Leaf vessel length and stem-node connectivity in woody angiosperms.

Xylem vessel length is an under-characterized trait, particularly within leaves. We quantified leaf vessel length distributions and examined nodal structure and morphology in nine woody species using silicone injection, microscopy, and microCT imaging. We tested how vessel length coordinates with leaf morphology, life history, and stomatal conductance. Leaf vessels were short (mean = 2.46 cm) and terminated with high frequency in the nodal region, with no open vessels extending from the leaf into the secondary xylem of the stem. Within a focal species, vessel diameter was positively correlated with stomatal conductance, indicating that wider vessels were capable of supporting greater transpiration rates. Across species, mean leaf vessel length was positively associated with both vessel diameter and leaf size. Deciduous species possessed wider vessels and larger leaves than evergreen ones, whereas simple and compound leaves did not differ. Vessel length, particularly the distribution of vessel endings, is a critical trait for understanding how plants balance hydraulic efficiency and safety from spread of embolism and pathogens. The leaf-stem junction is a hydraulic transition zone characterized by frequent vessel terminations and vascular reorganization, with implications for whole-tree hydraulic architecture.