Kohlenstoff in Schweizer Waldböden – bei Klimaerwärmung eine potenzielle CO2-Quelle | Soil organic carbon in Swiss forest soils – a potential CO2 source in a warming climate

Abstract

Soils contain the largest carbon stocks of terrestrial ecosystems. The expected climatic warming may turn soils into a CO2 source by increasing the mineralization of soil organic matter. However, changes in soil carbon (C) are hardly detectable because the expected changes within some years are much smaller than the large amounts of C stored in soils. Our approach was to quantify changes in soil C storage along natural climatic gradients by comparing C stocks of more than 250 soil profiles at different altitudes across Swiss forest ecosystems. In addition, we studied the response of soil CO2 effluxes to an experimental soil warming by 4°C at the alpine treeline. The carbon dynamics along the natural and experimental temperature gradients strongly suggest losses of soil carbon under climatic warming. Soil warming at the treeline induced 25% to 40% higher soil CO2 effluxes during three treatment years. In Swiss forest ecosystems, soil carbon stocks decrease with decreasing altitude and thus, they decline with increasing mean temperatures, but also with a changing dominance from coniferous to deciduous trees. This decrease in soil carbon is particularly strong in the organic layer. Translating the decline in soil carbon with decreasing altitude to the expected climatic warming by 1.8 to 4°C during the next century suggests carbon losses of 15 to 34 million t C from Swiss forest soils, which would cancel out the C sink in Swiss forests of several decades. The CO2 lost from soils would foster the climatic warming.