invited Talk, Joint European Stable Isotope User Meeting (JESIUM), Giens, France: 2008-08-31 - 2008-09-05
To our current knowledge about 70 % of the global N2O emissions originate from soils. Hence N2O exchange between soil and atmosphere is of outstanding importance for its regional and global budget. Climate models predict an increasing frequency of extreme meteorological boundary conditions in future that result in a higher frequency of drying/rewetting and freezing/thawing of soils. Such drastic changes of the meteorological boundary conditions to soils are obviously influencing the turnover of N in soils, however, our knowledge about the mechanisms and relevance of such conditions with respect to N2O production and consumption processes is very limited. So far, studies on emissions of nitrous oxide from soils mostly focus on fluxes between soil and atmosphere and thus represent an integration of heterogeneous biogenic activities along soil profiles. In this study N2O fluxes between soil and atmosphere were monitored during a drying/rewetting and a freeze/thaw experiment in a Norway spruce forest in the Fichtelgebirge, Germany. In addition to N2O flux measurements soil gas samples from six different soil depths were analysed in time series for N2O concentration as well as isotope abundance to investigate N2O dynamics within the soil. Analysis of N2O concentrations and their isotope signatures along soil profiles enables localisation of sources and sinks in soils as well as identification of production and consumption processes and therefore enlarges our knowledge on processes affecting aboveground N2O fluxes. Our data emphasize the outstanding role of microbial N2O consumption in this forest soil and therefore are of particular importance for an improved mechanistic understanding of source as well as episodically reported N2O sink functions of soils.