Decoupling above- from belowground litter decomposition and impacts on stabilization of soil organic matter with increasing aridity

• Applicants: Professor Dr. Karsten Kalbitz; Dr. Marion Schrumpf; Dr. Cordula Vogel
• Subject Area: Soil Sciences
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511741712

Drylands cover large areas of the land surface and may continue to expand in the future due to climate change. Even though dryland soils have low organic carbon (OC) concentrations, they store a significant fraction of global soil OC stocks. However, predicting effects of increasing aridity on soil OC stocks is not yet possible because above- and belowground processes of litter decomposition and soil organic matter (SOM) stabilization are differently affected by aridity. Consequences of increasing aridity on abiotic processes, such as photochemical and thermal degradation, and consequences for SOM stabilization processes by aggregation and formation of mineral-associated organic matter (MAOM) are still unclear. The role of extracellular polymeric substances (EPS) is particularly unknown, as they can stabilize aggregates (increasing importance at drier conditions) and promote the formation of MAOM (increasing importance at wetter conditions). The overarching objectives of this project are to assess the differential response of above- and belowground litter decomposition to increasing aridity and to elucidate the consequences for SOM stabilization. We will take advantage of a unique steep gradient in precipitation found on common parent material in Israel. We hypothesize that increasing aridity results in increasing de-coupling of the mechanisms responsible for above- and belowground litter decomposition as well as SOM stabilization. Increasing aridity should slow down decomposition of belowground litter more than that of aboveground litter. Further, increasing precipitation should promote the formation of MAOM particularly from belowground litter whereas increasing aridity results in higher contribution of aggregation to SOM stabilization. We will study above- and belowground litter decomposition and SOM stabilization by applying 13C-labelled litter (shoots and roots) of an annual herbaceous plant along the aridity gradient. To account for the spatial heterogeneity in vegetation cover, we include areas under shrubs and inter-shrub herbaceous patches. The use of stable isotopes allows us to monitor litter decomposition and follow SOM formation under conditions as natural as possible along the gradient. We will measure 13CO2 fluxes in the field and combine these data with the incorporation of the 13C tracer into SOM fractions obtained by density fractionation, EPS, and aggregate stability. This will provide insights into stabilization mechanisms of SOM as a function of aridity and vegetation cover. This field study will be combined with laboratory-based experiments for getting deeper insights into the importance of abiotic processes for litter decomposition. Our complementary approach will improve our understanding of the controls of litter decomposition and SOM stabilization in semi-arid regions. This study will strongly improve the scientific base for soil C and earth system models in drying climates.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Professor Dr. Jose Gruenzweig