Comparison of transpiration characteristics of two typical coniferous species in Beijing mountainous area

The objective of this study is to provide references for the selection of afforestation tree species with drought resistance and lower water consumption in ecological conservation areas in Beijing through a comparison of transpiration characteristics of Pinus tabulaeformis and Platycladus orientalis. A portable photosynthesis system Li-6400 was used to measure the transpiration rate of the two species from May to October, 2006 in Miyun Reservoir of Beijing. The results show that for the two species, 1) the daily average transpiration rate was 2.18 and 1.95 mmol/(m2·s); 2) the daily average water use efficiency was 3.52 and 3.04 μmol/mmol; 3) the water use efficiency culminated at 11:00, and the photosynthetic rate presented a single-peak curve with a peak value appearing around 12:00. The results suggest the two species have similar transpiration characteristics except that the daily average water use efficiency of Pinus tabulaeformis is slightly higher than that of Platycladus orientalis. The transpiration rate was affected synthetically by environmental factors, and largely by stomatal conductance.