Responses of yield, CH4 and N2O emissions to elevated atmospheric temperature and CO2 concentration in a double rice cropping system

Elevated atmospheric temperature and CO2 concentration ([CO2]) can strongly affect yield, CH4 and N2O emissions in rice paddies. However, understanding of their response to combined temperature and [CO2] increases under field conditions is still limited. To study this issue further, an open-top chamber (OTC) platform was set up to simulate two levels of atmospheric temperature (ambient and 2 °C elevated) and two levels of [CO2] (ambient and 60 ppm elevated) during two rotations of double rice, including twelve independent OTCs and three un-chambered open field sites as trial plots. The experimental site is located in Hubei Province, Central China, which has a subtropical monsoon climate. In all four rice seasons, elevated CO2 induced an increment in grain yield by 11.4-19.7%, while also enhancing CH4 and N2O emissions by 19.8-52.6% and 102.4-140.0%, respectively, compared with ambient temperature and [CO2]. Elevated temperature enhanced CH4 emissions by 4.4-36.0%, and decreased N2O emissions by 1.5-10.5% in three rice seasons. Elevated temperature had different effects on grain yield, with a reduction of 1.0-3.2% in early rice and an increase of 6.3-9.2% in late rice. When elevated temperature and [CO2] were combined, there was a positive interaction that further enhanced CH4 emissions and yield of late rice, and an offsetting effect on N2O emissions and yield of early rice. Over the 2-year experiment, warming and CO2 enrichment caused an increase of 9.3-44.2% in greenhouse gas intensity, suggesting that more greenhouse gas emissions will be emitted to produce a unit mass of rice under projected global warming. These findings provide initial data for the estimation of CH4 and N2O emissions under elevated temperature and [CO2] in double rice cropping system, and stress the need for effective management practices that promote rice yield while reducing greenhouse gas emissions.