Origin of unusual behaviors of the tension wood cell wall and its biomechanical functions

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In the present study, the mechanism responsible for unusual behaviors and biomechanical functions of tension wood fiber was investigated in relation to the formation of the gelatinous layer (G-layer) .First, the deformation process of an isolated TW fiber caused by a certain biomechanical state change was formulated mathematically. And, the tension wood (TW) properties from a 70-year-old-specimen of Acer sieboldianum Miq. were analyzed by using the G-fiber model. The roles of the G-layer on the origins of (1) a high tensile growth stress, (2) a large longitudinal Young's modulus, and (3) a high longitudinal drying shrinkage in the TW xylem were discussed on the basis of the simulations using the G-fiber model.Next, the mechanism responsible for unusual hygro-mechanical properties of tension wood containing the gelatinous layer (G-layer) was investigated for the oblique upright branch of a 29-year-old Keyaki (Zelkova serrata) and the leaning stems of a 75 and a 40-year-old Kunugi oak (Quercus acutissima) trees. The result suggests that in the green state, the polysaccharide matrix in the G-layer behaves as a water-swollen gel ; however, it is transformed into a condensed and hard-packed structure by strong surface tension during moisture desorption, which is a form of xero-gelation. However, in the L-layer, condensation and subsequent xero-gelation of the polysaccharide matrix was prevented by the hydrophobic lignin that mechanically reinforces the matrix.