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Abstract. Leaves with toothed and lobed margins are frequent in deciduous forests but are rare in moist tropical forests. We hypothesize that leaf teeth may be important to deciduous species as sites of precocious, early season photosynthesis. To test this hypothesis we dosed leaves with '4CO2 and used autoradiography to examine the spatial distribution of photosynthesis within immature leaves of 18 woody species of North Carolina Piedmont forests. We found a significant concentration of early season photosynthesis on the margins of eight species with prominent teeth or lobes, but not in seven toothed or lobed leaf species and in none of the four entire-leaf species.
Key words: drip tips, function; forest tree leaves, temperate cf. tropical; leaf expansion and growth; leaf margin characteristics; leaf teeth and lobes; North Carolina (USA) Piedmont forests; photosynthesis, early season.
INTRODUCTION
Leaf-margin characteristics of tree species follow a predictable pattern based on climate. Tree species of cool, temperate forests generally have leaves with toothed or lobed margins, whereas moist, evergreen tropical forests contain almost exclusively species with entire-margined leaves (Bailey and Sinnott 1916, Cain and Castro 1959, Gentry 1969, MacArthur 1972, Givnish 1979). The proportion of tree species with nonentire leaves steadily increases along the tropical-totemperate gradient of decreasing mean annual temperature and increasing seasonality (Bailey and Sinnott 1916, Wolfe 1978a). In addition, the moisture and seasonality gradient from moist tropical forest to dry tropical forest corresponds to a similar, albeit less pronounced, gradient of increasing proportion of nonentire-leaved tree species (Gentry 1969, Richards 1996). The correlations between climate and leaf margin are sufficiently strong that paleobiologists routinely use leaf-margin statistics from fossil floras as indicators of past climate (Bailey and Sinnott 1916, Wolfe 1978b, Givnish 1987).
The climate-based pattern of leaf-margin morphology is not constrained by taxonomic classification; Bailey and Sinnott (1916) cite numerous examples of plant families wherein species characteristic of moist tropical forests have leaves with entire margins, whereas those species found in temperate forests generally have lobed or toothed margins. In addition, several genera that contain both tropical and temperate species have temperate species with toothed or lobed margins and tropical species with entire margins (e.g., Quercus; see Brenner 1902, MacArthur 1972). The fact that leaf margins with teeth or multiple lobes have evolved numerous...