Divergence in leaf phenology and stem growth patterns in four temperate tree species is tightly coupled to their differences in hydraulic strategies

Abstract The diversified patterns of seasonal changes in tree growth, including leaf phenology and stem radial growth dynamics, reflect inter-specific differences in adaptive strategies to the temperate climate regime with a strong seasonality. Quantifying the inter-specific differences in these patterns would deepen our understanding in the diversified adaptive characteristics of temperate trees but such information is yet limited. We monitored leaf phenology and stem radial growth dynamics in four temperate tree species commonly found in Northeast China (Acer truncatum, Tilia mandshurica, Juglans mandshurica, and Quercus mongolica) with a special reference to their divergent adaptations in maintaining hydraulic integrity over the winter. Our results showed that the two diffuse-porous species had significantly earlier leaf phenologies but later initiation of radial growth than the ring- and semi-ring-porous species. In the ring-porous species Q. mongolica, stem radial growth related to new xylem formation initiated much earlier than its leaf flush. This reflects the need to re-establish hydraulic function that has been severely damaged over the winter by freeze-thaw cycles. In contrast, despite being a semi-ring-porous species with large vessels vulnerable to frost-induced embolism, J. mandshurica is capable of generating positive pressure for embolism repair. This ability allowed it to achieve full leaf expansion far earlier than the new growth of stem xylem, much like the two diffuse-porous species. These findings reveal that divergence in one aspect of adaptation, such as hydraulics, can involve adaptive differentiation in suite of other related functions. These adaptations collectively shaped the diversified adaptive strategies of co-occurring temperate tree species.