Abstract: [Objective] To elucidate the effect of metaxenia on photosynthesis that promotes fruit enlargement in Carya cathayensis, the shape, gas exchange, chlorophyll content and chlorophyll fluorescence characteristics of C. cathayensis fruits pollinated with two different pollens during the fruit growth stages were measured. [Method] Two pollination combinations (C. cathayensis ×C.cathayensis or C. cathayensis ×C. illinoensis) were conducted in this study. The dynamic changes in photosynthetic area, dry mass, photosynthetic rate, chlorophyll content and chlorophyll fluorescence were investigated during the fruit growth stages. [Result] 1) The hickory fruits pollinated with pecan pollens (pp) were significant larger and greener than those pollinated with hickory pollens (hp). Compared with the hickory fruits pollinated with hp, the increasing rate of the surface area and dry mass per day per fruit was significant higher in hickory fruits pollinated with pp at the early and late fruit growth stages (from 50 to 73 d after pollination and from 103 to 120 d after pollination). The photosynthetic rate per area of exocarp in hickory fruits pollinated with pp was significantly higher than that in fruits pollinated with hp during 50 to 85 days after pollination. Moreover, a significant positive correlation was found between the dry mass increment and photosynthesis rate increment expressed on per fruit per day of hickory fruits. 2) The chlorophyll content of exocarp in fruits pollinated with pp was significantly higher than that in fruits pollinated with hp, and there was a significant positive correlation between the chlorophyll content and photosynthetic rate of exocarp in hickory fruits. 3) The Y, ETR and q_P in fruits pollinated with pp were significantly higher than those in fruits pollinated with hp at PAR of 1 265 μmol·m^-2s^-1. The light intensity of the maximum ETR in exocarp of hickory fruits pollinated with hp was significantly lower compared with that in fruits pollinated with pp during the fruit growth stages. The light intensity of the maximum ETR in exocarp of hickory fruits pollinated with hp significantly decreased at the late fruit growth stage (from 103 to 120 d after pollination), decreased by about 50%. The Y(NO) in exocarp of hickory fruits pollinated with hp significantly increased from 103 to 120 d after pollination. Compared with pericarp of hickory fruits pollinated with hp, the exocarp of fruits pollinated with pp had higher Y(II) and lower Y(NO). [Conclusion] At the early fruit growth stage (from 50 to 73 d after pollination), the faster increase in dry mass of the fruits pollinated with pp was due to the higher photosynthetic surface area and photosynthetic rate; at the late fruit growth stage (from 103 to 120 d after pollination), the faster increase in dry mass of the fruits pollinated with pp was due to the increased photosynthetic surface area. At the late fruit growth stage (from 103 to 120 d after pollination), the fruits pollinated with hp was more susceptible to light damage. It is suggested that the higher dry mass of fruits pollinated with pp might to related to the adaptability of high-light at the late growth stages.

Key words: hickory, exocarp, gas exchange parameters, chlorophyll fluorescence, biomass production