Soil microbial metabolism and organic carbon pool sas affected by prescribed burning in pine plantations of Southern Italy.

Prescribed burning is an important tool in forest management to reduce wildfire risk but it may produce alterations in organic C pool and microbial metabolism with consequences on C cycle and CO2 emission towards the atmosphere. This study aims at evaluating the effect of prescribed fire performed in Pinus pinaster and P. halepensis plantations of Cilento e Vallo di Diano National Park (Southern Italy) on total organic C, extractable organic C, microbial C, metabolic quotient (qCO2: mg CO2-C g-1 Cmic h-1) and rate of C mineralization (CMR: mg CO2-C g-1 Corg h-1) measured in the fermentation layer and in the soil beneath (0-5 cm depth) during the first 5 months after fire. No effect due to prescribed burning was found on total organic C neither in fermentation layer nor in soil beneath and only temporary increases in extractable organic C were found in fermentation layer of both plantation and in soil of P. pinaster plantation. However, some changes were caused by prescribed burning in the other parameters, mainly in fermentation layer, in particular, a reduction in microbial C and an increase in metabolic quotient, during the whole study period, and an increase in C mineralization rate in the first 5 h (P. pinaster plantation) or 11 d (P. halepensis plantation) since burn. Temporary increases in metabolic quotient and in C mineralization rate were also found in soil of P. pinaster plantation where a longer residence time of the flame occurred compared to that observed in the P. halepensis one. Data suggest that stress conditions produced by fire in fermentation layer caused a change in microbial activity towards a more dissipative metabolism (high qCO2), with a consequent possible increase in CO2 emission to the atmosphere. However, this possible increase should be counterbalanced by a decrease in CO2 emission due to the reduction in wildfire frequency and intensity that could occur if prescribed burning is used as a forest management tool.