Evidence that Ammonia-Oxidizing Archaea are More Abundant than Ammonia-Oxidizing Bacteria in Semiarid Soils of Northern Arizona, USA
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Autotrophic ammonia-oxidizing communities, which are responsible for the rate-limiting step of nitrification in most soils, have not been studied extensively in semiarid ecosystems. Abundances of soil archaeal and bacterial amoA were measured with real-time polymerase chain reaction along an elevation gradient in northern Arizona. Archaeal amoA was the predominant form of amoA at all sites; however, ratios of archaeal to bacterial amoA ranged from 17 to more than 1,600. Although size of ammonia-oxidizing bacteria populations was correlated with precipitation, temperature, percent sand, and soil C/N, there were no significant relationships between ammonia-oxidizing archaea populations and any of the environmental parameters evaluated in this study. Our results suggest that in these soils, archaea may be the primary ammonia oxidizers, and that ammonia-oxidizing archaea and ammonia-oxidizing bacteria occupy different niches.
We would acknowledge the following funding sources: Office of Science (BER), U.S. Department of Energy, Grant no. DE-FG02–04ER63883, the National Science Foundation, Grant No. DEB-0416223. K.A. was supported by an NSF IGERT fellowship (grant no. DGE-0549505). We would like to thank Paul Dijkstra, Joey Blankinship, and Ben Moan for their assistance with field work and site data.
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