## 3 Results and Discussion
### Thermal Stability of SOM  
Below 150 \({}^{\circ}\)C, the evaporation of residual water takes place, and the thermal degradation of SOM started between 150 and 180 \({}^{\circ}\)C. To assess the possible link between SWR and thermal stability of SOM, we analyzed the data recorded between 150 and 600 \({}^{\circ}\)C. The studies that used TG in soil analysis (and applied a 10\({}^{\circ}\)C min\({}^{-1}\) heating rate) reported that SOM degradation starts at around 200 \({}^{\circ}\)C [42; 43]. Lower temperatures associated with SOM degradation may indicate lower thermal stability of OM in studied soils. This also follows from DTG values that culminated between 275 and 300 \({}^{\circ}\)C. The rate of weight loss recorded during the exotherm usually reaches maximum at higher temperatures when topsoil samples are subjected to TG. For example, [PERSON] et al. [44], who analyzed composids and used a similar experimental setting, reported a maximal rate of weight loss below 300 \({}^{\circ}\)C. Similar DTG profiles were observed by [PERSON] et al. [45], who assessed changes in litter properties during decomposition using TG. This suggests that the studied soils contain a significant portion of raw (thermally labile) OM. It is worth noting that weight loss recorded between 150 and 200 \({}^{\circ}\)C may be due to the evaporation of volatile organic substances and not thermal degradation of SOM. The results of correlation analysis helped to identify the differences in thermal stability of respective organic functional groups. [PERSON]'s correlation coefficients were calculated to describe the link between FTIR peak areas and DTG data recorded between 150 and 600 \({}^{\circ}\)C. The correlations are plotted in Figure 5. Each of the eight graphs expresses the collinearity between the peak area integrated in a given wavenumber interval and the weight loss rate at a specific temperature. A significant positive correlation indicates that the SOM component containing a functional group is thermally modified or degraded at the given temperature. For example, the peak areas associated with three IR bands of CH vibrations showed similar correlation patterns across the temperature scale. These bands include 3020-2800, 1475-1460, and 1395-1365 cm\({}^{-1}\). The correlation reached a maximum around 230 \({}^{\circ}\)C, which suggests that aliphatic structures, responsible for SWR, are degraded at relatively low temperatures [46]. On the other hand, the r values associated with 1455-1400 and 1190-1135 cm\({}^{-1}\) peak areas differed from the previous group. The correlation of 1455-1400 and 1190-1135 cm\({}^{-1}\) peak areas and DTG showed maxima at higher temperatures, specifically at 300 and 370 \({}^{\circ}\)C. In the case of the 1455-1400 cm\({}^{-1}\) band, the absorption is caused by stretching and bending vibrations of carboxylates and also partially by C-O stretching in the phenolic group [47; 48]. In the 1190-1135 cm\({}^{-1}\) interval, various groups may be detected, and phenolic C-O stretching is one of them [22; 34]. These observations suggest that phenolic structural units are more thermally stable in comparison to other aliphatic groups. It also follows from the correlation of the 1560-1530 cm\({}^{-1}\) peak that showed r values around 0.7 even at T \(>\) 350 \({}^{\circ}\)C. Besides amides, the absorption in this band is also partially caused by aromatic C [48]. The positive correlation between 1740-1710 cm\({}^{-1}\) peak areas and DTG was significant across a wider temperature range with the r values culminating around 350 \({}^{\circ}\)C. This was due the decarboxylation process that started at the beginning of the exotherm and proceeded up to higher temperatures. Depending on the nature of the sample and experimental setting, the temperature interval for SOM decarboxylation may range from 250 up to 370 or even 420 \({}^{\circ}\)C [49]. To find out whether TG data are related to WDPT and MED variability, we used an approach similar to that of [PERSON] [50].