Immediate- and Short-term Wildfire Impact on Soil Microbial Diversity and Activity in a Mediterranean Forest Soil

Wildfires are a driving factor of forest soils and their biota, especially in fire-prone ecosystems. Fire effects on soil microbial community are complex and still largely unknown. Greater knowledge is needed as fire frequency is expected to increase with human-induced climate change. This study aims at assessing the effects of a single moderately severe wildfire on microbial community diversity and activity in a Mediterranean forest soil by DNA molecular screening (polymerase chain reaction-denaturing gradient gel electrophoresis). For this purpose, the soil of a burned area was sampled 3 days and 10 months after the fire and compared with the soil of an unburned contiguous area. For the DNA fingerprinting, we analyzed both extracellular and intracellular DNA fractions of the soil metagenome. The fire impact on soil was also rated in terms of selected enzyme activities, as reliable bioindicators of biogeochemical cycles. An immediate fire-induced general decrease in enzyme activities and more durable changes in the bacterial and fungal communities structure were found, although microbial biomass was not significantly affected. Litter layer was completely turned to char and ash by the fire, but after 10 months, it showed a fair amount of DNA, a structured microbial community, and a good enzymatic activity. Overall, such relatively fast recovery was likely caused by the microbial biomass that survived the fire, which evidently adapted to the new soil conditions.