Xiuzhen Shi1, Hang-Wei Hu1, Ji-Zheng He1, Deli Chen1, Helen Suter1
Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia
The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to reduce N losses from agricultural systems by slowing nitrification and promote nitrogen (N) use efficiency. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in nitrification and N2O production, however, their responses to DMPP amendment and the possible reasons for the variable efficacy of DMPP across different soils are not well known. Here we compared the effects of DMPP on the abundance and metabolic activity of ammonia oxidizers using quantitative PCR and 13CO2-DNA-stable isotope probing (SIP) method in an acidic pasture soil and an alkaline vegetable soil. Results showed that DMPP significantly inhibited nitrification in the vegetable soil only, and this was coupled with a significant decrease in AOB abundance. The 13CO2-DNA-SIP results indicated the involvement of AOA and AOB in active nitrification in both soils, but DMPP only inhibited the assimilation of 13CO2 into AOB 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.