Comparison on the Transpiration Values Measured with Portable Steady Porometer Method and Whole-tree Weighing Method

Transpiration rate of Platycladus orientalis,Pinus tabulaeformis,Robinia pseudoacacia and Hippophae rhamnoides were measured by portable steady porometer(Li-1600) and whole-tree weighing method(BP-3400) in growing season of 2004,artificially controlling water amount in pot experiment,in semi-arid region of the Loess Plateaus.It indicated that transpiration rate of leaves rose when soil water content increased;measured value of portable steady porometer were always higher than measured value of whole-tree weighing,the ratios of measured value of two methods rose with increasing soil water content,but reduced when soil water content reached field moisture capacity;the ratios of measured value of portable steady porometer and whole-tree weighing of Robinia pseudoacacia and Hippophae rhamnoides was 2.50 and 2.57 respectively in July,the ratios of measured value of portable steady porometer and whole-tree weighing of Platycladus orientalis and Pinus tabulae formiswas 2.48 and 2.28 respectively in August,the ratios of measured value of portable steady porometer and whole-tree weighing method of Platycladus orientalis,Pinus tabulaeformis,Robinia pseudoacacia and Hippophae rhamnoides was 1.19,1.86,1.53 and 1.97 respectively in October.The conclusion would be regarded as the reference of forest tree transpiration in semi-arid region of Loess Plateau.