Effects of the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate on Nitrification and Nitrifiers in Two Contrasting Agricultural Soils

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N2O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a N-15 tracing and (CO2)-C-13-DNA-stableisotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N2O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The N-15 tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The (CO2)-C-13-DNA-SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of (CO2)-C-13 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter. IMPORTANCE The combination of the N-15 tracing model and (CO2)-C-13-DNA-SIP technique provides important evidence that the nitrification inhibitor DMPP could effectively inhibit nitrification and nitrous oxide emission in an alkaline soil through influencing the abundance and metabolic activity of AOB. In contrast, DMPP amendment has no significant effect on nitrification or nitrifiers in an acidic soil, potentially owing to the low abundance of AOB and the possible adsorption of DMPP by organic matter. Our findings have direct implications for improved agricultural practices through utilizing the nitrification inhibitor DMPP in appropriate situations, and they emphasize the importance of microbial communities to the efficacy of DMPP.