Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 52, Issue 21, Pages 12349-12357Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.8b03791
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Funding
- Canada Foundation for Innovation
- Natural Sciences and Engineering Research Council of Canada
- University of Saskatchewan
- Government of Saskatchewan
- Western Economic Diversification Canada
- National Research Council Canada
- Canadian Institutes of Health Research
- DOE Office of Science by Brookhaven National Laboratory [DE-SC0012704]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
- USDA National Institute of Food and Agriculture, Hatch project [CA-R-ENS-5151-H]
- Department of Energy, Office of Biological and Environmental Research, Subsurface Biosphere Research program [DE-SC0016544]
- Harvard Forest LTER program [NSF-DEB 1237491]
- University of Massachusetts
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The formation of reactive manganese (Mn) species is emerging as a key regulator of carbon oxidation rates, and thus CO2 emissions, in soils and sediments. Many subsurface environments are characterized by steep oxygen gradients, forming oxic-anoxic interfaces that enable rapid redox cycling of Mn. Here, we examined the impact of Mn(II)(aq) oxidation along oxic-anoxic interfaces on carbon oxidation in soils using laboratory-based diffusion reactors. A combination of cyclic voltammetry, X-ray absorption spectroscopy, and X-ray microprobe imaging revealed a tight coupling between Mn(II)(aq) oxidation and carbon oxidation at the oxic-anoxic interface. Specifically, zones of Mn(II)(aq) oxidation across the oxic-anoxic transition also exhibited the greatest lignin oxidation potential, carbon solubilization, and oxidation. Microprobe imaging further revealed that the generation of Mn(III)-dominated precipitates coincided with carbon oxidation. Combined, our findings demonstrate that biotic Mn(II)(aq) oxidation, specifically the formation of Mn(III) species, contributes to carbon oxidation along oxic-anoxic interfaces in soils and sediments. Our results suggest that we should regard carbon oxidation not merely as a function of molecular composition, which insufficiently predicts rates, but in relation to microenvironments favoring the formation of critically important oxidants such as Mn(III).
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