Title: Community Composition and Activities of Denitrifying Bacteria in Soils

Few studies have directly compared denitrifying community composition and activities in soils by coupling molecular-genetic techniques and traditional measures of denitrification. I investigated communities of denitrifying bacteria from adjacent meadow and forest soils in the Cascade Mountains, Oregon. A key gene in the denitrification pathway, N2O reductase (nosZ), served as a marker for denitrifying bacteria. Denitrifying enzyme activity (DEA) was an order of magnitude higher in meadow than in forest soils. Denitrifying community composition differed between vegetation types based on multivariate analyses of nosZ T-RFLPs. Screening 225 nosZ clones yielded 47 unique denitrifier genotypes. The majority of nosZ fragments sequenced from meadow or forest soils were most similar to nosZ from Rhizobiaceae in α-Proteobacteria. In a second study, I examined denitrifying bacteria from three adjacent habitats in Oregon: agricultural soil that received N-fertilizer inputs, naturally vegetated riparian soil, and creek sediment. The ratio of N2O produced as a result of denitrification in the presence of glucose (10 mM) and NO3- (5 mM) was higher fo