selected from the inner part of the canopy. The leaves were
enclosed, while intact on the tree, in a plastic bag covered with
aluminum foil and left 90 min for stem and leaf water potential to
equilibrate before measurement. Two pressure chambers were
used simultaneously to complete each set of measurements rapidly
to minimize the time elapsed between the first and the last measurement
of each set. The average of two leaves was taken to
represent each replicate. Midday measurements of leaf and stem
water potentials were taken during several days in mid-summer.
Diurnal measurements of leaf and stem water potential were taken
on 4 Aug. 1993. Diurnal measurements started at 0700 HR and
ended at 1800 HR. Before each measurement of leaf water potential,
stomatal conductance was measured using a portable photosynthesis
system (LCA2, ADC, U.K.). The same leaves were used for
stomatal conductance and leaf water potential measurements.
Total light interception, for evaluation of canopy coverage, was
measured “on 4 Aug. 1993, when annual shoot and leaf development
was complete. Light intensity reaching the soil surface was
measured with an 80-cm, 80-sensors line PAR Ceptometer (Delta