The Effects of the Environmental Stress on the Wood Formation in Acacia mangium Chunhua ZHANG, Hisashi ABE Katsushi KURODA & Takeshi FUJIWARA Wood Anatomy and Quality Laboratory Department of Wood Properties Forestry and Forest Products Research Institute Acacia mangium, one of the tropical plantation tree species, grows very fast and forms heartwood at a comparatively early stage of the growth. These features make it an ideal tree species for use in simulation experiments. In order to investigate the effects of various stresses to the wood formation, we planted and raised Acacia mangium trees in an artificial climate chamber.

Materials & Methods Acacia mangium seeds were sowed after heat- treatment, and raised for 9 months in an artificial climate chamber which produced a tropical climate. DayNight Temperature 30 ℃ 25 ℃ Moisture75% Lighting13hr.11hr. Setting conditions of the artificial climate Chamber The 9-month-old young trees were divided into four groups, and separately subjected to cold stress, drought stress and light stress for a month. One remaining group was used as the control. Stress treatment conditions WaterTemperaturePhoton flux density Control Three times a week 30 ℃ (day)25 ℃ (night) 450  mol m -2 s -1 Cold stress Three times a week 15 ℃ (day)10 ℃ (night) 450  mol m -2 s -1 Drought stress Every two weeks 30 ℃ (day)25 ℃ (night) 450  mol m -2 s -1 Light stress Three times a week 30 ℃ (day)25 ℃ (night) 70  mol m -2 s -1

After being raised for 7 more months, all the trees were felled and wood samples were collected from the base of the stems and examined by light and electron microscopy. Results & Discussion In spite of having lived only 17 months, the cold stressed sample tree had already formed heartwood, and further, its fixing solution appeared yellow brown due to the extracted colored heartwood substances. Unstained section of the cold stressed sample tree also showed the colored heartwood substances which were distributed over the whole heartwood.

ControlCold stress Light stressWater stress Results & Discussion A great number of starch were detected in the cold stressed sample tree than in individuals from the other groups. Moreover, numerous starch-rich living wood fibers were observed on the outer part of the xylem. Transverse electron micrograph of the cold stressed sample tree LF = living wood fiber; S = starch grain

Conclusion The trees which were subjected to drought stress formed many narrow vessels. It might be considered that a water shortage restricted the expansion of these vessels. However, those which underwent light stress did not show a significant change during the wood formation in this study. For acquiring further information, of course, continuous experiments are necessary. Acacia mangium, a tropical tree species, is very sensitive to cold stress. Thank you for your attention! Welcome to my poster for discussing!