## 3 Results
### Spatio-Temporal Variations of Seasonal GPP and Annual GPP
#### 3.3.2 Temporal Variations  
The spatial distribution of the trends of GPP\({}_{\rm ann}\) and GPP\({}_{\rm max}\) in the SRYR from 2001 to 2019 are shown in Figures 6a and 6b. The GPP\({}_{\rm ann}\) and GPP\({}_{\rm max}\) in the SRYR both showed insignificantly increasing trends (\(p\) > 0.05), with rates of 1.76 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\) and 0.03 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\), respectively. The significantly increasing GPP\({}_{\rm ann}\) and GPP\({}_{\rm max}\) (\(p\) < 0.05) accounted for 28.2% and 14.5% of the SRYR, respectively, and were mainly distributed in the west and north. A total 13.5% of the pixels had a decreasing GPP\({}_{\rm ann}\), which was mainly distributed in the central SRYR.  
Figure 5: Spatial distribution of **(a)** average GPP\({}_{\rm ann}\), **(b)** GPP\({}_{\rm max}\), **(c)** GPP\({}_{\rm spr}\), **(d)** GPP\({}_{\rm sum}\), **(e)** GPP\({}_{\rm aut}\) and **(f)** GPP\({}_{\rm win}\) in the SKYR from 2001 to 2019. The frequency distribution of vegetation phenology is shown in the lower left corner.  
Figure 6: Spatial distribution of the trends of (**a**) annual \(\mathrm{GPP}_{\mathrm{ann}}\), (**b**) \(\mathrm{GPP}_{\mathrm{max}}\), (**c**) \(\mathrm{GPP}_{\mathrm{spr}}\), (**d**) \(\mathrm{GPP}_{\mathrm{spr}}/\mathrm{GPP}_{\mathrm{ann}}\), (**e**) \(\mathrm{GPP}_{\mathrm{sum}}\), (**f**) \(\mathrm{GPP}_{\mathrm{sum}}/\mathrm{GPP}_{\mathrm{ann}}\), (**g**) \(\mathrm{GPP}_{\mathrm{aut}}\) and (**h**) \(\mathrm{GPP}_{\mathrm{aut}}/\mathrm{GPP}_{\mathrm{ann}}\) in the SRYR  
from 2001 to 2019. The trend with 0.05 significance level (\(p<0.05\)) is shown in the upper right corner, with red representing a decreasing trend and blue representing an increasing trend at a significance level of 0.05 (\(p<0.05\)), and the inter-annual variation is shown in the lower left corner.  
GPP\({}_{\text{spr}}\) exhibited a significantly increasing trend (\(p<0.01\)) with a rate of 0.36 g-C-m-2-yr-1 (Figure 6c). Most areas of the SRYR (96.2%) showed increasing GPP\({}_{\text{spr}}\), and areas with a significantly increasing trend reached 55.9% of the SRYR. GPP\({}_{\text{sum}}\) exhibited an insignificantly increasing trend (+1.37 g-C-m-2-yr-1, \(p>0.05\)), and areas with a significantly increasing trend (\(p<0.05\)) were 24.1% of the SRYR, which shared a similar distribution with the significantly increasing GPP\({}_{\text{ann}}\) (Figure 6e). GPP\({}_{\text{aut}}\) showed an insignificantly decreasing trend (\(-0.32\) g-C-m-2-yr-1, \(p>0.05\)) and had spatial heterogeneities (Figure 6g). GPP\({}_{\text{aut}}\) increased in the region where the EOS was delayed (Figure 4b) while it decreased in the region where the EOS advanced.  
The results also indicated that the proportions of GPP\({}_{\text{spr}}\) (Figure 6d) and GPP\({}_{\text{sum}}\) to GPP\({}_{\text{ann}}\) (Figure 6f) in the SRYR both experienced insignificantly increasing trends (\(p>0.05\)), while the proportion of GPP\({}_{\text{aut}}\) to GPP\({}_{\text{ann}}\) (Figure 6h) showed an insignificantly decreasing trend (\(p>0.05\)). This indicated that the contribution of spring and summer GPP to annual GPP was increasing and that of autumn GPP was decreasing.