Recently, 7 months of continuous plant water potential data were collected from a single shrub.
A PSY1 Stem Psychrometer was installed on a Banksia spinulosa shrub in Armidale, New South Wales, Australia on January 9th, 2013, and was uninstalled on July 11th, 2013. The 7 months of continuous data is shown below, as well as the installation site and the PSY1 chamber.
Measuring plant water potential continuously for 7 months is completely unprecedented in plant physiology. Traditionally, scientists and managers have had to rely on the pressure chamber, such as the Scholander pressure chamber, to measure plant water potential. Not only is this approach destructive, but only one manual measurement can be taken at a time. In order to collect 7 months of data with a pressure chamber, you would need to constantly employ a researcher to measure a plant every 10 minutes, 24 hours a day, for 7 long months. This amounts to approximately 30,000 measurement events! The cost to employ a worker to do this would be prohibitive, not to mention the plant would probably have no leaves remaining!
Admittedly, 7 months of continuous data with the PSY1 Stem Psychrometer is difficult to achieve. Normally, a single installation can yield 2 to 3 weeks of continuous data. It all depends on the species you want to measure. After 2 to 3 weeks, the PSY1 chamber or thermocouples become too dirty for reliable measurements. But as you can see from the images below, the chamber on our 7 month installation is very clean, as is the installation site.
The data itself, shown below, shows a remarkable sequence of plant physiological events. At the start of the measurement period, Armidale was experiencing an extreme heat wave. Plant water potential was reaching a low -4.8MPa during the heat wave. The plant was recovering at night so even though the day time weather was extreme, this species was well adapted to handle it. Around the start of March there was an extreme rain event in Armidale, and even extensive flooding. This is reflected in a few days of 0MPa recorded by the PSY1 Stem Psychrometer. Between March and June, Armidale experienced a drought where barely a drop of rain fell on the city. During this period, night time plant water potential slowly declined to approximately -1.0MPa. Again, this shows how remarkably adapted this species is to this environment. This species can last 3 months without rainfall and still not, by textbook definition, be under drought stress!
This PSY1 Stem Psychrometer installation highlights the potential of this instrument to improve our understanding of plant physiology. It also provides an irrigation management tool .