Abstract: The photosynthetic characteristics of leaves in 7-year-old guanximiyou pomelo variety under field conditions were studied by using the Li-6400 portable photosynthesis system. The results were as follows : (1) The diurnal variation of net photosynthetic rate (P_n) of peripheral leaves in sunny days presented bimodal carve , the first peak occurred at 8:00- 10:00 , P_n was 15.77μmol·m^-2·s ^-1 , the second peak occurred after 14:00 , the value was lower than the first one ; In overcast days , the daily change of P_n had one peak , the value approach the first peak value of P_n in sunny days ; in both sunny and overcast days , the diurnal variation of P_n of inner leaves showed the one or two peak or indention carve. (2) The seasonal variation of P_n also approach bimodal carve by the average of P_n. (3) Among shoots in different months , there were differences in the responses of leaves P_n to light intensity and CO₂ . The light compensate and saturated point of leaves was 16～46μmol·m^-2·s ^-1 and 1 026 - 1 656 μmol·m^-2·s ^-1 respectively , the apparent quantum efficiency between 0.01725 and 0.05431 , these showed that the leaves of guanximiyou had the higher utilization efficiency on weak light and in strong light ; the CO₂ compensate and saturated point was 51 - 80μmol·mol - 1 and 822 - 926μmol·mol ^-1 respentively , the carboxying efficiency between 0.01769 and 0.05191. (4) P_n had obvious positive relationship with Cond , Trm and PAR, most of them were obvious or remarkable. P_n had obvious negative relationship with Ci , majority of them were remarkable. There were complex relationship between P_n and Tair , Tl , RH , Vpdl . (5) There were no marked relation between P_n and the chlorophyll content and specific leaf weight (SLW) of leaves. (6) The proper temperature of photosynthesis were 24 - 34 ℃.

Key words: Citrus L., Citrus grandies L., Photosynthetic characteristic, Physo-ecological factors