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5th Swiss Geoscience Meeting, Geneva 2007
Storage and turnover of soil organic matter in highelevation grasslands of the Alps
Leifeld Jens*, Zimmermann Michael*, **, Conen Franz*** & Fuhrer Jürg*
*Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, 8046
Zürich ([email protected])
** now at School of Geosciences, University of Edinburgh, UK
*** Environmental Geosciences, University of Basel, Switzerland
Potential feedbacks of soil organic matter (SOM) in colder environments to
global environmental change are relatively uncertain due to lack of data and our
still limited system understanding. We sampled grassland soils along an elevation gradient in the Valais, Swiss Alps to investigate storage and turnover of soil
organic carbon (SOC) in relation to environmental conditions. The total amount
of SOC (0-20 cm) did not change with altitude, but the share of particulate organic carbon (POC) increased to a maximum of > 80% of SOC in the topsoil (05 cm) of the highest site. Radiocarbon dating and calculation of carbon turnover
indicated a strong decline in reaction rates at higher elevations which could not
be explained by temperature effects only. A comparison of turnover times as
derived from radiocarbon dating to those from the widely applied soil carbon
turnover model RothC indicated an underestimation of mean residence times by
the latter. A high correspondence between pool sizes in the RothC model and
physico-chemical fractions of the soils was described in an earlier study mainly
for temperate soils (Zimmermann et al. 2007) but could not be reproduced for
the colder sites in the present study, suggesting that stabilization mechanisms
differ from that of temperate soils
We further developed a novel approach for determining relative SOM stabilities
by means of 15N signatures in different soil fractions and how they compare to
the corresponding 14C signature (Conen et al. 2007). The conclusions are a
general increase in stability of mineral-associated (MOM) relative to particulate
organic matter (POM) with increasing soil depth at all altitudes and the largest
relative differences in stability between MOM and POM for all soil depths at the
lowest altitude.
REFERENCES
Conen, F., Zimmermann, M., Leifeld, J., Seth, B. and Alewell, C., 2007. Relative
stability of soil carbon revealed by shifts in d15N and C:N ratio. Bio-geosciences
Discussions 4: 2915-2928.
Zimmermann, M., Leifeld, J., Schmidt, M.W.I., Smith, P. and Fuhrer, J., 2007.
Measured soil organic matter fractions can be related to pools in the RothC
model. European Journal of Soil Science 58: 658-667.