Date of Award

Spring 2026

Document Type

Open Access Thesis

Department

Earth and Ocean Sciences

First Advisor

Xuefeng Peng

Abstract

Nitrous oxide (N2O), a potent greenhouse gas, can be produced by microorganisms inhabiting marine environments. While bacterial denitrification is a major source of N2O, the role of marine fungi in this process remains poorly constrained. This thesis investigates the contribution of marine fungi to N2O production from salt marsh sediments, while also isolating new N2O-producing marine fungi and advancing methodological approaches for quantifying denitrification. First, we conducted experiments to quantify the fungal contribution to N2O production using salt and brackish marsh sediments collected from the North Inlet–Winyah Bay National Estuarine Research Reserve in South Carolina during the summer and winter of 2024. Antimicrobial compounds (chloramphenicol and captan) were used to specifically inhibit either prokaryotes or eukaryotes. Sediment slurry incubations were performed with ¹⁵N- labeled nitrate, and the production of ¹⁵N-labeled N2O was measured. Results indicate that fungi in salt marsh sediments can contribute up to 62% of total N2O production under anoxic conditions, demonstrating that fungal denitrification represents a substantial and previously underappreciated source of estuarine N2O. Second, I optimized chromatographic conditions for measuring potential denitrification rates using the acetylene block method with gas chromatography (SRI 8610C GC). Methodological refinements improved N2O detection sensitivity and clarified analytical constraints associated with low-concentration samples. Finally, I isolated two N2O-producing fungal strains (Cadophora sp. and Coniochaeta sp.) from the water columns of Narragansett Bay  and the adjacent North Atlantic Ocean. Both strains produced N2O under anaerobic conditions and preferentially utilized nitrite over nitrate, providing evidence that open- ocean fungi possess the metabolic capacity for incomplete denitrification. Overall, this work demonstrates that marine fungi are active and potentially significant contributors to N2O production in both estuarine sediments and offshore waters.

Rights

© 2026, Qintiantian Nong

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