Soil-atmosphere methane exchange in undisturbed and burned Mediterranean shrubland of southern Italy

Soils represent the primary biotic sink for atmospheric methane (CH4). Uncertainty is associated, however, with global soil CH4 consumption because of the few data available from many areas and, in particular, from Mediterranean type ecosystems. In this study, soil-atmosphere CH4 exchange was measured for one year in a coastal Italian shrubland (maquis), from both undisturbed areas and areas treated with experimental fire. Although fire represents one of the most frequent disturbance factors in seasonally dry environments, very few studies in these ecosystems have focused on its effect on soil CH4 fluxes. Significant differences in soil ammonium content, water content, and temperature were measured between burned and unburned plots, however, no statistical differ ences were observed for CH4 fluxes. CH4 fluxes varied between -0.39 and -16.1 mg CH4 m(-2) day(-1) and temporal variations were mainly driven by variations in soil water content and temperature. The highest CH4 oxidation rates were measured during the driest and warmest period. Low gravimetric soil water content in the top 10 cm, as well as high NH4+ concentration, did not seem to reduce methanotrophic activity, suggesting that maximal CH4 oxidation activity might take place deeper in the soil profile, at least during part of the year.