Thesis title: Diversity of ammonia-oxidizing archaea in soils under managed and native conditions
When and Where: July 18th 11:30am, Anderson 22
Committee: Dr. Sally Brown (chair), Dr. David Stahl, and Dr. Steven Fransen
Ammonia oxidizing archaea (AOA) contribute to a significant portion of ammonia oxidation in soil. These organisms have significant impacts on plant proliferation, as well as production of fugitive gases. AOA community distribution patterns are influenced by multiple factors, of which, biogeography has emerged as an important variable. Developing an understanding of community differences in AOA amid differing land management types may provide tools to understand differences in N use efficiency and other, broader impacts of AOA on soil and atmospheric biogeochemistry. The goal of this study was to assess whether agriculturally managed soils displayed shifts in AOA community diversity in contrast to non-managed soils located in close proximity. Soil was collected from two sites in eastern Washington with similar climate and precipitation patterns. At both sites soil was collected from the surface horizon (0-15 cm) of the adjacent native shrub-steppe (dominated by bunchgrass) and from switchgrass cultivated fields. AOA communities were evaluated by terminal restriction fragment length polymorphism (TRFLP) targeting subunit A of the Archaeal ammonia monooxygenase and analyzed using multivariate statistical approaches. At both the slightly alkalkine and slightly acidic agricultural sites, significant differences in AOA community diversity were observed based on the contribution of differing terminal restriction fragments (TRFs) to managed and native soils based on analysis of similarity (ANOSIM, R value greater than 0.6 p<0.05). In contrast, native soils displayed higher similarity to one-another, despite significant spatial separation, than either agriculturally influenced site. In native soils located adjacent to a slightly acidic switchgrass cultivated site, TRFs affiliated with members of the genus Nitrososphaera were abundant. The same genus were found in significantly lower abundance in cultivated sites. In contrast, TRFs attributed to the genus Nitrosotalea were dominant in the switchgrass cultivated site, but were detected in substantially lower abundance in the cultivated site. In addition, a higher number of TRFs were observed in the non-managed areas, indicative of a more diverse AOA community. At the slightly alkaline site, similar differences between native and cultivated AOA communities were also observed. However, the most abundant TRFs in the native soils were non-detectable in the cultivated areas, suggesting a complete replacement of native ecotypes. Preliminary TRF identification suggests different phylogentically distinct members of the genus Nitrosophaera are responsible for the observed shifts between native and cultivated soils. Taken together, our results suggest that agricultural land-management significantly alters AOA community diversity patterns for the soils examined. These results can inform future reseatch to assess whether these soils are also attributed with differing rates of nitrogen usage and production of fugitive gases, parameters that would be useful for modeling the impacts of switchgrass cultivation on nitrogen cycling soil ecosystems.