## 3 Results
### Relationship Between SIF\({}_{760}\) with GPP and ET Under Tidal Influence  
The SIF\({}_{760}\)-GPP relationship was fitted using an exponential correlation model (\(y\ =a\times\ x^{b}\)). Across various moisture and temperature levels, significant correlations were evident with optimal conditions enhancing correlation strength and linearity. Stress from moisture or temperature weakened this relationship. Significant SIF\({}_{760}\)-GPP correlations were observed within a VPD range of 0.4 to 2.5 kPa, with peak R\({}^{2}\), maximal coefficient a, and exponent b nearest to 1 occurring at 1 to 1.2 kPa VPD (Figure 9). Significant correlations were also found within air (11 to 33 \({}^{\circ}\)C) and soil (12 to 29 \({}^{\circ}\)C) temperature ranges, with optimal linearity at 27 to 29 \({}^{\circ}\)C air and 18 to 20 \({}^{\circ}\)C soil temperatures. Notably, a negative correlation emerged at an air temperature above 35 \({}^{\circ}\)C. In summary, the SIF\({}_{760}\)-GPP relationship was most linear under optimal conditions but grew complex under stress. The linear relationship between SIF\({}_{760}\) and ET was generally positive, turning negative under drought. Significant positive correlations were observed at a VPD below 3.0 kPa and within specific air and soil temperature ranges (10-35 \({}^{\circ}\)C air and 13-30 \({}^{\circ}\)C soil temperatures) (Figure 9). Significant positive correlations were observed at a VPD \(<\) 3.0 kPa, peaking at 1.0-1.2 kPa, weakening with air temperature \(>\) 29 \({}^{\circ}\)C, and turning negative when the VPD \(>\) 3.5 kPa. Overall, SIF\({}_{760}\) and ET displayed a significant positive linear correlation disrupted by drought and weakened by high temperature. Figure 8: Relationships between the observed (with the subscript ‘\({}_{\text{obs}}\)’) and simulated (with the subscript ‘\({}_{\text{sim}}\)’) (**a1,a2**) gross primary productivity (GPP), (**b1,b2**) evapotranspiration (ET), (**c1,c2**) solar-induced chlorophyll fluorescence (SIF\({}_{760}\)) at different (**a1,b1,c1**) water temperatures, and (**a2,b2,c2**) salinities under tidal flooding. The coefficient of determination (R\({}^{2}\)) (blue bars) and bias (red lines) across various groups are displayed in the inset at the bottom right. More details of R\({}^{2}\), bias, and root-mean-square error (RMSE) can be found in Tables S2 and S3. Under tidal inundation, the correlation between \(\mathrm{SIF}_{760}\) and GPP weakened (R\({}^{2}\) = 0.33), with narrower VPD and temperature ranges for significant correlations (Figure 10). Nearly linear and significant positive correlations were found within narrower VPDs, air, soil, and water temperature ranges (VPD 0.6 to 1.8 kPa, air temperature 17-26 \({}^{\circ}\)C, soil temperature 20-25 \({}^{\circ}\)C, and water temperature 20-28 \({}^{\circ}\)C) under inundation (Figures 10 and 11). Negative correlations (b < 0) emerged at higher VPDs (>2.0 kPa) and extreme air temperatures (<18 \({}^{\circ}\)C or >29 \({}^{\circ}\)C). Additionally, increasing VPD and tidal-induced salinity led to decreasing R\({}^{2}\) and correlation coefficients, indicating a weakened correlation and reduced GPP growth. When salinity >3%, no significant correlation was found. Under tidal inundation, the \(\mathrm{SIF}_{760}\)-GPP relationship was disrupted and weakened by drought, temperature stresses, and tidal salinity stress. Interestingly, under tidal inundation, the linear correlation between \(\mathrm{SIF}_{760}\) and ET improved (R\({}^{2}\) = 0.47), with narrower ranges for significant correlations (VPD at 0.4-2.0 kPa, air temperature at 19-32 \({}^{\circ}\)C, soil temperature at 20-25 \({}^{\circ}\)C, and water temperature at 20-25 \({}^{\circ}\)C) and a negative correlation at higher air temperatures (30-32 \({}^{\circ}\)C), with no significant correlation beyond 32 \({}^{\circ}\)C (Figures 10 and 11). Furthermore, tidal-induced salinity stress severely disrupted this correlation, with significant correlations only observed at salinities of 0-0.5% (Figure 11).