrub (18%), and grass (16%) pixels. The \(\text{GPP}_{\text{TG}}\) of most forest and grass pixels had a higher annual value than the \(\text{GPP}_{\text{MTG}}\), whereas the \(\text{GPP}_{\text{TG}}\) of most shrub pixels had a lower annual value than the \(\text{GPP}_{\text{MTG}}\). Although the _rRMSE_ between annual \(\text{GPP}_{\text{BEPS}}\) and \(\text{GPP}_{\text{BTL}}\), showed a similar value in the forest (47%), shrub (44%), and grass (50%) pixels, the \(R^{2}\) between annual \(\text{GPP}_{\text{BEPS}}\) and \(\text{GPP}_{\text{BTL}}\) in forest pixels was higher than that in shrub and grass pixels by 0.13 and 0.33, respectively. The \(\text{GPP}_{\text{BEPS}}\) of most forest and grass pixels presented a lower annual value than the \(\text{GPP}_{\text{BTL}}\). Figure 4: Comparisons between annual \(\text{GPP}_{\text{MTL-LUE}}\) and \(\text{GPP}_{\text{MOD17}}\) (the first row), \(\text{GPP}_{\text{MTL-LUE}}\) and \(\text{GPP}_{\text{TL-LUE}}\) (the second row), \(\text{GPP}_{\text{MTG}}\) and \(\text{GPP}_{\text{TG}}\) (the third row), and \(\text{GPP}_{\text{BTL}}\) and \(\text{GPP}_{\text{BEPS}}\) (the forth row) in forest (**a**), shrub (**b**), grass (**c**), and all (**d**) pixels. As shown in Figure 5, the relationships between annual GPP\({}_{\rm BTL}\) and GPP\({}_{\rm MTL-LUE}\) (\(R^{2}\) = 0.29, \(RMSE\) = 399 gC m\({}^{-2}\)yr\({}^{-1}\)), and GPP\({}_{\rm MTL-LUE}\) and GPP\({}_{\rm MTG}\) (\(R^{2}\) = 0.34, \(RMSE\) = 798 gC m\({}^{-2}\)yr\({}^{-1}\)) were closer than that between annual GPP\({}_{\rm BTL}\) and GPP\({}_{\rm MTG}\) (\(R^{2}\) = 0.02, \(RMSE\) = 821 gC m\({}^{-2}\)yr\({}^{-1}\)). The GPP\({}_{\rm MTG}\) of almost all pixels had a higher annual value than the GPP\({}_{\rm BTL}\) and the GPP\({}_{\rm MTL-LUE}\), and the GPP\({}_{\rm MTG}\) of the most pixels was similar to GPP\({}_{\rm BTL}\). The difference between annual GPP\({}_{\rm BTL}\) and GPP\({}_{\rm MTL-LUE}\) in grass pixels was lower than that in shrub and forest pixels, with \(rRMSE\) decreased by 11% and 17%, respectively. Forest and shrub pixels showed a lower \(rRMSE\) value between annual GPP\({}_{\rm MTL-LUE}\) and GPP\({}_{\rm MTG}\) than grass pixels by 23% and 22%, respectively.