Comparative sectoriality in temperate hardwoods: hydraulics and xylem anatomy

In wood, lateral transport of water and minerals occurs readily in 'integrated' trees but is more restricted in 'sectored species'. Dye distribution and a novel hydraulic technique are used to quantify species-specific differences in sectoriality in three temperate hardwoods, Betula papyrifera, Acer saccharum and Quercus rubra. Sectoriality was related to key elements of xylem structure: intervascular pitting, vessel diameter and vessel grouping. Perfusion of 0.5% safranin through isolated roots showed root-to-branch dye transport was most extensive in B. papyrifera and least extensive in Q. rubra. To test sectorialty using hydraulics, 20 m M KCl solution was pushed at 0.1 MPa through 5-cm wood segments, before and after occluding the direct axial outlet with glue, with flow rate measured in grams of solution expelled over time. Direct ( axial) conductance ( g MPa-1 s(-1)) through unglued outlets was compared with indirect ( tangential) conductance around occluded outlets. Species with high indirect/direct conductance ratios ( Integration Index) are the most integrated. Integration Index ranged from 0.26 in B. papyrifera to 0.02 in Q. rubra. Macerates showed that B. papyrifera has much greater percentage of cell wall area covered with intervascular pits than does A. saccharum or Q. rubra. Vessel grouping was closest in B. papyrifera and vessels were most isolated in Q. rubra. Widest diameter vessels occurred in Q. rubra, where they concentrated in springwood. Intervascular pitting, vessel diameter and grouping are wood traits that contribute to the continuum of sectoriality in trees, and may influence the ability of tree species to dominate in homogeneous or in patchy environments. (c) 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150, 61-71.