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

Elevated CO2 (eCO(2)) 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 eCO(2), 200 mu mol mol(-1) higher than the ambient CO2 (aCO(2)), 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 aCO(2), eCO(2) 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 eCO(2) 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 O-2 concentration ([O-2]) in the surface soil. The mitigating effect of eCO(2) 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 [O-2] 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.

Automated summary

This study investigated the effects of elevated CO2 (eCO2) and different rice cultivars on CH4 and N2O emissions in Chinese subtropical rice systems. The results showed that eCO2 increased rice yield and decreased CH4 and N2O emissions. The strongly responsive cultivars had lower emissions and were associated with higher soil Eh and [O-2] levels.