Date of Graduation

8-2022

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Savin, Mary C.

Committee Member

Philipp, Dirk

Second Committee Member

Stenken, Julie A.

Third Committee Member

Rojas, Alejandro

Keywords

Grassland soil; Microdialysis; Nitrification; Nutrient cycling; qPCR; Soil biology

Abstract

Nitrogen (N) biogeochemical cycling entails close networking between soil nutrients, plant species and resulting microbial communities, and abiotic factors such as temperature, moisture, and pH. To better understand transformations of N in soil microsites, which are known to be rich in N-cycling behavior, the microdialysis technique was employed to generate in situ data on temporal alterations of N during wetting-drying conditions in both the field and laboratory. The objectives were to 1) determine the lifespan of the microdialysis technique in field conditions, 2) evaluate the ability of the method to yield N fluxes that would be differential between the two plant communities, and 3) better understand N fluxes in soil associated with changing soil water content (wetting and drying). Microdialysis was deployed for approximately five months in the field and microdialysis sampling generated N fluxes that were distinct in soils of the two plant communities. While KCl extraction data resulted in greater inorganic N in orchardgrass soil in June, microdialysis, qPCR analysis of amoA gene abundances, and other physicochemical data such as pH supported the notion that native grass soil provided greater nitrification potential which could indicate the greater potential for N uptake in soil with native plants. Nitrogen fluxes were measured for five days in a lab study to provide greater detail in temporal data on the fluxes of nitrate-N, ammonium-N, and amino acid fluxes upon rewetting of field-moist and air-dried soil. There were also some significant parallels when comparing diffusive flux results of the field and laboratory studies. Frequent rainfall and drying events in the field resulted in increased nitrate-N fluxes which were analogous to the results of the lab study when using field-moist soil, signifying that the presence of water in the soil increased mineralization rates, which led to increased nitrification processes and a decrease of detectable ammonium-N and amino acids in soil solution. Nitrogen fluxes measured in the field during drought where similar to the flux patterns observed in the air-dried soil in the lab study. The addition of water resulted in a flush of mineralization and increased ammonium-N and amino acid fluxes. In this way, expansion of the current knowledge base of N cycling by the use of a tandem approach utilizing microdialysis flux and microbial functional genes could provide more insights into microsite N processes which dictate larger biogeochemical processes. Furthering our understanding of the effects of wetting/drying cycling on N movement in the soil will only become more pertinent as more frequent and extreme climatic conditions persist.

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