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 pdΨ md) was also calculated.