Formation and composition of agarwood co-induced by CO₂ coupling with liquid substances in Aquilaria sinensis

Objective To investigate the effect of CO₂ coupling with liquid substances (inorganic salts, hormones, and fungi) on agarwood induction in Aquilaria sinensis, seek a new method for the efficient induction of agarwood, and provide a basis for artificial induction technology promoting agarwood formation.

Method The method of coupling CO₂ with three liquid substances (inorganic salts, hormones, and fungi) was used to induce agarwood formation in 13-year-old A. sinensis trees for one year. Samples were taken to observe the changes of tissue structure and inclusions in the sections of agarwood-bearing parts of A. sinensis trees, and detect the differences of content and chemical composition in alcohol-soluble volatile oil.

Result 1) Different induction treatments depleted the starch granules in the xylem of the incense tree to different degrees. The invasive materials in the wood thin-walled cells were entering into the adjacent ducts through the semi-ciliated pores between the ducts and thin-walled cells, and accumulated until the ducts were completely blocked. 2) CO₂ and three liquid substances (inorganic salts, hormones, and fungi) induced differences in the accumulation of oil-like substances in ray thin-walled cells, axial thin-walled cells and ducts, with only a small amount of oil-like substances in CK-1 (Only filled with gas CO₂) and no oil-like substances observed in CK-2 (Only punching, not filled with gas CO₂). 3) The range of induced discoloration was greatly affected by the induction method, the distance of induced discoloration was shorter with the farther location of the treated holes, and the range of discoloration in the combined CO₂ and inorganic salt induction treatment was the largest. 4) The content of alcohol-soluble volatile oil varied significantly among the different induction treatments, and the more black-brown resin it contained, the higher the content. The GC-MS results showed that 74 compounds were identified after the five induction treatments, 11 of which were common components, and the relative contents of some alcohol-soluble volatile oil components varied greatly among treatments.

Conclusion By comparing and analyzing the differences in alcohol-soluble leachate content, characteristic components, and content of incense produced by the five induction methods, it was found that CO₂ coupled with inorganic salts induced the best quality of agarwood produced by A. sinensis, the characteristic components and their contents were higher than those of other treatments. The sediment produced by combined induction of CO₂ and fungi were followed, and the quality of the sediment produced by filling CO₂ only was poor.