Anatomical groups of tension wood defined for this study. Unlignified G-layer stained in blue in Cecropia palmata (a), lignified G-layer stained in red in Sextonia rubra (b) and No G-layer in Theobroma grandiflorum.
Gravitropic movements in angiosperm woody stems are achieved through the action of bark and/or wood motor, depending on the bark and wood fibre anatomy (with trellis structure or not; with G-layers or not). Bark motor is as efficient as wood motor to recover from tilting in young trees of 21 tropical species.
Context Angiosperm trees produce tension wood to control their orientation through changes in stem curvature. Tension wood is classified into 3 anatomical groups: with unlignified G-layer, with lignified G-layer and without G-layer.
Aims This study aimed at assessing whether this anatomical diversity reflects a diversity in efficiency of gravitropic movement.
Methods The study was conducted on tropical seedling from the three anatomical groups. Seedlings were staked and grown tilted. At the end of the experiment, changes in curvature when releasing the stem from the stake and when removing bark were measured. Three parameters were computed to compare the global efficiency of gravitropism (stem gravitropic efficiency) and the specific efficiency of motor mechanism based on wood (maturation strain of tension wood) and bark (standardized debarking curvature).
Results The maturation strain of tension wood was similar between species with unlignified and lignified G-layer. Species without G-layer exhibited low maturation strain and large debarking curvature, showing they rely on bark for gravitropism. Bark and wood achieved similar motor efficiency.
Conclusion Lignin does not affect the generation of tensile stress in the G-layer. Bark can be as efficient as wood as a motor of gravitropic movements.
Bark, Biomechanics, G-layer, Lignification, Tension wood, Tropical rainforest
Ghislain, B., Alméras, T., Prunier, J. et al. Annals of Forest Science (2019) 76: 107. https://doi.org/10.1007/s13595-019-0899-7
The datasets generated during and/or analysed during the current study are available in the Data INRA repository (Ghislain et al. 2019) at https://doi.org/10.15454/DU1O18.