Abstract: Cultivation of Citrus sinensis is wide-spread in various latitude areas in China. Based on observation and researches, it is found that within the same plantation, under identical management levels and at same age, the growth and development of Citrus sinensis are influenced by the length of illumination period caused by site factor variation. The nutritional and reproductive growths of Citrus sinensis are most favorable at an average diurnal illumination period of above 9.5 hours, secondarily of 8 hours and most unfavorable of below 6-6.5 hours.

Key words: δ13C, δ15N, maximum photosynthetic rate, water use efficiency, nitrogen use efficiency