Elevated O3 Reduces Nitrogen Oxide Emissions from Rice Paddy Fields Under Warming

Elevated tropospheric ozone (O3) and global warming can affect nitrous oxide (N2O) and nitric oxide (NO) emissions from rice paddies, but their interactive effect is poorly understood. Two-year field observations of soil properties were implemented to quantify the impact of elevated O3 and warming on N2O and NO fluxes and identify dominant regulatory factors. Results indicated that elevated O3 reduced N2O and NO fluxes, whereas warming increased N2O and NO fluxes, relative to respective ambient conditions. The combined O3 elevation and warming treatment resulted in reductions in N2O and NO fluxes compared to the warming treatment. The N2O and NO emissions under elevated O3 and warming were primarily associated with significant changes in soil dissolved organic carbon (DOC) and NH4+. Furthermore, under warming treatment, N2O and NO emissions were also linked to significant variations in soil NO3−, but were independent of soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and pH. This study found that high O3 concentrations significantly suppress nitrogen oxide emissions from paddy fields under warming. This suppression necessitates the explicit integration of O3 into agroecosystem emission prediction frameworks for accurate estimation of nitrogen oxide fluxes.