Anatomy of the vessel network within and between tree rings of Fraxinus lanuginosa (Oleaceae)

Abstract

The three-dimensional (3-D) arrangement of vessels and the vessel-to-vessel connections in the secondary xylem of the stem of the ring-porous hardwood tree Fraxinus lanuginosa were studied in series of thick transverse sections with epifluorescence microscope and confocal laser scanning microscope. Vessels were traced in sequential sections, and vessel networks were reconstructed in two segments of wood with dimensions of 2 × 1.4 × 21.2 mm(3) and 2 × 1.4 × 5.8 mm(3) (tangential × radial × axial). The arrangement of vessels and intervessel pits were visualized by scanning electron microscopy in low-density polyethylene microcasts and on exposed tangential faces of growth-ring boundaries. The vessels deviated from the stem axis in the tangential direction and, to a lesser extent, in the radial direction. Some neighboring vessels were twisted around each other. Vessels that appeared solitary in single sections were found to be sequentially contiguous with a number of other vessels, forming networks that extended in the tangential direction and across growth-ring boundaries. In the 21.2-mm wood block, all earlywood vessels at the growth-ring boundary made contact with latewood vessels in the previous tree ring. Within a growth ring however, only a single contact was observed between individual earlywood and latewood vessels. Densely arranged intervessel pits were characteristic in the regions where adjacent vessels made contact with each other. Such bordered pits were abundant in the tangential walls of vessel elements adjacent to growth-ring boundaries. Therefore, bordered pits appear to provide the pathway for the radial transport of water via the vessel network across growth-ring borders. Fiber-tracheids, observed as terminal cells in the tree rings, might also contribute to the apoplastic transfer of water across ring borders.

Bordered pit structure and function determine spatial patterns of air‐seeding thresholds in xylem of Douglas‐fir (Pseudotsuga menziesii; Pinaceae) trees

“…The morphology of the pits will determine the water tension at which the tracheid becomes vulnerable to embolism. These pits (including both the borders and their membranes) may vary in morphology and frequency between species , within species (Jutte and Spit, 1968), among organs (Shane et al, 2000), and between earlywood and latewood in the same growth ring (Kitin et al, 2004). Therefore, the spatial distribution of pit morphologies will affect the spatial distribution of vulnerability to embolism, which in turn will determine the effect of drought on water availability at different locations within the tree.…”

Intégration des voies de transport de l’eau dans un érable : réponses du flux de sève à une ablation de branche

“…67 (2010) branch. Spreading of fluxes with tree height may occur due to tangential drift of conducting vessels around the stem axis, which has been shown as a general occurrence (Kitin et al, 2004;Zimmermann, 1983). The way for the tangential drift is shorter in the inner stem xylem, which evidently can explain the fact that responses on branch severing were detected only in the inner xylem of the opposite stem side (see Fig.…”

“…So, the problem of the topology of the vascular connections between roots and branches is quite difficult, especially for integrated species. Integration within the stem xylem may occur not only through intervessel pits of adjusted vessels (Orians et al, 2005), but also due to crossgraining of xylem vessels, which deviate from their axial path (Kitin, 2004;Zimmermann, 1983). For integrated topology it is still not clear which kind of integration and under which circumferences prevails: is it integration of independent pipes anatomically sharing space in the stem xylem due to the crossgrained network of xylem vessels or is it integration of pipes interconnected through pit membranes?…”

“…The cross-grained network of conducting vessels leads to their radial and especially tangential drift from the axial tree line (Kitin, 2004;Zimmermann, 1983), and thus to integration within the stem xylem, which increases with tree height. Integration of the axial pipes via intervessel pits was ignored, supposing that it should be predominantly responsible for horizontal transport (Kitin et al, 2004) and thus for water redistribution within the tree xylem, with its importance increasing under severe environmental conditions. Details of the experiments supporting the hypothesis of the study are described in the following section.…”

“…mineral nutrients (Orians et al 2004), measurements of branch hydraulic properties (Zanne et al, 2006), X-ray computed microtomography (Steppe et al, 2004) or complex microscopic analysis (Kitin et al, 2004). It was hypothesized that measurements of radial sap flow patterns in the stem xylem and their changes due to severing treatments would help to recognize axial water pathways leading from the opposite roots through the stem xylem to different fractions of the crown.…”