Aldossari, Nouf2023-09-192023-09-192021-05https://hdl.handle.net/11299/257033University of Minnesota Ph.D. dissertation. May 2021. Major: Land and Atmospheric Science. Advisor: Satoshi Ishii. 1 computer file (PDF); vii, 211 pages.Nitrate runoff through subsurface tile drainage is of serious concern in the Upper Midwest because surface water contamination with nitrate can cause various negative consequences in the surrounding and downstream environments. Woodchip bioreactor is a promising technology to remove nitrate from subsurface drainage; however, its removal efficiency can decrease at low temperatures (i.e., 5 ◦C) due to the low activity of the microorganisms. Some studies added cold-adapted denitrifying bacteria to the woodchip bioreactor to improve nitrate removal, although the improved nitrate removal did not last long due to the washout of the inoculated bacteria. Some fungi also reduce nitrate via denitrification, but denitrifying fungi have not been used for nitrate removal applications. The overall goal of my thesis research is to show the efficacy of fungal inoculation to improve nitrate removal in woodchip bioreactors at cold temperatures. I first reviewed the current knowledge regarding fungal denitrification (Chapter 2). I then isolated cold-adapted and nitrate-reducing fungi from soil and woodchip bioreactors (Chapter 3). These fungi were then inoculated to woodchip bioreactor mesocosms to evaluate the usefulness of the fungal inoculation (Chapter 4). The whole genome of one of the cold-adapted and nitrate-reducing fungus, Mortierella hyaline strain SCG-10, was sequenced to identify the key genes for fungal denitrification (Chapter 5). Adding M. hyaline strain SCG-10 improved the nitrate removal efficiency in the woodchip bioreactor mesocosms at 5 ◦C. Moreover, M. hyaline was able to degrade the complex carbon compounds in wood chips, providing more labile carbon to denitrifiers present in the woodchip bioreactor mesocosms. This thesis sheds light on the significant role of fungi in nitrate removal. Field application of these fungi should be tested in the future to make larger impacts.enThesis or Dissertation