Uni-Bayreuth grafik-uni-bayreuth


Goldberg, S*; Gebauer, G: N2O isotope and concentration profiles - a new tool to identify biogenic processes in soils
Poster, International Symposium Soil processes under extreme meteorological conditions, Bayreuth: 25.02.2007 - 28.02.2007

Studies on emissions of nitrous oxide from soils mostly focus on fluxes between soil and atmosphere. At present our knowledge about N2O production and consumption and the localisation of these processes in soils is scarce. For this century an increasing frequency of extreme meteorological boundary conditions is expected that result in a higher frequency of drying/rewetting and freezing/thawing of soils especially in higher elevation areas. In this study the effects of freeze/thaw events on the fluxes of N2O between soil and atmosphere were investigated. To identify underlying reasons for phenomena like increased N2O emissions due to freeze/thaw events a new approach was applied. Additional to N2O flux measurements between soil and atmosphere δ15N and δ18O values of N2O as well as N2O concentrations in soil profiles were measured. In this freeze/thaw experiment in a 145-year-old Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge, Germany, the snow cover was removed from the experimental plots. Every two weeks fluxes of N2O between soil and atmosphere were measured using a closed chamber technique in conjunction with a photoacoustic infrared gas analyser. Over the whole freezing period the manipulated plots showed up to 20-fold higher N2O fluxes between soil and atmosphere compared to the control plots. Parallel to this very low N2O concentrations of 1.32±1.88 ppm (mean±SD; n=10) were recorded over the whole soil profiles (6 different depth from 6 to 70 cm) of the control plots. In the manipulated plots considerably higher N2O concentrations were detected in the soil air (19.37±15.57 ppm; n=16). The observed isotope signatures (δ15N: -26.18 to +11.21‰; δ18O: +18.18 to +65.57‰) were neither typical for N2O from nitrification (δ15N: -75‰; δ18O: +22.4‰) nor denitrification (δ15N: -55 to -36‰; δ18O: 0 to +50‰). Both, δ15N and δ18O can only be interpreted as a result of parallel production and consumption of N2O through denitrification. The data show, that N2O concentrations in soil air can exceed the exchange with the atmosphere by several orders of magnitude.

Letzte Änderung 19.03.2007