The Functional Significance of Leaf Shape Variation - Towards a Consensus from Gene to Community
Royer, Dana , Wilf, Peter , Kooyman, Robert M. .
Leaf teeth boost gas-exchange rates early in the growing season: experimental evidence and implications for tooth function.
Leaf teeth are conspicuous morphological features whose presence and distribution have long been correlated with ecological gradients: notably, the proportion of toothed species in a flora inversely correlates with temperature, and toothed species are usually more common in riparian habitats than in adjacent non-riparian habitats. Despite these strong associations, little is known about tooth function. Here, we test the hypothesis of Baker-Brosh and Peet (1997, Ecology 78: 1250-1255) that teeth boost rates of carbon uptake early in the growing season. We measured the seasonal patterns of leaf-margin photosynthesis and transpiration for 60 species from two temperate regions with differing climates (Pennsylvania and North Carolina). Physiological activity was greatest for toothed species early in the growing season (first 30 days) and leaf margins were more active in the colder Pennsylvania sample. These results indicate that teeth may help maximize carbon gain when temperature is limiting but moisture availability is not and thus our results may provide a selection mechanism for why toothed species are proportionally more abundant in cold environments.
Our experiments demonstrate that teeth boost photosynthetic uptake but that there is an associated cost in the form of enhanced transpirational losses. Both of these effects can be mechanistically linked with the general observation that toothed species are more common in riparian habitats, because such habitats are usually not water-limited and are dominated by fast-growing gap specialists. To further investigate this ‘riparian influence’ in different habitats, and test if the effects cited above transfer to evergreen rainforest, we determined topographic position (five categories running from ridge top to creek bottom) and recorded other ecological variables (e.g., level of site disturbance, dispersal mode) and percent of toothed species for 231 plots within the eastern Australian subtropical rainforests. We will discuss these observations and how they may improve our understanding of tooth function.
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1 - Wesleyan University, Department of Earth and Environmental Sciences, Middletown, CT, 06459, USA
2 - Pennsylvania State University, Department of Geosciences, University Park, PA, 16802, USA
3 - National Herbarium of NSW, Sydney, NSW, 2000, Australia
Presentation Type: Symposium or Colloquium Presentation
Location: Williford B/Hilton
Date: Monday, July 9th, 2007
Time: 3:00 PM