Objective  The differences of reproductive compensation mechanism, resource allocation and adaptive strategy between male and female plants of relict plant Cercidiphyllum japonicum under the influence of reproductive pressure were discussed in order to provide some references for the study of physiological ecology of dioecious tree species in Tertiary relict plants under the background of global climate change.

Method In this study, C. japonicum, a tertiary relict dioecious plant originated from the Cretaceous in Beijing National Botanical Garden, was used as the research object. The morphology, photosynthetic parameters, chlorophyll content, chlorophyll fluorescence parameters, stoichiometric characteristics and defensive substance content of male and female plants at different developmental stages in the growing season were dynamically monitored and correlation analysis was performed.

Result (1) Under the influence of high temperature period in summer, the photosynthetic capacity of male and female plants of C. japonicum decreased to a certain extent, which was manifested by the decrease of net photosynthetic rate and the decrease of stomatal conductance and transpiration rate to reduce water loss. The photoprotection strategy was used to protect itself from heat and photoinhibition, reduce the maximum photochemical quantum yield and photochemical quenching coefficient, increase non-photochemical quantum yield, increase antioxidant enzyme activity to enhance tissue antioxidant activity, and increase flavonoid secondary metabolites to enhance stress resistance. (2) The single leaf area, specific leaf mass, annual twig length and leaf expansion efficiency of female plants were significantly higher than those of male plants. The photosynthetic rate, water use efficiency, chlorophyll a, total chlorophyll content, maximum photochemical yield and anthocyanin content of female plants were significantly higher than those of male plants from July to August.

Conclusion Female plants have a reproductive cost compensation mechanism, which uses higher photosynthetic capacity for reproductive compensation, and increases resource input for growth and reproduction at the expense of chemical defense, and adopts a ‘radical’ adaptive strategy, while male plants invest more resources for defense and adopt a ‘conservative’ adaptive strategy.