Are radial changes in vascular anatomy mechanically induced or an ageing process? Evidence from observations on buttressed tree root systems

Abstract

To investigate the effect of changes in mechanical loading conditions on radial anatomical patterns, we here compare the trunk with the roots in two locations of three species of buttressed trees. The proximal part of the buttress roots is highly mechanically loaded throughout juvenile growth whereas the distal part of the buttresses is though to be mechanically unimportant at formation but become progressively more mechanically loaded during growth. We measured the frequency and diameter of the vessels and the vessel area fraction, and from this calculated the specific conductivity of tissue samples of the core-, intermediate-and outer wood. As in previous studies there was an increase in vessel size, vessel area fraction and specific conductivity from the pith to the bark in the trunk. In the proximal part of the buttress roots, however, there was no increase in vessel size and conductivity from core wood and out in agreement with the high mechanical loading found here throughout growth. There was instead a decrease in vessel size, vessel area fraction and specific conductivity from core-to outer wood in the distal part of the buttress roots in accordance with the increase in mechanical loading. Hence, it appears that the radial anatomical patterns are not a passive function of cambial ageing but may be modified in response to local mechanical loading.

The decreasing radial wood stiffness pattern of some tropical trees growing in the primary forest is reversed and increases when they are grown in a plantation

“…Therefore, juvenile wood in trees is not by default more flexible than mature wood, and increasing wood stiffness in trees is not a function of passive cambial aging. Instead, wood is produced as a function of the imposed environmental constraints (Christensen-Dalsgaard et al 2008).…”

Interrelations between hydraulic and mechanical stress adaptations in woody plants

“…Further, the generally observed pattern 16,17 that vessel size increases radially from the pit to the bark was not observed throughout the structure. 18 In the proximal parts of the buttress roots, which are highly mechanically loaded throughout growth and development, the vessels maintained the small size found at the pith throughout the transect. In the distal parts of the buttress roots, in which the mechanical loading increases during growth, the vessels decreased rather than increased in size from the pith to the bark.…”

“…In the distal parts of the buttress roots, in which the mechanical loading increases during growth, the vessels decreased rather than increased in size from the pith to the bark. 18 Since the adaptation of the xylem tissue towards re-enforcing highly strained areas appear associated with changes in the vessel anatomy reducing the conductivity, radial changes in vessel size may not only be a function of cambial ageing, but also influenced by changes in stresses during growth.…”

Convergent Vessel Diameter–Stem Diameter Scaling across Five Clades of New and Old World Eudicots from Desert to Rain Forest

“…There are centuries' worth of literature documenting wider conduits in larger stems (recent examples include Carlquist 1966Carlquist , 1969Carlquist , 1984, and many others; Aloni and Zimmermann 1983;Rury 1985;Baas et al 1988;Ewers et al 1990;Butterfield et al 1993;Lens et al 2004;Olson and Rosell 2006;Wheeler et al 2007;Christensen-Dalsgaard et al 2008;Terrazas et al 2008;Zach et al 2010; Vá zquez-Sá nchez and Terrazas 2011). However, the notion that stem size should predict average vessel dimensions seems contradicted by the reiterated observation that average vessel diameter appears to reflect climate.…”