サラワク熱帯雨林におけるフタバガキ科林冠構成種の不均一な気孔開閉による蒸散速度の調節

抄録

The transpiration rates of five canopy tree species of Dipterocarpaceae-Dipterocarpus pachyphyllus, Dryobalanops aromatica, Shorea parvifolia, Shorea pilosa, and Shorea smithiana-were examined in lowland tropical rainforest at Lambir, Sarawak, Malaysia. During early morning on clear days, the transpiration rate increased in proportion to the vapor pressure difference between air and leaves. However, at around noon, the transpiration rate began to fluctuate. In order to interpret this fluctuation, the distribution pattern of stomatal opening was examined using the pressure infiltration method. Tiny patches of color appeared on the leaf surface due to dye infiltration through open stomata. The transpiration rate in the afternoon was clearly proportional to the relative area of the colored patches. This patchy opening of stomata was considered to be the cause of the transpiration fluctuation at that time. It is conclude that the five canopy tree species examined have a highly elaborate transpiration regulation mechanism which works effectively under high temperature by quick repetition of open-close action of stomata in maintaining transpiration rate at certain level to keep leaf temperature persistently lower than that of the air.