## 3 Results
The results of the PCA performed on soils collected under herbs highlighted that the first two axes accounted, respectively, for 48% and 14% of the total variance (Figure 3D). Soil C, available fraction of Ca, and DHA were positively correlated to the first axis (Figure 3D). Available fractions of Al, Cu, Mg, and Pb were positively correlated to the second axis; whereas, pH and available fraction of K were negatively correlated to it (Figure 3D). Figure 2: Mean values (\(n=12\), \(\pm\) s.e.) of the enzymatic activities (hydrolase: HA; dehydrogenase: DHA; \(\beta\)-glucosidase: \(\beta\)-GLU) measured in surface (0–10 cm) soils collected inside the Vesuvius National Park (Southern Italy) in unburnt (UB) and burnt (B) soils under different vegetation covers (P: pine; HO: holm oak; BL: black locust; H: herbs). Figure 3: Graphical display of the first two axes of the Principal Component Analysis on the soil abiotic (pH; water content: WC; organic matter: OM; C and N, available fractions of Al, Ca, Cu, Fe, K, Mg, Mn, Na, and Pb) and biotic (hydrolase: HA; dehydrogenase: DHA and \(\beta\)-glucosidase: \(\beta\)-GLU) properties measured in unburnt (empty) and burnt (full) soils covered by pine (yellow in panel **A**), holm oak (green in panel **B**), black locus (blue in panel **C**), and herbs (red in panel **D**) in soils collected inside the Vesuvius National Park (Southern Italy) in summer (dot) and fall (square) 2018, and winter (triangle) and spring (rhombus) 2019. The results of PERMANOVA showed that soil abiotic and biotic properties significantly (\(p\) = 0.002) varied among different seasons only for soils covered by \(p\) and significantly (\(p\) = 0.04) varied between UB and B only for soils covered by HO. The coefficients of variation (CVs) calculated for all enzymatic activities widely varied for both seasonality and fire in soils under the investigated vegetation covers, although with different extents (Table 4). In more detail, the CVs calculated for HA showed the widest variability both for seasonality and for fire in soils covered by P (Table 4); they were wider for seasonality than for fire in soils under HO and BL (Table 4); conversely, they were wider for fire under H (Table 3). The CVs calculated for DHA highlighted the widest variability for seasonality in soils covered by P and for fire in soils covered by H (Table 4). The CVs for DHA were wider for seasonality than for fire only under P (Table 4); they were similar for seasonality and fire under HO and BL (Table 4); finally, they were wider for fire under H (Table 3). The CVs calculated for \(\beta\)-GLU showed the widest variability both for seasonality and for fire in soils covered by H (Table 4); they were wider for seasonality than for fire in soils covered by P and BL (Table 4); conversely, they were wider for fire under HO (Table 4). The results of the multiple linear regressions performed to highlight the main abiotic factors that controlled the enzymatic activities at different seasons and in UB and B soils are, respectively, reported in Tables 5 and 6. In more detail, at different seasons, the factors that controlled the enzymatic activities regardless of the vegetation cover mainly were the available fraction of micro- and macro-nutrients, such as Ca, Fe, Mn, Mg, and Na (Table 5). Instead, in unburnt and burnt soils, the enzymatic activities were also controlled by the available fractions of metals such as Al, Cu, and Pb and by some other abiotic properties such as WC, pH, OM, and total C and N (Table 6).