## 2 Materials and Methods
### Soil Analyses  
In the laboratory, the soil samples were sieved (<2 mm) and analyzed for pH, water (WC), and organic matter (OM) contents, total concentration of carbon (C) and nitrogen (N), and available fraction of Al, Ca, Cu, Fe, Mg, Mn, Na, and Pb. Soil pH was measured with a pH meter on aqueous extract obtained by adding distilled water to soil (2.5:1 = w:w), whereas WC was determined gravimetrically by drying fresh soil at 105 \({}^{\circ}\)C until reaching constant weight. Total C and N concentrations were determined by gas-chromatography (Thermo Finnigan, CNS Analyzer) on dried and pulverized (Fritsch Analysette Spartan 3 Pulverisette 0) samples. OM was calculated multiplying by 1.724 the C\({}_{\rm org}\) determined  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sampling Site** & **Vegetation cover** & **Fire** & **Coordinates** \\ \hline HO1 & Holm Oak & Burnt & 40\({}^{\circ}\)80/72\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 14\({}^{\circ}\)43/46\({}^{\prime\prime}\) \\  & Holm Oak & Unburnt & 40\({}^{\circ}\)80/88\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 14\({}^{\circ}\)43/92\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 40\({}^{\circ}\)80/23\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 40\({}^{\circ}\)44/15\({}^{\prime\prime}\) \\  & Holm Oak & Unburnt & 40\({}^{\circ}\)81/03\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 40\({}^{\circ}\)81/67\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 14\({}^{\circ}\)40/86\({}^{\prime\prime}\) \\  & Holm Oak & Unburnt & 40\({}^{\circ}\)81/99\({}^{\prime\prime}\) \\  & Holm Oak & Unburnt & 14\({}^{\circ}\)39/96\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 40\({}^{\circ}\)79/71\({}^{\prime\prime}\) \\  & Holm Oak & Burnt & 14\({}^{\circ}\)43/87\({}^{\prime\prime}\) \\  & Holm Oak  
by gas-chromatography (Thermo Finnigan, CNS Analyzer) on samples previously treated with HCl (10%, v:v). Available fraction of Al, Ca, Cu, Fe, Mg, Mn, Na, and Pb was assessed on air-dried soil samples with diethylenetriamine pentacetic acid, CaCl\({}_{2}\), and triethanolamine at pH 7.3 \(\pm\) 0.05 according to [PERSON] and [PERSON] [33]. The element concentrations were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS Aurora M90, Bruker). Accuracy of element measurements was checked by concurrent analysis of standard reference material (BCR CRM 142R--Commission of the European Communities, 1994). The overall element recovery ranged from 80%-120% for all the investigated soil samples. Hydrolase activity (HA) was determined by adding to 1 g of fresh soil 7.5 mL of 60 mM potassium phosphate at pH 7.6 and 0.100 mL of fluorescein diacetate (FDA). The reaction mixture was incubated at 30 \({}^{\circ}\)C for 20 min, after which the fluorescein was extracted with 7.5 mL of acetone. The extract was centrifuged at 5000 rpm for 5 min and the absorbance of the supernatant was measured at 490 nm and the results were expressed as mmol of FDA produced for 1 g of dry soil in 1 h [25]. Dehydrogenase activity (DHA) was determined by adding to 1 g of fresh soil 1 mL of 1.5% 2,3,5-triphenyltetrazolzolium chloride (TTC) dissolved in 0.1 M Tris-HCl buffer at pH 7.5. The reaction mixture was incubated at 30 \({}^{\circ}\)C for 24 h in the dark, after which the triphenylformazan (TFF) was extracted with 8 mL of acetone. The extract was centrifuged at 3500 rpm for 15 min and the absorbance of the supernatant was measured at 546 nm and the results were expressed as mmol of TFF produced for 1 g of dry soil in 1 h [15]. \(\beta\)-glucosidase activity (\(\beta\)-GLU) was determined by adding to 1 g of fresh soil 4 mL of modified universal buffer (MUB) pH 6 and 1 mL of 0.025 M p-nitrophenyl \(\beta\)-D-glucopyranoside (PNP). The reaction mixture was incubated at 37 \({}^{\circ}\)C for 1 h, after which the enzymatic reaction was stopped by cooling on ice for 15 min. Then, 1 mL of 0.5M CaCl\({}_{2}\) and 4 mL of 0.1M tris-hydroxymethylaminomethane-sodium hydroxide (THAM-NaOH) pH 12 was added.