P02 Organic matter cycling in forest floors of temperate mixed forests.

Our project is centered on improving our understanding of organic matter cycling in temperate mixed forest floors. We aim to examine the key roles of different input and output pathways. Organic matter comes from various sources like foliage, roots, or mycorrhiza. This organic matter is either mineralized, leached, transformed into stable soil organic matter, or transferred into mineral soil by soil fauna. While turnover rates and source contributions (e.g., for mineral-associated organic matter) have been studied extensively within the mineral soil, similar knowledge for the forest floors is still scarce.

We will study forest floors of temperate mixed forests across four altitudinal gradients in Germany and Switzerland. These sites vary in their parent material and mean annual temperature. We plan to measure carbon fluxes as CO₂ and dissolved organic matter regularly. Using isotopic analyses of ¹³C, ¹⁵N, and ²H, we aim to uncover how different sources contribute to carbon pools in both forest floor and mineral soil.

To better understand turnover rates, we'll use isotopic tracer experiments with labeled beech and maple litter in both lab and field settings. The lab work will highlight the role of earthworm species in organic matter processing. In the field, we'll partner with researchers from the University of Göttingen to explore how different soil fauna affect the forest floor.

Further cooperations include linking isotope signals with organic matter quality measurements done by the Technical University Munich as well as links to nutrient cycling investigated by the University of Freiburg.