N2O and CH4 fluxes in a temperate heathland under future climatic conditions
1
Mette S. Carter, 1Per Ambus, 1,2Kristian Albert, 1Klaus S. Larsen, 1,3Michael Andersson, 2Louise C.
Andresen, 1Teis N. Mikkelsen and 1Claus Beier
1
Risø National Laboratory for Sustainable Energy, Technical University of Denmark, Roskilde,
Denmark, mette.sustmann.carter@risoe.dk; 2Biological Institute, University of Copenhagen, Denmark;
3
Institute of Environment and Sustainability, JRC, Ispra, Italy
For the first time we investigate how biosphere-atmosphere exchange of greenhouse gases are affected
by the simultaneous influence of three climatic variables, simulating the climatic scenario as predicted
for Denmark in year 20751. The study site is a Danish heathland. Fluxes of the two greenhouse gases
methane (CH4) and nitrous oxide (N2O) was measured in a full factorial design with elevated CO2 (510
ppm by FACE fumigation), elevated temperature (1-2 °C achieved by passive night time warming) and
extended summer drought as treatment variables. Gas fluxes was obtained by static chamber enclosures
applied at weeky to monthly intervals from June 2006 to October 2007. Generally emission rates of
N2O were small (<10 µg N m-2 h-1). Night time warming had an enhancing effect on the N2O fluxe
(P=0.01) whereas the N2O fluxe was reduced when ambient temperature was combined with elevated
CO2 (P=0.02). Soil moisture to a large extent controled the N2O fluxes (P<0.001) with peak rates
occuring after heavy rainfalls. Annual CH4 fluxes were not significantly affected by the treatments.
Fluxes of CH4 were generally downward with consumption rates fluctuating between 20 and 140 µg
CH4-C m-2 h-1. Soil uptake of CH4 increased with increasing soil temperatures (P=0.002). However, the
process was depressed by heavy summer rain when also episodic events of CH4 emissions occured. In
conclussion, after 1-2 years of climatic perturbations we observed that warming gave rise to higher
N2O fluxes. Warming also enhanced the decomposition of leaf litter and the higher N2O flux may
partly result from a higher net mineralization rate.
1
Mikkelsen, T. N. et al. 2008 Experimental design of multifactor climate change experiments with elevated CO2, warming
and drought: the CLIMAITE project. Functional Ecology 22(1), 185-195. doi: 10.1111/j.1365-2435.2007.01362.x