Soil N2O emissions in a Mediterranean shrubland disturbed by experimental fires

Abstract

In the present work, post-burning soil N2O fluxes and related microbial processes were investigated in a Mediterranean shrubland subjected to experimental fires. Nine plots were selected, of which three were used as controls, three were burned with low-intensity fire and three with higher intensity fire. N2O fluxes, soil humidity and temperature were measured starting 2 days before burning and for 1 year after fire. Potential net nitrification, denitrification enzyme activity, mineral N and organic C were measured from soil samples collected periodically after burning. Cumulative data indicate a doubling of N2O production in burned plots over 1 year. Burned plots showed an increase of frequency of hot spots of N2O production. A slight detrimental effect of fire on the analysed biological activities was detected only immediately after burning. After 3 months, both potential net nitrification and denitrification enzyme activity had mostly recovered and potential net nitrification 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 it was mostly of autotrophic origin, most probably due to the significant increase of soil NH4+ after burning.