Study reveals coordinated evolution of xylem and bark hydraulics in temperate tree species
A new study on eight temperate Rosaceae tree species found that xylem and bark hydraulic traits are functionally coordinated, with more permeable bark developing alongside more efficient but embolism-vulnerable xylem. The research, published on bioRxiv, examined branches across species with different ecological preferences and linked these traits to climate variables such as temperature, vapor pressure deficit, and isothermality. The findings suggest that drought resistance in woody plants cannot be fully understood by studying xylem function alone, and that bark traits must be considered as part of an integrated hydraulic strategy.
Researchers assessed hydraulic coordination between xylem and bark in branches of eight temperate woody Rosaceae species, measuring xylem hydraulic efficiency and safety alongside bark traits governing water permeability, hygroscopic water exchange, water storage, and anatomy. They found that bark water vapor conductance (Gbark) increased with both maximum xylem hydraulic conductivity and xylem vulnerability to embolism (P50), indicating that species with more efficient but more drought-vulnerable xylem also developed more permeable bark. Species with higher Gbark also showed faster rehydration from atmospheric water vapor, suggesting a functional link between bark permeability and hygroscopic water uptake. Both Gbark and P50 showed phylogenetic conservation and were associated with climatic factors including air temperature, vapor pressure deficit, and isothermality. Species from warmer, high-VPD environments with greater diurnal temperature variability tended to combine higher bark permeability with more embolism-vulnerable xylem, pointing to a climate-driven shift from embolism avoidance toward embolism tolerance strategies. The authors conclude that xylem and bark hydraulics in Rosaceae co-evolved along gradients of evaporative demand, and that a complete picture of woody angiosperm drought resistance requires integrating bark function into hydraulic frameworks.
What's missing
As a preprint posted on bioRxiv, this study has not yet undergone formal peer review, so its methods and conclusions have not been independently validated by external experts. The study is limited to eight Rosaceae species in temperate zones, which may constrain the generalizability of findings to other plant families, growth forms, or climate regions. The authors do not appear to address whether the observed bark-xylem coordination holds under experimentally induced drought conditions, leaving open questions about mechanistic causality versus correlation.
What different sources said
- bioRxivCenter
The coordination between xylem and bark hydraulics in temperate Rosaceae species
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