Assessing the efficiency of dimethylpyrazole-based nitrification inhibitors under elevated CO2 conditions

Abstract

Nitrification inhibitors (NIs) are useful tools to reduce nitrogen (N) losses derived from fertilization in agriculture. However, it remains unclear whether a future climate scenario with elevated CO2 could affect NIs efficiency. Thus, the objective of this work was to study whether the increase of atmospheric CO2 concentration would affect the efficiency of two dimethylpyrazole-based NIs: 3,4-dimethylpyrazol phosphate (DMPP) and 3,4-dimethylpyrazol succinic acid (DMPSA) in a plant-soil microcosm. To do so, Hordeum vulgare var. Henley plants were grown in soil fertilized with ammonium sulphate (AS) with or without NIs under controlled environmental conditions at ambient CO2 (aCO2) or elevated CO2 (eCO2; 700 ppm). In the soil, mineral nitrogen and N2O emission evolution were monitored together with nitrifying and denitrifying population that were quantified by qPCR. In the plant, biomass, total amino acid content and isotopic discrimination of N and C were measured. Both NIs showed greater efficiency to maintain soil NH4+ content under eCO2 compared to aCO2, as a consequence of 80% reduction of AOB abundance in eCO2. Indeed, both inhibitors were able to lessen 53% the N2O emissions in eCO2 compared to aCO2. Regarding the plant, DMPP and DMPSA negatively affected plant biomass at aCO2 but this effect was restored at eCO2 due to a better ammonium tolerance associated with an increase in total amino acid content. Overall, DMPP and DMPSA NIs were highly efficient under eCO2, reducing N2O emissions and keeping N in the soil stable for longer while maintaining plant biomass production.