| Autor: |
Obradović, Nikola1 (AUTHOR), Joshi, Prachi1,2 (AUTHOR), Arn, Silvan1 (AUTHOR), Aeppli, Meret1,3 (AUTHOR), Schroth, Martin H.1 (AUTHOR) martin.schroth@env.ethz.ch, Sander, Michael1 (AUTHOR) michael.sander@env.ethz.ch |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Biogeosciences. Nov2023, Vol. 128 Issue 11, p1-17. 17p. |
| Abstrakt: |
Electron transfer to peat particulate organic matter (POM) as terminal electron acceptor (TEA) in anaerobic respiration has been hypothesized to lower methane emissions from peatlands by competitively suppressing methanogenesis and/or allowing for anaerobic oxidation of methane. We herein provide evidence for two critical aspects of this hypothesis: (a) peat POM is present in a reduced state in situ in the anoxic peat subsurface, and (b) reduced POM at the oxic‐anoxic interface in peat soils can be oxidized by dissolved oxygen (DO), restoring its TEA capacity. We reacted reduced POM from three ombrotrophic bogs in Sweden with DO in soil‐packed column‐breakthrough experiments (CBEs), mimicking oxidation reactions at the oxic‐anoxic interface. Breakthrough of DO was substantially retarded relative to the inert tracer bromide, consistent with DO reduction by POM. Control experiments confirmed abiotic DO reduction and excluded DO consumption through aerobic respiration. Modeling DO breakthrough revealed fast and slowly reacting POM moieties with reaction times spanning minutes to days. Complementary push‐pull tests (PPTs) in the anoxic subsurface of one bog confirmed results from laboratory CBEs: lower recoveries of injected DO compared with bromide supported DO reduction by reduced POM. Rates of reduction of injected DO decreased with increasing number of injections, consistent with continuous oxidation of reduced POM. Electron‐donating capacities of POM to DO in CBEs and PPTs were comparable at 40–130 μmol e−/g dry POM. Our results substantiate that POM is a regenerable TEA at oxic‐anoxic interfaces in peat soils and, thereby, may substantially lower CH4 emissions from peatlands. Plain Language Summary: Northern peatland soils contain large amounts of carbon stored as peat particulate organic matter (POM). Understanding how microorganisms turn over this carbon is important because turnover can release not only carbon dioxide but also methane, a more potent warming gas. Recent literature proposes that microorganisms in oxygen‐free parts of peat soils can turn over carbon substrate molecules by oxidation to carbon dioxide coupled to transferring electrons liberated in this process to POM. This newly proposed pathway is expected to substantially lower methane formation and emissions but relies on POM's ability to accept electrons. However, continuous electron transfer to POM in oxygen‐free soil parts would eventually consume the capacity of POM to accept electrons, at which point methane formation would set in. In our work, we show that the electrons stored in POM under anoxic conditions can be transferred to dissolved oxygen (DO) which periodically enters the peat soils by various means. Reaction with DO thus restores POM's capacity to accept electrons in subsequent oxygen‐free periods and thus its potential to suppress methane emissions. Our findings will help to better understand the role of POM in peatland carbon turnover to carbon dioxide and methane. Key Points: Peat particulate organic matter (POM) in the anoxic subsurface of three Swedish ombrotrophic bogs is present in reduced statesPeat POM transfers 40–130 μmol e− per g to dissolved oxygen with reaction times spanning from minutes to daysPOM acts as regenerable terminal electron acceptor in anaerobic respiration at oxic‐anoxic interfaces in peat soils [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
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