『Abstract
Using published and new chronosequence datasets from the European
Alps and the Wind River Range (Rocky Mountains, USA), we report
for the first time a chronosequence of more than 1 Ma for soil
organic carbon, nitrogen and organic matter (SOM) fractions from
alpine soils. The investigated parameters include total carbon
and nitrogen as well as the stable (resistant to H2O2 oxidation) C and N fractions. Time trends were
analysed and are reported on the basis of stocks and concentrations.
The accumulation rates of C and N strongly decreased with increasing
soil age. Differences in trends between the European Alps and
the Wind River Range might be attributed to the factor climate.
For the drier Wind River Range, an asymptotic value of about 15
kg C m-2 was reached after about 15 ky while an asymptotic
value of 20-25 kg C m-2 was measured for the moister
European Alps after about 3 ky. The difference in N stocks between
the two regions was less obvious. For both areas, N was in the
range of 0.5-2 kg N m-2. Using the exponential decay
model, a steady state of C and N (stable and total) concentrations
in the topsoil seemed to be reached after <1 ky (Alps) and 10
ky (Wind River Range). The retardation effect observed for the
Wind River Range could probably be due to aeolian influx. For
both areas, the asymptotic value of the stable fraction of C and
N was in the range of 1-3 kg C m-2 and 0.2-0.4 kg N
m-2, respectively. The stable organic fraction often
has an age close to the age of the soils and consequently can
reach thousands of years. The relative proportion of N and amides
was higher in the stable organic fraction compared to the bulk
soil.
The sequestration rates of org. C and N in soils of the European
Alps and the Wind River Range can reach very high values in very
young soils whereas in old soils sequestration rates are several
orders of magnitude lower. Old soils often integrate several cold
and warm phases and different vegetation types. Nonetheless, the
factor Time seems to be very dominant and covers the track
of other factors in old soils.
Keywords: Chronosequence; Organic C; Nitrogen; Sequestration;
Accumulation; Stable carbon』
1. Introduction
2. Study sites
3. Materials and methods
3.1. Soil sampling
3.2. Total content and fractionation of organic matter
3.3. DRIFT measurements
3.4. Radiocarbon dating of organic matter fractions
3.5. Carbon and nitrogen stocks
3.6. Surface age dating
4. Results
4.1. Stocks and accumulation rates of organic C and N as
a function of soil age
4.2. Labile and stable organic matter
4.3. Age of the stable organic C
5. Discussion
6. Conclusions
Acknowledgements
References