Arid and semi-arid ecosystems cover a significant portion of the Earth’s surface, but the environmental factors that influence microbial diversity and community structure in these systems remain unclear. In this study we determined how the overall soil microbial community structure, as well as the structure of a specific functional group, change along an elevation gradient in northern Arizona. This study focused on four sites on the C. Hart Merriam Elevation Gradient that were named according to life zone; great basin desert, grassland, pinyon-juniper woodland, and ponderosa pine forest. Average annual precipitation ranges from about 180mm to over 680mm along the 800m change in elevation. Soil characteristics also vary among these sites; including pH, which decreases from 7.8 at the great basin desert to 6.0 in the ponderosa pine forest. The microbial diversity at each site was characterized by pyrosequencing a portion of bacterial and archaeal 16S genes. To assess the structure of the ammonia-oxidizing community, which plays a key role in the cycling of nitrogen, we characterized the functional gene amoA. Abundance of archaeal and bacterial amoA genes were quantified with real-time PCR. Clone libraries and TRFLP profiles for archaeal and bacterial amoA were developed.
Results/Conclusions
Bacteria and archaea communities varied across the elevation gradient sites. Actinobacteria were the predominant bacteria 16S sequences at the lower three sites, while Proteobacteria sequences were nearly as abundant as Actinobacteria sequences in the ponderosa pine forest. Ammonia-oxidizing archaea were more abundant than ammonia-oxidizing bacteria across all sites. The abundance of ammonia-oxidizing bacteria was significantly correlated with annual temperature and precipitation, but the abundance of ammonia-oxidizing archaea was not related to any of the environmental parameters measured. These results suggest that climate characteristics may play an important role in determining the structure of microbial communities in these semiarid ecosystems.
