Metabolites change reveal insights into the heartwood color formation mechanism of <i>Dalbergia odorifera</i>

Dalbergia odorifera T. Chen, an indigenous species in Hainan Island, China, had high economic and cultural values. Its sapwood was light yellow, while heartwood was rich in colors of red, yellow, orange, and black. The colorful oily deposits were found in the vessels, fibers, and parenchyma cells of the heartwood. The contents of extractives, flavonoid, and anthocyanin in heartwood were found to be 11.83%, 34.88 mg/g, and 705.84 μg/g, 3.29 times, 12.37 times, and 9.51 times higher than those of sapwood, respectively. More extractives, flavonoids, and anthocyanins appeared in the transition zone in the heartwood area position with abundant metabolites. Among them, flavonoids accounted for 26.2%. The relative content of metabolites, such as anthocyanins, chalcone, flavone, and anthraquinone increased greatly in heartwood. The formation of the red-yellow-orange mixed color of D. odorifera heartwood was related to these metabolites.