Abstract
Net photosynthesis rate (NPR) and transpiration rate (TRR) of the trees of R.umbellata (R.u.) and P. tobira (P.t.) were measured under various soil water conditions with the Portable Photosynthesis System (LI-COR Inc.) on August 25, 1989.Under the good soil water conditions (pF 1.8-1.9), R.u. showed NPR of 16-19 mgCO 2 /dm2 /hr and TRR of 3-4 gH20/d rdm2/hr in the daytime and P.t. showed NPR of 13-16 mgCO2 /dm2 /hr and the same TRR as R.u., and highly positive correlations were also found between NPR and TRR in both species. However, according to soil drought, NPR in the afternoon decreased rapidly and the correlation between NPR and TRR became insignificant. The response of P.t. to soil drought was slower than that of R.u. This supposes that P.t. has much tolerance of drought more than R.u. has.
