The PSY1 Stem Psychrometer was installed on Eucalyptus to measure the xylem water potential. The water potential was logged every 10 minutes.
The summer in Australia is October to March. The data is for late October. Winter is April to September and is cool and usually with rainfall.
The initial 6 day period shows a water potential of -0.8 MPa on sunny cloud free days (Figure 1, Days 1,2 and 5).
Cloudy days with reduced evaporative demand have lower xylem water potential. Figure 1 shows this as -0.6 MPa (Day 6) and below -0.4 MPa (Day 7) on rainy days. In fact after the rainfall event on Day 6 the night time water potential was 0.0 MPa (Day 6) for the first time.
These trees are well watered having received large amounts of rainfall in the proceeding winter months. Then the water potentials of -0.8 MPa on sunny cloud free days is expected to become more negative as summer progresses, temperatures increase and the soil becomes drier.