Abstract: A laboratory incubation experiment was conducted to evaluate the effects of nitrification inhibitors dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) applied with urea fertilizer on the N₂O emission, nitrogen transformation rate, and microbial community structure in meadow brown soil (Shenyang, Northeast China), cinnamon soil (Yuncheng, Central China), and silt loam soil (Minnesota, USA). In meadow brown soil, both of the two nitrification inhibitors reduced the N₂O emission by 54.1%-75.9%, but had no effects on soil mineral nitrogen content. The DCD inhibited the nitrification potential of meadow brown soil by about 24%, while the DMPP was inefficient under the higher soil moisture content. In cinnamon soil, the DMPP had significant inhibitory effect on the N₂O emission and nitrification potential, with the N₂O emission decreased by 85.5% and 66.7% and the nitrification potential reduced by 97.2% and 96.4% under lower and higher soil moisture contents, respectively. The DCD in cinnamon soil showed a weak inhibitory effect on the N₂O emission (decreased by 24.6%-57.5%) under lower soil moisture content, and no effect under the higher soil moisture content. The DMPP in silt loam soil decreased the N₂O emission by 42.9% and 53.1% under lower and higher soil moisture contents, respectively, while the DCD was inefficient under higher soil moisture content. In meadow brown soil and cinnamon soil, applying urea fertilizer alone promoted the growth and reproduction of soil ammoniaoxidizing bacteria (AOB) effectively, while the application of DCD and DMPP decreased the abundance of AOB by 4.1%-63.5% but had little effects on the abundance of soil ammoniaoxidizing archaea (AOA) and denitrifying bacteria. As compared with AOB, AOA were dominant in meadow brown soil and cinnamon soil, but the abundance of AOB amoA had a significant positive correlation with soil nitrification potential, indicating that soil AOB played more important role in the nitrification of these two soils.

Key words: microbial diversity, 16S rRNA, next generation sequencing (NGS), selection strategy