## 4 Discussion  
LAI is an important input in the model of several ecosystems for the purpose of predicting productivity and biomass; thus, it is important to correctly estimate the LAI [33; 34]. The LAI estimation for an ecosystem such as peatland is complicated, as there is always a layer of mosses and slow decaying litter. In this work, the measured LAI, which represents the PAI of the vascular plant, does not correlate with modeled LAI. The decomposition process in peatland is slow [18], and a significant amount of litter was present at the beginning of the measurement, especially for the CL site, where the proportion of vascular plants is significantly higher (Figure 8). Therefore, after the winter, due to partial decomposition and no new biomass formation, the measured LAI was decreasing for the next few months before the vascular plants started to grow and contributed to the total measured LAI. As the biomass once created gets dry but remains on the plot, the measured LAI reaches a peak and then shows almost a stable pattern till September. On the contrary, modeled LAI showed a clear seasonal pattern, where the increase in LAI in March and April is mostly due to the contribution from mosses which are getting greener, whereas, from May, the vascular plants also start to grow and significantly contribute to the modeled LAI [35]. There is less proportion of Carex spp. in CR in relation to _Sphagnum_ spp. and _Oxycoccus palustris_, whereas in the CL site, the proportion of _Carex_ spp. is higher. The less biomass of _Carex_ spp. means lower measured LAI; therefore, the difference between measured and modeled LAI is more than 100% for the CR site. The LAI values are high for CL, but the differences between measured and modeled LAI were observed to be lower for CL than for the CR site. This data can be easily understood when we consider the contribution of signals from mosses along with vascular plants for modeled LAI, whereas measured LAI considered vascular plants only. The observation indicates that measured LAI from the SunScan probe (DELTA-T, Burwell, UK) and modeled LAI are two different kinds of values (transmission and reflectance-based LAI estimation), especially for peatland. Measured LAI has significant value only when we are estimating the properties of vascular plants. Figure 7: A comparison between measured and modeled Sun-induced fluorescence (SIF). The dashed line represents the theoretical ideal performance of the model. For the overall biomass and productivity analysis, modeled LAI might be more important, as it includes biomass of vascular and non-vascular plants, and it should be considered for peatlands. Thus, for the same reason, we used the modeled LAI value for the estimation of SIF through the SCOPE model. The observation of various VIs is considered an efficient method for detecting the changes in the plant physiology at the ecosystem level, but VIs have their limitations; therefore, other indices such as SIF have been developed that can better present the physiological status of the vegetations [15; 36]. In this study, NDVI, EVI, and NIRv showed a seasonal pattern for both the studied sites and was observed to be highly correlated with modeled LAI, but the correlation with measured LAI was observed to be poor (Figure 5), which can be again explained through the non-consideration of mosses and part of the litter interference in measured LAI. The NDVI gets saturated in July and August at the CL site (due to high LAI indicating higher biomass. Figures 3 and 4). This property of NDVI is well known and has contributed to red spectrum consideration, which reaches its peak with high LAI in the growing season [37], whereas the EVI and NIRv are considered to be more sensitive to canopy variation in comparison to NDVI [38].