## 3 Results and Discussion
### Thermal Stability of SOM
We calculated the mass loss values of the sample that were recorded per 10 \({}^{\circ}\)C temperature increase, starting from 150-600 \({}^{\circ}\)C and ending with 590-600 \({}^{\circ}\)C. This way, the number of possible predictors used in the regression analysis was reduced from 1350 to 45 (sample's weight was recorded 30 times per minute during TG analysis, which means that within the 150 and 600 \({}^{\circ}\)C interval, 1350 values were recorded). Since in the 150-600 \({}^{\circ}\)C interval SOM degradation takes place, 45 mass values may be expressed as the portions of SOM (%) in the sample degraded/volatilized per 10 \({}^{\circ}\)C. These mass portions of SOM were tested in multiple regression analysis as partial predictors along with soil moisture and FTIR data. A possible link between the degraded SOM portions and WDPT and MED data is indicated in Figure 6, by plottingthe correlation coefficients across the 150-600 \({}^{\circ}\)C temperature interval. The figure shows that the significance level (\(p<0.05\)) for positive correlation was exceeded at around 250 \({}^{\circ}\)C and at higher temperatures above 480 \({}^{\circ}\)C. Plotted correlation coefficients give us a hint about degradation of SOM components responsible for WR. Although the r values at temperatures above 480 \({}^{\circ}\)C were even higher, it is probable that most hydrophobic SOM components were degraded during the initial stage of exotherm, as this was reported previously [46] and the positive correlation observed \(>\)480 \({}^{\circ}\)C refers to degradation of carbonaceous residue of these substances. Figure 5: Correlations (Pearson’s) between FTIR peak areas and the rate of weight loss (DTG) recorded in 150 and 500 \({}^{\circ}\)C interval (0.29; 0.38; 0.47 values correspond to \(p<0.05\); 0.01; and 0.001 significance level). The statistically explained portion of WDPT and MED variances ranged from 64 up to 73 % when field moisture of topsoil and FTIR data were used as explanatory variables. Using the amounts of SOM that degraded during 10 \({}^{\circ}\)C temperature increments as the predictors (along with FTIR and soil moisture data) led to a further increase in the R\({}^{2}\) value (up to 0.89). Weight losses recorded in five temperature intervals were successfully tested as partial predictors of WDPT and/or MED values: 150-160, 200-210, 320-330, 340-350, and 440-450 \({}^{\circ}\)C. The regression equations are given in Tables S1 and S2. Since the weight loss rate, recorded between 320 and 350 \({}^{\circ}\)C, was highly correlated with SOC content in the sample (r \(>\) 0.9), it is not surprising that SOM degraded in this temperature interval is positively related to WR data. The interpretation of other regression terms is, however, less straightforward. It is possible that weight loss that occurred at lower temperatures is caused by volatilization of the most labile organic substances, which are polar and hence hydrophilic. This is in accordance with the negative value of the partial regression coefficient associated with these two regression terms. However, this is only a hypothesis that should be verified by further research. The interpretation of the last regression term, associated with weight loss  
moderate heating. This suggests that all soils contained hydrophobic structural units that may cause WR, depending on their spatial arrangement. The results of thermal analysis suggest that OM in studied topsoil is relatively labile, containing a significant portion of accumulated raw OM. This followed from DTG values, which culminated below 300 \({}^{\circ}\)C. Similar thermal degradation profiles were observed in the case of partially decomposed litter or nonstabilized composts. This indicates that there is a link between thermal ability of OM in studied soils and their susceptibility to WR. Strongly acidic pH, higher C/N ratio, and coarse soil texture support the accumulation of certain organic inputs, rather than their transformation and SOC stabilization.