Graduate Thesis Or Dissertation
 

Quantitative Metatranscriptomics and Biogeochemical Rate Measurements Reveal Microbial Pathways Driving Carbon and Nitrogen Cycles in an Arctic Lagoon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n87100398

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  • Microbial communities in Arctic coastal lagoons drive biogeochemical cycles at the terrestrial-marine interface and help to determine the fate and form of resources like nitrogen (N) and carbon (C) as they are delivered to the Arctic Ocean. Though rising rates of primary production in the Arctic Ocean are well-characterized, the microbial mechanisms underpinning coastal biogeochemical cycles are underexplored, particularly during winter. To better define the microbial drivers of Arctic estuarine N and C cycling across seasons, we measured microbial gene expression, nitrification, and inorganic C assimilation rates in the waters of Elson Lagoon on the western Beaufort Sea coast under ice covered (April), spring break up (July), and open water conditions (August) of 2021. Microbial community gene expression was assessed using quantitative metatranscriptomic sequencing to measure per-liter transcript abundances alongside in situ light and dark 15N-ammonium, 15N-urea, and 13C-bicarbonate stable isotope tracer incubations. Nitrification was measurable only during ice cover, when we observed relatively high potential (dark) rates for an Arctic coastal system and found evidence for strong light inhibition of this process even during late winter. Light and dark C assimilation rates were equal during ice cover, followed by large increases in both during break up and open water. Microbial community gene expression was strongly influenced by the extreme shifts in seasonal conditions in the lagoon, and total transcript abundances varied by almost one order of magnitude across seasons. The archaeal ammonia oxidizer Nitrosopumilus expressed most nitrogen cycle transcripts during ice cover, while transcripts for urea metabolism and other forms of N uptake were most abundant during break up and open water. We observed low expression of chemoautotrophic C assimilation transcripts by nitrifying microorganisms, with heterotrophs or unclassified taxa appearing to perform most dark C assimilation across all seasons. This study demonstrates that microbial community gene expression varies alongside seasonal shifts in Arctic lagoon N and C cycle rates, with important implications for the metabolic pathways that drive these cycles.
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  • Beaufort Lagoon Ecosystems Long-Term Ecological Research
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  • This work was funded by a National Science Foundation Graduate Research Fellowship (NSF award #1840998), a North Pacific Research Board Graduate Student Research Award, and the Beaufort Lagoon Ecosystems Long-Term Ecological Research program (NSF award #1656026).
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  • Pending Publication
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  • 2022-11-29 to 2023-12-30

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