Physiological Measurements
Physiological measurements were made monthly for four months in 2018 and
for three months in 2019 starting at 45 DAFB on days that were cloud
free and temperature not exceeding 30°C. Means were calculated for all
sampling times during the season. Stomatal conductance, transpiration
rate and net CO2 assimilation were measured on two
sun-exposed mature leaves per replicate between 10am and 12pm using a
LI˗6400XT infrared gas analyzer (Li˗COR, Lincoln, NE, USA). Reference
CO2 concentration was set at 400 ppm, leaf temperature
at 25 °C, and photosynthetic photon flux density inside the chamber was
set to 1,500 μmol m−2 s −1. After
clamping, the leaf was allowed to equilibrate until reference and sample
values stabilized. To assess water status, fully mature expanded leaves
were chosen from inside the canopy closest to the base of the tree and
leaf water potential was allowed to equilibrate with the stem in a
silver reflective bag for at least 90 minutes. Then, stem water
potential was measure using a Scholander System Pressure Chamber
Instrument (PMS Instrument Co., Albany, OR, USA) at solar noon.