Short-term elevated O3 exerts stronger effects on soil nitrification than does CO2, but jointly promotes soil denitrification

AimsAtmospheric CO2 and O-3 concentrations have been increasing, with important consequences on the biogeochemical cycle in agroecosystems. However, little is known about the interactive effect of elevated CO2 and O-3 on soil nitrogen cycling processes mediated by soil microbes.MethodsWe conducted open-top chamber facilities to assess the impacts of short-term elevated CO2 and O-3 on soil nitrification and denitrification rates, and the abundances of soil N cycling-related genes for two rice cultivars (Nanjing 5055 vs. Wuyujing 3) in paddy soil.ResultsElevated CO2 potentially increased the abundance of nitrification-related genes (AOA amoA + 40.9%, AOB amoA + 23.4%, nxrB + 8.6%). Elevated O-3 potentially reduced the abundances of AOA and AOB amoA, nxrA, and nxrB by 3.1-23.8%. Combined treatment showed detrimental effects on the abundances of AOA and AOB amoA, and nxrA by 17.6-36.0%, indicating that short-term elevated O-3 exerted stronger effects on soil nitrification than CO2. Similarly, both individual and combined treatments decreased the abundance of comammox amoA. Additionally, the individual and combined treatments stimulated the abundance of denitrification-related genes by 4.2-11.9%, except narG. Accordingly, the denitrification rates were significantly increased by 77.2-89.1% under all treatments, particularly for Nanjing 5055. Furthermore, the abundance of nifH mediating N fixation was reduced by elevated CO2 and combined treatments.ConclusionsElevated CO2 and O-3 may promote soil N losses by increasing the abundances of denitrification-related genes, restraining N fixation-related genes, and potentially threatening food production, highlighting the detrimental impacts of ongoing elevated CO2 and O-3 on soil N retention capacity in the future.