The Choat Lab

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

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:

We are now seeking a highly motivated PhD student to contribute to a new Australian Research Council Discovery project that aims to resolve a number of long-standing questions regarding hydraulic function of plants: at what point in the process of water stress do emboli form in xylem conduits? How do plants recover from these drought-induced disruptions to water transport?

In the project, the student will utilize cutting edge non-invasive imaging techniques to study the dynamics of drought-induced cavitation in plants. These techniques allow unambiguous measurement of how cavitation is propagated within and between different plants organs (leaves, stems, roots). These measurements will be used to establish thresholds in lethal water stress for a range of plant species.

The student will be based at HIE but will be expected to travel to the University of Tasmania for collaborative work with A. Prof. Tim Brodribb during the course of the project. There will also be opportunities for travel to France for collaborative work with Dr Sylvain Delzon and Dr Herve Cochard (INRA), and Dr Philippe Marmottant (CNRS).

To apply for this scholarship please contact me at b.choat@westernsydney.edu.au

Further details on the application process can be found here.

Applications close on 31 March 2017.

Drought- and heat-induced regional tree mortality events around the world.

Brendan Choat was a co-author on a study recently published in PNAS. The study, lead by Bill Anderegg (University of Utah) discovered a strong link between the mortality of tree species resulting from drought and plant hydraulic traits. Data were gathered from 33 published studies of tree mortality that included 475 tree species and more than 760,000 individual trees. Mortality rates for each species were then compared to 10 tree physiological traits, searching for commonalities. The traits included wood density, rooting depth, and basic leaf characteristics as well as plant hydraulic traits such as vulnerability to embolism and sapwood specific conductivity. The results provide support for the hypothesis that hydraulic traits capture key mechanisms determining mortality and highlight that physiological traits can improve vegetation model prediction of tree mortality during climate extremes.

Congratulations to PhD student Jen Peters who was recently awarded a Student Research Grant from the Wet Tropics Management Authority! The title of Jen’s research grant is “Assessing Vulnerability to Water Limitation of Australian’s Tropical Rainforest” and will contribute to her thesis project examining the vulnerability of Australian forests to drought. This grant will fund her research at the Daintree Rainforest Observatory where she will characterize stem and leaf vulnerability to drought stress for the dominant tree canopy species.

Jen Peters (right) at the Daintree Rainforest study site.

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 →

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.

Cover caption: Continue reading →

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.

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 →

Herve, Rosana and Brendan at Mt Banks, NSW

We were lucky enough to receive a visit from Dr Herve Cochard, aka “The General” of INRA. Herve, a world leader in plant hydraulics, is a close collaborator with the lab and a co-sponsor of Rosana’s Marie Curie Fellowship. Here we are at Mt Banks in the Blue Mountains NP, NSW.