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Pot experiments were conducted to determine the effects of nitrogen (N) fertilization rate on the photosynthetic efficiency of 'Huangguogan' (Citrus reticulata × Citrus sinensis). We observed that plant growth increased with increasing N. Maximum values for parameters evaluated were recorded for an N addition rate of 120 g per year. Leaf chlorophyll content was positively correlated with the leaf N content. The relative reduction in photosynthetic rate (PN) at high N (150 and 180 g) correlated with the parallel decreases in the leaf N content. Rubisco activity was positively correlated with the initial slope of the PN/Ci response curve.indicating that N supplement improved photosynthesis by enhancing carboxylation and CO2 diffusion, photosynthetic capacity increased with N supply up to 120 g. Thereafter, the rate of increase declined with any further increase in N supply. These results provide a reference for a rational application of nitrogen fertilizer in orchards of 'Huangguogan'.