Responses of Ammonia-Oxidizing Bacteria and Archaea in Two Agricultural Soils to Nitrification Inhibitors DCD and DMPP: A Pot Experiment

Taking two important agricultural soils with different pH, brown soil (Hap-Udic Luvisol) and cinnamon soil (Hap-Ustic Luvisol), from Northeast China, a pot culture experiment with spring maize (Zea mays L.) was conducted to study the dynamic changes in the abundance and diversity of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) populations during maize growth period in response to the additions of nitrification inhibitors dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) by the methods of real-time polymerase chain reaction (PCR) assay, PCR-denaturing gradient gel electrophoresis (DGGE), and construction of clone library targeting the amoA gene. Four treatments were established, i.e., no urea (control), urea, urea plus DCD, and urea plus DMPP. Both DCD and DMPP inhibited growth of AOB significantly, compared to applying urea alone. Soil bacterial amoA gene copies had a significant positive linear correlation with soil nitrate content, but soil archaeal amoA gene copies did not. In both soils, all AOB sequences fell within Nitrosospira or Nitrosospira-like groups, and all AOA sequences belonged to group 1.1b crenarchaea. With the application of DCD or DMPP, community composition of AOB and AOA in the two soils had less change except that the AOB community composition in Hap-Udic Luvisol changed at the last two growth stages of maize under the application of DCD. AOB rather than AOA likely dominated soil ammonia oxidation in these two agricultural soils.