Predawn and middayΨ
The predawn and midday Ψ of leaf (Ψ pd andΨ md, respectively) were measured once a month
from May to September 2019 using a model 3005 pressure chamber (Soil
Moisture Equipment Corp., Santa Barbara, CA, USA) to evaluate the water
states of the plants. In the field, eight healthy and similar-sized
individuals at each site were selected and marked, and from each of
them, one distal twig with leaf attached was sampled and the water state
measured immediately after the twig was cut. TheΨ pd and Ψ md values were
measured 20 min before sunrise and at solar noon, respectively. In
accordance with our previous diurnal measurements, theΨ md was considered the minimum leaf Ψ (G.
Q. Xu & Li, 2008). TheΨ difference
(Ψ pd–Ψ md) was also
calculated.