Effects of nitrogen supply on the photosynthetic capacity of the hybrid citrus cultivar 'Huangguogan'

Abstract

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'.

Keywords

• apparent co2/light-compensation point; diurnal respiration; maximum fluorescence; mesophyll conductance; steady-state fluorescence.