## 3 Results
### Responses of SIF\({}_{760}\), GPP, and ET to Meteorological Factors  
GPP was underestimated during periods of high VPD (>3.0 kPa), indicating drought stress, with positive biases observed across other ranges (Figure 6). Similarly, within the optimal temperature range, the simulation bias was relatively minimal, but outside this range, as vegetation experienced low- or high-temperature stress, the bias increased. Specifically, GPP was underestimated at air temperatures of 20-26 \({}^{\circ}\)C and soil temperatures of 19-23 \({}^{\circ}\)C, while it was overestimated at air temperatures below 20 \({}^{\circ}\)C or above 27 \({}^{\circ}\)C and soil temperatures below 17 \({}^{\circ}\)C or above 23 \({}^{\circ}\)C. These findings suggested significant influences of both drought and temperature stresses on GPP in coastal wetlands. ET exhibited greater sensitivity to moisture and temperature changes. As the VPD increased, the bias and deviations of ET simulation grew, with the bias and RMSE of ET simulation reaching 0.40 mm h\({}^{-1}\) and 0.89 mm h\({}^{-1}\) at VPD values of 2.0\(-\)2.5 kPa. Similarly, elevated air and soil temperatures led to increased bias, which declined after a threshold. As shown in Figure 6, the ET simulation bias peaked at 0.96 mm h\({}^{-1}\) when air temperature reached 35 \({}^{\circ}\)C, with RMSE peaking between 29 and 31 \({}^{\circ}\)C. For soil temperature, the bias peaked at 28 \({}^{\circ}\)C, and RMSE peaked at soil temperatures between 24 and 25 \({}^{\circ}\)C. Thus, ET was more responsive to moisture changes than temperature, and drought stress induced greater bias and deviations than temperature stress. Figure 4: Daily variations in the observed and simulated (**a**) canopy solar-induced chlorophyll fluorescence at 760 nm (SIF\({}_{760}\)), (**b**) gross primary productivity (GPP), and (**c**) evapotranspiration (ET) during 2019. The response of \(\mathrm{SIF}_{760}\) to moisture and temperature variations differed. With increasing VPD, \(\mathrm{SIF}_{760}\) simulations bias enlarged, reaching 0.38 W m\({}^{-2}\) um\({}^{-1}\) sr\({}^{-1}\) at a VPD of 3.0\(-\)3.5 kPa (Figure 6). Air temperatures increased then increased deviations, while soil temperature increases did not affect deviation occurrence but increased bias, reaching a minimum at soil temperatures of 21\(-\)24 \({}^{\circ}\)C, while bias increased at temperatures above 36 \({}^{\circ}\)C. Conversely, with soil temperature increases, bias peaked at 28 \({}^{\circ}\)C. Thus, \(\mathrm{SIF}_{760}\) was sensitive to both moisture and temperature stresses, exhibiting a unique response to air and soil temperature changes unlike GPP and ET. Figure 5: Relationships between the observed and simulated (with the subscript ‘\({}_{\mathrm{sim}}\)’) canopy-level solar-induced chlorophyll fluorescence at 760 nm (\(\mathrm{SIF}_{760}\)) (**a1,a2**), gross primary productivity (GPP) (**b1,b2**), and evapotranspiration (ET) (**c1,c2**), where (**a2,b2,c2**) represent the vegetation under flooding. The lines represent the lines of best fit for the simulations and observations of \(\mathrm{SIF}_{760}\), ET and GPP. (The colors represent the development stages of vegetation, with darker shades indicating the early and rapid stage (rapid, from March to May), peak vegetation stage (peak, from June to August), flowering and ripening stage (ripen, from September to November), and wilt vegetation stage (wilt, from December to February), while the grey lines represent the overall data, encompassing each stage.) The corresponding values of the coefficient of determination (R\({}^{2}\)) (bars) and bias (lines) are displayed on the right-hand side (**a3,b3,c3**). The significance of the correlation is indicated by “_a**  
Simulated \(\text{SIF}_{760}\), GPP, and ET Under Tidal Influence in Response to Meteorological Factors  
Under tidal influence, significant GPP overestimation occurred at a higher VPD, with bias reaching 3.40 umd m\({}^{-2}\) s\({}^{-1}\) at a VPD \(>\) 2.5 kPa (Figure 7).