## 3 Results
### Effects of Low Temperature on the GPP/SIF Ratios for Different PFTs
#### 3.3.1 Global Satellite Dataset  
As can be seen from Figure 9, we found that the seasonal pattern in the GPP/SIF ratio differed among PFTs. For tropical regions, TrEBF, TrDBF, and TrC3 GRA generally exhibited a slightly \"bowl-shaped\" seasonal pattern for the GPP/SIF ratio. For temperate regions, TeEBF similarly presented a \"bowl-shaped\" seasonal variation in the GPP/SIF ratio, while the seasonal patterns of TeENF and TeDBF exhibited a slight \"hump-shape\". For Boreal regions, BoENF, BoDBF, BoDNF, and BoC3 GRA generally showed a clear \"hump-shaped\" seasonal pattern for the GPP/SIF ratio. In addition, the seasonal pattern of the GPP/SIF ratio for C4 GRA, C3 CRO, and C4 CRO generally presented a \"bowl-shape\". By reducing the effects of the canopy structure, the ratio of GPP to the total SIF (calculated as SIF divided by the escape probability; see the Supplementary Materials) also showed a \"hump-shaped\" pattern for many PFTs, while the \"bowl-shaped\" seasonal pattern was largely corrected, except for C4 CRO (Figure S1). Figure 8: Relationship between SIF and GPP for groups A and B of TeC3 GRA, C4 GRA, and C3 GRO (2018–2020). Each panel also lists the slope and determination coefficient obtained in the linear regression with no intercept. The color bar represents the fraction of point density, normalized by the maximum point density. Groups A of TeC3 GRA, C4 GRA, and C3 GRA generally experienced more low-temperature stress than group B. From Figure 10, we can see that group A of TeC3 GRA, C4 GRA, and C3 GRO generally showed a clear \"'hump-shaped\" seasonal pattern for the GPP/SIF ratio, whereas the corresponding B groups generally exhibited a slightly \"bowl-shaped\" seasonal pattern for the GPP/SIF ratio. It should be noted that the seasonal variations in the GPP/SIF ratio were affected by growth temperature conditions. For C3 CRO, although all samples together exhibited a \"bowl-shaped\" seasonal pattern for the GPP/SIF ratio, group A separately exhibited a \"hump-shaped\" seasonal pattern. By reducing the effects of the canopy structure (Figure S2), a similar \"hump-shape\" can be observed in group A. Therefore, there were noticeable differences in the seasonal patterns of the GPP/SIF ratio between the selected samples that experienced low-temperature stress and those that grew under relatively warm conditions. The influence of temperature conditions on the SIF-GPP relationship was further investigated using a linear regression and correlation analysis method. From Figure 11, we can see that the relationship between the GPP/SIF ratio and temperature differed among PFTs; however, the GPP/SIF ratio generally decreased under low-temperature conditions for some of those PFTs which experienced low-temperature stress. The GPP/SIF ratio generally exhibited a positive correlation with temperature in group A among the PFTs, while the GPP/SIF ratio in group B had no significant relationship with temperature (Figure 11; Table 3). Figure 9: Seasonal dynamics of the GPP/SIF ratio for different PFTs (2018–2020). The black lines are the mean values, and the shaded areas represent the standard deviation intervals. Figure 10: Seasonal dynamics of the GPP/SIF ratio in groups A and B for TeC3 GRA, C4 GRA, and C3 CRO (2018–2020). The black lines are the mean values, and the shaded areas represent the standard deviation intervals.