Soil N2O emissions in a Mediterranean shrubland disturbed by experimental fires

Fire is a widespread disturbance in Mediterranean ecosystems and its frequency is expected to increase in the future due to climatic change. In the present work post burning soil N2O fluxes and several related microbial processes were investigated in a Mediterranean shrubland, where experimental fire was induced. Nine plots were selected in the study site, of which, 3 were used as control, 3 were burned with fire of low intensity (LF) and 3 with fire of higher intensity (IF). N2O fluxes, soil humidity and temperature, were measured staring 2 days after burning for one year. Soil was sampled 4 days, and 3, 5 and 8 months after burning and potential net nitrification (PNN), denitrification enzyme activity (DEA), mineral N and organic C, were measured. Cumulative data indicate a doubling of N2O production in burned plots in one year. This was mainly due to the increase of frequency of hot spots of N2O production in burned plots. A slightly detrimental effect of fire on the analysed biological activities was detected only immediately after burning. After 3 months both PNN and DEA had mostly recovered and PNN further increased, over control levels, in the following months. Fire seemed to induce a change in the main source of N2O, which in control plots was represented by heterotrophic activity (50-75%), whereas, in burned plots was mostly of authotrophic origin, and this was particularly evident in LF plots. This most probably was supported by the significant increase of soil NH4+ content following biomass burning.