Abstract: In this paper, the effects of nitrogen (N) fertilization on the wheat leaf photosynthesis under long-term elevated atmospheric CO₂ concentration (760 μmol·mol^-1) was studied, based on the measurements of photosynthetic gas exchange parameters and light intensity-photosynthetic rate response curves at jointing stage. Under the long-term elevated atmospheric CO₂ concentration, applying sufficient N could increase the wheat leaf photosynthetic rate (P_n), transpiration rate (T_r), and instantaneous water use efficiency (WUE_i). Comparing with those under ambient atmospheric CO₂ concentration, the P_n and WUE_i under the elevated atmospheric CO₂ concentration increased, while the stomatal conductance (G_s) and intercellular CO2 concentration (C_i) decreased. With the increase of light flux intensity, the P_n and WUE_i under the elevated atmospheric CO₂ concentration were higher those under ambient atmospheric CO₂ concentration, G_s was in adverse, while C_i and T_r had less change. At high fertilization rate of N, the G_s was linearly positively correlated with P_n, T_r, and WUE_i, and the G_s and C_i had no correlation with each other under the elevated atmospheric CO₂ concentration but negatively correlated under ambient atmospheric CO₂ concentration. At low fertilization rate of N, the G_s had no correlations with P_n and WUE_i but linearly positively correlated with C_i and T_r. It was suggested that under the elevated atmospheric CO₂ concentration, the wheat leaf P_n at low N fertilization rate was limited by non-stomatal factor.

Key words: elevated atmospheric CO₂ concentration, nitrogen fertilization rate, photosynthesis, wheat, land use change, habitat quality, InVEST, basin, BeijingTianjinHebei Area.