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Explore the relationship between leaf morphology, photosynthesis, and shade tolerance across different tree species. Investigate how leaf shape impacts plant fitness and light interception.
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Leaf Area : Perimeter RatioShade Tolerance and Photosynthesis Brigette Jones and DunyaOnen Physiological Ecology Spring 2007
Background • One of the simplest questions to ask in plant physiological ecology is “Why are the leaves shaped like that?” • Leaf morphology is highly variable, and leaf functionality is directly related to plant fitness • Strong selective pressure • Additionally many studies have shown that leaf morphology, rather than biochemistry often governs photosynthesis acclimation • Many factors potentially influence shape, and many measures of shape • Incident radiation determining Ps
Sassafras • In light-limiting environments- • Potentially advantageous to extend the leaf in many directions (increase lobbing??, decrease area: edge) • Maximize angle and place variety for light interception • Niklas 1988 showed that Sassafras leaves were more strongly, and more frequently lobed on the interior parts of the branches, where light was intermittent and limiting
Question is mostly unanswered-studies tend to look at other morphological parameters, or don’t connect perimeter to physiological responses, such as photosynthesis • Or are limited to one species, or don’t cover a range of leaf shapes • There must be a function for leaf shape, or such variance would be unlikely-an ideal would have evolved
Hypothesis • Photosynthesis will decrease with increasing Area : Perimeter ratio independent of tree species Predictions • Tree species with greater shade tolerance will have lower A:P • ratios • Within species with plastic leaf morphology, A:P will be lower for shade leaves than sun leaves
Study species were chosen from the avaliable local pool to represent a range of shade tolerance and leaf shape
Tree Species • Paper Birch (Betulapapyrifera)- low shade tolerance, teardrop shaped leaf • American Elm (Ulmusamericana)-moderate shade tolerance, egg-shaped leaf • Northern Red Oak (Quercusrubra)- high shade tolerance, moderately pinnately lobed leaf • Sugar Maple (Acer saccharum)- very high shade tolerance, moderately palmately lobed leaf