Radiation quality was an important environmental cue to stimulate seed germination in Acacia mangium. The photo-synthetic CO2 assimilation rate, dark respiration rate, total biomass, and relative growth rate of seedlings grown under monochromatic radiation were significantly lower than those of seedlings grown under full spectrum radiation. Blue and red radiation induced shade-avoidance and shade-tolerant responses of A. mangium seedlings, respectively. and Hua Yu, Bee-Lian Ong.