Nitrite stimulates HONO and NOx but not N2O emissions in Chinese agricultural soils during nitrification

The long-lived greenhouse gas nitrous oxide (N₂O) and short-lived reactive nitrogen (Nr) gases such as ammonia (NH₃), nitrous acid (HONO), and nitrogen oxides (NO_x) are produced and emitted from fertilized soils and play a critical role for climate warming and air quality. However, only few studies have quantified the production and emission potentials for long- and short-lived gaseous nitrogen (N) species simultaneously in agricultural soils. To link the gaseous N species to intermediate N compounds [ammonium (NH₄⁺), hydroxylamine (NH₂OH), and nitrite (NO₂^‒)] and estimate their temperature change potential, ex-situ dry-out experiments were conducted with three Chinese agricultural soils. We found that HONO and NO_x (NO + NO₂) emissions mainly depend on NO₂^‒, while NH₃ and N₂O emissions are stimulated by NH₄⁺ and NH₂OH, respectively. Addition of 3,4-dimethylpyrazole phosphate (DMPP) and acetylene significantly reduced HONO and NO_x emissions, while NH₃ emissions were significantly enhanced in an alkaline Fluvo-aquic soil. These results suggest that ammonia-oxidizing bacteria (AOB) and complete ammonia-oxidizing bacteria (comammox Nitrospira) dominate HONO and NO_x emissions in the alkaline Fluvo-aquic soil, while ammonia-oxidizing archaea (AOA) are the main source in the acidic Mollisol. DMPP effectively mitigated the warming effect in the Fluvo-aquic soil and the Ultisol. In conclusion, our findings highlight the important role of NO₂^‒ in stimulating HONO and NO_x emissions from dryland agricultural soils. In addition, subtle differences of soil NH₃, N₂O, HONO, and NO_x emissions indicated different N turnover processes, and should be considered in biogeochemical and atmospheric chemistry models.