The Impacts of Disruptive Environmental Change on Vital Microbial Ecosystems

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2023

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Abstract

Microbes both affect the global nutrient and carbon cycles that influence climate change and our modern environment, and are in turn influenced by environmental change. Through resource acquisition, metabolism, symbiosis with plants and other organisms, and functional & taxonomic composition, microbial communities determine ecosystem services and stability. Through a mix of experiments, observational studies, and theory, we investigate the dynamic interplay between microbes and their changing environment.

In our first research chapter, we address these questions using data from a longterm whole-ecosystem warming experiment at a boreal peatland. We explore how temperature and CO2 jointly influence communities of abundant, diverse, yet poorly understood non-fungi microbial Eukaryotes (protists). Using a combination of high-throughput fluid imaging and 18S amplicon sequencing, we demonstrate a taxonomic convergence but a functional divergence of microbes in response to warming and elevated CO2 ; we find novel evidence that warming effects on functional composition are reversed by elevated CO2 and amplified in larger microbes. These findings show how the interactive effects of warming and rising CO2 could alter the structure and function of peatland microbial food webs — a fragile ecosystem that stores 25% of terrestrial carbon.

In our second research chapter, we examine National Ecological Observatory Network (NEON) 16S amplicon sequencing data from a forest fire to examine the impact of fire on soil microbial communities. We report drastic fire-induced shifts in bacterialcomposition post-fire, with a reduction in alpha- and beta-diversity and no significant recovery of the soil microbiome 1-year post-fire. We also show that certain bacterial clades are clear indicators of fire, with heat-tolerant taxa increasingly dominant post-fire within our study plots, while other clades are indicative of a system without fire. These findings show how forest fires in landscapes adapted to infrequent fire regimes — such as moist, montane communities — may contain soil microbiomes that are less likely to recover post-fire, a concern as climate change alters many regions globally and large-scale forest fires become increasingly common in areas that have not historically experienced them.

In our last research chapter, we experimentally investigate the effects of temperature, genetic diversity, nutrient levels, and competition on body size (M) and density (N) in Tetrahymena thermophila, based on a unified differential equation model. Our findings highlight the crucial role of environmental conditions in shaping the body size and density of T. thermophila, emphasizing the intricate effects of environmental change on ecosystems. Our model analysis further reveals the specific parameters influenced by temperature, genetic diversity, competition, and resource availability, providing insights into the underlying mechanisms driving population dynamics. Our study sheds light on the complex interplay between body size, environmental factors, and ecological dynamics, contributing to a better understanding of these vital microbial ecosystems.

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Kilner, Christopher (2023). The Impacts of Disruptive Environmental Change on Vital Microbial Ecosystems. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/29206.

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