Publication Date

April 2017


Dana Royer


Earth & Environmental Sciences


English (United States)


The physiognomy (size and shape) of fossilized leaves has been analyzed to reconstruct the mean annual temperature (MAT) of ancient environments. Colder temperatures often select for larger and more abundant leaf teeth—serrated edges on leaf margins—as well as a greater degree of leaf dissection. Accurate paleotemperature estimates play important roles in testing climate models used for predicting future patterns of climate change. Paleotemperature estimates can be compared with atmospheric CO2 concentrations from the same period to help constrain climate sensitivity. However, to be able to accurately predict paleotemperature from the morphology of fossilized leaves, leaves must be able to react quickly and in a predictable manner to changes in temperature. By growing Acer rubrum plants in growth cabinets under different temperatures, Royer (2012) found that this species develops more highly dissected leaves (larger, more frequent teeth, and a higher perimeter/area ratio) in cooler temperatures than it does in warmer temperatures. To expand this work, my research examines the extent to which temperature affects leaf morphology in four additional tree species: Caprinus caroliniana, Acer negundo, Ilex opaca, and Ostrya virginiana. Saplings of these species were grown in two growth cabinets under different temperatures. Carpinus caroliniana leaves had a significantly lower total number of leaf teeth as well as a lower ratio of total number of leaf teeth to internal perimeter, and Acer negundo leaves had a significantly lower feret diameter ratio (measure of leaf dissection) in the warm temperature treatment compared to the cool treatment. In addition, a two-way ANOVA was used to test the influence of temperature and species on leaf physiognomy. It revealed that all plants, regardless of species, tended to develop more highly dissected leaves with more leaf teeth in the cool treatment. Since the cabinets maintained equivalent moisture, humidity, and CO2 concentration between the two treatments, these results demonstrate that these species could rapidly adapt to changes in temperature. It was not always the case, however, that all species reacted identically to temperature changes. For example, Acer negundo, Carpinus caroliniana, and Ostrya virginiana all had a higher number of total teeth in the cool treatment compared to the warm treatment, but the opposite was true for Ilex opaca. Such differences in temperature response question a fundamental assumption in all models predicting paleotemperature from the physiognomy of fossilized leaves: a given climate will inevitably select for the same leaf physiognomy, regardless of species composition. To more accurately compensate for differences among species, it would be useful for models to incorporate phylogenetic information on the species in question.



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