# Increasing Ecosystem Fluxes Observed from Eddy Covariance and Solar-Induced Fluorescence Data
## 4 Discussion  
Our results indicate that site-level SIF showed a strong agreement with flux tower GPP at global sites (Figure S2a-c). However, the SIF-ET correlations were consistently lower than the SIF-GPP relationships (Figure S2d-f). This difference was likely attributed to the closer physiological link between SIF and GPP compared to SIF and ET at the canopy/leaf scale [79; 80]. Theoretically, changes in SIF directly reflect plant photosynthesis due to the immediate energy flux emitted during the light reaction [81; 82]. Thus, increases (or decreases) in SIF correspond to positive (or negative) changes in plant photosynthesis at the canopy scale [83]. Linked by the electron transport rate (J), the SIF-GPP relationship can be broken into two components: SIF-J and J-GPP. The SIF-J relationship, governed by energy allocation in the light reaction, can be modeled using the Mechanistic Light Response (MLR) model [84]. Meanwhile, the J-GPP relationship is linked to carbon assimilation during the Calvin cycle and aligns with the Eco-Evolutionary Optimality (EEO) theory [85], which states that stomata maximize carbon gain while minimizing water loss [86]. This highlights SIF's key role in providing physiological insights for estimating both GPP and ET. The SHAP analysis further revealed that SIF accounted for 24-49% of GPP variability across all PFTs (excluding EBF), a significantly higher contribution than any climatic factors (Figures 4 and S3). The high contribution of SIF is likely because it is the only vegetation state variable included in the predictor set, capturing all effects associated with canopy structure and APARchl variability. In contrast, SIF had a weaker influence on terrestrial ET, primarily through its role in linking photosynthesis and stomatal transpiration [39]. Increases in SIF enhance transpirations via stomatal opening, which is driven by photosynthesis [35; 87; 88]. However, soil and canopy evaporation, which are substantial components of ET, are more strongly controlled by environmental factors like temperature and VPD rather than photosynthesis [89]. For example, [PERSON] et al. [35] showed that correlations between ET and SIF could be influenced by VPD, air temperature, and radiation at the site level. Consistent with this, our SHAP results indicate that temperature, rather than SIF, was the dominant driver of ET variability across most PFTs (Figures 4 and S3). These findings highlight the importance of incorporating both SIF and meteorological factors when estimating ET. The derived ECSIF datasets presented spatial patterns and temporal trends in global GPP, ET, and WUE consistent with observations (Figures 5-7, S4, S6 and S7). Previous studies reported global GPP estimates of 106-145.8 Pg C yr\({}^{-1}\) and ET estimates of 417-574 mm yr\({}^{-1}\) across various periods and resolutions. These values align with the 124.8-130.8 Pg C yr\({}^{-1}\) for GPP and 460.4-583.8 mm yr\({}^{-1}\) for ET obtained from six ECSIF datasets (Table 4). Meanwhile, ECSIF products showed 1.55-2.03 g C kg\({}^{-1}\) H\({}_{2}\)O yr\({}^{-1}\) of global WUE during 2001-2020, falling within the range of 1.53-1.96 g C kg\({}^{-1}\) H\({}_{2}\)O yr\({}^{-1}\) from previous estimates [22; 44; 90; 91]. In terms of temporal trends, ECSIF products showed significant trends of 0.16-0.26 Pg C yr\({}^{-2}\) for global GPP during 2001-2020. These values are close to the 0.2-0.46 Pg C yr\({}^{-2}\) reported [PERSON] et al. [5], [PERSON] et al. [42], [PERSON] et al. [58], and [44] for the similar periods. However, global trends in ET showed large differences among various studies [92]. ECSIF products showed positive trends of 0.45-0.87 mm yr\({}^{-2}\) of global ET during 2001-2020, which were similar to 1.09 mm yr\({}^{-2}\) caused by [PERSON] et al. [44] for the period 2001-2020. These positive values were much lower than the value of 2 mm yr\({}^{-2}\) from PML-V2 datasets for similar periods [5].