42. Leaf Temperature

Organised by Andrea Leigh, University of Technology Sydney. First meeting was held 21-24 April 2008 at Macquarie University.	PARTICIPANTS MAY INCLUDE Andrea Leigh - U Technology, Sydney (Leader) Marilyn Ball - Australian National U John Close - Australian National U Dave Ellsworth - U Western Sydney Adrienne Nicotra - Australian National U Sanna Anika Sevanto - U Helsinki (Finland) Steve Vogel - Duke U (USA)
Apr 08 >

Now, more than ever, an understanding of what governs leaf temperature in a fluctuating environment is crucial. In many environments, both the occurrence and magnitude of extreme temperature spikes are projected to increase over coming decades. Different plant groups will undoubtedly vary in their resilience against such events, due primarily to variation in leaf morphological characteristics. The most dominant influence on leaf temperature is generally considered to be leaf size, yet other traits are also important.

Thick leaves occur in environments experiencing temperature extremes, both hot and cold. In hot dry environments, dissipation of heat that would normally occur via transpiration is not an option. Stomata close at high temperatures causing leaves to heat rapidly. In the cold context, such as under a clear alpine night sky, avoiding rapid temperature excursions to ice nucleation temperatures can be critical. Extreme temperature events that are biologically relevant to a leaf occur on relatively short time scales and often are typical in natural unsteady conditions. Although rarely measured, rapid air movements below human perception, i.e. < 0.5 m/s, can have a dramatic effect on leaf temperature. Leaves that heat or cool slowly relative to these time scales are buffered against thermal damage. Leaf area and thickness both interact to influence the rate at which a leaf heats or cools. Leaf thickness becomes important in environments where leaf area is relatively conserved, often the case in desert and alpine environments.

We are investigating thermal damage to leaves as a function of leaf thickness using a simple thermal model of leaf temperature under hot, sunny conditions with fluctuating air movement. The model demonstrates that when wind speed drops dramatically, the temperature of thin leaves rapidly escalates to critical damage levels. By contrast, the temperature of thick leaves responds relatively slowly. Thick leaves are thus buffered against thermal damage, especially if they are small in area.

Evolutionary and ecological implications are wide reaching; for example regarding our ability to predict distribution of plant taxa or functional types, particularly in regions where plants operate at their physiological limits. There is also potential to generate easily measurable leaf characteristics for vegetation models that urgently require robust plant thermotolerance parameters.

Last updated July 2008