『Abstract
In mountain regions of Central Europe an increase of soil frost
periods id predicted for this century due to reduced snow fall.
To investigate the effects of freezing and thawing on soil N2O fluxes in a mature Norway spruce forest in
the mountainous Fichtelgebirge, Germany, the natural snow cover
on three experimental plots was removed to induce soil frost.
Three plots with natural snow cover served as controls. Soil N2O fluxes were recorded in biweekly to monthly
intervals during the frost and subsequent thawing period of the
below-average cold winter in 2005/2006 and in the above-average
warm winter in 2006/2007. In addition, N2O
concentrations and isotope signatures in soil air were measured
along soil profiles in six different depths (from 6 to 70 cm).
The soil of the snow removal plots was frozen down to 15 cm depth
from January to April 2006 while the soil of control plots remained
unfrozen under snow cover. Both soil freezing and thawing resulted
in almost tenfold enhanced N2O fluxes on
snow removal plots contributing 64% to annual N2O
emissions. In the subsequent winter without soil frost no effects
were observed. Vertical gradients of N2O
concentrations together with isotope abundance suggest that the
subsoil of all plots was a probably weak, but continuous N2O source throughout the year. Isotope signatures
and N2O concentration gradients in the soil
profile indicate that microbial N2O production
and reduction of N2O to N2
did not or just marginally occur in frozen soil layers of the
snow removal plots. Consequently, elevated N2O
fluxes in the late winter were attributed to the release of accumulated
N2O originating from the subsoil. At unfrozen
soil, however, N2O emissions were reduced
due to a shift of the N2O production-consumption
ratio towards more consumption in the topsoil of both the control
and snow removal plots. These findings contradict the general
assumption that N2O production in organic
layer is responsible for bursts of N2O due
to soil frost.
Keywords: N2O; N2O consumption;
15N; 18O; Soil frost; Stable isotopes; Thawing』
Introduction
Methods
Site description
Experimental design
Measurements of N2O fluxes
Gas sampling along soil profiles
Measurement of N2O isotope ratios and N2O concentrations
Data analysis
Results
Soil matric potential, air and soil temperature
N2O fluxes
N2O concentration and isotope profiles
Discussion
Conclusions
Acknowledgments
References