The influence of ozone pollution on CO2, CH4, and N2O emissions from a Chinese subtropical rice–wheat rotation system under free-air O3 exposure

Abstract A better understanding of the effects of ozone (O 3 ) on greenhouse gas (GHG) emissions in rotational rice ( Oryza sativa L.)–wheat ( Triticum aestivum L.) systems is essential for reducing potential GHG emissions in agroecosystems due to the projected increase in O 3 concentrations. Rice and wheat were rotationally grown in a free-air O 3 enrichment platform, and crop production and N 2 O, CH 4 , and CO 2 emissions from the soils were investigated as well as the global warming potential (GWP) of the GHGs. Exposure to elevated O 3 (50% greater than ambient O 3 ) slightly reduced the total biomass of wheat and significantly decreased that of rice, significantly decreased the root to total biomass ratio of wheat and slightly increased that of rice. Elevated O 3 significantly increased the CO 2 emission but did not influence the CH 4 and N 2 O emissions in the rice–soil system; however, elevated O 3 did not influence the CO 2 emission, significantly increased the CH 4 emission, and significantly reduced N 2 O emissions in the root-free soil during the rice season. Elevated O 3 increased the CO 2 emission and decreased the CH 4 and N 2 O emissions in the wheat–soil system and root-free soil during the wheat season, although the decrease in N 2 O emission in the wheat–soil system was not significant. The effects of elevated O 3 on GHGs emissions and biomass accumulation were related to crop species, plant coverage, and GHG type. Elevated O 3 significantly increased the GWP in the rice–soil system and the GWP per unit of rice yield; however, it did not change the GWP in the wheat–soil system or in the root-free soil during the wheat–rice growing period, nor did it change the GWP per unit of wheat yield. Considering the decreases in wheat and rice dry matter, reducing CO 2 emissions and planting O 3 -tolerant crop cultivars during future elevated O 3 scenarios, especially during the rice-growing season, should be a primary focus of the research aimed at reducing the GWP and increasing the soil C and N sequestration of rotational rice–wheat cropping systems.