## 5 Conclusions  
This paper describes the reaction of the sun-induced chlorophyll fluorescence (SIF) emission and the canopy reflectance to increasing water limitation for both a mustard and a lettuce stand during a field experiment that lasted their entire growing seasons. The SIFA emission was decomposed into a biochemical component, being the fluorescence emission efficiency (\(\epsilon_{760}\)) and a structural component, being the Fluorescence Correction Vegetation Index (FCVI). Such operation was not done for SIFB. In addition, the photochemical reflectance index (PRI) was monitored. Both plants showed a biochemical reaction to increasing stress, most notably in the fluorescence emission efficiency (\(\epsilon_{760}\)). The reaction of \(\epsilon_{760}\) to increasing stress was observed in two ways. First, \(\epsilon_{760}\) decreases according to the stress intensity. Second, \(\epsilon_{760}\) and PAR show an anticorrelation under water-limited days and a positive correlation under light-limited days. Under intensely stressed days, SIFBY and PAR also showed an anticorrelation. Given the more isohydric nature of the mustard plant, it showed a clearer biochemical reaction compared to the lettuce.  
In addition to the biochemical reaction, the lettuce also showed a change in its canopy structure. The structural reaction is visible through diurnal variations in the FCVI. This behaviour was not observed for the mustard FCVI. Given the anisohydric nature of the lettuce plant, it was expected to show more variations in its turgor pressure compared to the mustard. This is consistent with the large diurnal variation in leaf angle by the lettuce canopy. In addition to the SIF, PRI (photochemical reflectance index) decreases in the case of stress. Affected by both the plant development and the leaf biochemistry, a high temporal resolution of PRI measurements is needed to unravel the leaf biochemistry and plant development effects. The findings in this paper contribute to the monitoring of plant water status. Whereas this paper explains the reaction of the leaf biochemistry and the canopy structure at the local scale, the same logic can be applied at larger scale.  
The structural reaction (FCVI) is a valuable stress indicator if the seasonal and daily dynamics in the canopy can be disentangled. The seasonal dynamics are influenced by vegetation growth, whereas the short-term dynamics are related to changes in leaf angle, which are influenced by the turgor pressure. The biochemical reaction is a decrease in \(\epsilon_{760}\) during periods of a low soil water availability and high water demand and is especially interesting information for the FLUorescence EXplorer (FLEX) mission. The photochemical reflectance index (PRI) provides additional information on the plant's biochemistry, but its dependency on the canopy structure hampers a clean interpretation of PRI in terms of leaf biochemistry.  
**Author Contributions:** Conceptualization, S.D.C., H.V., P.D. and F.J.; Data curation, S.D.C.; Formal analysis, S.D.C.; Funding acquisition, S.D.C., H.V. and F.J.; Investigation, F.J.; Methodology, F.J.; Project administration, H.V. and F.J.; Resources, H.V. and F.J.; Software, F.J.; Supervision, P.D. and F.J.; Writing--original draft, S.D.C.; Writing--review & editing, H.V. and F.J. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research has been funded by the Fonds pour la Formation a la Recherche dans l'Industrie et dans l'Agriculture (FRIA, Belgium) and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy--EXC 2070--39073234.  
**Data Availability Statement:** The data are available upon request.  
**Acknowledgments:** We express our gratitude to [PERSON] for the box sketches and to [PERSON], [PERSON] and [PERSON] for the help during the fieldwork.  
**Conflicts of Interest:** The authors declare no conflict of interest.