Abstract: Transpiration rate (Tr), stomatal resistence (Dr), leaf water patential (Lp) and its corresponding environmental factors of seven tree species have been measured with LI-1600 steady state prometer and pressure chamber. When the soil water potential in 2m depth is-0.04—-0.20MPa, the light intensity is the main factor to influence Tr, which is mainly influened by Dr. The relationship between Li and Dr can be expressed by following formula: Dr=ae^b/Li, thus light intensity according to its influence on Tr can be divided into three regions: Weak light region, Tr=K/Dr, Transition region, Tr=K·ψ_(L-A)/Dr; light saturation region, Tr=a·ψ_(L-A)+b where a, b and K are coefficients, ψ_(L-A) is the difference of leaf-air water potential.

Key words: Transpiration rate, Stomatal resistance, Difference of leaf-air water potential, Light intensity