PHD, Kent State University, 2023, College of Arts and Sciences / Department of Biological Sciences

Climate change is exerting profound and far-reaching impacts on ecosystems worldwide, encompassing both aquatic and terrestrial environments. The evolving precipitation patterns and shifting temperature regimes impact fluctuations in hydrology, resulting in shifts in redox conditions which can impact the availability of nutrients like phosphorus (P). Phosphate, the bioavailable form of P, is only present in small amounts within soils, making the biological demand greater than soil phosphate availability. The majority of soil P is present in non-labile forms including organic P and phosphate sorbed to metal oxides like iron (Fe). Microorganisms must content with geochemical and other abiotic factors to access phosphate from these non-labile sources through the use of various strategies including the secretion of enzymes, the production of phosphate solubilizing acids, as well as indirect mechanisms associated with the reduction of Fe oxides. The primary goal of this dissertation was to advance our understanding of how microorganisms access both labile and non-labile forms of P in the presence of changing hydrologic and redox conditions which impact the speciation of Fe that is present, altering phosphate availability. Specifically, I investigated 1) how phosphate availability changes across a permafrost thaw gradient (palsa, bog, and fen) in the presence of iron oxides, 2) how microorganisms access and mobilize chemically diverse phosphorus sources under contrasting redox conditions, and 3) how changes in hydrology, redox, iron mineralogy, and phosphate availability drive shifts in microbial community composition, specifically iron oxidizers, reducers, and phosphate solubilizers. In our first study assessing microbial phosphate accessibility across a permafrost thaw gradient, we found that near surface redox conditions changed as a function of permafrost thaw which impacted phosphate availability. Reducing conditions in the bog promoted the dissolution of Fe oxides, (open full item for complete abstract)

Committee: Lauren Kinsman-Costello (Advisor); Christie Bahlai (Committee Member); David Costello (Committee Member); Christopher Blackwood (Committee Member); Elizabeth Herndon (Committee Member); Timothy Gallagher (Committee Member) Subjects: Biogeochemistry; Climate Change; Ecology; Geobiology; Geochemistry; Microbiology; Mineralogy; Soil Sciences