Impact of N-input by wet deposition on N-trace gas fluxes and CH4-oxidation in spruce forest ecosystems of the temperate zone in Europe

In an effort to elucidate the impact of N-deposition from the atmosphere on trace gas fluxes (N2O, NO, CH4) from soils of temperate coniferous forests, two spruce forest sites in Germany and Ireland with comparable edaphic and climatic conditions, but with pronounced differences in the amounts of N-input from the atmosphere were compared at different seasons. At the site in Germany trace gas fluxes as well as wet deposition of NH+4 and NO-3 were recorded continuously over the entire year 1994. Correlation analysis between fluxes and N-input data were performed, in order to elucidate if a direct effect between flux and N-deposition could be demonstrated. At all sampling dates N2O fluxes at the site receiving high atmospheric N-input (Höglwald, Germany) were significantly 1.5–5 fold higher than N2O emission rates at the site receiving low N-input by wet deposition from the atmosphere (Ballyhooly, Ireland). In contrast to the Höglwald site, at which only emission of N2O to the atmosphere was observed, at certain periods the Ballyhooly soil functioned as a sink for atmospheric N2O. Methane oxidation rates were significantly lower at the Höglwald site compared to the Ballyhooly site. At the Höglwald site it could be demonstrated by correlation analysis that the input of NH+4 and NO-3 by wet deposition significantly altered emissions of N2O and NO (stimulation) and of CH4 oxidation (reduction). The coefficient of determination was better for NH+4 than for NO-3 for all trace gases studied and was best for the relation between NO emission rates and NH+4-input.