Abstract: In order to provide the theoretical support for the change of maize physiological processes under global climate change based on the experimental data and provide the evidence for parameter adjustment for crop models, the effects of elevated atmospheric CO2 concentration (eCO2) and its interaction with nitrogen application on the dynamic of concentrations of carbon and nitrogen assimilates and the yield of maize, one of the C4 crops, were studied based on the free air CO2 enrichment (FACE) system. The summer maize variety ZHENGDAN 958 was planted to conduct the field experiments. Four treatments were set under two atmospheric CO2 concentrations, ambient CO2 concentration (aCO2, 400μmol·mol−1) and elevated CO2 concentration(eCO2, 550μmol·mol−1) at two nitrogen levels including zero nitrogen (ZN) and conventional nitrogen (CN, 180 kg N·ha−1) The maize yield and some other physiological parameters were measured including the concentration and dynamic of carbon assimilates (ie. soluble sugar, starch and total carbon), nitrogen assimilates (ie. nitrate, free amino acid, soluble protein, insoluble nitrogen compounds including cell wall-N and thylakoid-N, and total nitrogen), and C/N ratio since flowering of summer maize in the functional leaves. Results showed that: (1) The above-ground biomass and yield of summer maize did not show significant increase under eCO2 possibly due to unexpected disturbance from insect pests at this study. (2) Under eCO2, the concentration of carbon assimilates, including soluble sugar and starch, showed significantly (P<0.05) increase in the functional leaves after flowering. For the nitrogen assimilates, the concentration of some assimilates with simple components, including nitrate, free amino acids, soluble protein, as well as total N and C/N ratio showed increase to some extent (P>0.05); while the concentration of structural N components, including thylakoid-N and cell wall-N, were decreased significantly at later period after flowing, implying the synthesis of structural N components were impacted under eCO2. (3) Under N application, both the carbon assimilates (ie. soluble sugar and starch at most stages) and major nitrogen assimilates were increased significantly in the functional leaves after flowering, as well as the biomass and yield of summer maize. While the concentration of total C did not show significant change in the functional leaves. (4) N application under eCO2 could promote the concentration of simple fractions of carbon assimilate (ie. soluble sugar and starch at most stages) and initial nitrogen assimilates (ie. Nitrate, free amino acids and soluble protein) in the functional leaves of maize, as well as total C, above-ground biomass and yield. Therefore, under the future climate change characterized by increased atmospheric CO2 concentration, appropriate N management and regulation in physiological processes would be helpful in promoting the carbon and nitrogen assimilation and beneficial to the high yield and good quality of maize.

Key words: Maize(Zea mays L.), Elevated atmospheric CO2, Nitrogen fertilizer, Carbon and nitrogen metabolism