Objective To investigate the process between growth and defense of Aquilaria sinensis, and reveal physiological mechanism of agarwood formation in response to fungi and mechanical damage stress.

Method Two methods including injection of fungal agent and drilling with mechanical damage were used to induce agarwood formation with the three-year-old Aquilaria sinensis trees. Subsequently, hormone content, antioxidant enzyme activity, total phenols and terpenoids content, and photosynthesis and chlorophyll fluorescence characteristics were periodically analyzed during agarwood formation.

Result At the initial stress stage, the contents of defense related hormones, jasmonic acid, salicylic acid and ethylene increased significantly, while the contents of growth related hormones, gibberellin, and auxin decreased. At the later stress stage, the contents of jasmonic acid, salicylic acid, and ethylene gradually decreased, while the contents of gibberellin and auxin gradually increased. The activities of antioxidant enzymes and the contents of phenols and terpenes were significantly higher in the stress groups than those of the control group. The contents of phenols and terpenoids increased with the increase of treatment duration, and the rate of increase decreased. Three months after treatments, the photosynthesis and chlorophyll fluorescence were inhibited, while inhibition was alleviated after six months .

Conclusion In response to the stress of fungus and mechanical damage, defense related hormones increase significantly, as well as the activities of antioxidant enzymes. In addition, the secondary metabolic defense products such as phenols and terpenes increase and photosynthesis is inhibited. The strength of defense response decrease with the increase of treatment duration and trees recover the growth. Thus, agarwood formation is the process to that Aquilaria sinensis trees produce secondary metabolites by strengthening the defense response, which is a trade-off between growth and defense.