Comparison of anatomical characteristics and chemical compositions between sapwood and heartwood of Michelia macclurei

Understanding the anatomical and chemical properties of sapwood and heartwood is important for the utilization of wood. In this study, the anatomical characteristics and chemical compositions of sapwood (SW) and heartwood (HW) of Michelia macclurei Dandy were investigated and compared. Six locations at SW and HW were selected and studied. The wet chemical method and Fourier Transform Infrared Spectroscopy (FTIR) technology were used to analyze the chemical compositions in SW and HW. The results showed that the fiber wall thickness, fiber lumen diameter, fiber wall thickness-to-lumen ratio, vessel lumen diameter and vessel frequency were significantly different between SW and HW. However, the ray frequency did not differ significantly between SW and HW. Less lignin (22.42%) in HW than SW (25.56%), proved that cell walls in HW were not completely lignified. As the heartwood accumulated substances, the extractives in HW was significantly higher than SW. The FTIR relative absorbance of 1502 cm-1 of lignin decreased from SW to HW. The two-dimensional heteronuclear single-quantum coherence (2D-HSQC) NMR spectra showed that the main lignin substructure, β-O-4′ aryl ether, was higher in SW (66.99%) than HW (58.22%). The S/G ratio in SW was about 1.8 times higher than that in HW, indicating that SW had more S-lignin. The alkaloids, a class of antifungal extractives of Michelia, were found to be mainly present in HW. These results contribute to a better understanding of sapwood and heartwood properties, which is of value for the further utilization of Michelia macclurei Dandy.