N2O and CH4 fluxes in undisturbed and burned holm oak, scots pine and pyrenean oak forests in central Spain

We investigated N2O and CH4 fluxes from soils of Quercus ilex, Quercus pyrenaica and Pinus sylvestris stands located in the surrounding area of Madrid (Spain). The fluxes were measured for 18 months from both mature stands and post fire stands using the static chamber technique. Simultaneously with gas fluxes, soil temperature, soil water content, soil C and soil N were measured in the stands. Nitrous oxide fluxes ranged from -11.43 to 8.34 lg N2O–N m -2 h -1 in Q.ilex, -7.74 to 13.52 lg N2O–N m -2 h -1 in Q. pyrenaica and -28.17 to 21.89 lg N2O–N m -2 h -1 in P. sylvestris. Fluxes of CH4 ranged from -8.12 to 4.11 lg CH4– C m -2 h -1 in Q.ilex, -7.74 to 3.0 lg CH4 –C m -2 h -1 in Q. pyrenaica and -24.46 to 6.07 lg CH4–C m -2 h -1 in P. sylvestris. Seasonal differences were detected; N2O fluxes being higher in wet months whereas N2O fluxes declined in dry months. Net consumption of N2O was related to low N availability, high soil C contents, high soil temperatures and low moisture content. Fire decreased N2O fluxes in spring. N2O emissions were closely correlated with previous day’s rainfall and soil moisture. Our ecosystems generally were a sink for methane in the dry season and a source of CH4 during wet months. The available water in the soil influenced the observed seasonal trend. The burned sites showed higher CH4 oxidation rates in Q. ilex, and lower rates in P. sylvestris. Overall, the data suggest that fire alters both N2O and CH4 fluxes. However, the magnitude of such variation depends on the site, soil characteristics and seasonal climatic conditions.