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Methane Cycling along an Altitudinal Transect in a Northern Boreal Watershed

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Title: Methane Cycling along an Altitudinal Transect in a Northern Boreal Watershed
Author(s): Horten, Hannah
Contributor: University of Helsinki, Faculty of Biological and Environmental Sciences
Degree program: Master's Programme in Environmental Change and Global Sustainability
Specialisation: Environmental Change
Language: English
Acceptance year: 2021
Abstract:
Methane (CH4) is a powerful greenhouse gas that has been increasing in total atmospheric concentration since the late 1980s. While more of this gas is being produced through anthropogenic sources, a significant part is still produced by microbial methanogenesis. This process, in combination with atmospheric CH4, provides methane oxidizing bacteria, methanotrophs, with consumable CH4. In this way, methanotrophs are an important part of the CH4 cycle. Most models estimating changes to CH4 concentrations as a result of increasing anthropogenic byproducts often fail to consider the importance of these bacteria as a sink. Methanotrophs have been long studied, but more still needs to be discovered about their functionality in varying ecosystem types. These microbes are cosmopolitan, found in diverse environments across the globe. In this study, soil samples collected from a boreal forest in Pallas, FI were used to measure how well soil properties can be used to approximate potential CH4 oxidation rate. The abundance of methanotrophs was analyzed in soils ranging from upland to peatland using qPCR targeting the methanotrophic bacteria specific pmoA alpha-subunit of the methane monooxygenase gene. Soil samples were also analyzed for microbial biomass, percent carbon, and percent nitrogen. Sample pH and bulk density were also measured. Significant correlations were observed for bulk density and soil layer type (pearsons r = 0.659, p-value = 0.027), pH and percent carbon (pearsons r = -0.582, p-value = 0.014), pH and bulk density (pearsons r = 0.778, p-value = 0.002), and low affinity potential CH4 oxidation rate and microbial biomass in upland and peat-forest ecosystem types (pearsons r = -0.569, p-value = 0.043). Methanotroph abundance was significantly correlated with potential oxidation rates at low and high affinity conditions when analyzed across all sampling locations (pearsons r = 0.854 p-value = 1.27e-05; pearsons r = 0.602, p-value = 0.011). Methanotroph abundance and potential CH4 oxidation under both low and high affinity conditions were not found to be significantly correlated in upland and peat-forest soils alone when peatland samples were omitted. Soil properties show a moderate accuracy to predict high affinity potential oxidation uptake in upland and peat-forest soils when trained using all sample data. The soil properties used in this analysis do not show any ability to predict potential CH4 oxidation under low affinity conditions. All model findings are exploratory and further testing and development would be necessary to strengthen the findings.
Keyword(s): Methanotrophs methane oxidation upland soils peatland soils


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