## 3 Results
### Factors That Determine Fluorescence Emissions in the O\({}_{2}\)A and O\({}_{2}\)B Bands  
SIFA was significantly correlated with APAR in the spruce forest (\(R^{2}\) = 0.69; \(p\) < 0.001, Figure 9) and in the beech forest (\(R^{2}\) = 0.80; \(p\) < 0.001). A positive slope in the relationship between APAR and fluorescence emission in the O\({}_{2}\)B band was recorded in the beech forest, with \(R^{2}\) = 0.79 (\(p\) < 0.001). SIFB in the beech forest did not show a close relationship to APAR with \(R^{2}\) = 0.27 (\(p\) < 0.001). Relationships between these data at 30 min intervals tended to be lower. We show the relationship between fluorescence and NDVI for data at high light intensities, with highlighted \(R^{2}\) values for estimations during the summer (Figure 10). In deciduous beech trees, the highest SIFB was estimated for the start and end of the season for the forest with low NDVI. A negative correlation between NDVI and SIFB (\(R^{2}\) = 0.57; \(p\) < 0.001) was recorded. The observed relationship was due to an overlapping between spectra of fluorescence and absorption spectrum by chlorophyl  
Figure 9: Dependency of fluorescence in O\({}_{2}\)A band (SIFA) and O\({}_{2}\)B band (SIFB) on amount of absorbed photosynthetically active radiation (APAR). Relationships between black points refer to averaged data across 2 h interval at midday on days with almost no clouds. N = 80 for spruce data set and N = 93 for beech data set. Grey points data refer to relationships on selected days between the data in 30 min intervals between 10:00 to 14:00 h. The asterisk indicates statistical significance of the result (** for \(p\) <0.001, ** for \(p\) <0.01). **  
was recorded for the SIFB-NDVI relationship in the spruce forest, with \(R^{2}\) = 0.62 (\(p\) < 0.001). Trends in seasonal data deteriorate mostly with seasonality in NDVI. A similar pattern in the relationship was observed in the case of the spruce forest for the relationship between SIFA and NDVI, with lower \(R^{2}\) = 0.40 (\(p\) < 0.001). NDVI had no impact on SIFA in the beech forest (Figure 10); rather, a positive trend was observed here. The trends cannot be scaled more directly between days. It appears that within days, trends are more strongly influenced with PAR, but seasonality with NDVI precludes larger generalization of the relationship between the data. SIFA was significantly correlated (\(R^{2}\) = 0.48; \(p\) < 0.001) with GPP in the spruce forest (Figure 11), but a somewhat poorer relation between SIFA and GPP was seen from the beech forest (\(R^{2}\) = 0.37; \(p\) < 0.001). SIFB was associated with GPP data in the spruce forest with \(R^{2}\) = 0.29 (\(p\) < 0.001). SIFB was efficient in estimating GPP of the beech forest with \(R^{2}\) = 0.61 (\(p\) < 0.001) but with a negative slope in the relationship, contrary to the other graphs. For the data with GPP of the beech forest in the range 15 to 35 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\), we recorded \(R^{2}\) = 0.49 (\(p\) < 0.001). Seasonality of fluorescence emissions in O\({}_{2}\)A and O\({}_{2}\)B bands with foliar chlorophyll concentrations of the trees propagated into a seasonal trend in the SIFA-SIFB ratio (Figure 12). The dynamics of the SIFA-SIFB ratio were similar between the forests at the start of the season. An increase was observed in the ratio between SIFA and SIFB above 1 at the start of the season (Figure 12). However, the established trend diverged later in the season, and the response in the ratio diverged between forests in August. The SIFA-SIFB ratio increased to values of 1.4 in spruce forest, with increasing reabsorption of SIFB emission by vegetation cover. The SIFA-SIFB ratio in beech forest decreased with senescence in the leaves towards end of the season and reached zero with leaf fall. Figure 10: Dependency of fluorescence emission in O\({}_{2}\)A band (SIFA) and O\({}_{2}\)B band (SIFB) on NDVI of the spruce and beech forests. Black points refer to fluorescence and NDVI data in time intervals with significant relationship between fluorescence emission and NDVI.