The Mechanism of Promoting Agarwood Formation in Aquilaria sinensis by Girdling

Agarwood is highly valued; however, its formation process is relatively slow. In this study, carbon isotope labeling was used to investigate the effects of girdling on agarwood formation. The starch, soluble sugar, and essential oil contents of the stems above the girdle were higher than those of the stems below the girdle and those of stems without girdling. Carbon isotope labeling revealed that girdling obstructed the transport of non-structural carbohydrates synthesized by the leaves to the stem below the girdle. The concentration of 13C in starch, soluble sugars, and essential oils in stems above the girdle was significantly higher than that in stems below the girdle and in stems without girdling. Phenotypic observations revealed that the area of agarwood formation was more extensive in regions closer to the phloem. Slice staining and variations in starch and soluble sugar content showed that starch was converted into soluble sugars during agarwood formation. This study demonstrates that newly synthesized non-structural carbohydrates from leaves following agarwood-inducing treatment contribute as raw materials for agarwood formation. Girdling increases the levels of non-structural carbohydrates in the stem above the girdle, thereby enhancing agarwood formation.