Linkage between N(2)O emission and functional gene abundance in an intensively managed calcareous fluvo-aquic soil

The linkage between N(2)O emissions and the abundance of nitrifier and denitrifier genes is unclear in the intensively managed calcareous fluvo-aquic soils of the North China Plain. We investigated the abundance of bacterial amoA for nitrification and narG, nirS, nirK, and nosZ for denitrification by in situ soil sampling to determine how the abundance of these genes changes instantly during N fertilization events and is related to high N(2)O emission peaks. We also investigated how long-term incorporated straw and/or manure affect(s) the abundance of these genes based on a seven-year field experiment. The overall results demonstrate that the long-term application of urea-based fertilizer and/or manure significantly enhanced the number of bacterial amoA gene copies leading to high N(2)O emission peaks after N fertilizer applications. These peaks contributed greatly to the annual N(2)O emissions in the crop rotation. A significant correlation between annual N(2)O emissions and narG, nirS, and nirK gene numbers indicates that the abundance of these genes is related to N(2)O emission under conditions for denitrification, thus partly contributing to the annual N(2)O emissions. These findings will help to draw up appropriate measures for mitigation of N(2)O emissions in this ‘hotspot’ region.