Ammonia-oxidizing microorganisms in soil are of great scientific interest because their activity directly impacts agricultural yields, water quality, and global climate change. These organisms control the rate of nitrification during which ammonia is converted to nitrate. This often results in nitrogen loss from an ecosystem, because nitrate is leached much more readily than ammonium and nitrate may be converted to gaseous forms of nitrogen, including nitrous oxide, a potent greenhouse gas. Ammonia-oxidizing microorganisms are very difficult to isolate from environmental samples and consequently the environmental parameters that control their growth have not been identified. A new technique, stable isotope probing with 18O-labeled water, has been developed that does not require cultivation of ammonia oxidizers to study their growth in soil. In this new approach the DNA of only growing microorganisms is labeled with 18O from 18O-water added to soil. The 18O-labeled DNA can be separated from non-labeled DNA so that the abundance of DNA sequences unique to ammonia-oxidizers may be quantified in the labeled DNA fraction. This abundance represents the growth of ammonia oxidizers in soil. The impact of nitrogen source, temperature, plant litter, water, pH and soil bulk density, on growth of ammonia oxidizing microorganisms will be investigated in semi-arid soils in northern Arizona, where mean annual precipitation ranges from 141 to 558 mm.
This project will also encompass several important educational initiatives. Native American high school teachers will be offered opportunities to gain research experience in microbiology in order to help them develop curriculum regarding the impact of reclaimed water on the San Francisco Peaks, a sacred site to many tribes in northern Arizona. In addition, an established collaboration with the Center for Science Teaching and Learning at Northern Arizona University will be enhanced by the development of a new course in the Master of Arts in Science Teaching program. The course will focus on how microbiology can be used to teach Arizona content standards in high schools. Finally, each year an undergraduate and a graduate student at Northern Arizona University will be educated in environmental microbiology and will be funded to conduct research.
