| Microbes are an essential part of the biosphere, yet we are only beginning to characterize their communities in the environment. Understanding the factors that limit the distribution of microbes is a current challenge. It is well established that temperature and precipitation are the major factors restricting the distribution of most flora and fauna. The C. Hart Merriam Elevation Gradient located on the San Francisco Peaks in northern Arizona is a site of early research on the distribution of plants and animals. My dissertation research is focused on the soil microbial communities along this elevation gradient. In Chapter 2, I characterize bacterial and archaeal communities in great basin desert, desert grassland, pinyon-juniper woodland and ponderosa pine forest soils. Community structure differed between these soils due to changes in the relative abundance of the dominant phyla. Ammonia-oxidizers, a functional group of bacteria and archaea, are the focus of Chapters 3 and 4. Ammonia-oxidizing communities are quantified and characterized in Chapter 3. Ammonia-oxidizing archaea are more abundant than ammonia-oxidizing bacteria in all soils, and ammonia-oxidizing bacteria have more restricted distributions. In Chapter 4, I describe the application of a novel stable isotope probing technique with H,'8O to study the activity of ammonia-oxidizers. This study suggests that the activity of ammonia-oxidizing bacteria increases in response to elevated ammonium. |
