Relationships of leaf diffusion resistance of Populus clones to leaf water potential and environment.

Leaf diffusion resistance (r 1) of the upper and lower leaf surfaces of several Populus clones was related to leaf water potential (ψ1), light intensity, vapor pressure deficit (VPD), and temperature by intrinsicallylinear, logarithmic multiple regression analyses. Regression equations accounted for up to 80% of variation in r 1 data. Light intensity and VPD varied among clones in importance in influencing r 1. Pronounced sensitivity of r 1 of certain clones to VPD was related to drought resistance in their parentage. Increasing r 1 was significantly positively correlated with ψ1, in apparent contradiction to prevailing concepts of stomatal response to water status, and this relationship was probably attributable to effects of other environmental variables on ψ1 and r 1. Leaf resistance decreased after a storm characterized by winds in excess of 160 km·h-1. Cuticular disruption and altered stomatal response may have been responsible for the storminduced r 1 decrease.