Soil organic carbon and nitrogen accumulation rates in cold and alpine environments over 1 Ma

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 b1 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.