The ratio of lignin substructures and crystallinity index of heartwood (HW) and sapwood (SW) samples.

The relative abundance of different inter-lignin linkages was determined by the integration of corresponding cross peaks in the HSQC spectra. Crystallinity index (CrI) of all samples was calculated using both the height of the XRD patterns or the area underneath. A (β-aryl ether); B (phenylcoumaran); C (resinol); S (syringyl); S′ (oxidized syringyl); G (guaiacyl).