Date of Award

Spring 2026

Abstract

Permafrost is perennially frozen soil that underlays 11% of Earth’s total surface and stores 33%of the planet’s global soil carbon stocks in the form of soil organic matter. Rising global temperatures are causing permafrost to thaw. Permafrost thaw often creates a heterogeneous patchwork of redox conditions on the landscape, resulting in a diversity of microbial metabolisms using alternate terminal electron acceptors. In aerobic respiration, microbes use oxygen as TEAs and soil organic matter as an electron donor; anaerobic respiration is carried out when microbes use alternate electron acceptors, such as NO3-, Fe3+, SO42-, and CO2. Understanding microbial responses to changing redox conditions is critical to understanding the drivers shaping the post-thaw microbiome. However, many soil microbes are unculturable, so their growth responses across different temperature and redox conditions—components of their optimal niche space—is unkown. To identify the niche of microorganisms that proliferate after permafrost thaw, I conducted an incubation experiment where permafrost (collected from near the I-1 retrogressive thaw slump south of the Toolik Field Station in July 2022) was provided a non-limiting concentration of one of four terminal electron acceptors (O2, NO3-, Fe(OH)3, and SO42-) at five temperatures (4, 10, 15, 20, and 25°C). I measured CO2 and CH4 flux throughout the incubation and collected the absolute and relative abundances of microbial taxa within the communities at the end of the 35-day incubation. Analysis showed that both temperature and redox define the niche of many microbial taxa in the post-thaw community. There were approximately 1000 taxa found to be unique into each TEA treatment, with an additional ~400 taxa found across all TEA treatments. Similar trends persisted across the temperature gradient. vii Comparing the incubation microbial communities to samples collected in the field showed that the communities in the field were significantly different from the incubation communities. Understanding the niches of microbes that proliferate under post-thaw conditions will allow for a better understanding of how soil organic matter is cycled in a changing Arctic.

Document Type

Master's Thesis

First Advisor

Jessica Gilman-Ernakovich

Second Advisor

Ruth Varner

Third Advisor

Stuart Grandy

Degree Name

Master of Science

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