Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Program Name/Specialization

Biological and Chemical Sciences

Faculty/School

Faculty of Science

First Advisor

Dr. Jennifer Baltzer

Advisor Role

Associate Professor and Canada Research Chair in Forests and Global Change

Abstract

Air temperature is increasing at three or more times the global average in high latitudes, causing widespread permafrost thaw across the boreal biome. Since the boreal biome stores 30-40% of global terrestrial carbon (C), of which about 30-45% is found in permafrost soils, this temperature increase could cause a large efflux of C to the atmosphere. Climate warming and permafrost thaw are also expected to alter plant community composition and productivity and, given the link between plant functional traits and ecosystem C fluxes, may alter overall ecosystem function. Across the boreal biome of western Canada, we know surprisingly little about warming-induced changes in plant functional traits, thus narrowing the ability to understand and model warming-induced changes on ecosystem function. I aimed to address this knowledge gap through three main objectives: 1. exploring understory plant community composition and community-level trait variation across four boreal peatland sites spanning 15° of latitude; 2. understanding the implications of permafrost thaw-induced environmental changes on vascular plant community composition and community-level traits along gradients in aboveground tree biomass and active layer; 3. determining how understory plant community composition and community-level traits mediate ecosystem C fluxes following increased nutrient availability at depth and whether responses differ with canopy density. I found that the large-scale climatic gradient had a small influence on community composition and community-level traits compared to within-site environmental gradients. In addition, a thicker active (seasonally thawed) layer increased community-level traits. Similarly, nutrient increases in shallow soil (~20 cm) increased community-level traits of vascular plants and forest floor C fluxes, but only when canopy was sufficiently open. Importantly, variation in community-level traits found throughout my dissertation was generally explained by species turnover. Thus, my research suggests that local increases in active layer thickness, and nutrient and light availability will drive changes in plant community composition toward species that enhance community-level productivity, thereby enhancing plant-mediated C uptake of peatland sites. However, this increased plant productivity is unlikely to account for C loss with continued warming and permafrost thaw in the long term due to concomitant changes in fluxes attributable to soil microbial activity.

Convocation Year

2022

Convocation Season

Spring

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