Axial conduit widening in woody species: a still neglected anatomical pattern

Abstract

Within a tree the lumen of the xylem conduits varies widely (by at least 1 order of magnitude). Transversally in the stem conduits are smaller close to the pith and larger in the outermost rings. Axially (i.e. from petioles to roots) conduits widen from the stem apex downwards in the same tree ring. This axial variation is proposed as being the most efficient anatomical adjustment for stabilizing hydraulic path-length resistance with the progressive growth in height. The hydrodynamic (i.e. physical) constraint shapes the whole xylem conduits column in a very similar way in different species and environments. Our aim is to provide experimental evidence that the axial conduit widening is an ineluctable feature of the vascular system in plants. If evolution has favoured efficient distribution networks (i.e. total resistance is tree-size independent) the axial conduit widening can be predicted downwards along the stem. Indeed, in order to compensate for the increase in path length with growth in height the conduit size should scale as a power function of tree height with an exponent higher than 0.2. Similarly, this approach could be applied in branches and roots but due to the different lengths of the path roots-leaves the patterns of axial variations of conduit size might slightly deviate from the general widening trend. Finally, we emphasize the importance of sampling standardization with respect to tree height for cor- rectly comparing the anatomical characteristics of different individuals

Root to branch wood anatomical variation and its influence on hydraulic conductivity in five Brazilian Cerrado species

“…Vessel diameter is a crucial parameter in the identification of plant adaptation strategy to survive in specific environmental conditions (Sperry et al 2006). Available literature indicates that the variation in vessel diameter is associated with habitat of the tree species and at various height of a tree (Anfodillo et al 2013).…”

Earlywood vessel features in Quercus faginea: relationship between ring width and wood density at two sites in Portugal

“…In Q. alba, also belonging to the white oaks subgroup as Q. faginea, Phelps & Workman (1994) found that site quality was only expressed in the vessel proportion of trees at younger ages. According to Anfodillo et al (2013), tree size largely contributes to determine the vessel diameter, meaning that for the same age trees at site 1 seem to be taller showing wider vessels than trees grown at site 2. The decrease of ring width with age corresponded to a more constant vessel area and number, and to an increase of vessel frequency and proportion.…”

“…Recently, the number of studies focusing on the variation of vessel features (e.g., with age, growth and site) and their relation to other wood characteristics (e.g., density) has increased, although data is still scanty and results are often species-specific. The main tendencies in studies on vessel diameter variation have been recently discussed by Anfodillo et al (2013), with special attention to the relationship between axial conduit widening and tree height.…”

“…Recently, the number of studies focusing on the variation of vessel features (e.g., with age, growth and site) and their relation to other wood characteristics (e.g., density) has increased, although data is still scanty and results are often species-specific. The main tendencies in studies on vessel diameter variation have been recently discussed by Anfodillo et al (2013), with special attention to the relationship between axial conduit widening and tree height.Vessels are key contributors to wood density, that is inversely proportional to their size and number (Savidge 2003). In oaks, vessel proportion (i.e., the percentage of xylem cross-section occupied by vessels) is one of the major anatomical factors affecting latewood density (Rao et al 1997) and specific gravity (Zhang & Zhong 1992).…”

ECOLOGIC FEATURES OF WOOD ANATOMY OF Casearia sylvestris SW (SALICACEAE) IN THREE BRAZILIAN ECOSYSTEMS

“…Current researches also indicate that observed differences, when considering the diameter of xylem vessel among different environments, are primarily driven by plant length (diameter's and trunk's height). Those are strictly related to the weather conditions and indirectly lead to a relation between vessel sizes and climate (ANFODILLO et al 2013;OLSON;ROSELL, 2013;LONGUI et al 2014).…”