Date of Award
12-1-2025
Degree Name
Master of Science
Department
Molecular Biology Microbiology and Biochemistry
First Advisor
Hamilton-Brehm, Scott
Abstract
The overuse of fertilizers has doubled the amount of reactive nitrogen in the environment. Agricultural runoff then carries these pollutants into the waterways eventually causing severe ecological damage such as the Gulf of Mexico dead zone. Nitrogen plays an important role in all life on this planet, here we describe two complementary projects that investigate ways to mitigate nitrogen pollution. The first project investigates denitrification rates in soil after the Len Small Levee breached in 2016 which reconnected the Dogtooth Bend Floodplain with the Mississippi briefly. The denitrification process that began in the hydrologically activated soils was hypothesized to be controlled by bacterial and fungal communities in floodplain soils. Core samples were taken from four locations, including a control, and incubated with artificial river water while monitored for nitrogen gas production using a membrane inlet mass spectrometry (MIMS). Under both oxic and anoxic incubations each sample from the Dogtooth Bend produced dinitrogen with higher gas production from the anoxic than the oxic cores. Polymerase chain reaction was unable to detect a complete bacterial denitrification pathway and failed to amplify any fungal denitrification genes. Next generation sequencing (NGS) revealed a diverse bacterial and fungal communities capable of partial or complete reduction of oxidized nitrogen molecules. The second project tested whether a hydrothermally treated microalgae as a potent biostimulant (Honey Shyne™) would enhance crop performance and enrich denitrifying microorganisms in the soil. A field study using dent corn sectioned into separate plots was given a onetime drench application of Honey Shyne™ at different growth intervals, including a combination application. The produced biostimulant was found to contain undetectable amounts of total nitrogen, minimal nitrate (0.0003%), phosphorus (0.0291%), and potassium (0.0275%) which characterizes it as not a fertilizer. A higher amount of protein or amino acids were detected in the biostimulant, but at concentrations that is 99.63% lower than other protein-based fertilizers. At the conclusion of the study, plots of corn that received biostimulant at emergence were found to have statistically significant increases in cob length (11.05%) and kernel yield mass (+17%) relative to controls. Results from the cob length and kernel yield receiving Honey Shyne™ were calculated to be statically significant. NGS conducted on the soil after harvest found that denitrifying bacteria and fungi were also present in all soil receiving Honey Shyne™. The results from these two projects show that recruiting denitrifying microorganisms could mitigate nitrogen pollution. Wetlands are known as vital environmental filters that remove excess nitrogen and improve downstream water quality. Cores from the Dogtooth Bend flood plain produced dinitrogen when incubated with river water, demonstrating that restored hydrologic connectivity can reactivate denitrification and support nutrient removal. Additionally, using a biostimulant derived from algae processed by a hydrothermal process increased crop yields and encouraged denitrifying bacteria and fungi in soil could reduce the need for fertilizers. Together, by periodically reconnecting the Mississippi river to wetlands throughout the length of the river and changing all farming nutrient practices to less nutrient intense biostimulants may buffer and lower reactive nitrogen to within pre-industrial concentrations.
Access
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