Comparative studies on transpiration speed and water use efficiency for different age stages of Pinus taiwanensis
The transpiration and water physio-ecologic characteristics of needles of Pinus taiwanensis in different age stages were measured in field on typical sunny days at different seasons by using Li-6400 photosynthetic apparatus and the measured trees were selected in a natural community at 1 400 m altitude of Huangshan Mountain.The effect factors(stomata conduction,CO2 concentration in cell clearance photosynthetic active radiance,air temperature,relative humidity,etc.)were determined as well.The results were as follows:The diurnal variation of average transpiration rate for one-year-old needles of different age stages for Pinus taiwanensis all show obvious double curves,and the same thread of transpiration rate and stomata conduction is observed at juvenile stage.The seasonal variation of average transpiration speed of Pinus taiwanensis shows that it is higher in summer than that in any other seasons.The water use efficiency curves are also double peaked,and shows significant differences in different age stages of the tree species as the order of young to middle age(5.062juvenile(3.383)middle age(3.011).