Interplay of weathering, mineral formation, and stabilization of soil organic matter in Um-brisols/umbric horizons

• Applicant: Professor Dr. Thilo Rennert
• Subject Area: Soil Sciences
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553299732

Umbrisols are defined by the umbric topsoil horizon, which is, among other properties, characterized by its dark colour, structure, and low "base saturation". The umbric horizon is a commonly thick mineral horizon, accumulating soil organic matter (SOM). Umbrisols/soils with umbric horizon are widespread in several European mountains and low-mountain ranges. The few available studies on SOM composition and contents point to soil-type specific processes and properties that control SOM stabilization, which, however, are not fully understood yet. This project aims to obtain a mechanistic understanding of the processes that control the stabilization of SOM in Umbrisols/umbric horizons. Studying Umbrisols/soils with umbric horizon from the southern Caucasus, Slovenia, and lowland and low-mountain range areas in Slovakia under different land-use and climate, we will focus on soil constituents that affect SOM stabilization, and on the characterization and distribution of SOM among fractions that differ in their rate of SOM cycling. Additionally, we will conduct weathering experiments that enable the identification of proceeding processes. We hypothesize that i) variable silicate weathering provides SOM-stabilizing agents, including short-range ordered aluminosilicates, Al-hydroxy-interlayered minerals, and Al-SOM complexes, ii) fire-borne SOM contributes to stabilized SOM at forested low-mountain sites, iii) SOM stabilization is expressed by thermal SOM properties, and iv) depending on the progress of weathering/soil formation, short-range ordered aluminosilicates evolve, are mobilized and transported, or are dissolved. The hypotheses will be tested by a combination of soil characterization, including spectroscopic techniques, soil fractionation, and weathering experiments with subsequent modelling. The results of the project will enhance our general understanding of SOM stabilization processes and dynamics in mountain areas and low-mountain ranges, which will be affected especially by climate change, and particularly our understanding of processes in a yet less-studied soil environment.

• DFG Programme: Research Grants