Abstract
BACKGROUND: Fertilizer addition can contribute to nitrogen (N) losses from soil by affecting microbial populations responsible for nitrification. However, the effects of N fertilization on ammonia oxidizing bacteria under C(4) perennial grasses in nutrient-poor grasslands are not well studied. METHODS: In this study, a field experiment was used to assess the effects of N fertilization rate (0, 67, and 202 kg N ha(-1)) and grass species (switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii)) on ammonia-oxidizing bacterial (AOB) communities in C(4) grassland soils using quantitative PCR, quantitative reverse transcription-PCR, and high-throughput amplicon sequencing of amoA genes. RESULTS: Nitrosospira were dominant AOB in the C(4) grassland soil throughout the growing season. N fertilization rate had a stronger influence on AOB community composition than C(4) grass species. Elevated N fertilizer application increased the abundance, activity, and alpha-diversity of AOB communities as well as nitrification potential, nitrous oxide (N(2)O) emission and soil acidity. The abundance and species richness of AOB were higher under switchgrass compared to big bluestem. Soil pH, nitrate, nitrification potential, and N(2)O emission were significantly related to the variability in AOB community structures (p < 0.05).