Effects of the nitrification inhibitor nitrapyrin on N2O emissions under elevated CO2 and rising temperature in a wheat cropping system

Nitrogen (N) fertilizer input will likely increase to meet the food demands of a growing population under climate change conditions, characterized by increasing atmospheric CO₂ concentration and temperature. Nitrification inhibitors have the potential to reduce N₂O emissions from N fertilized croplands. However, it remains unclear whether future climate change scenarios could affect the effectiveness of nitrification inhibitors. In a two-year study, winter wheat (Triticum aestivum L.) was cultivated in climate-controlled growth chambers with an elevated CO₂ concentration (ambient +200 μmol mol⁻¹) and increased temperature (ambient +2 °C). Urea was applied with or without nitrapyrin (0.5 % of urea-N). In this study, we measured nitrous oxide (N₂O) fluxes, soil ammonium and nitrate levels, and the abundance of five nitrogen-cycling genes related to nitrification (amoA of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA)) and denitrification (nirS, nirK and nosZ). Key findings included the following: 1) without nitrapyrin, cumulative N₂O emissions were not significantly altered by increased temperature, but decreased 24.9 % by the combination of elevated CO₂ and temperature treatment and 17.5 % by the elevated CO₂ alone. NO₃⁻-N accumulation occurred in soils under increased CO₂ and temperature, both individual and in combination; 2) nitrapyrin effectively reduced AOB abundance, inhibiting NO₃⁻-N accumulation and N₂O emission, irrespective of CO₂ concentrations and temperature. However, under the combination of elevated CO₂ and temperature conditions, the efficiency of nitrapyrin in reducing N₂O emission was lower (−13 % to −49 %) than that in the control (−28 % to −65 %) and elevated CO₂ (−32 % to −71 %) conditions. This reduced effectiveness of the combined treatment can be attributed to the inability of nitrapyrin to inhibit the AOA, nirS and nirK genes. Thus, nitrapyrin is expected to reduce N₂O emissions under future climate change scenarios, but the efficacy may be lower than previously expected when CO₂ concentration and temperature increase simultaneously. The indirect effects of nitrapyrin on denitrifiers under climate change scenarios should be considered in future research.