The Power of Movement in Plants
Mocko, Kerri , Jones, Cynthia S. , Nicotra, Adrienne B. .
“Service to the plant”: Solar tracking and leaf shape in Pelargonium.
Solar tracking in plants describes the temporary and reversible movement of leaves in response to light. Darwin recognized that this phenomenon provided a “service to the plant” that has since been studied by ecophysiologists, most extensively in arid environments. Under cool temperatures and non-water stressed conditions, plants display diaheliotropic movements that maintain leaves perpendicular to incident light, maximizing photon flux density to achieve high photosynthetic rates throughout the day. Under hot, dry conditions, paraheliotropic movements parallel to solar incidence reduce photon flux density to prevent thermal damage and enhance water use efficiency. Examined mostly in species with pulvini and pinnate leaves, there has been little direct attention to the effect of leaf shape on the extent of solar tracking. Leaf energy exchange with the environment depends on the physical properties of a given leaf shape such that an entire leaf has a thicker boundary layer and less heat transfer with the environment than a highly dissected leaf. Therefore, dissected leaves are predicted to maintain temperatures closer to ambient. However, energy budgets for any shape of leaf can be influenced by changes in leaf angle. We measured diurnal changes in leaf inclination and azimuth of two closely related co-occurring geophytic Pelargonium species of contrasting leaf shape. While both species tracked the sun during the course of the day, there was more movement in highly dissected leaves. Under winter growing conditions, leaves of the dissected species moved to intercept more solar radiation and heat up more quickly than the non-dissected species. Between species, differences in leaf shape and solar tracking combined to result in similar maximum leaf temperatures. Thus the full extent of Darwin’s “service to the plant” results from the synergistic effects of leaf movement and morphology.
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1 - University of Connecticut, Department of Ecology and Evolutionary Biology, 75 N. Eagleville Road, Unit 3043, Storrs, CT, 06269-3043, USA
2 - Australian National University, School of Botany and Zoology, Bld 116 Daley Rd, Canberra, ACT, 0200, Australia
Presentation Type: Symposium or Colloquium Presentation
Location: Ballroom 2/Cliff Lodge - Level B
Date: Monday, July 27th, 2009
Time: 10:45 AM