Wood properties and chemical composition of the eccentric growth branch of Viburnum odoratissimum var. awabuki

Abstract

To clarify the wood properties and chemical composition of branches of Viburnum odoratissimum produced by unusual eccentric growth, we investigated growth strain (GS), basic density (D b), microfibril angle (MFA), elastic moduli (E L and E L/D b), creep deformation, cellulose crystalline features, and lignin structure in upper and lower sides of the branches, and considered the correlations among these factors. In most measuring positions, the distribution of GS showed that higher tensile GS was in the upper side and compressive GS was in the lower side of the branch, which combines GS features of reaction wood. However, the generation of GS in the lower side was different from that in compression wood, because E L/D b and MFA had a negative correlation. The creep compliance curves show that the upper-side wood had low rigidity and high viscosity, whereas the lower-side wood had large rigidity and low viscosity. Relative creep had a negative relation with MFA in the upper side, which is unusual. The cellulose crystalline features showed no obvious difference between both sides of the branch; however, the lignin with less β-O-4 proportion and less S units but more G units seemed to exist in the lower side because of a decreased syringyl/guaiacyl (S/G) molar ratio. This suggests that cell wall could be reinforced by lignin resulting in lower viscosity in the lower side of the branch. Additionally, the S/G ratio showed a relatively high correlation with GS in the lower side. These results suggest that lignin structure plays an important role in adapting to environmental changes during eccentric growth for V. odoratissimum.