Evaluating Soil Carbon Persistence Using Ramped Oxidation and Radiocarbon Analysis

Understanding the persistence, stability and turnover time of soil organic carbon (SOC) is essential for predicting terrestrial carbon storage, ecosystem responses to climate change, and strategies to enhance sequestration. However, linking SOC stability to specific soil properties remains challenging, with global models often underestimating SOC residence times compared to empirical observations (e.g., Shi et al., 2020). Radiocarbon (¹⁴C) provides a powerful tool for addressing these gaps by adding a temporal dimension to SOC studies.

Conventional approaches typically use physical or chemical fractionation to create operational pools for ¹⁴C analysis (e.g., Haddix et al., 2020), such as mineral-associated organic matter (MAOM). While informative, these pools themselves represent mixtures of diverse chemical components. An emerging approach is that of thermal-based methods such as ramped oxidation (ROx). These offer an alternative by partitioning SOC according to activation energy (e.g., Hanke et al., 2023), providing valuable insights into mechanisms of SOC stabilization (Stoner et al., 2023).

We applied ROx combined with ¹⁴C analysis to samples from a study that examined how converting temperate grassland to coniferous forest influences below-ground carbon dynamics in Scotland (Joly et al., 2025). As part of this work, we also quantified pyrogenic carbon (PyC), a fire-derived SOC fraction known for its long environmental residence times, in bulk soils and sub-fractions to assess its contribution to SOC persistence. By comparing ¹⁴C signatures from conventional fractionation with those from thermal fractions, including PyC, we evaluate the added value of ROx in revealing SOC age structure and persistence. These insights advance understanding of SOC stabilization processes and inform predictions of land-use change impacts on soil carbon storage.

Acknowledgments

We acknowledge support from the UK Natural Environment Research Council (NERC) via the National Environmental Isotope Facility (NEIF) grant (NE/S011587/1) and the NERC project grant NE/P011098/1.

References

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