2026-12-09, 16:30–16:45 (Europe/Athens), Amphitheater I
Soil organic matter (SOM) underpins soil health and climate mitigation, yet its internal dynamics remain difficult to assess at scale. In particular, partitioning soil organic carbon (SOC) into particulate (POC) and mineral-associated (MAOC) fractions, key to understanding carbon persistence, is analytically demanding and rarely available in monitoring programmes. Here, we propose a simple but powerful alternative: the fraction of SOC in SOM (foc).
We synthesised 14 datasets comprising 9,503 soil observations across Europe and globally, spanning mineral and organic soils, croplands, grasslands, woodlands, peatlands, permafrost regions, and seagrass habitats. Across this diverse gradient, foc was remarkably constrained (0.38–0.58), consistent with the carbon content of plant inputs and processed organic matter, and a consistent linear relationship between SOC and SOM (mean slope ≈0.54).
Crucially, foc varied systematically with habitat and soil category, forming a clear ecological and biogeochemical gradient. Lowest values occurred in permafrost and marine sediments, intermediate values in croplands and grasslands, and highest values in semi-natural and woody systems. Organic soils showed higher foc values than mineral soils, reflecting advanced decomposition and increased carbon density.
Linking this indicator to soil functioning, we demonstrate that foc correlates with SOM fractions: higher foc values align with increased particulate organic carbon (POC), supporting its interpretation as a proxy for decomposition state and carbon stabilization pathways. This provides a practical route to infer POC and MAOC distributions without costly fractionation analyses.
Our findings position foc as a scalable, process-informed indicator of soil organic carbon dynamics that integrates biological inputs, decomposition, and physical protection mechanisms. Because it can be derived from routine measurements of SOC and SOM, foc has immediate applicability for national soil monitoring, land-use planning, and evaluation of soil carbon policies.
Sabine is a senior soil ecologist with an interest in the links between soils, plants and the atmosphere under global change. She currently coordinates climate change research from the UKCEH's long-term Heathland Climate Change Infrastructure , which has been running since 1999. Her work revolves around the connections between climate change, ecosystem processes and soil.
Sabine is leading soils-related work as part of the EU soil horizon project AI4SoilHealth, bringing together UK, EU and global datasets featuring soil and ecosystem metrics to derive cost-effective and continental-scale soil health indicators. She is also involved in the Norwegian project CLIMASOIL investigating impacts of climate change on soil hydraulic properties and carbon storage.