G05_05

Capturing Radiocarbon Distributions in Soil Organic Matter Using a Thermal Fractionation Approach

Stoner S^1,2,  Sierra C^1,3, Doetterl S², Trumbore S¹

¹Max Planck Insitute For Biogeochemistry, Jena, Germany, ²ETH Zürich USYS, Zürich, Switzerland, ³Swedish University of Agricultural Sciences, , Sweden

Understanding soil organic matter (SOM) dynamics requires knowledge and quantification of diverse soil processes and characteristics of SOM. Radiocarbon in SOM aggregates into a single metric a large variety soil carbon (C) processes, resulting in a C pool with a range of ages reflecting the drivers of C turnover. However, a mean bulk soil radiocarbon value often lacks crucial details. Here, we present techniques for predicting and measuring radiocarbon distributions in soils. Compartmental models constrained by radiocarbon can predict the distribution of ¹⁴C at any point in time as a model output, highlighting the controls of fast and slow cycling C, and the effect of the "bomb spike" on mean soil ¹⁴C. In addition, new research on thermal fractionation of SOM, through heating soil at a constant rate and using temperature of decomposition as a proxy for activation energy, allows for the rapid collection of multiple C fractions along a meaningful gradient of stability. The resulting profile of CO₂ release and ¹⁴C concentration as a function of temperature can be transformed into a mass-weighted distribution of radiocarbon within a soil sample. We present these novel methods, compare their ability to estimate ¹⁴C distribution, and present case studies of their application. Applying radiocarbon through a combination of simple but powerful models and high-throughput laboratory techniques will better constrain our ability to detect and understand diverse controls of carbon stabilization in complex systems.