Water-stressed or not, the mechanical acclimation is a priority requirement for trees
Periodic bending of young poplars increase the wood production whatever their hydric status; especially in the most highly stressed zones; improving the mechanical behaviour of the stem.
The ability of trees to acclimate the building of their structures to windy conditions under various hydric conditions is essential in the context of the predicted climate changes. In this study, we investigated the biomechanical responses of young poplar trees to periodic controlled bending stimulations that mimic the mechanical effect of trees growing under windy conditions. This treatment was conducted for 5 months in well-watered conditions or under hydric stress. Results demonstrate the high impact of thigmomorphogenesis on growth processes, even under the water shortage. While axial growth was reduced by mechanical stimulations and hydric stress, radial growth was strongly increased by the periodic stem bending. The secondary growth was preferentially increased in the direction of highest longitudinal strains leading to the ovalisation of the cross-section. This ovalisation yielded 16%, regardless the hydric condition and generated a huge increase of the bending rigidity of the trees (+ 212%). Further, we observed a differential growth between the side growing under tension and the side growing under compression. A Finite Element model was built to investigate the mechanical benefits of the anisotropic cross-section shapes. This FE model enlightened the modulation of the spatial stress distribution that lead to a reduction of the stress in the weakest zones of the trunk; suggesting an improvement of the mechanical safety margin of wood. Thigmomorphogenesis acclimation appears as a complex and costly, but necessary process for the long-term mechanical support of the trees, even under hydric stress conditions.
KeywordsMechanical stress Hydric stress Tree acclimation Thigmomorphogenesis Tree biomechanics Wood
The authors thank Christelle Boisselet, Patrice Chaleil, Pierre Conchon, Aline Faure, Brigitte Girard, Stéphane Ploquin and Romain Souchal (UMR UCA-INRA PIAF) for their technical support and Evelyne Toussaint and Joseph Gril (UMR UCA-Institut Pascal) for constructive discussions and suggestions. This work was supported by grants from the Auvergne-Rhônes-Alpes Regional Council and from EFPA department of National Institute for Agronomic Research (INRA).
Compliance with ethical standards
Conflict of interest
Authors declare that they have no conflict of interest.
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