Swiss Federal Institute for Forest, Snow and Landscape Research WSL

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Avalanche Bulletin

Soil carbon: sink or source for CO2?

Soils play an important role in the global carbon cycle, as they store large amounts of carbon and large amounts of carbon dioxide (CO2) are exchanged between soils and the atmosphere. We are studying the effects of changes in climate and land use on soil carbon storage.

Sampling of a grassland soil above treeline to quantify its carbon stock. At WSL, about 2000 soil profiles have been sampled and analysed. Foto: Frank Hagedorn

In Switzerland, soils store about 80% of the terrestrial carbon and 7-8 times as much as the atmosphere as CO2. Temperature, moisture and litter inputs exert a main control on soil carbon cycling. As a consequence, changes in climate and land use affect C fluxes between soils, vegetation, and the atmosphere. In particular, forest disturbances by storms, insects or intense forest exploitation can induce carbon losses from soils.

Key objectives

  • How much and in which form is carbon stored in Swiss forest soils?
  • What are the effects of changes of climate warming, drought and disturbances?
  • What are the effects of climate change induced vegetation shift on soil carbon?
  • How does afforestation and management impact soil carbon?
  • What are the effects of permafrost on the CO2 balance of alpine soils?

Approaches

  • Field and lab experiments: Response of C fluxes and pools to increased soil temperatures, drought, elevated CO2, and N deposition.
  • Stable isotopes and radiocarbon: tracing carbon in soil pools and fluxes.
  • Monitoring of fluxes: measuring soil CO2 fluxes and DOC leaching in forests.
  • Carbon inventory: estimates of C stocks of Swiss forest soils.
Die Böden des Tessins speichern pro Fläche am meisten Kohlenstoff in den Schweizer Waldböden. Die schwarze Farbe stammt von den hohen Gehalten an ‚Black Carbon’ – Überbleibsel und Zeugen häufiger Waldbrände. Bild: Marco Walser, WSL
Soils of Southern Switzerland (Ticino) have the highest C stock per area of Swiss forest soils. They are characterized by a black color originating from their high contents of “black carbon”, remnants and witnesses of frequent forest fires. Photo: Marco Walser, WSL
Organische Bodensubstanz ist ein Kontinuum von frischer Streu bis zu stark umgewandeltem 'Humus', und reicht von einfachen niedermolekularen Komponenten bis zu komplexen, hochmolekularen Verbindungen. Bild: Beat Frey, WSL
Soil organic matter is a continuum from fresh litter to highly transformed 'humus', and ranges from simple low molecular weight components to complex high molecular weight compounds. Long-term carbon storage is primarily determined by the interactions of soil organic matter with minerals. Photo: Beat Frey, WSL
Using a large net we collect leaf litter of a mature beech, which we have previously labelled with isotopes. The leaf litter is distributed again on various forest soils, allowing us to follow how much of the litter is decomposed, leached or incorporated into the mineral soil by soil fauna. Foto: Frank Hagedorn, WSL
In an irrigation experiment in a dry pine forest (Pfynwald, Valais), we wrapped 100-year-old pine trees in plastic foils. Subsequently, we exposed them to highly labeled 13CO2. Four days later, the label reached the soil and distributed up to 6 m away from the tree trunk. Drought slowed down and reduced the carbon transfer to the soil. Foto: Frank Hagedorn, WSL

Publications

Guidi C., Frey B., Brunner I., Meusburger K., Vogel M.E., Chen X., … Hagedorn F. (2022) Soil fauna drives vertical redistribution of soil organic carbon in a long‐term irrigated dry pine forest. Glob. Chang. Biol. 28(9), 3145-3160. https://doi.org/10.1111/gcb.16122 Institutional Repository DORA

Hagedorn F., Gavazov K., Alexander J.M. (2019) Above- and belowground linkages shape responses of mountain vegetation to climate change. Science. 365(6458), 1119-1123. https://doi.org/10.1126/science.aax4737 Institutional Repository DORA

Hagedorn F., Krause H.M., Studer M., Schellenberger A., Gattinger A. (2018) Boden und Umwelt: organische Bodensubstanz, Treibhausgasemissionen und physikalische Belastung von Schweizer Böden. Thematische Synthese TS2 des Nationalen Forschungsprogramms «Nachhaltige Nutzung der Ressource Boden» (NFP 68): Vol. 2. Bern: Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung. 93 p. Institutional Repository DORA

Gosheva S., Walthert L., Niklaus P.A., Zimmermann S., Gimmi U., Hagedorn F. (2017) Reconstruction of historic forest cover changes indicates minor effects on carbon stocks in Swiss forest soils. Ecosystems. 20(8), 1512-1528. https://doi.org/10.1007/s10021-017-0129-9 Institutional Repository DORA

Hiltbrunner D., Zimmermann S., Hagedorn F. (2013) Afforestation with Norway spruce on a subalpine pasture alters carbon dynamics but only moderately affects soil carbon storage. Biogeochemistry. 115(1-3), 251-266. https://doi.org/10.1007/s10533-013-9832-6 Institutional Repository DORA

Projects

RICH-SOIL: Radiocarbon Inventory of Swiss Soils

RICH-SOIL gains insight into soil C cycling by determining radiocarbon signatures in Swiss soil C pools and fluxes. The project analyses archived samples, national soil inventory, and the LWF (Long-term-Monitoring of Forests Ecosystem) program.

Forest Floor: Carbon cycling in forest floors

The project quantifies carbon fluxes in forest floors along gradients in climate and bedrock in Switzerland and Germany. The approach is to measure radiocarbon contents in C pools and fluxes, and tracing isotopically labelled (13C, 15N, 2H) litter in the forest floor and in the mineral soil beneath.

DRYSOM: Soil organic matter dynamics under drought

DRYSOM assesses soil organic matter (SOM) to drought in a long-term irrigation experiment (Pfynwald). Responses range from a suppressed processing through microbial and faunal communities, decreases in carbon inputs from trees into soils, to shifts in soil carbon storage.

Impacts of forest disturbances on soil carbon stocks

Disturbances of forest ecosystems by storms and dieback following drought and insect infestation are increasing with ongoing climatic changes. We study the magnitude of C losses following disturbances by combining field studies, modelling, and a meta-analysis.

Can forest expansion in mountain ecosystems generate a positive feedback to climate change: the unseen role of mycorrhizae

Teaser

Unprecedented Permafrost Thaw – Unlocking Ground for New Life and Release of Old Soil Carbon, Pollutants, and Pathogens (ExtremeThaw)

The ExtremeThaw project is working to enhance our understanding of rapid permafrost thaw in Switzerland’s alpine regions, helping to shape effective response strategies.

Repetition of the forest soil inventory in Switzerland

The repetition of the forest soil inventory provides the basis for representative forest soil monitoring throughout Switzerland. Through the connection to the sampling network of the National Forest Inventory, a variety of possibilities for the use and evaluation of the collected soil data are possible.

Seeing the wood for the trees: the elusive function of dark septate root endophytes in carbon-rich polar and alpine ecosystems

Mycorrhizal fungi play a major role in the turnover of soil organic matter (SOM), providing their plant hosts with nutrients by decomposing SOM, whilst in direct competition with free living microbes.

Arctic greening and its climate change feedback: cascading long-term effects of above- and belowground linkages

This SPI Exploratory Grant is aimed at equipping the ALTER experiment (Abisko, Sweden) for long-term monitoring of belowground vegetation and microbial dynamics.

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