Humic acids as electron acceptors in wetland decomposition

Keller, Jason K.; Weisenhorn, Pamela; Megonigal, J. Patrick

doi:10.1016/j.soilbio.2009.04.008

Cited by 153 publications

(88 citation statements)

References 27 publications

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“…The reasons for such imbalance are unclear at the moment, but one possible answer is the use of organic oxidants for the degradation of organic matter, e.g. certain humic compounds that are reduced while others are concomitantly oxidized to CO 2 (Heitmann et al, 2007;Keller et al, 2009). Based on our observations, we hypothesize that organic oxidants are more important in the more oligotrophic than the mesotrophic peatlands.…”

Section: Discussionmentioning

confidence: 78%

Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems

2010

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Abstract. The degradation of organic matter to CH 4 and CO 2 was investigated in three different boreal peatland systems in Finland, a mesotrophic fen (MES), an oligotrophic fen (OLI), and an ombrotrophic peat (OMB). MES had similar production rates of CO 2 and CH 4 , but the two nutrientpoor peatlands (OLI and OMB) produced in general more CO 2 than CH 4 . δ 13 C analysis of CH 4 and CO 2 in the presence and absence methyl fluoride (CH 3 F), an inhibitor of acetoclastic methanogenesis, showed that CH 4 was predominantly produced by hydrogenotrophic methanogenesis and that acetoclastic methanogenesis only played an important role in MES. These results, together with our observations concerning the collective inhibition of CH 4 and CO 2 production rates by CH 3 F, indicate that organic matter was degraded through different paths in the mesotrophic and the nutrient-poor peatlands. In the mesotrophic fen, the major process is canonical fermentation followed by acetoclastic and hydrogenotrophic methanogenesis, while in the nutrient-poor peat, organic matter was apparently degraded to a large extent by a different path which finally involved hydrogenotrophic methanogenesis. Our data suggest that degradation of organic substances in the oligotrophic environments was incomplete and involved the use of organic compounds as oxidants.

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Section: Discussionmentioning

confidence: 78%

Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems

2010

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“…Furthermore, it was not known how the prevalence of Fe(III) reduction impacts CH 4 production in this ecosystem. The high ratios of CO 2 :CH 4 dissolved in soil pore water and produced in anaerobic laboratory incubations indicate an ecosystem with an abundance of alternative e − acceptors for anaerobic respiration (Updegraff et al, 1995;van Hulzen et al, 1999;Keller and Bridgham, 2007;Keller et al, 2009). In the absence of alternative e − acceptors, roughly equimolar concentrations of CO 2 and CH 4 would be produced (i.e., a ratio of one), whereas values observed in incubations and dissolved in soil pore water were generally orders of magnitude higher.…”

Section: Discussionmentioning

confidence: 99%

Water-table height and microtopography control biogeochemical cycling in an Arctic coastal tundra ecosystem

et al. 2012

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Abstract. Drained thaw lake basins (DTLB's) are the dominant land form of the Arctic Coastal Plain in northern Alaska. The presence of continuous permafrost prevents drainage and so water tables generally remain close to the soil surface, creating saturated, suboxic soil conditions. However, ice wedge polygons produce microtopographic variation in these landscapes, with raised areas such as polygon rims creating more oxic microenvironments. The peat soils in this ecosystem store large amounts of organic carbon which is vulnerable to loss as arctic regions continue to rapidly warm, and so there is great motivation to understand the controls over microbial activity in these complex landscapes. Here we report the effects of experimental flooding, along with seasonal and spatial variation in soil chemistry and microbial activity in a DTLB. The flooding treatment generally mirrored the effects of natural landscape variation in water-table height due to microtopography. The flooded portion of the basin had lower dissolved oxygen, lower oxidation-reduction potential (ORP) and higher pH, as did lower elevation areas throughout the entire basin. Similarly, soil pore water concentrations of organic carbon and aromatic compounds were higher in flooded and low elevation areas. Dissolved ferric iron (Fe(III)) concentrations were higher in low elevation areas and responded to the flooding treatment in low areas, only. The high concentrations of soluble Fe(III) in soil pore water were explained by the presence of siderophores, which were much more concentrated in low elevation areas. All the aforementioned variables were correlated, showing that Fe(III) is solubilized in response to anoxic conditions. Dissolved carbon dioxide (CO 2 ) and methane (CH 4 ) concentrations were higher in low elevation areas, but showed only subtle and/or seasonally dependent effects of flooding. In anaerobic laboratory incubations, more CH 4 was produced by soils from low and flooded areas, whereas anaerobic CO 2 production only responded to flooding in high elevation areas. Seasonal changes in the oxidation state of solid phase Fe minerals showed that net Fe reduction occurred, especially in topographically low areas. The effects of Fe reduction were also seen in the topographic patterns of pH, as protons were consumed where this process was prevalent. This suite of results can all be attributed to the effect of water table on oxygen availability: flooded conditions promote anoxia, stimulating dissolution and reduction of Fe(III), and to some extent, methanogenesis. However, two lines of evidence indicated the inhibition of methanogenesis by alternative e-acceptors such as Fe(III) and humic substances: (1) ratios of CO 2 :CH 4 evolved from anaerobic soil incubations and dissolved in soil pore water were high; (2) CH 4 concentrations were negatively correlated with the oxidation state of the soluble Fe pool in both topographically high and low areas. A second set of results could be explained by increased soil temperature in the flooding treatment,...

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“…It is possible that adding the Fe(III) amendment as an amorphous solid created a coating over surface-attached microorganisms that slowed microbial activity for a period of time. Another possibility is that reduced respiration was caused by the 1-unit decrease in pH in Fe(III)-amended slurries (data not shown; Keller et al (2009)). A third possibility is that Fe(III) directly inhibited methanogenesis through a mechanism that does not shunt electrons to a CO 2 -yielding respiration process, as shown to occur in pure methanogenic cultures (van Bodegom et al, 2004).…”

Section: Role Of Electron Acceptorsmentioning

confidence: 96%

Electron donors and acceptors influence anaerobic soil organic matter mineralization in tidal marshes

Sutton‐Grier

Keller

Koch

et al. 2011

Soil Biology and Biochemistry

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Humic acids as electron acceptors in wetland decomposition

Cited by 153 publications

References 27 publications

Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems

Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems

Water-table height and microtopography control biogeochemical cycling in an Arctic coastal tundra ecosystem

Electron donors and acceptors influence anaerobic soil organic matter mineralization in tidal marshes

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