Carbon fluxes in forest floors

• Applicant: Dr. Frank Hagedorn
• Subject Area: Soil Sciences
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457330647

The forest floor (FF) represents the most active compartment in soils with the most rapid turnover of organic matter. In the FF, plant detritus is either mineralised to CO2, leached as dissolved organic C into deeper soils, transformed into stable organic matter by microbial communities or transferred into the mineral soil through soil fauna. The relative importance of these C fluxes is uncertain and context-dependent. Project P2 aims at quantifying the pathways of C cycling within the FF and into the uppermost mineral soil, and to identify their controlling factors along the environmental gradient and experimental set-up of the RU. The experimental approach of P2 is (1) to measure C fluxes and the natural stable isotope signatures of C pools and fluxes along environmental gradients and (2) to trace isotopically labeled litter in C, N and H fluxes in the FF and the mineral soil beneath in a joined RU-experiment. P2 will quantify soil CO2 effluxes and DOC leaching and their 13C and radiocarbon signatures at 8 study sites along gradients in MAT on silicate and carbonate parent materials and one gradient in P stocks (covering the priority gradient of the RU). Moreover, P2 will measure the natural abundances of 13C, 15N, and 2H as well as radiocarbon contents of soil organic matter fractions in the FF and uppermost mineral soil separated according to their density by P3 at all 12 study sites of the RU. In the joint labeled litter experiment, P2 will first produce large amounts of labeled litter for the entire RU. Then, P2 will trace the fate of 13C, 2H and 15N labeled foliage litter in respired CO2 and leached dissolved organic matter (collaborating with P1) and in distinct pools in the FF and uppermost mineral soil at the 8 study sites together with P3. The flux data will be linked to the transport of labeled litter by soil fauna (P6) and the uptake by microbial communities (P7) as well as for 15N by mycorrhiza and fine roots (P8) and trees (P9). Overall, this allows a holistic assessment on C, N, H cycling in FFs und the mineral soil beneath. The expected outcome of P2 is the quantification of the pathways and formation rate of FF materials and soil organic matter in the uppermost mineral soil. By linking these data to climatic conditions and soil fertility, the project will identify the controls of organic matter fluxes in the FF and uppermost mineral soil. In the second phase of the RU, P2 intends to continue the tracing of the labeled litter, include other tree species, measure the isotopic signal in specific components and determine organic matter fluxes in the FF in response to drought.

• DFG Programme: Research Units
• Subproject of: FOR 5315: FOREST FLOOR: Functioning, Dynamics, and Vulnerability in a Changing World
• International Connection: Switzerland
• Cooperation Partner: Dr. Patrick Schleppi