Abstract:

Objective: This study was carried out with the aim to provide scientific bases for the wood processing and utilization of Catalpa bungeana wood through the characterization of the heterogeneity of chemical compositions in various heights and radial regions. Method: The contents of benzyl alcohol extracts, polysaccharides and lignin of the heartwood and sapwood at various heights of C. bungeana wood were analyzed. The structural features of the lignin in the corresponding regions were also characterized through whole cell wall dissolving system combined with two-dimensional heteronuclear single-quantum coherence NMR technique. Result: The contents of the benzyl alcohol extracts in sapwood of C. bungeana wood were higher than those in the heartwood. More extracts were found in the heartwood near the sapwood compared with those in the heartwood near the tree heart. There were some differences in the chemical compositions of the extracts between the sapwood and heartwood of C. bungeana. However, no relationship could be found between the extract contents and tree heights, and the differences in extract content between sapwood and heartwood at different heights were identical. The lignin content in sapwood of C. bungeana was lower than that in heartwood. However, no relationship could be found between the lignin contents and heights. The lignin of C. bungeana wood was made up of guaiacyl(G) and syringyl(S) phenylpropane units. The molecular structure of the lignin at various heights of the C. bungeana wood was similar with each other. However, more β-5' linkages could be found in the lignin of the heartwood as compared with the lignin of the sapwood. Xylan was the predominant polysaccharide in hemicelluloses of the C. bungeana wood. The content of the polysaccharides in sapwood was higher than that in heartwood. However, no obvious differences in the content of the polysaccharides in the wood obtained from various heights. Conclusion: There were obvious differences in content and molecular structure of the chemical compositions between sapwood and heartwood of the C. bungeana. The accumulation of lignin and biosynthesis of chromogenic substances both occurred during the formation of heartwood of C. bungeana. Some differences in content of the chemical compositions could also be found in the wood at various heights of the C. bungeana. However, the differences had nothing to do with the tree heights. The molecular structures of the chemical compositions in a specific region at various treat heights were almost the same. The differences of chemical composition content and properties in radial direction should be taken into account during the processing of the C. bungeana wood.

Key words: Catalpa bungeana wood, chemical compositions, extracts, lignin, molecular structure, heterogeneity