Elevated atmospheric CO2 reduces CH4 and N2O emissions under two contrasting rice cultivars from a subtropical paddy field in China

Elevated CO₂ (eCO₂) and rice cultivars can strongly alter CH₄ and N₂O emissions from paddy fields. However, detailed information on how their interaction affects greenhouse gas fluxes in the field is still lacking. In this study, we investigated CH₄ and N₂O emissions and rice growth under two contrasting rice cultivars (the strongly and weakly responsive cultivars) in response to eCO₂, 200 μmol mol^-1 higher than the ambient CO₂ (aCO₂), in Chinese subtropical rice systems relying on a multi-year in-situ free-air CO₂ enrichment platform from 2016 to 2018. The results showed that compared to aCO₂, eCO₂ increased rice yield by 7%–31%, while it decreased seasonal cumulative CH₄ and N₂O emissions by 11%–59% and 33%–70%, respectively, regardless of rice cultivar. The decrease in CH₄ emissions under eCO₂ was possibly ascribed to the lower CH₄ production potential (MPP) and the higher CH₄ oxidation potential (MOP) correlated with the higher soil redox potential (Eh) and O₂ concentration (O₂]) in the surface soil. The mitigating effect of eCO₂ on N₂O emissions was likely associated with the reduction of soil soluble N content. The strongly responsive cultivars had lower CH₄ and N₂O emissions than the weakly responsive cultivars, and the main reason might be that the former induced higher soil Eh and O₂] in the surface soil and had larger plant biomass and greater N uptake. The findings indicated that breeding strongly responsive cultivars with the potential for greater rice production and lower greenhouse gas emissions is an effective agricultural practice to ensure food security and environmental sustainability under future climate change scenarios.