## 4 Discussion
### General Purpose of the Study  
We provided an overview of fluorescence dynamics in O\({}_{2}\)A and O\({}_{2}\)B band in deciduous beech and evergreen spruce forests. The dynamics of fluorescence parameters at fine temporal scale is difficult to obtain from measurements using airborne sensors due to constructional limitations of the sensors and long revisit periods between the measurements. We used daily measured data of fluorescence at forest sites to explore possibilities of using this signal as a physiological measure. Deciduous and evergreen forest were selected for the measurements, which offer distinct and specific dynamics in leaf area index and photosynthetic pigments in the season. Fluorescence parameters showed specific response to photosynthesis of trees, both seasonally and within days, dependent on forest NDVI and APAR. In addition, the dynamics of canopy shadow fraction in the measured area may be affecting the measured signal, as shown in the analysis. Data showed that the changes are linked to GPP of the forests, and therefore, the signals can be scaled to GPP in studies conducted at higher spatial level.  
We summarize major outcomes from the study into six points:  
* fluorescence in the O\({}_{2}\)A band shows positive correlation with APAR and GPP in forest stands (Figures 9 and 11);
* fluorescence in the O\({}_{2}\)B band is influenced with canopy NDVI (Figure 10);
* self-shading within canopy can impact daily observed dynamics of fluorescence at O\({}_{2}\)A band (Figures 7 and 8);
* in the evergreen needle forest, fluorescence in the O\({}_{2}\)B band decreases towards autumn more strongly than O\({}_{2}\)A fluorescence, coherently with decreasing GPP (Figure 5), the change being linked to sensitivity of the emission to foliar NDVI;
* a negative correlation is recorded in the beech forest in the relationship between SIFB and GPP, the trend is related to NDVI seasonality, and the connection between the data deteriorates under lower PAR levels (Figure 11);
* the ratio between fluorescence emissions at O\({}_{2}\)A and O\({}_{2}\)B bands shows similar response at the start of the season at both forest sites, but the trend diverges towards autumn dependent on tree species and dynamics of NDVI (Figure 12).  
diurnal cycle of SIF. Daily data also showed that detected fluorescence at the O\({}_{2}\)A line was influenced by canopy shadow fraction. Measurements also showed that structural properties of the forests can affect the scaling of the SIF signal to ground measurements of GPP.  
Conceptualization, D.K.; methodology, D.K., J.N. and L.S.; software, D.K., J.N. and L.S.; formal analysis, D.K.; data curation, D.K.; writing--original draft preparation, D.K.; writing--review and editing, D.K. and J.G.; visualization, D.K., J.N. and L.S.; project administration, O.U. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Ministry of Education, Youth, and Sports of the Czech Republic within the National Infrastructure for Carbon Observations--CzeCOS (No. LM2018123) and SustES--Adaptation Strategies for Sustainable Ecosystem Services and Food Security under Adverse Environmental Conditions (CZ.02.1.01/0.0/0.0/16_019/0000797).  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to uniqueness of the dataset.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.