Contrast in vulnerability to freezing-induced xylem embolism contributes to divergence in spring phenology between diffuse- and ring-porous temperate trees

Abstract

The spring phenology and growth strategy of temperate tree species can be strongly linked to their sensitivity to frosts, which deserve more profound investigations under the background of climate warming particularly considering the advancement of spring phenology as well as the increase in frequency and intensity of spring cold waves. Spring phenologies, stem radial growth characteristics, frost sensitivity of leaves and stem hydraulic systems were studied in five diffuse-porous and five ring-porous temperate tree species under a common garden condition. The results showed that the spring leaf phenology of the diffuse-porous species was one to two weeks earlier than that of the ring-porous species. The ring-porous species had significantly higher stem hydraulic conductivity than the diffuse-porous species (1.81 and 0.95 kg·m −1 ·s −1 ·MPa −1 , P < 0.05) but were more vulnerable to freeze-thaw induced xylem embolism than the latter. After a simulated freeze-thaw event, the average percentage loss of hydraulic conductivity in the current year shoots increased from 26.0% (native embolism) to 86.7% in the ring-porous species, while it only increased from 21.3% to 38.3% in the diffuse-porous species. The spring phenology was clearly correlated with vulnerability to freeze-thaw induced embolism, with the more vulnerable ring-porous species exhibited substantially delayed phenology to reduce risks of catastrophic hydraulic dysfunction during spring frosts. Nevertheless, ring-porous species can offset the postponed onset of growth and gained even higher annual growth due to significantly higher hydraulic efficiency and leaf gas exchange rates. Contrasts between ring-porous and diffuse-porous species in resistance to freeze-thaw induced embolism suggest that they face different selective pressures from early spring frosts, which may at least be partially responsible for their divergence in spring phenology and growth strategy and can potentially lead to different responses to climate regime shifts.