Doctor of Philosophy (PhD)
Department of Environmental Sciences
Microorganisms are the major drivers of biogeochemical transformations of carbon and nitrogen in wetlands. These processes are crucial for ecological sustainability and are heavily impacted by human activities. How anthropogenic stress affects the microbial drivers of carbon storage and nutrient cycling in wetlands is not well understood. I investigated the response of wetland soil microbial communities to three different types of anthropogenic stress using DNA sequencing. First, I studied the effect of warming on microbial carbon processing in a peatland underlaid by permafrost by comparing the abundances of specific genes between sites subjected to five years of warming and controls. Warming induced significant changes in genes for functional pathways, carbohydrate-active enzymes, and taxonomic diversity. Analysis of predicted metabolic pathways indicated the abundance genes for the superpathway of methanogenesis were significantly greater in the warmed treatment. Furthermore, a significant increase in several species of methanotrophs was observed with warming. Second, I evaluated how the soil microbial community in a salt marsh denuded of vegetation by an oil spill responded to potential habitat restoration strategies for promoting ecosystem function. These treatments included planting Spartina alterniflora and fertilizer application. There was a significant impact of fertilizer application in the absence of transplants and the effect diminished once vegetation took hold. Planted sites developed statistically indistinguishable soil microbial community compositions represented by a cohort of sulfate-reducing bacteria. Third, I examined the environmental factors related to the recovery of the soil microbial community eight years after the Deepwater Horizon oil spill. I collected soil samples from sites that were exposed to differing amounts of oil during the spill. Microbial species abundances were structured along a longitudinal gradient; however, there was a significant effect of oiling level that was distinguishable from the spatial autocorrelation. The microbial species abundance pattern was not well explained by soil and vegetation differences at the sites after controlling for spatial autocorrelation. Overall, microbial community structure was significantly altered by warming and oil pollution, and not by fertilizer application when vegetation was present. This work improves our understanding of how wetland soil microbial communities respond to different types of anthropogenic stress.
Cagle, Grace Ann, "Responses of Wetland Soil Microbial Communities to Different Types of Anthropogenic Stress" (2021). LSU Doctoral Dissertations. 5714.
Available for download on Sunday, November 03, 2024