Publication Date

Spring 2019

Degree Type


Degree Name

Master of Science (MS)


Biological Sciences


Sabine Rech


arid, biogeochemical, desert, microbial ecology, nifH, nitrogenase

Subject Areas

Molecular biology; Microbiology


Animals, plants, and microbes all rely on nitrogen to be readily available to build amino acids. The earth’s atmosphere is made of 78% nitrogen gas, but this molecule has a strong triple bond that prevents many species from utilizing it directly. Nitrogen fixation must occur in order for individuals to incorporate this nitrogen into their genome. The Mojave Desert is the most arid region in North America, averaging 3.5 inches of rain annually at its lowest elevation. Despite the extreme arid conditions, many species are supported in the region, all of which must rely on some form of nitrogen. This research addresses how aridity affects nitrogen fixation rates in soil microorganisms. It is predicted that there will be an increase in the nitrogen-fixing gene number, nifH, in more arid climates. Soil samples were collected from four sites across a 153-mile precipitation transect of the Mojave Desert, ranging from semi-arid to arid climates, over three years. Genomic DNA was isolated and quantified. Quantitative PCR was performed with primers targeted at the nifH gene of nitrogenase. Nitrogenase gene copy number tended to increase in more arid regions. Site number and yearly precipitation had significant effects on total nifH abundance. Percent crust and percent vegetation had significant effects on the 2009 sites. These results show that there is the potential for higher levels of nitrogen fixation in arid regions, which can be affected by yearly precipitation or other site factors