Methane emissions in japonica rice paddy fields under different elevated CO2 concentrations

There are significant differences in future atmospheric CO 2 concentration under different carbon emission scenarios. Most studies have investigated the effects of elevated CO 2 concentrations on CH 4 emissions from paddy fields under a fixed CO 2 concentration. However, atmospheric CO 2 concentration are gradually increasing. Therefore, the relationship between elevated CO 2 concentrations and CH 4 emissions in paddy fields is still poorly understood. To investigate the effects of elevated CO 2 concentrations on CH 4 emissions and their mechanisms in paddy fields, a field experiment was conducted using open–top chambers during the 2018–2019 rice ( Oryza sativa L.) growing seasons. The experimental treatments included three CO 2 concentration levels: ambient CO 2 concentration (C), low elevated CO 2 concentration (C 1 , 120 μmol mol –1 above C in 2018; C 2 , 160 μmol mol –1 above C in 2019), and high elevated CO 2 concentration (C 3 , 200 μmol mol –1 above C). CH 4 fluxes were measured using a transparent static chamber–laser greenhouse gas analyzer. The results showed that elevated CO 2 concentrations had no significant effect on CH 4 emissions in paddy fields, but they significantly increased the CH 4 emission/yield ratio, which increased linearly with increasing CO 2 concentration. In addition, there was a significant linear correlation between CH 4 flux and the shoot biomass of rice. Stepwise regression analysis showed that the linear model based on soil urease activity and dissolved organic carbon and ammonium content explained 76% of the variation in CH 4 emissions during the 2018 rice–growing season. Meanwhile, the linear model based on soil invertase activity and dissolved organic carbon and nitrate content explained 73% of the variation in CH 4 emissions during the 2019 rice–growing season. Moreover, the linear model based on rice shoot biomass and soil dissolved organic carbon content explained 88% of the variation in CH 4 emissions during two rice–growing seasons. Overall, the shoot biomass of rice, the activities of invertase and urease, and the unstable C and N substrate content in soil effectively controlled CH 4 emissions in a japonica rice paddy field.