Soil microbial responses to climate change in the arctic Tundra

Propster, Jeffrey Ryan (2022) Soil microbial responses to climate change in the arctic Tundra. Doctoral thesis, Northern Arizona University.

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Abstract

Increases in Arctic temperatures have thawed permafrost and accelerated tundra soil microbial activity, releasing greenhouse gases that amplify climate warming. Warming has also accelerated shrub encroachment across the tundra, altering litter quality and causing further changes to soil microbial processes. Understanding how individual microbial taxa will respond to warming and resultant ecosystem changes can provide insights into the underlying mechanisms that will determine net soil carbon flux to the atmosphere. We quantified the growth response of individual bacterial and fungal taxa to the long-term effects of warming using a 29-year field experiment in moist acidic tussock tundra. To uncouple the direct effects of warming on microbial growth rates from effects mediated by other ecosystem responses to warming, we conducted a parallel short-term warming experiment (3 months). Intact soil was assayed in the field for 30 days using 18O-labeled water, and taxon-specific rates of 18O incorporation into DNA were estimated as a proxy for growth. We evaluated the responses of taxonomic and functional groups and explored possible interactions among taxa via microbial growth network analysis. The phylogenetic conservation of bacterial and fungal growth rates was also investigated. Short-term warming was found to increase the average growth rates of the bacterial community, and an cohort of bacteria emerged that did not have measurable growth in other treatments. However, fungal growth rates did not change, and the diversity of fungal growers decreased. Thus, increases in bacterial growth and emergent growing bacteria in short-term warming could be interpreted as a warming-induced shift from a fungi-dominated community to a community of predominately disturbance-associated bacteria. The long-term warming increased the growth of both kingdoms, especially bacteria for which the average relative growth rate was approximately 2.5-fold higher than the control. Further, the stimulated growing community was similar to the control suggesting resilience in the long-term. Network analysis corroborated these findings as short-term warming largely altered network structure and reduced network stability while long-term warming supported much of the network structure that occurred in the control and increased network stability. Growth network analysis also revealed that negative correlations involving fungi contributed to network stability. Many microbial functional groups responded strongly to long-term warming that have consequential effect on tundra ecosystem processes, namely bacterial methanotrophs (Methylacidiphilales) and shrub-associated nitrogen fixers (Rhizobiales and Frankiales) and ectomycorrhizal fungi and wood saprotrophs. The investigation of the phylogenetic organization of bacterial growth detected coherence in relative growth rates within broad taxonomic levels with orders tending to have similar growth rates in all treatments. However, we found less consistent evidence for phylogenetic organization of fungal growth rates. Phylogenetic and functional coherence of microbial growth rates could facilitate predictions of the effects of climate change on microbial growth and explicit incorporation of soil microorganisms into taxonomically informed soil models.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Arctic tundra; climate change; field qSIP; network analysis; phylogenetic organization; soil bacterial growth
Subjects:	Q Science > QK Botany
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Biological Sciences
Date Deposited:	13 Jun 2023 17:47
Last Modified:	13 Jun 2023 17:47
URI:	https://openknowledge.nau.edu/id/eprint/6014

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