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

摘要

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 μg N₂O–N m−2 h−1 in Q.ilex, −7.74 to 13.52 μg N₂O–N m−2 h−1 in Q. pyrenaica and −28.17 to 21.89 μg N₂O–N m−2 h−1 in P. sylvestris. Fluxes of CH₄ ranged from −8.12 to 4.11 μg CH₄–C m−2 h−1 in Q.ilex, −7.74 to 3.0 μg CH₄–C m−2 h−1 in Q. pyrenaica and −24.46 to 6.07 μg 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.