Sex-specific responses of flower and leaf phenology to spring warming of a dioecious tree species

Spring phenology is closely linked to plant growth and reproduction and is highly sensitive to environmental changes. For dioecious species, the temporal overlap between female and male flowering is critical for their successful pollination. However, it remains largely unclear whether males and females respond differently to climate change and how this may influence the phenological synchrony between the sexes. By conducting twig experiments, we investigated how the flower and leaf phenology of male and female individuals of a dioecious tree species, Cercidiphyllum japonicum, responded to the changes in temperature and photoperiod. Male individuals flowered and unfolded their leaves earlier than female individuals in most cases, reflecting sexual dimorphism in spring phenology. Elevated temperature significantly advanced the flowering and leaf unfolding in both sexes, while shortened photoperiod had no significant effect on either phenophase. The time interval between flowering and leaf unfolding tended to be shortened under warming in males but not in females. Interestingly, the flowering time of females was more sensitive to temperature than that of males. These findings suggest that spring warming may paradoxically enhance reproductive fitness in this species by reducing the flowering time gap between sexes, highlighting the critical need to consider sex-specific responses when predicting population dynamics under climate change.