Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Forest Science (PhD)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Evan Kane

Advisor 2

Jason Keller

Committee Member 1

Stephen Techtmann

Committee Member 2

Sarah Green

Committee Member 3

Erik Lilleskov

Abstract

Boreal peatlands store approximately one third of the earth’s terrestrial carbon, locked away in currently waterlogged and frozen conditions. Peatlands of boreal and arctic ecosystems are affected increasingly by shifting hydrology caused by climate change. The consequences of these relatively rapid ecosystem changes on carbon cycling between the landscape and the atmosphere could provide an amplifying feedback to climate warming. Alternatively, the advancement of terrestrial vegetation into once waterlogged soils could uptake carbon as a sink. Previous work suggests that fens will become an increasingly dominant landscape feature in the boreal. However, studies investigating fens, their response to hydrologic and vegetative change, and their carbon cycling dynamics are relatively few compared with other peatland types. This research investigates the biological and geochemical controls over carbon dioxide and methane cycling in a central Alaskan rich fen. The research concentrates on how these processes react to changes in water table and vegetation composition. The objectives of this body of research were to 1) Gain insights on how water table change affects carbon dioxide and methane transformation in a boreal rich fen from the pore water to the atmosphere; 2) Assess the mechanistic controls of specific boreal rich fen plant functional groups on carbon cycling; and 3) Profile the microbial community of a boreal rich fen and report on its response to water table change and specific plant functional groups. Although the oxidation of methane is prevalent in the studied rich fen, a raised water table and associated root exudates from greater sedge abundance fuels greater methane production than oxidation, for a net effect of greater methane production. However, the net methane that is released from the fen site is likely diminished compared with expected emissions due to the oxidizing nature of sedge, grass, and horsetail rhizospheres. Methanogens may also be in competition with other microorganisms for metabolic resources in this fen, which is recharged by the cyclic rewetting characteristic of these ecosystems. Overall, fens as a peatland type appear to have a resilience buffer in their carbon cycling response to hydrologic change more so than other peatland types.

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