Using Sycamore leaves to reconstruct ancient light environments.

Light environments strongly influence the composition and structure of terrestrial ecosystems and climates. Further, light intensity impacts both a plant’s leaf morphologic traits and its chemical composition, making it possible to quantify how these variables change in response to light intensity. Thus, it is possible to use leaf morphology and chemical composition to reconstruct ancient light environments, which can provide critical insights into past environments. Here, we present results focused on the development of a proxy for light availability using leaf size and shape (physiognomy) and chemical composition from modern Sycamore leaves that were grown under varying degrees of light availability in an outdoor light experiment. We found notable differences in leaf physiognomic variables, such as leaf area and perimeter, across light environments; and results from 13C NMR spectroscopy also indicate differences between light environments, with more abundant in lipids and less abundant in lignin found in low light conditions. Physiognomic and geochemical data were used to develop three different multivariate models for predicting daily light integral (DLI) that can applied to the fossil record. Using these models, we analyzed early Paleocene Platanites fossil leaves from the San Juan Basin, New Mexico to reconstructed ancient light conditions to help understand light availability and its impacts on the ecosystem and plant communities of early Paleocene.