Closed project (2013-2017) involving 3 partners (AGPF-INRA orléans, LMGC Laboratoire de Mécanique et Génie Civil, ECOFOG UMR Ecologie des Forêts de Guyane).
Coupled physiological and micro-mechanical approach on maturation stress generation in tension wood.
A key element of the biomechanical design of trees is their ability to generate large mechanical stresses in wood at the stem periphery. This function is necessary for the tree to control the orientation of its axes, and therefore to grow in height, maintain its branches at an optimal angle or achieve adaptive reorientations. This «maturation stress« appears in wood fibres at the end of the formation of their secondary cell wall, but the underlying biophysical process is still unknown. Understanding the mechanism of maturation stress generation is a question of paramount importance in tree physiology, with important technological outcomes regarding wood processing and also for biomimetic inspiration in material design. As this research needs to integrate knowledge from plant biology, chemistry, physics and mechanics, the project will be supported by three complementary partners, with excellent expertises on tree biomechanics, micromechanics, wood diversity, tree physiology and molecular biology. This partnership will be complemented with a large network of French and international laboratories covering extra-competences needed for the project. Two plant models are chosen, poplar will represent the species developing a specific unlignified gelatinous layer (G-layer) like most temperate species and simarouba will represent non-G-layer species like two third of tropical species. Whereas most researches have been concentrated on G-layer species, our project is a pioneer in the study of the maturation stress mechanisms in non-G-layer species. The strategy relies on i) the determination of both the structural organisation and the mechanical behaviour of wood constituents along the sequence of cell maturation from the cambium to the mature wood and ii) the identification of associated molecular triggers allowing these changes. The observations performed at different scales (macromolecular constituents, cell-wall layer, macroscopic wood), will feed a micro-biomechanical model that will be developed to test the consistency between hypothetic mechanisms and observations made at each level. The research plan is organised in 5 tasks (Molecular triggers, Cellulose and matrix organisation and behaviour, Cell-wall behaviour, Micro-mechanical modelling, Hypotheses testing) designed to solve this old question that still remains enigmatic.