Maturation Stress and Wood Properties of Poplar (Populus × euramericana cv. ‘Zhonglin46’) Tension Wood

Understanding the maturation stress and wood properties of poplar tension wood is critical for improving lumber yields and utilization ratio. In this study, the released longitudinal maturation strains (RLMS), anatomical features, physical and mechanical properties, and nano-mechanical properties of the cell wall were analyzed at different peripheral positions and heights in nine artificially inclined, 12-year-old poplar (Populus × euramericana cv. ‘Zhonglin46’) trees. The correlations between the RLMS and the wood properties were determined. The results showed that there were mixed effects of inclination on wood quality and properties. The upper sides of inclined stems had higher RLMS, proportion of G-layer, bending modulus of elasticity, and indentation modulus of the cell wall but a lower microfibril angle than the lower sides. At heights between 0.7 m and 2.2 m, only the double-wall thickness increased with height; the RLMS and other wood properties such as fiber length and basic density fluctuated or changed little with height. The RLMS were good indicators of wood properties in the tension wood area and at heights between 0.7 m and 1.5 m. The results of this study present opportunities to better understand the interactions and effects of these two phenomena, which both occur quite frequently in poplar stands and can influence the wood quality of valuable assortments.