Comparative metabolomics analysis reveals the color variation between heartwood and sapwood of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook

To reveal the correlation between the metabolites profiles and the wood color variation, metabolomics analysis of heartwood (HW) and sapwood (SW) of Chinese fir at two different ages was performed. The metabolite profiling was obtained using ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometer (UPLC/Q-TOF-MS/MS). The results demonstrated that a total of 12,581 metabolites were obtained, of which 850 were annotated to the Human Metabolome Database (HMDB). Principal component analysis (PCA) and orthogonal partial least squares-discriminantion analysis (OPLS-DA) displayed a distinctly variation from HW group and SW group, 21 phenolic compounds including flavonoids, coumarins and derivatives, and stilbenes accumulated most in the HW group, which could be responsible for the darker of HW. As for variation in metabolites between tree ages, the HW and SW from older Chinese fir accumulated greater frequency of secondary metabolites than those from the younger ones. The metabolic pathway enrichment analysis revealed the flavonoid biosynthesis pathway extremely changed between the groups of HW and SW, HW-24Y and HW-19Y, and SW-24Y and SW-19Y, respectively, implying that the identified flavonoid metabolites in this study could clarify the wood color difference between HW and SW in kaihua 3 clone Chinese fir. The results of this study may provide valuable information regarding how the metabolic compositions and the potential of flavonoid pathway alter the wood coloring.