Global environmental change affects plant physiological and ecosystem processes.The interaction of elevated CO2,drought and nitrogen(N) deficiency result in complex responses of C4 species photosynthetic process that challenge our current understanding.An experiment of maize(Zea mays L.) involving CO2 concentrations(380 or 750 μmol mol-1,climate chamber),osmotic stresses(10% PEG-6000,-0.32 MPa) and nitrogen constraints(N deficiency treated since the 144th drought hour) was carried out to investigate its photosynthesis capacity and leaf nitrogen use efficiency.Elevated CO2 could alleviate drought-induced photosynthetic limitation through increasing capacity of PEPC carboxylation(V pmax) and decreasing stomatal limitations(SL).The N deficiency exacerbated drought-induced photosynthesis limitations in ambient CO2.Elevated CO2 partially alleviated the limitation induced by drought and N deficiency through improving the capacity of Rubisco carboxylation(V max) and decreasing SL.Plants with N deficiency transported more N to their leaves at elevated CO2,leading to a high photosynthetic nitrogen-use efficiency but low whole-plant nitrogen-use efficiency.The stress mitigation by elevated CO2 under N deficiency conditions was not enough to improving plant N use efficiency and biomass accumulation.The study demonstrated that elevated CO2 could alleviate drought-induced photosynthesis limitation,but the alleviation varied with N supplies. Global environmental change affects plant interaction and ecosystem processes. The interaction of elevated CO2, drought and nitrogen (N) deficiency in complex responses of C4 species photosynthetic process that challenge our current understanding. An experiment of maize (Zea mays L.) involving CO2 concentrations (380 or 750 μmol mol-1, climate chamber), osmotic stresses (10% PEG-6000, -0.32 MPa) and nitrogen constraints (N deficiency treated since the 144th drought hour) were carried out to investigate its photosynthesis capacity and leaf nitrogen use efficiency. Elevated CO2 could alleviate drought-induced photosynthetic limitation through increasing capacity of PEPC carboxylation (V pmax) and decreasing stomatal limitations (SL). The N deficiency exacerbated drought-induced photosynthesis limitations in ambient CO2. Elevated CO2 partially alleviated the limitation induced by drought and N deficiency through improving the capacity of Rubisco carboxylation (V max) and decreasing SL. Plants with N deficiency trafficking more N to their leaves at elevated CO2, leading to a high photosynthetic nitrogen-use efficiency but low whole-plant nitrogen-use efficiency. Stress mitigation by elevated CO2 under N deficiency conditions was not enough to improving plant N use efficiency and biomass accumulation. The study demonstrates that elevated CO2 could alleviate drought-induced photosynthesis limitation, but the alleviation varied with N supplies.