Soil water content modulates the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on nitrifying and denitrifying bacteria

In the last decades, intensive agriculture management and the application of nitrogen fertilizer have led to high nitrogen losses to the environment. Among these losses is the soil emission of the potent greenhouse gas nitrous oxide (N2O) which is mainly produced by the soil microbial processes of nitrification and denitrification. The use of nitrification inhibitors with ammonium based fertilizers can be an efficient mitigation strategy to decrease these nitrogen losses. Soil water content and temperature are major factors controlling N2O production and, so, also the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to reduce these emissions. In this work we study the effect of soil water content and temperature on the abundance of soil bacteria, ammonia-oxidizing bacteria and denitrifying bacteria, and on the performance of DMPP modulating these different bacterial populations responsible for N2O production/consumption. The effect of DMPP on the abundance of the different bacterial populations was dependent on soil water content. Under 40% of soil water filled pore space (WFPS), the application of DMPP caused an expected decrease of the target amoA gene abundance while narG, nirK and nosZ gene abundances also decreased probably due to an indirect effect induced by the lack of substrate for denitrifiers. Under 80% of WFPS, while the application of DMPP did not induce any change in the amoA gene abundance, an unexpected increase in non-target denitrifying gene abundances (narG, nirK and nosZ) was observed at either 10°C or 20°C incubation temperatures. This finding opens a new gate of research in the use of DMPP, where nitrous oxide reductase enzyme gene (nosZ) abundance and expression should be studied in the future in order to better understand the performance of DMPP not only inhibiting nitrification, but also affecting the non-target denitrification process.