Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Brian Branfireun

2nd Supervisor

Dr. Zoe Lindo

Joint Supervisor

Abstract

Northern peatlands are the world’s most efficient terrestrial ecosystems at storing carbon. The effects of global climate change are expected to be intensified in high latitude regions of the northern hemisphere, where peatlands are a dominant landscape feature. Accordingly, there is concern that climate change will change peatlands from carbon sinks into carbon sources. In order to better understand the impacts of climate change on peatland ecosystems, the research presented in this dissertation focuses on several mesocosm experiments conducted to develop a better understanding of the interactive effects of three key climate change stressors (increased atmospheric CO2, increased temperature, decreased water table elevation) on northern peatland vegetation structure and carbon cycling functions. Experimental findings include observations that temperatures between 4 and 8°C above ambient conditions triggered a plant community restructuring event, supporting the expansion of graminoids at the expense of Sphagnum mosses. This change in plant community was associated with an increase in dissolved organic carbon (DOC) concentration and lability, characteristics that indicate enhanced carbon release and a threat to northern peatland carbon stores. These findings were extended through further analysis to determine that differences in plant community structure were mechanistically linked to changes in carbon cycling functions through the introduction of microbial priming-like effects. Specifically, rooting growth forms increased belowground DOC lability, stimulating microbial activity and increasing respired CO2 rates — likely through the introduction of simple root exudates. These findings were then placed into the broader context of northern peatland climate change research using stable state theory as a framework to clarify the key factors that threaten peatland stability, point towards disturbance thresholds, and provide insights on the short- and long-term impacts of state shifts on northern peatland carbon uptake and storage.

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