Diversity of anatomical structure of tension wood among 242 tropical tree species

Abstract

Angiosperm trees produce tension wood to actively control their vertical position. Tension wood has often been characterised by the presence of an unlignified inner fibre wall layer called the G-layer. Using this definition, previous reports indicate that only one-third of all tree species have tension wood with G-layers. Here we aim to (i) describe the large diversity of tension wood anatomy in tropical tree species, taking advantage of the recent understanding of tension wood anatomy and (ii) explore any link between this diversity and other ecological traits of the species. We sampled tension wood and normal wood in 432 trees from 242 species in French Guiana. The samples were observed using safranin and astra blue staining combined with optical microscopy. Species were assigned to four anatomical groups depending on the presence/absence of G-layers, and their degree of lignification. The groups were analysed for functional traits including wood density and light preferences. Eighty-six% of the species had G-layers in their tension wood which was lignified in most species, with various patterns of lignification. Only a few species did not have G-layers. We found significantly more species with lignified G-layers among shade-tolerant and shade-demanding species as well as species with a high wood density. Our results bring up-to-date the incidence of species with/without G-layers in the tropical lowland forest where lignified G-layers are the most common anatomy of tension wood. Species without G-layers may share a common mechanism with the bark motor taking over the wood motor. We discuss the functional role of lignin in the G-layer.

Do woody vines use gelatinous fibers to climb?

“…Our frequent observations of extraxylary G‐fibers complement recent findings that extraxylary tissues play important roles in movements that were previously attributed solely to xylem. For example, experiments on artificially inclined trees demonstrated that bark also influences plant posture (Ghislain et al ., 2019a,b), and Lehnebach et al . (2020) showed that phloem G‐fibers arranged in a trellis network produce higher tensile stress than species with a phloem trellis network of ordinary fibers do.…”

Tree growth forces and wood properties

“…11). 3), two species had a lignified G layer (Eschweilera & Qualea), one a peculiar multilayered G layer (Laetia) and three no G layer fibre (Jacaranda, Virola, Simarouba), according to a recent classification based on 242 tropical species (Ghislain et al 2019). Measurement of MFA on the 3 species represented in Fig.…”

“…Figure 12. Comparative anatomy of compression wood and normal wood for the conifer species CW: compression wood; NW: normal woodFor hardwoods, a majority of G-layer type TW (3 poplars, Miconia, Carapa, Ocotea, Cecropia, Eperua) were studied (Table3), two species had a lignified G layer (Eschweilera & Qualea), one a peculiar multilayered G layer (Laetia) and three no G layer fibre (Jacaranda, Virola, Simarouba), according to a recent classification based on 242 tropical species(Ghislain et al 2019). Measurement of MFA on the 3 species represented in Fig.13(Ruelle et al 2007) showed lower values for TW (2° to 14°) than for NW (10° to 35°), with some overlap around 10°-14°.…”

Wood and the Activity of Dead Tissue

“…For extended axial tensile stress generation, most hardwoods form tension wood fibers, which possess a characteristic G‐layer, which can be structurally very diverse, as recently investigated for tropical tree species. [ 57 ] The G‐layer is an additional layer, which can fill the entire lumen of the tension wood fiber (Figure 2 tension wood microscopy image and schematics and Figure 4E) and consists in many trees of almost pure cellulose with a microfibril angle of ≈0°. This results in an extremely high axial stiffness, which is beneficial for high tensile stresses, but only if a certain contractibility is allowed at the same time.…”