Year of Award

2015

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Cellular, Molecular and Microbial Biology

Other Degree Name/Area of Focus

Microbial Evolution, Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

James E. Gannon

Commitee Members

William E. Holben, Scott R. Miller, Douglas W. Raiford, Carsten Suhr Jacobsen

Abstract

Despite the fact that microorganisms are the major drivers of global biogeochemical cycles, the relationship of microbial community activity and greenhouse gas production is still largely unexplored. The body of work presented here identifies previously unknown microbial community structure in bare ice, tracks shifts in permafrost active layer microbial communities along a moisture gradient, examines microbial trends throughout the Arctic growth season under climate change scenarios, and goes beyond identifying organisms working to link the structure and function of microbial communities to process level measurements. With deep sequencing of 16S rRNA, this study determined that bare ice collected from the Greenland Ice Sheet contains similar phyla to what has been detected on snow and cryoconite holes. Surprising results from this data set reveled extreme heterogeneity in ice samples even on a relatively small scale of 40 meters. In Zackenberg, GL permafrost active layer samples were collected from a soil moisture gradient. High throughput 16S rRNA sequencing revealed that moist active layer communities are more similar to dry active layer communities than those detected in fen samples. The fen samples were the only samples exhibiting net methane emissions. Given the microbial data, the permafrost in this area would have to collapse and form wetlands in order to become a likely methane source. To better understand microbial responses to climate change scenarios, communities were studied throughout the Arctic growth season on Disko Island, GL under increased snow accumulation and soil warming manipulations in situ. Phylogenetic and linear discriminant analyses of 16S rRNA genes and transcripts revealed microbial community succession with seasonal trends and the susceptibility of microbial community structure to increased soil warming and snow accumulation. Additionally, quantitative PCR of key functional genes illustrated that the activity of methane and nitrogen cycling organisms varied seasonally. The activity of methane cyclers corresponded to the peak in methane oxidation observed during the Arctic summer. The activity of nitrogen cyclers correlated to measured N pools. This work represents initial steps in developing a framework that links microbial community structure and activity in situ to biogeochemical cycles in the Arctic.

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© Copyright 2015 Frances Rose Gilman