Ozone-Induced Alterations in Rhizospheric Nitrogen Pools and Their Implications for N2O Emissions in Rice Soil

Elevated tropospheric ozone (O3) may alter nitrous oxide (N2O) emissions from rice soils by affecting soil nitrogen pools and microbial activity. Understanding these interactions is essential for predicting the future behavior of rice ecosystems under elevated ozone stress. This study investigates the responses of N2O flux in relation to soil nitrogen (N) pools and microbial activity in rice soil subjected to four levels of elevated tropospheric O3 (UC (ambient [O3] in an open-field, 30 ± 5 ppb), CC (ambient [O3] within an open-top chamber (OTC), 30 ± 5 ppb), EO40 (elevated [O3] within an OTC, 40 ± 5 ppb), and EO60 (elevated [O3] within an OTC, 60 ± 5 ppb). Rice soil exposed to e[O3] exhibited significant reductions in microbial biomass nitrogen (29%), ammoniacal nitrogen (30%), and nitrate nitrogen (32%) concentration over ambient (CC). Rhizospheric denitrifier populations decreased by 11%, whereas seasonal N2O emission was decreased by 21% under e[O3] as compared to CC. The PLS-PM model revealed that nitrifiers and denitrifiers exert a direct influence on N₂O emissions, with a more pronounced effect under e[O3] conditions compared to the CC. These insights enhance our understanding of the complex interactions between soil, plants, and microbial communities in an O3-enriched environment.