Effect of Warming and Elevated O₃ Concentration on CO₂ Emissions in a Wheat-Soybean Rotation Cropland

A deeper understanding of the effects of experimental warming and elevated ozone (O₃) concentration on carbon dioxide (CO₂) fluxes is imperative for reducing potential CO₂ emissions in agroecosystems, but are less understood particularly in rotational wheat (Triticum aestivum)-soybean (Glycine max) croplands. In order to understand such effects on CO₂ fluxes from winter wheat-soybean rotation, a field experiment was conducted by using the open-top chamber (OTCs) during the growing seasons of 2012 and 2013 at an agro-ecological station in southeast China. The experimental treatments included the control (CK), experimental warming (T, crop canopy temperature increased by ~2 °C), elevated O₃ concentration (O, O₃ concentration about 100 ppb) along with temperature enhancement (OT, elevated ~2 °C temperature plus 100 ppb O₃). The results showed that warming significantly increased the mean CO₂ fluxes (MCF) and the cumulative amount of CO₂ (CAC) from soil and soil-crop systems, while elevated O₃ and warming enhancement (OT) significantly reduced MCF and CAC. Besides, warming significantly reduced the biomass of winter-wheat, but it insignificantly decreased the biomass of soybean in the harvest period. The O and OT treatments significantly reduced the biomass of winter-wheat and soybean cropping systems in the harvest time. Both warming and elevated O₃ concentration decreased the temperature sensitivity coefficients (Q₁₀) in soil respiration during the experimental period. Overall, our results indicate that elevated O₃ concentration compensates the effect of warming on CO₂ emission to some extents, which has a positive feedback impact on the climate system.