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Interrogating the methane paradox in freshwater wetland soils: A combined multi-omics and geochemical approach

Angle, Jordan C
http://rave.ohiolink.edu/etdc/view?acc_num=osu1524093386162629

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Microbiology.
The methane paradox - the phenomenon of unexpected biological methane production in oxygenated habitats – has been long-documented in marine waters and more recently inferred in freshwater lakes and soil habitats. In Chapter 1, the two primary mechanisms underpinning this phenomenon are described. I then identify the biomarkers and organisms implicated thus far in methane production from oxygenated habitats. Lastly, the contributions of the methane paradox to site-wide emission estimates and the implications of this process for global methane predictions are discussed. Chapter 2 presents the first genome enabled understanding of organisms performing the methane paradox in well-oxygenated soils. Oxygenated soils from a freshwater wetland located adjacent to Lake Erie contained significantly higher in situ methane concentrations and nine times greater methanogenic activity than corresponding deeper soils. Metagenomic and metatranscriptomic sequencing resulted in the discovery of Candidatus Methanothrix paradoxum, a novel acetoclastic methanogen species which accounted for nearly all of the inferred methanogenic activity in oxygenated soils. This oxic surface activity was estimated to contribute up to 80% of site-wide methane fluxes. Chapter 3 extends the genomic analyses to the larger methanogenic community in the Lake Erie freshwater wetland. Here I first compare methane production potential rates across surface and deep soils and show surface soils typically have greater methane production rates than deeper, anoxic soils. Metagenomic analyses demonstrated distinct clades of mcrA sequences from surface and deep soils and metatranscriptomic analyses were used to profile the activity of these sequences in each depth. This chapter also provides a more detailed genome-resolved investigation of the dominant and active methanogen across the site, Candidatus Methanothrix paradoxum. Lastly, the metabolic potential and activity of other methanogen genomes from both surface and deep habitats are initially described. Chapter 4 is a summary and discussion-oriented chapter focused primarily on how higher water levels at the wetland are affecting dissolved oxygen concentrations and the subsequent effect upon methanogenesis in these soils. First, I leverage publicly-available water level data and preliminary geochemical and methanogenic activity measurements to assess the role of hydrology as a driver of methanogenesis across the site. This prior Fall (2017), water levels up to 1.4 meters higher than my earlier dissertation sampling events (Chapters 2 and 3) resulted in the first reported anoxic conditions in surface soils at this site. Methane production potential data collected from these deep soils was higher than in years prior, while surface soils was similar to previous years. This finding, while preliminary, has important ramifications as it suggests that aerobic carbon decomposition in the surface soils may be not be required to “unlatch” more recalcitrant carbon leading to the generation of methanogenic substrates and sustaining methane production in these soils – a concept expanded upon in Chapter 4. This chapter ends with summarizing unanswered questions throughout the dissertation, including the status of isolation attempts for Candidatus Methanothrix paradoxum and introducing future efforts to characterize dissolved organic carbon and study anaerobic microsites in the bulk oxic soils. Cumulatively, this work provides an alternative view the to the paradigm that methanogenesis is only relegated to anoxic portions of the soil column. Findings generated here revealed the identity, activity, and distribution of methanogens along freshwater wetland gradients - insights vital to predicting greenhouse gas flux from these climatically relevant ecosystems. A greater understanding of the microbiology facilitating methane emissions in terrestrial saturated soils could improve the accuracy of methane emissions modeling efforts currently underway.
Kelly Wrighton (Advisor)
Gil Bohrer (Committee Member)
Joseph Krzycki (Committee Member)
Virginia Rich (Committee Member)
Michael Wilkins (Committee Member)
170 p.
Microbiology
methane; methanogenesis; methane paradox; wetland

Recommended Citations

Citations

  • Angle, J. C. (2018). Interrogating the methane paradox in freshwater wetland soils: A combined multi-omics and geochemical approach [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524093386162629

    APA Style (7th edition)

  • Angle, Jordan. Interrogating the methane paradox in freshwater wetland soils: A combined multi-omics and geochemical approach. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1524093386162629.

    MLA Style (8th edition)

  • Angle, Jordan. "Interrogating the methane paradox in freshwater wetland soils: A combined multi-omics and geochemical approach." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524093386162629

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.