EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Soil organic carbon in alpine environments under a warming climate 

Annegret Udke1, Michael Zehnder2, Christian Rixen2, Markus Egli3, and Frank Hagedorn1
Annegret Udke et al.
  • 1Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
  • 2WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 3University of Zurich, Department of Geography, Geochronology, Zurich, Switzerland

Climate warming is most pronounced in cold regions impacting plant-soil system with counteracting effects on ecosystem carbon storage. Whereas upward migration of plants (alpine greening) in a warmer climate potentially results in carbon uptake from the atmosphere and sequestration in the soil, increased decomposition at higher temperatures can enhance carbon release from the soil. Carbon losses from soils might be particularly high in soils where large amounts of carbon have accumulated under past climatic conditions. To infer soil organic carbon (SOC) changes of alpine soils in a warming climate, we assessed SOC stocks and their stability change along elevational gradients in the Swiss Central Alps. In our study, we excavated 21 soil pits to the parent material along elevational gradients (2000 to 3100 m a.s.l.) on three different bedrock types (calcareous, amphibolitic and siliceous) and analyzed their SOC stocks, stable isotope composition, and C stability by a soil incubation experiment. First results show a distinct elevation pattern with a strong decline in SOC storage with decreasing vegetation cover above 2700 m a.s.l.. However, soils on amphibolitic bedrock still contained substantial amounts of SOC even at elevations above 3000 m a.s.l. (0.8% SOC; >1.4 kg C/m2). As soils at this high elevation were buried under a few decimeter thick debris layer and no plants were present, it seems likely that these are remnants of fossil soils. In support, the buried soil organic matter (OM) had rather high δ13C values of -23.2‰ and narrow CN ratios of 10.7, indicating that they consist of strongly transformed OM. Analysis of their radiocarbon contents and CN analysis of stones will provide further information on the origin of these high elevation soils. Regardless of their origin, these soils represent a CO2 source. Soils released 0.2-0.5% of their SOC contents within one month upon incubation at 10 and 22°C in the laboratory. Moreover, in situ chamber measurements at the end of August 2022 showed a mean CO2 efflux of approximately 3.6 mg CO2-C/m2h to the atmosphere. Along the studied gradient, the δ13C values of surface soils strongly decreased with decreasing elevation. At the same time, the SOC mineralizability and soil C/N ratios showed a pronounced increase towards the soils at lower elevation having a dense grassland cover. This indicates that along with increasing SOC stocks, the contribution of relatively fresh OM with high turnover rates increases. Overall, our results show that there is a transition from the accumulation of SOC with alpine greening, reflected by alpine soils at lower elevations (< 2700 m a.s.l.), to buried SOC releasing C (possibly ancient C) at high elevation. Future measurements will provide further insight into the rapidity and magnitude of SOC stock changes in alpine terrain with ongoing climate warming. 

How to cite: Udke, A., Zehnder, M., Rixen, C., Egli, M., and Hagedorn, F.: Soil organic carbon in alpine environments under a warming climate , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13855,, 2023.