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Leaf gas exchange and stable isotope discrimination in response to extreme conditions in temperate forest tree species

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Professor Lucas Cernusak

College of Science and Engineering
James Cook University, Cairns, Australia


Fellowship Period: 02.2022-06.2022 / 11.2022-12.2022

Lucas Cernusak is an Associate Professor in the Ecology and Zoology group at James Cook University, Cairns.  His main research interest is to understand the environmental and biological controls on carbon dioxide and water vapour exchange between leaves and the atmosphere.  He is also interested in improving the interpretation of stable isotope signals in plant organic material, to better understand how leaf gas exchange has responded to global climate change through time and how it varies across ecological gradients.


Activities within WSL Fellowship

As part of a WSL funded project (PPF2020), we developed a new experimental facility for measuring leaf gas exchange and on-line stable isotope discrimination under controlled environmental conditions.  With this facility, we assessed how these processes responded to temperatures ranging from 5°C to 40°C while the leaf-to-air vapour pressure difference was held nearly constant at 0.8 ± 0.2 kPa.  Such a temperature response at constant, low vapour pressure deficit has not been previously achieved.  We observed that stomatal conductance increased monotonically with increasing temperature under these conditions in saplings of four European tree species.  Whereas stomatal conductance steadily increased, net photosynthesis reached a maxim at 30°C to 35°C, and then declined.  The decline in net photosynthesis coincided with a decline in mesophyll conductance to carbon dioxide, as deduced from concurrent measurements of carbon and oxygen isotope discrimination.  The increase in stomatal conductance with temperature could be plausibly explained by the decreasing viscosity of water driving an increase in whole-plant hydraulic conductance.  In contrast, the permeability of mesophyll cell membranes to carbon dioxide appeared to decline at the highest temperatures.  These contrasting responses resulted in an uncoupling of net photosynthesis from stomatal conductance at the highest temperatures, with important implications for modelling leaf gas exchange in response to global warming.


Cooperation within WSL


Cooperation outside of WSL

Meisha Holloway-Phillips (University of Basel)
Ansgar Kahmen (University of Basel)
Paolo Benettin (EPFL Lausanne)
Nina Buchmann (ETH Zurich)