Collaborative Research: Manganese(III)-driven carbon oxidation at oxic-anoxic interfaces

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Soils are a large and dynamic terrestrial of carbon on earth. How fast microbes oxidize carbon determines how much either stays in soils or is emitted as carbon dioxide. Even a small increase in soil carbon oxidation rate could increase the amount of carbon dioxide in the atmosphere, impacting global climate. Manganese (Mn) is an abundant and potent oxidizer, but its impact on the rate of soil carbon oxidation is not known. This project will provide new understanding of how manganese compounds change how fast carbon is oxidized in soils. This new scientific knowledge will help improve our predictions of future carbon dioxide emissions and will help society develop new strategies to limit emissions. This project will work with diversity programs on campus and in the local community to empower women and minority students to pursue STEM careers. The formation of Mn-based oxidants is emerging as a key regulator of C oxidation rates, and thus CO2 emissions, in soils. Although dissolved Mn(III) species are among the most potent oxidants in environmental systems, the controls on Mn(III)-driven carbon oxidation are virtually unknown. The overall objective of this project is to identify fundamental geochemical and microbial factors controlling the rate of Mn(III)-mediated carbon oxidation in soils. Our central hypothesis is that oxic-anoxic interfaces are "hotspots" for the enzymatic formation of dissolved Mn(III), which subsequently depolymerizes and solubilizes otherwise resistant organic matter, and so enhances microbial CO2 production. The proposed research integrates microsensor, spectroscopic, and multi-omics approaches to resolve coupled Mn and carbon cycles across fine-scale gradients in soils. To accomplish the overall objective, the specific aims are to (i) define the geochemical controls on Mn(III) formation along oxic-, (ii) identify the microbial drivers of Mn(III) formation, and (iii) assess the impact of Mn(III) formation on C oxidation at oxic-anoxic interfaces in soils. Disseminating the resulting dataset will support efforts to incorporate the coupling of Mn and C redox cycles into biogeochemical models. Integrating the highly significant Mn-dependence of C oxidation into models for the first time is expected to vastly improve accuracy in predicting environmental and human impacts on soil CO2 emissions. The project team will work to incorporate this multidisciplinary research effort into strategies to empower women and minority graduate, undergraduate and high school students to pursue STEM careers. A three-point plan integrates this research with direct interdisciplinary education and public outreach, which includes: (i) graduate training in biogeochemistry for one minority PhD student, (ii) opportunities for independent research for three minority undergraduate students in partnership with the Harvard Forest REU program, and (iii) multi-day workshops for a total of 45 female minority students from a local high school hosted in collaboration with Girls Inc. Holyoke, Massachusetts. Educational materials developed for the workshops will be disseminated through participation in the annual Massachusetts Envirothon. A thorough evaluation plan was developed in collaboration with Harvard Forest and Girls Inc. staff to measure the success of the proposed Broader Impacts activities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.