PARENT SESSION
Tuesday, August 8, 1:30-5:00 pm
COS 42 - Microbial ecology
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: L Aldrich-Wolfe

Ammonia-oxidizing bacteria or ammonia-oxidizing archaea - who is the dominant nitrifyer in northern Arizona soils?

Adair, Karen^*,1, Hart, Stephen¹, Hungate, Bruce¹, Schwartz, Egbert¹, ¹ Northern Arizona University, Flagstaff, AZ

ABSTRACT- One of the major challenges in soil microbial ecology is to link microbial processes to specific microorganisms in the environment. Nitrification is the biological oxidation of ammonia to nitrate and is an important step in the nitrogen cycle. There are several potential consequences of nitrification in soils, including nitrogen loss from the system, nitrate pollution of waterways, and production of the greenhouse gas nitrous oxide. The general consensus in the microbial ecology literature is that in most soils with pH >5 chemoautotrophic ammonia-oxidizing -Proteobacteria are responsible for the rate-limiting step of nitrification. The ubiquity of nonextremophilic ammonia-oxidizing Crenarchaeota has been demonstrated in ocean sediments and water columns, but their importance in semi-arid soils has not yet been determined. The objective of this research is to determine the contributions that ammonia-oxidizing bacteria and ammonia-oxidizing archaea make in nitrification that occurs in northern Arizona soils. In situ gross nitrification rates and nitrification potentials were measured in five different ecosystems (great basin, grassland, pinyon-juniper, ponderosa pine and mixed conifer) and two seasons (post-snowmelt and monsoon). The abundance of the amoA sequences specific to ammonia-oxidizing bacteria and ammonia-oxidizing archaea in each soil were measured with real-time PCR. Nitrification potentials were significantly different between sites on both sampling days. The relative abundance of amoA sequences specific to ammonia-oxidizing bacteria differed significantly between sites during the monsoon season, but not following snowmelt. When data from all ecosystems were pooled, the abundance of amoA sequences specific to ammonia-oxidizing bacteria was more than 2270 times greater during the monsoon season. There were significant differences in relative abundance of amoA sequences specific to ammonia-oxidizing archaea between sites in the monsoon season. The dominant group of nitrifyers, ammonia-oxidizing bacteria or ammonia-oxidizing archaea, differed between ecosystems.

Key words: microbial ecology, nitrification, Southwest