The Functional Significance of Leaf Shape Variation - Towards a Consensus from Gene to Community
Leigh, Andrea , Nicotra, Adrienne B. , Ball, Marilyn C , Close, John , Jones, Cynthia S. , Schlichting, Carl .
The functional significance of leaf shape variation: leaf morphology correlates with thermal and hydraulic traits.
The two-dimensional proportions – size and shape – of leaves determine boundary layer thickness and, in theory, the rate at which heat is transferred between leaf and air. This prediction is supported by laboratory studies on artificial leaves but evidence from real leaves under field conditions is scant. Additionally, leaf temperature studies usually involve point measurements, rather than detailed information on the thermal profile of whole leaves. We used infrared imagery to measure thermal properties of Proteaceae and Geraniaceae leaves under field and laboratory conditions respectively. Results for field measurements showed that leaves with a greater leaf area, effective width, or less dissected margin had a longer time constant for cooling, a larger temperature range across their surface, and a greater leaf-to-air temperature difference. Notably, the positive correlation between these leaf shape features and the leaf-to-air temperature difference was evident only in hot, sunny conditions. In milder overcast conditions, the opposite was true: the leaf-to-air temperature difference decreased with increasing leaf size. The spatial distribution of temperatures across individual leaves was uneven, due to surface irregularities that increased with size. In the laboratory, when comparing leaves of a narrower range of sizes, the major determinant of the time constant for cooling was leaf water content. Within single leaves, the time constant varied spatially, with the leaf base cooling more slowly than the tips of the lobes. These differences were consistent regardless of the degree of dissection of the leaf, but because more dissected leaves have relatively more margin, they had on average lower time constants for cooling. We suggest that under certain conditions, factors such as irregular morphology and uneven distribution of water play a more important role than the effect of leaf size and shape on boundary layer resistance in governing leaf thermal properties.
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1 - Australian National University, School of Botany and Zoology, Bld 116 Daley Rd, Canberra, ACT, 0200, Australia
2 - Australian National University, Research School of Biological Sciences, Canberra, ACT, 0200, Australia
3 - Australian National University, Department of Physics and the Australian Centre for Quantum Atom Optics, Canberra, ACT, 0200, Australia
4 - University of Connecticut, Dept. of Ecology and Evolutionary Biology, Storrs, CT, 06269, USA
5 - University of Connecticut, Ecology & Evolutionary Biology, 75 North Eagleville Road, U-3043, Storrs, Connecticut, 062693043, USA
time constant for cooling
Presentation Type: Symposium or Colloquium Presentation
Location: Williford B/Hilton
Date: Monday, July 9th, 2007
Time: 1:30 PM