## 4 Discussion
### Tidal Effects on SIF\({}_{760}\), GPP, and ET Modeling and Underlying Mechanisms
Under flooded conditions, it has been shown in recent studies that a self-protection mechanism is characterized by an increase in NPQ and a decline in photosynthetic activity, light energy conversion efficiency, and electron transport rate [62]. This mechanism may weaken the relationship between NPQ and GPP under tidal inundation, but it can enhance the linear correlation between SIF and GPP. Meanwhile, the water and salt stress induced by tidal inundation alters the photosynthesis and transpiration processes of vegetation. While transpiration may increase under high-temperature stress as a means of heat dissipation, the insulating properties of tidal water can alleviate the effects of such temperatures. Nonetheless, excessively high temperatures nonetheless disrupt plant physiological functions, consequently affecting the interplay between SIF and GPP, as well as ET. Additionally, plant photosynthesis, water balance, and transpiration are all inhibited under salinity stress, leading to complex changes in the relationships between SIF and GPP, as well as ET. Although SIF maintains a significant correlation with GPP and ET within a low salinity range, beyond this range, salinity stress disrupts this correlation. In addition to environmental factors, the uncertainties intrinsic to observation and modeling processes cannot be overlooked when utilizing SIF to track the dynamics of GPP and ET in coastal wetlands. Firstly, although eddy covariance observation is currently considered the most accurate method for estimating GPP in non-destructive ecosystems [63], the algorithms for flux partitioning are based on terrestrial ecosystems and do not account for the unique tidal processes in coastal wetlands. This often leads to a certain uncertainty despite the field measurement data. Secondly, exogenous materials and the energy brought by periodic tidal inundation can disrupt energy balance in the short term and simultaneously influence the photosynthesis, transpiration, and radiation transfer processes of vegetation. However, these changes are not adequately reflected in current models. Therefore, when applying SIF to track GPP or ET in coastal salt marsh wetlands, it is imperative to propose parameterized schemes that reflect the impact of tidal inundation and carefully consider these uncertainty factors. Despite the aforementioned challenges, SIF, as a novel remote sensing signal, shows significant potential for multi-scale estimation of the carbon and water cycles in coastal wetlands. With the deployment of fluorescence satellites and the enhancement of their detection accuracy, coupled with in-depth exploration of how tidal dynamics influence the relationships between SIF and both GPP and ET, we anticipate a more precise quantification of the carbon and water cycle processes in coastal wetlands using SIF. This will facilitate large-scale, high spatiotemporal resolution monitoring and estimation of GPP and ET in coastal wetland ecosystems. To achieve this goal, it is necessary to further quantify the impacts of tidal inundation on radiation transfer and vegetation physiology, as well as the exogenous substances and energy introduced by tidal processes. As a result of these efforts, SIF is poised to become a powerful tool in studying the carbon and water cycles in coastal wetlands, providing crucial support for revealing the response mechanisms of coastal wetland ecosystems to environmental changes and ultimately contributing to more accurate, large-scale, high spatiotemporal resolution monitoring and estimation of carbon and water cycles in these ecosystems.