Abstract: In order to understand the effects of rootstocks on photosynthetic physiology of Huangguogan， trifoliate orange， red tangerine and orange were used as rootstocks，Huangguogan seedling tree was set as the control， the daily variation of parameters and photosynthetic response curves of net photosynthetic rate （Pn）， transpiration rate （Tr）， intercellular CO2 concentration （Ci） and stomatal conductance （Gs）， contant of ribulose 1，5biphosphate carboxylase/oxygenase （Rubisco） and Rubisco activase， and the expression of rbcS， rbcL and rca genes were determined and compared in fruit mature period. The results showed that the net photosynthetic rate curve showed a double peak type with a photosynthetic noon break， net photosynthetic rate of three kinds of grafted trees were higher than the seedling trees; the diurnal variation of transpiration rate showed a single peak type， and the diurnal changes of water use efficiency were double peak type. In addition， the leaves with orange rootstock showed higher carboxylase activity of Rubisco and net photosynthetic rate and higher expression levels of rbc and rca genes than those others. Comprehensive comparative analysis showed that the orange rootstock was suitable as rootstock for Huangguogan.

Key words: Huangguogan, photosynthetic characteristics, Rubisco, RCA, gene expression