Date of Award

Fall 2024

Project Type

Dissertation

Program or Major

Natural Resources and Environmental Studies

Degree Name

Doctor of Philosophy

First Advisor

Erik A Hobbie

Second Advisor

Barrett N Rock

Third Advisor

Adam Wymore

Abstract

High latitude ecosystems are characterized by permafrost (perennially frozen ground), short growing seasons, and slow decomposition, and these characteristics of arctic ecosystems make them particularly sensitive to climate change. Alterations to arctic ecosystem functions are responding to recent climate disturbances such as increased active soil depths caused by thawing permafrost, transformation of dry ombrotrophic ecosystems to wetland communities, increased occurrence of wildfires in areas where wildfires are historically scarce, increased vegetation productivity, and shifts in plant phenology. Despite major ecosystem transformations and extreme climatic events in the Arctic during the previous decades, uncertainties persist largely because of nuances with climate feedback mechanisms. To disentangle Arctic climate uncertainties, many manipulative field experiments simulating environmental changes have been implemented. This dissertation aims to advance our understanding of biological mechanisms involved in nutrient dynamics as Arctic ecosystems respond to permafrost thaw, wildfires, and increased nutrient availability. I focus on both a peatland complex in a discontinuous permafrost zone of northern Sweden (the southern extent of permafrost that includes both permafrost free and zones of intact permafrost) and a tussock tundra community in the continuous permafrost zone of northern Alaska. I have witnessed both a real-time altered ecosystem functioning from permafrost loss in a discontinuous permafrost zone and a permafrost thaw as a result of an Arctic wildfire. The research I present here is at the intersection of ecosystem ecology, soil biogeochemistry, and plant biology to better understand mechanisms and potential feedbacks involved in the role of nutrient cycling in Arctic climate change. As permafrost is a major source of carbon, macronutrients, and micronutrients, thawing permafrost provides a new source of nutrients that were unavailable and previously frozen. In chapter one, I investigate how nutrient availability affects methane production and oxidation in a thawing permafrost mire. I quantified metals and inorganic and organic forms of nitrogen, phosphorus, and carbon across four neighboring plant communities with different active soil depths. This work provides insights of potential feedback mechanisms that affect microbial methane production and oxidation as permafrost thaws in a northern peatland mire. Shifting from the belowground activities to aboveground vegetation, my second chapter investigates interspecies nutrient response to wildfire and nutrient fertilization. Tundra wildfires were once considered infrequent and limited in severity; however, current research indicates increasing frequency and severity of tundra. Consequently, research on plant succession from Arctic wildfires is limited and underlying mechanisms of plant succession trajectories are still unclear. Recent research indicates increased nitrogen and phosphorus availability after the 2007 Anaktuvuk wildfire drove abundance and growth of certain species while other species have yet to recover twelve years after the wildfire. My research investigates interspecies responses to increased nutrients twelve years after wildfire and whether wildfire or nutrient fertilization have led to foliar nutrient enrichment or dilution. For chapter three, I used selected vegetation spectral reflectance indices to detect and characterize plant foliar properties in response to wildfire and nutrient fertilization from the same experimental site as chapter two. These spectral characteristics are used to detect changes in plant vitality and are strongly tied to photosynthetic pigments (chlorophyll and anthocyanin), foliar cellular anatomy, and foliar morphology. I used the red edge inflection point, anthocyanin index, and moisture stress index to investigate vegetation properties such as foliar pigment concentrations and foliar nutrient concentrations, and their responses to nutrient fertilization and wildfire.

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