Short-term effect of wildfire on the chemical, biochemical and microbiological properties of Mediterranean pine forest soils

The short-term effects of wildfire on the characteristics of Mediterranean pine forest soils, exposed to semiarid climatic conditions, were evaluated by measuring different chemical, biochemical and microbiological parameters 9 months after the fire. Soils in which the fire had been intense showed higher electrical conductivity values than unburnt soils. All burnt soils had higher contents of nitrates, exchangeable NH4+ and available P and K while their contents of total organic C, extractable C, humic acids, water-soluble C and total and water-soluble carbohydrates were, in general, lower than those of unburnt soils. Microbial biomass-C in burnt soils represented from 50% to 79% of that of unburnt soils; basal respiration and dehydrogenase activity were also negatively affected by fire. In general, fire decreased urease and N-alpha-benzoyl-L-argininamide hydrolysing protease activities. Alkaline phosphatase activity in burnt soils was 29-87% that of the respective unburnt control soil. Arylsulphatase activity was also lower in burnt soils as was beta-glucosidase activity, although in this case the differences from values of unburnt soils were not always statistically significant.