Does the nitrification inhibitor dicyandiamide affect the abundance of ammonia-oxidizing bacteria and archaea in a Hap-Udic Luvisol?

To date, there are several studies on the responses of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to nitrification inhibitors, but only a limited number of observations are available for higher than regular application rates. Here, we report the results of a study investigating the responses of AOB and AOA to the nitrification inhibitor, dicyandiamide (DCD). DCD suppressed growth of AOB significantly, whereas there was no significant difference between a single or a double dose of DCD on inhibiting the growth of AOB for 91 days. AOA abundance was stable among treatments, regardless of the addition of a single or a double dose of DCD. When DCD was applied alone, the AOA abundance was not appreciably changed at day 14. The results clearly show that AOA was not sensitive to the nitrification inhibitor DCD under our experimental conditions.