Anaerobic Microsites Have an Unaccounted Role in Soil Carbon Stabilization

The Science

Mechanisms controlling soil carbon storage and feedbacks to the climate system remain poorly constrained. Here, a research team a led by Stanford University shows that anaerobic microsites stabilize soil carbon by shifting microbial metabolism to less efficient anaerobic respiration and protecting reduced organic carbon compounds from decomposition.

The Impact

Without recognizing the importance of anaerobic microsites in stabilizing carbon in soils, terrestrial ecosystem models are likely to underestimate the vulnerability of the soil carbon reservoir to disturbance induced by climate or land-use change. Further, carbon mitigation strategies based largely on land management can be optimized accordingly to maximize soil storage.

Summary

Soils represent the largest carbon reservoir within terrestrial ecosystems. The mechanisms controlling the amount of carbon stored and its feedback to the climate and Earth system, however, remain poorly resolved. Global land models assume that carbon cycling in upland soils is entirely driven by aerobic respiration; the impact of anaerobic microsites (small oxygen poor sites in the soil) prevalent even within well-drained soils is missed within this framework. Here, they show that anaerobic microsites are important regulators of soil carbon persistence, shifting microbial metabolism to less efficient anaerobic respiration, and selectively protecting otherwise bioavailable, reduced organic compounds such as lipids and waxes from decomposition. Further, shifting from anaerobic to aerobic conditions leads to a 10-fold increase in volume-specific mineralization rate, illustrating the sensitivity of anaerobically protected carbon to disturbance. The vulnerability of anaerobically protected carbon to future climate or land-use change thus constitutes a yet unrecognized soil carbon–climate feedback that should be incorporated into terrestrial ecosystem models.

Principal Investigator(s)

Scott Fendorf
Stanford University
[email protected]

Marco Keiluweit
University of Massachusetts, Amherst
[email protected]

Funding

This work was supported by the Terrestrial Ecosystem program (Award Number DE-FG02-13ER65542) and Subsurface Biogeochemistry Research program (Award Number DE-SC0016544) of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. A portion of this research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility sponsored by BER and located at Pacific Northwest National Laboratory.

References

Keiluweit M., Wanzek T., Kleber M., Nico P., and Fendorf S. “Anaerobic microsites have an unaccounted role in soil carbon stabilization.” Nature Communications 8, 1771 (2017). DOI:10.1038/s41467-017-01406-6