Effects of elevated air CO2 concentrations on the carbon and nitrogen contents of rice and winter wheat

Abstract

Investigating the effects of different air CO2 concentrations on the carbon (C) and nitrogen (N) contents of straw and roots of different generations of crops is crucial to predict crop responses to elevated CO2. We performed a field experiment with open-top chambers (OTCs) and applied consecutively elevating CO2 concentrations (120 ppm and 160 ppm during the investigated 2018 rice and 2018–2019 winter wheat seasons, respectively, with a consecutive increase of 40 ppm per year beginning from the first winter wheat–rice rotation season in November 2015) and a continuously elevated CO2 concentration of 200 ppm during each season. The results indicated that elevated CO2 concentrations generally increased the root C content of both rice and winter wheat. The most obvious effects between the treatments appeared in the crops grown from seeds harvested in the OTCs each season. An elevated CO2 concentration increased the rice root N content, with more obvious effects over multiple generations that had been planted in the OTCs for three or four growing seasons than on a single generation that was planted in the OTCs for only one growing season. An elevated CO2 concentration also induced an increase in the ratio of C to N (C/N) in the roots of rice and in the straw and roots of winter wheat. The C content of the rice and winter wheat roots increased significantly with increasing root N content. The enhancement effect of an elevated CO2 concentration on the C and N content and the C/N ratios in rice and winter wheat is more significant for multiple generations than for one generation.