Teasing Out Molecular Details of Arctic Soil Organic Carbon Degradation Under Warming

Pinpointing how fast different organic carbon molecules degrade under warming scenarios.

The Science

The breakdown of organic matter in soils is a critical factor in the release of carbon into the atmosphere as carbon dioxide and methane. Scientists have gained new understanding of how soil organic carbon (SOC) degrades at the molecular scale in the warming soil of the Arctic tundra. Using ultrahigh-resolution mass spectrometry techniques, Oak Ridge National Laboratory (ORNL) and Environmental Molecular Sciences Laboratory (EMSL) collaborators found certain molecular components are disproportionately more susceptible to microbial degradation than others. The researchers developed a biodegradation index to facilitate incorporating these findings into detailed carbon cycle models.

The Impact

Arctic soils contain significant stores of carbon. Integrating new knowledge about the biodegradation of organic matter in these soils into detailed models can improve predictions of global carbon cycling and climate feedbacks.

Summary

Understanding how different organic molecules are degraded in the soil is essential for predicting how greenhouse gas fluxes may respond to global climate change. The rate of microbial SOC degradation is controlled not only by temperature, but also by substrate composition. Using ultrahigh-resolution mass spectrometry at EMSL, a Department of Energy Office of Science user facility, a team of scientists from ORNL, Oakland University, and EMSL determined the susceptibility and compositional changes of dissolved organic carbon in a warming experiment at –2 or 8°C with a tundra soil from the Barrow Environmental Observatory in northern Alaska. Based on their chemical compositions, organic carbon molecular formulas were grouped into nine classes, among which lignin-like compounds dominated both the organic and mineral soils and were the most stable. Organic components such as amino sugars, peptides, and carbohydrate-like compounds were disproportionately more susceptible to microbial degradation than others in tundra soil. The findings suggest that biochemical composition is one of the key factors controlling SOC degradation in Arctic soils and should be considered in global carbon degradation models to improve predictions of Arctic climate feedbacks.

Principal Investigator

Baohua Gu
Oak Ridge National Laboratory
gub1@ornl.gov

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
paul.bayer@science.doe.gov

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

The Next-Generation Ecosystem Experiments (NGEE)–Arctic project is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

References

Chen H. M., Z. Yang, R. K. Chu, and N. Tolic, et al. "Molecular insights into Arctic soil organic matter degradation under warming". Environmental Science & Technology 52 (8), 4555-4564  (2018). http://dx.doi.org/10.1021/acs.est.7b05469.