Contrasting Warming and Ozone Effects on Denitrifiers Dominate Soil N₂O Emissions

Abstract

Nitrous oxide (N₂O) in the atmosphere is a major greenhouse gas and reacts with volatile organic compounds to create ozone (an air pollutant) in the troposphere. Climate change factors such as warming and elevated ozone (eO₃) affect N₂O fluxes, but the direction and magnitude of these effects are uncertain and the underlying mechanisms remain unclear. We examined the impact of simulated warming (control + 3.6 °C) and eO₃ (control + 45 ppb) on soil N₂O fluxes in a soybean agroecosystem. Results obtained showed that warming significantly increased soil labile C, microbial biomass, and soil N mineralization, but eO₃ reduced these parameters. Warming enhanced N₂O-producing denitrifers ( nirS- and nirK-type), corresponding to increases in both the rate and sum of N₂O emissions. In contrast, eO₃ significantly reduced both N₂O-producing and N₂O-consuming ( nosZ-type) denitrifiers but had no impact on N₂O emissions. Further, eO₃ offsets the effects of warming on soil labile C, microbial biomass, and the population size of denitrifiers but still increased N₂O emissions, indicating a direct effect of temperature on N₂O emissions. Together, these findings suggest that warming may promote N₂O production through increasing both the abundance and activities of N₂O-producing microbes, positively feeding back to the ongoing climate change.