The sensitivity of ginkgo leaf unfolding to the temperature and photoperiod decreases with increasing elevation

Climate change substantially affects plant phenology, resulting in earlier vegetation onset across temperate and boreal regions. Phenological shifts caused by warming may alter species interactions across trophic levels because of species-specific responses, and influence the reproductive success of dioecious species if the phenological sensitivity to warming (S-T) differs between genders. We used twigs collected from male and female gingko trees at three elevations on Tianmu Mountain in eastern China. The twigs were cultivated in climate chambers to determine the effects of three temperatures (10, 15, and 20 degrees C) and two photoperiods (8 and 16 h). We observed slightly earlier leaf unfolding dates in male twigs (1 day), and a higher heat requirement (growing degree hours) for leaf unfolding in female (14,334 +/- 588 degrees C) compared to male twigs (13,874 +/- 551 degrees C). Similar responses to temperature (S-T = 3.7 days degrees C-1), photoperiod and elevation were observed across genders. The long photoperiod treatment shortened the time to leaf unfolding by 9.1 days, but temperature and photoperiod effects on leaf unfolding differed significantly depending on the elevation of the donor trees. Specifically, ST was higher (4.17 days degrees C-1) and the photoperiod effect on ST was larger (decreased by 1.15 days degrees C-1) at the lowest elevation than at the higher elevations (ST = 3.26 days degrees C-1; decreased by 0.48 days degrees C-1). This may be related to environment-induced local adaptations and self-protection mechanisms of trees at high elevations to avoid frost damage. Our results indicate that the photoperiod and genetic adaptations to local environments influenced the warming-induced phenological responses in ginkgo, but these responses were generally similar between the genders. For a given species, individuals in different climates may exhibit different phenological responses to higher temperatures, with individuals in warmer regions likely becoming increasingly limited by the photoperiod as the climate warms further.