## Discussion
### Sensitivity Analysis of Vegetation Groups  
Observed vegetation information (i.e., SIF and trait-sensitive VIs) showed a large heterogeneity in and around the peatland area (Figures 4 and 7). VIs and SIF maps from the pine forest, grassland, and peatland sites showed a clear structural-functional relationship [36]. A visual comparison of obtained maps indicated that greenness indices, non-greenness indices, and SIF represented different patterns for different vegetation groups. Inside the peatland area, alder forest, and low birch bush were characterized by rich green biomass during July, as represented by high values of greenness-sensitive indices. NDVI values of deciduous forest, meadows, mesic pastures, and alder forest showed saturation at values around 0.8, which is in agreement with [PERSON] et al. [36]. Some of the less-vegetated areas (e.g., herbaceous vegetation of forest clearing zones and mowed grasslands) showed less green vegetation coverage during the campaign time. Peatland calcareous fens were characterized with less dense vegetation [62] and showed the lowest greenness index values. The EVI, sensitive to canopy structure [28] and vegetation biomass [51], performed best for the regions where the green biomass was high, like alder forest, meadows and mesic pastures, riparian forests, and secondary forest communities with _Alnus glutinosa_. Although not shown, EVI was significantly correlated with greenness indices at both vegetation group and plant species composition levels, which was in agreement with [PERSON] et al. [63]. Furthermore, it was observed that the regions with the high greenness index values, like the deciduous forest, secondary forest communities with _Alnus glutinosa_, meadows and mesic pastures, Alder forest, and low birch bush, were characterized by low PRI values. PRI is an indicator of the xanthophyll cycle activity, and it increases with a decrease in SIF signals, as shown by different studies [64; 65; 66]. A negative relationship between SIF and PRI was also confirmed by our data. PRI denotes that the vegetation groups such as mowed meadows and mesic pastures, post-agriculture land, and forest clearings with high PRI values may have a higher rate of xanthophyll cycle activity, and vice-versa conditions applied to vegetation groups with low PRI. Sometimes encroachment, grazing/burning, and alleviation are the main stressors to the plants [67], which might be the reason behind high PRI signals at the post-agriculture land, mowed meadows, and mesic pastures, as well as herbaceous vegetation of forest clearing zones. PRI is also known to negatively correlate with the ratio of carotenoids to chlorophyll pigment concentrations [68], which may also explain the lower PRI in these areas. The HyPlant sensor offered a unique opportunity to track not only far-red O\({}_{2}\)A band signals, but also to capture narrower red O\({}_{2}\)B band signals [37]. In our study, we reported both SIF bands at 760 nm and 687 nm from peatland vegetation groups and plant communities. However, the study by [PERSON] et al. [69] showed that red fluorescence--rather than far-red--to be more sensitive to describe plant physiological process and canopy net photosynthesis. Apart from this study, only a few recent studies such as [PERSON] et al. [28], [PERSON] et al. [37], [PERSON] et al. [66], [PERSON] et al. [70], [PERSON] et al. [71], [PERSON] et al. [72], and [PERSON] et al. [73] exploited both the red and far-red SIF signals, mainly for agriculture or forest areas; therefore, future investigations are necessary for different landscapes [16]. To the best of our knowledge, we are the first to explore both SIF signals for heterogeneous peatland ecosystems. In our study, the SIF signals varied from 0 to 3.21 and to 2.93 for SIF\({}_{760}\) and SIF\({}_{687}\), respectively, where SIF\({}_{760}\) appeared to be more sensitive than SIF\({}_{687}\) over the whole study area. According to [PERSON] et al.