USING SYCAMORE LEAVES TO RECONSTRUCT ANCIENT LIGHT ENVIRONMENTS

Light environments strongly influence the composition and structure of terrestrial ecosystems and climates. Thus, reconstructing light environments in the past can provide critical insights into past environments. Further, light intensity impacts both a plant’s morphology and its chemical composition, making it possible to quantify how these variables change in response to changes in light intensity to reconstruct ancient light environments. Here, we present results focused on the development of a proxy for light availability using leaf size and shape (physiognomy) variables and organic biomarkers from modern Sycamore leaves that were grown under varying degrees of light availability in an outdoor light experiment. Preliminary results show notable differences in leaf physiognomic variables, such as leaf area and number of teeth, across light environments; and results from ¹³C NMR spectroscopy also indicate differences between light environments, with low light conditions being more abundant in carbohydrates and less abundant in lignin. Analyses of early Paleocene Platanites fossil leaf cuticle from multiple fossil sites indicates the potential to apply the proxy to ancient ecosystems. Physiognomic and geochemical analyses of modern Sycamore leaves will be used to develop a multivariate model for light environment that can be applied to the fossil record. Using the model, we will reconstruct ancient light conditions during the early Paleocene of the San Juan Basin to help understand light availability and its impacts on the ecosystem and plant communities of the early Paleocene.