Multi-layered structure of wood cell wall among hybrid poplars and its affect on mechanical properties

Tree hybridization is important in enhancing tree quality, adaptability, and genetic variability; however, the molecular basis of cell wall at the sublayer scale that contributes to superior performance remains unclear. This study adopted a new perspective and chose three poplar clones with parent-offspring relationship as material. The cellulose structure, lignin content, morphology of cells were analyzed, and the relationship between cell wall multi-layered structure and mechanical properties was explored. As the result, crystallinity of the Nanyang poplar, the hybrid progeny is the highest, ascribing to its larger crystallite width (3.90 nm) and length (9.02 nm), while its microfibril angle (MFA) is smaller and not significantly different from the parents (Clone No. 50, Clone No. 36) with low impact on its mechanical properties. Besides, Nanyang poplar with the highest thicker fiber cell wall and larger wall-to-lumen ratio. Superior microstructure result in Nanyang poplar with the highest macro-mechanical properties, including modulus of elasticity (MOE), modulus of rupture (MOR), hardness, compressive strength; as well as supreme cell wall mechanical properties. Correlation analysis results showed that, strongest correlation was observed between the degree of crystallinity and the macro-mechanical properties of wood, specifically MOE, MOR and compressive strength. Additionally, a significant correlation was found between lignin content and the hardness of wood.