October 18, 2017

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Developing a Molecular Picture of Soil Organic Matter-Mineral Interactions

Quantitative data will help improve land-carbon models.

The Science

The terrestrial biosphere plays an important role in the global carbon cycle, partly through how strongly organic compounds (i.e., ligands) and soil minerals bind. These binding sites—or interfaces—play an important role in the long-term persistence of soil carbon. In a new Nature Communications paper, researchers from Pacific Northwest National Laboratory found that both carbon chemistry and environmental conditions affect carbon persistence.

The researchers used dynamic force spectroscopy (DFS) to directly measure the strength with which different types of organic carbon binds to soil minerals and the conditions under which that organic carbon is released.

Unlike previous methods, DFS allows researchers to quantify the energy needed to separate organic molecules from minerals. That allows them to compare specific functional chemical groups and mineral types and to better understand when and how carbon is retained in soils or how easily it escapes to the atmosphere.

Changes to soil moisture, such as flooding and drought, change the nanoscale chemical environment (ionic strength and pH) in ways that alter the overall quality of carbon potentially solubilized in natural soils.

The Impact

This approach to obtaining direct and quantitative treatment of the organic-mineral interface could provide fundamental information and critical new measurements that may inform the next generation of process-rich land-carbon models.

Summary

Complex interactions among plants, microbes, and minerals mean soil organic matter (SOM) can reside in soils anywhere from months to millennia. In this study, researchers set out to better understand the factors that affect the SOM persistence and vulnerability at the mineral interface.

Until now, researchers had only limited, qualitative information about organic-minerals at this interface. Using DFS, however, they could make comparisons between specific functional groups and mineral types under varying environmental conditions. Their findings indicate that environmental factors, such as ionic strength and pH, produce the most drastic differences in binding energies.

Their approach to obtaining direct and quantitative treatment of the organic-mineral interface could fundamentally inform next-generation land-carbon models in which mineral-bound carbon is an important control on carbon persistence. In turn, such models would be at the cutting edge of current understanding of the terrestrial carbon cycle.

Principal Investigator

Vanessa Bailey
Pacific Northwest National Laboratory
Vanessa.bailey@pnnl.gov

Program Manager

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

Funding

This research was supported by the Chemical Imaging Initiative through the LDRD Program at Pacific Northwest National Laboratory (PNNL). V.L.B. was supported by the Terrestrial Ecosystem Sciences program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. [Author Correction to this article was published on 05 December 2017.]

References

Newcomb, C. J., N. P. Qafoku, J. W. Grate, and V. L. Bailey, et al. "Developing a molecular picture of soil organic matter-mineral interactions by quantifying organo-mineral binding". Nature Communications 8 396  (2017). https://doi.org/10.1038/s41467-017-00407-9.