The Choat Lab

Plant Hydraulics and Water Relations

Leave a comment

New paper: Direct test of X-ray microCT against hydraulically measured vulnerability to embolism formation

X-ray microtomography (microCT) cross sections (initial scan) of Eucalyptus camaldulensis stems at increasingly negative water potentials illustrate the spread of embolism (air-filled vessels, dark circles) under drought stress.

Embolism (air-filled vessels, dark circles) spread in Eucalyptus camaldulensis under drought stress.

X-ray microtomography allows us to scan plants noninvasively and at high resolution to examine the state of hydraulic failure in xylem conduits. In our recent article in New Phytologist, we directly compared theoretical estimates of hydraulic conductivity provided by microCT imaging with the loss of conductivity measured with a liquid flow meter. While imaging and hydraulic techniques have been compared before, this is the first time both methods were applied to the very same samples.
We show that results from these techniques corresponded well in a Eucalyptus species. Furthermore, we also describe a method to optimise microCT image analysis while overcoming some common potential constraints of current lab-based microCT systems.

Our results help strengthen X-ray microCT as a reference method for plant hydraulic questions, and introduce a reference-based way to calibrate imaging-based vulnerability analysis.

More information: Visualization of xylem embolism by X-ray microtomography: a direct test against hydraulic measurements

Leave a comment

MicroCT experiment at the Australian Synchrotron

We are currently at the Australian Synchrotron in Melbourne to study the hydraulic vulnerability of Eucalyptus trees to drought-induced embolism. The X-ray microCT facility allows us to non-invasively observe embolism in vessels and scan plants repeatedly during a drought treatment.

Below is a short time lapse clip showing how our study trees are mounted onto the microCT stage (which is operated by a robotic arm) and then rotated during the scan:

Leave a comment

Stem Psychrometry Workshop at HIE

Earlier this week, we held a Stem Psychrometry Workshop workshop at the Hawkesbury Institute for the Environment, in collaboration with manufacturer ICT International and the technology’s inventor Mike Dixon (University of Guelph, Canada).


ICT’s PSY-1 stem psychrometer allows automated, repeated measurements of plant water potential using high-precision thermocouples installed on a plant, and we have been using them in lab- and field based setups from the tropical rainforest in Far North Queensland to the semi-arid South Australian mallee. Continue reading

Leave a comment

Featured Article in Plant, Cell and Environment

Our article “Stem and leaf hydraulic properties are finely coordinated in three tropical rainforest tree species” was featured on the December 2015 cover of Plant, Cell and Environment.

The article (introduced here) investigates the internal coordination of hydraulic parameters in a tropical lowland rainforest. Most of our sampling for this study was done directly from the rainforest canopy using the Daintree Rainforest Observatory‘s canopy crane, which is pictured on the journal cover.

Hydraulic characteristics of rainforest trees. Journal Cover of Plant, Cell and Environment 38, Dec. 2015 Hydraulic characteristics of rainforest trees. Journal Cover of Plant, Cell and Environment 38, Dec. 2015

Cover caption: Continue reading

Leave a comment

Field work at the Daintree Rainforest Observatory

Our research on the limits to the resilience of forests and woodlands to drought takes us to a range of native forests and woodlands across Australia. In late November, we visited one of the tropical field sites, Daintree Rainforest Observatory at Cape Tribulation, Far North Queensland. The DRO is a unique research facility, which can provide easy access to the rainforest canopy using a canopy crane gondola (47 m tall, 55 m radius). We studied the vulnerability of stems and leaves of rainforest tree species to drought and other related hydraulics parameters.

Daintree Rainforest Observatory (photo: MN) Sampling from the rainforest canopy, at the Daintree Rainforest Observatory (photo: MN) Dawn above the rainforest canopy (photo: MN)

The video below is a short time-lapse clip which was recorded during leaf sampling for anatomical analyses in the canopy, using the DRO canopy crane. Continue reading

Leave a comment

Hydraulic vulnerability analysis using X-ray microCT

One of the major points of critique for hydraulic measurements of xylem vulnerability and embolism is that they are destructive measurements. In contrast, non-invasive imaging has made it possible to observe xylem function and the spread of embolism in living, intact plants without destructive sampling and associated artefacts.

In collaboration with Iain Young and Richard Flavel at the University of New England, Armidale, we recently scanned the stems of young Eucalyptus trees at high resolution using X-ray Micro Computed Tomography (microCT) to visualize the loss of hydraulic function at increasing levels of drought. This allowed us to analyse the species’ vulnerability to drought-induced embolism, and validate hydraulic data using an independent, non-destructive method.

MicroCT cross section of a Eucalyptus stem in which air-filled areas appear darker than water-saturated tissues. From the centre outwards, you can see the central pith and primary xylem, followed by a ring of embolised vessels in the outer xylem area.

MicroCT cross section of a Eucalyptus stem.

Continue reading

1 Comment

Paper: Leaf and stem hydraulics are finely coordinated in tropical rainforest trees

Water is one of the most limiting factors for terrestrial plant life. In dry conditions, hydraulic coordination of stems and leaves enables plants to maintain a safe water status and avoid hydraulic failure in the xylem. While such relationships have been shown for some tree species previously, little is known about hydraulic coordination in rainforest species which do not typically experience drought and represent a hydraulically understudied group of plants.

View across the daintree rainforest (photo: MN)

View across the daintree rainforest (photo: MN)

In our recent publication “Stem and leaf hydraulic properties are finely coordinated in three tropical rain forest tree species”, we studied plant hydraulics at the Daintree Rainforest Observatory in Far North Queensland and compared a number of hydraulic traits (including hydraulic vulnerability of stems and leaves, pressure-volume relations and in situ water potentials) in three tropical rain forest species. Continue reading