Axial Tracheids Widening Across Vein Orders in Ginkgo biloba Leaves and Their Relationship with Hydraulic Path Length

Leaves of vascular plants exhibit a tip-to-base xylem conduit widening pattern, which minimizes hydraulic resistance as leaves expand. The extent to which different leaf vein orders conform to this pattern remains largely unexplored, particularly in species with dichotomously branching veins. In this study, we focused on Ginkgo biloba, a model species with dichotomous venation, to explore tracheid variation across leaf vein orders and its linkage with hydraulic path length. Across 108 leaves from three sites, tracheid hydraulic diameter (D) scaled significantly with hydraulic path length (L) at an overall scaling slope of 0.33 (95% CI: 0.31–0.34, r2 = 0.53, p < 0.001). Scaling exponents differed significantly among sites and vein orders, and D decreased progressively with increasing vein order. This study provides a potentially valuable approach for investigating the effects of hydraulic path length on xylem conduit diameter and offers a framework for subsequent research on plant venation and hydraulic transport networks.