1 Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), CH-8903 Birmensdorf, Switzerland
2 Institute of Terrestrial Ecosystems, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland
3 Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
At Alptal, Switzerland, nitrogen (N) has been applied as NH4NO3 since 1995 in low doses during rain events to realistically mimic increased N deposition to a mature mountain spruce stand. Five years of measurements in a replicated plot design showed that N2O and CH4 emissions from the soil to the atmosphere increased due to the N addition. For CH4, this involved a shift from a net sink to a net source. CO2 emissions did not change significantly, although they averaged lower under simulated N deposition. The girdling of 40% of tree basal area in each plot, followed by subsequent felling of the girdled trees, increased emissions of N2O but reduced net emissions of CH4 from soils. CO2 and N2O emissions depended on soil temperature and soil water table depth. Soil temperature did not affect CH4 fluxes, whereas net CH4 production was higher when the water table was closer to the soil surface. Our data highlights the need that future investigations should focus more on the allocation of assimilates to tree roots in order to better quantify the ecosystem's C balance.
Keywords: Picea abies, carbon dioxide, methane, nitrous oxide, nitrogen deposition, tree girding