Distribution of vessel size, vessel density and xylem conducting efficiency within a crown of silver birch (Betula pendula)

Abstract

Spatial patterns in vessel diameter, vessel density and xylem conducting efficiency within a crown were examined in closed-canopy trees of silver birch (Betula pendula). The variation in anatomical and hydraulic characteristics of branches was considered from three perspectives: vertically within a crown (lower, middle and upper crown), radially along main branches (proximal, middle and distal part), and with respect to branch orders (first-, second-and third-order branches). Hydraulically weighted mean diameter of vessels (D h ) and theoretical specific conductivity of the xylem (k t ) exhibited no vertical trend within the tree crown, whereas leaf-specific conductivity of the xylem (LSC t ) decreased acropetally. Variation in LSC t was governed by sapwood area to leaf area ratio (Huber value) rather than by changes in xylem anatomy. The acropetal increase in soil-to-leaf conductance (G T ) within the birch canopy is attributable to longer path length within the lower-crown branches and higher hydraulic resistance of the shade leaves. D h , k t and LSC t decreased, while vessel density (VD) and relative area of vessel lumina (VA) increased distally along main branches. A strong negative relationship between vessel diameter and VD implies a trade-off between hydraulic efficiency and mechanical stability of xylem. D h and VD combined explained 85.4% of the total variation of k t in the regression model applied to the whole data set. Xylem in fast-growing branches (primary branches) had greater area of vessel lumina per unit crosssectional area of sapwood, resulting in a positive relationship between branch radial growth rate and k t . D h , k t and LSC t decreased, whereas VD increased with increasing branch order. This pattern promotes the hydraulic dominance of primary branches over the secondary branches and their dominance over tertiary branches. In this way crown architecture contributes to preferential water flow along the main axes, potentially providing better water supply for the branch apical bud and foliage located in the outer, betterinsolated part of the crown.

Crown architecture and its role in species interactions in mixed boreal forests

“…Scaling of conduit diameter with distance from the apex was observed inside the branches and stem when a defined growth ring was followed. Similar results regarding various species have been shown before (Sanio according to Bailey and Shepard 1915;Zimmermann 1978a;Tyree and Zimmermann 2002;Anfodillo et al 2006;Coomes et al 2007;Sellin et al 2008). However, scaling was negligible in the stem compared to more distal crown parts and steeper in B. pendula compared to the conifers (see also Mencuccini et al 2007).…”

“…Conduit frequency was also lower in the lateral branches of the conifers compared to the main branches, but no difference was found in B. pendula. Earlier studies on deciduous species have shown a decrease in conduit diameter and an increase in conduit frequency from the main to the lateral branches (Atala and Lusk 2008;Nygren and Pallardy 2008;Sellin et al 2008). Suggested biological mechanisms behind the acropetal decrease in cell size are distance from the auxin source (Aloni 1987;2001) and the turgor pressure gradient as turgor pressure decreases with increasing tree height leading to reduced cell expansion (Koch et al 2004;Woodruff and Meinzer 2011).…”

“…Conduit tapering as a function of the number of tree segments is assumed to be continuous at the whole-tree level and the number of conduits is unchanged throughout the entire crown. The WBE model has gained contradictory results concerning stems (Anfodillo et al 2006;Coomes et al 2007;Mencuccini et al 2007) and only few studies have considered branches in addition to the main stem (Atala and Lusk 2008;Sellin et al 2008) when testing the WBE theory. When branches have been considered, the whole-tree conduit tapering pattern has not been continuous at the tree level (Mencuccini et al 2007;Atala and Lusk 2008;Nygren and Pallardy 2008;Sellin et al 2008).…”

“…The empirical data set for hydraulic architecture was rather unique as it covered the whole tree, including below-and above-ground parts and different branching hierarchies (see also Atala and Lusk 2008;Nygren and Pallardy 2008;Sellin et al 2008). Hydraulic architecture measurements were connected with detailed architectural measurements covering the branching topology, which enabled various inter-linkage analyses.…”

Anatomical Characteristics of Garcinia lucida (Vesque) and Scorodophloeus zenkeri (Harms) Wood and Debarking Response in the South Region Cameroon

“…As trees consume large amounts of water, they have to develop mechanisms for protection against disturbance of their water balance whereas they should be able to restore the water pathway. Both the diameter and the density of vessels directly influence conductivity (Christensen-Dalsgaard, Fournier, Ennos, & Barfod, 2007;Sellin, Rohejarv, & Rahi, 2008).…”