Barrier zone formation and development in the stems of Aquilaria sinensis (Thymelaeaceae) and the effect on agarwood formation

Barrier and reaction zones are core parts of compartmentalization in trees. However, little is known about the relationship between them. Here, agarwood and barrier zone formation in Aquilaria sinensis trees were studied for the first time using compartmentalization theory. The main results were as follows: (1) Wounding methods had a very important influence on the occurrence of barrier zones in A. sinensis. (2) The barrier zone development process was divided into three phases based on the morphological features. (3) The agarwood resin mainly accreted during the barrier zone lag and division phases; then, after the barrier zone entered the differentiation phase, the resin no longer accreted and even tended to degrade. (4) In the application of the whole-tree agarwood-inducing technique, the barrier zone generally began to appear 10 months after the technique treatment, and the barrier zones were more severe in the lower part of the stem. (5) Considering the agarwood yield, agarwood resin filling degree and ethanol-soluble extract content, the serious barrier zone indeed reduced the agarwood productivity. This study is important for revealing the agarwood and barrier zone formation mechanism in Aquilaria trees. It also provides a good research model for considering the high economic value of agarwood when studying compartmentalization.