Title

The transition from stochastic to deterministic bacterial community assembly during permafrost thaw succession

Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Microbiology

Degree Name

Master of Science

First Advisor

Jessica G Ernakovich

Second Advisor

Stuart Grandy

Third Advisor

Kelley Thomas

Abstract

The Northern high latitudes are warming twice as fast as the global average and permafrost has become vulnerable to thaw. Changes to the environment during thaw leads to shifts in microbial communities and their associated functions, such as greenhouse emissions. Understanding how the ecological processes that structure the identity and abundance (i.e. assembly) of pre- and post-thaw communities may improve predictions of the functional outcomes of permafrost thaw. We characterized microbial community assembly during permafrost thaw using in situ observation and a laboratory incubation of soils from the Storflaket Mire in Abisko, Sweden where permafrost thaw has occurred over the past decade. In situ observations indicated microbial community assembly was driven by randomness immediately after thaw. As post-thaw succession progressed, environmentally-driven processes became increasingly important in structuring microbial communities. Furthermore, laboratory-induced thaw was reflective of assembly dynamics immediately after thaw, but lab studies might not capture the long-term effects of permafrost thaw on microbial community dynamics. Soil respiration results suggest the observed increase in stochastic assembly with thaw may result in increased carbon emissions due to poor fitness and low efficiency of the final community. Identification of dominant microbial community assembly processes has the potential to improve our understanding of the ecological impact of permafrost thaw and the permafrost–climate feedback.

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