Active Iron Phases Regulate the Abiotic Transformation of Organic Carbon during Redox Fluctuation Cycles of Paddy Soil

Iron (Fe) phases are tightly linked to the preservation rather than the loss of organic carbon (OC) in soil; however, during redox fluctuations, OC may be lost due to Fe phase-mediated abiotic processes. This study examined the role of Fe phases in driving hydroxyl radical (•OH) formation and OC tra...

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Bibliographic Details
Published in:Environmental science & technology 2021-10, Vol.55 (20), p.14281-14293
Main Authors: Chen, Ning, Fu, Qinglong, Wu, Tongliang, Cui, Peixin, Fang, Guodong, Liu, Cun, Chen, Chunmei, Liu, Guangxia, Wang, Wenchao, Wang, Dixiang, Wang, Peng, Zhou, Dongmei
Format: Article
Language:English
Subjects:
Biogeochemical Cycling
Carbon cycle
Carbon dioxide
Crystal structure
Crystallinity
Gamma irradiation
Green rust
Hydroxyl radicals
Iron
Irradiation
Microorganisms
Minerals
Organic carbon
Organic soils
Oxidation
Oxygenation
Phases
Soil chemistry
Soil conservation
Soils
Species
Transformations
γ Radiation
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Summary:Iron (Fe) phases are tightly linked to the preservation rather than the loss of organic carbon (OC) in soil; however, during redox fluctuations, OC may be lost due to Fe phase-mediated abiotic processes. This study examined the role of Fe phases in driving hydroxyl radical (•OH) formation and OC transformation during redox cycles in paddy soils. Chemical probes, sequential extraction, and Mössbauer analyses showed that the active Fe species, such as exchangeable and surface-bound Fe and Fe in low-crystalline minerals (e.g., green rust-like Fe phases), predominantly regulated •OH formation during redox cycles. The •OH oxidation strongly induced the oxidative transformation of OC, which accounted for 15.1–30.8% of CO2 production during oxygenation. Microbial processes contributed 7.3–12.1% of CO2 production, as estimated by chemical quenching and γ-irradiation experiments. After five redox cycles, 30.1–71.9% of the OC associated with active Fe species was released, whereas 5.2–7.1% was stabilized by high-crystalline Fe phases due to the irreversible transformation of these active Fe species during redox cycles. Collectively, our findings might unveil the under-appreciated role of active Fe phases in driving more loss than conservation of OC in soil redox fluctuation events.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.1c04073