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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Developing a Molecular Picture of Soil Organic Matter-Mineral Interactions

Vanessa Bailey
Pacific Northwest National Laboratory

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23 August 2017

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. This binding site—or interface—plays 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 chemistry of the carbon and environmental conditions affect it.

The researchers used dynamic force spectroscopy (DFS) to directly measure the strength with which different types of organic C bind to soil minerals, and the conditions under which that organic C 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 nano-scale chemical environment (ionic strength and pH) in ways that alter the overall quality of C 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 C is an important control on carbon persistence. In turn, such models would be at the cutting edge of our current understanding of the terrestrial C cycle.

BER PM Contact
Daniel Stover,
301-903-0289, Daniel.stover@science.doe.gov

PI Contact
Vanessa Bailey
PNNL
Vanessa.bailey@pnnl.gov, 509-371-6965

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 US Department of Energy, Office of Science, Biological and Environmental Research as part of the Terrestrial Ecosystem Sciences Program.

Publications
C. J. Newcomb, N. P. Qafoku, J. W. Grate, V. L. Bailey, J. J. De Yoreo, “Developing a molecular picture of soil organic matter-mineral interactions by quantifying organo-mineral binding.” Nature Communications, 8, Article number: 396. doi:10.1038/s41467-017-00407-9.

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 US Department of Energy, Office of Science, Biological and Environmental Research as part of the Terrestrial Ecosystem Sciences Program.


Schematic of the experimental setup. Common chemical functional groups from soil organic matter (SOM) were chosen to represent a model for interaction between organics and two model minerals: muscovite and goethite. Performing force measurements between these model organics and minerals enable us to quantitatively evaluate the binding energies.

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