CELL WALL UNDULATION AS SHADE PROXY IN CERCIDIPHYLLUM JAPONICUM LEAVES

Light environment affects leaf morphology from the whole blade down to the individual cells, and fossil leaf morphology is used as a proxy tool in reconstructing ancient ecosystems. Thus, constraining the morphological variability determined by light environment in modern plants allows for more accurate interpretation of fossil data. This study investigates the epidermal-cell and whole-leaf morphology of leaves from a Cercidiphyllum japonicum tree and how it correlates to light environment, with particular focus on cuticle cell wall undulations (UI), which can be used as a proxy for light environment when making pCO₂ models and reconstructing canopy cover. UI as a proxy for light is particularly important for reconstructing ancient pCO₂ levels, as the methods used require that the fossil leaves being used be from the same light environment (i.e. sun leaves). Previous studies show that the top sides of leaves tend to be less sinuous, and that sun leaves are also less sinuous than their shade counterparts. For this study, leaves were collected from one tree over two collection periods: one in fall of 2018, collecting sun, shade, and litter leaves just before senescence; the other collection period formed a time series, starting at bud burst in spring of 2019 and continuing to senescence in the fall. The comparisons of whole-leaf measurements to the UI trends of the cuticle cells of the leaves in the 2018 tests the robustness of UI in predicting a leaf’s light environment, as well as establishing the sun/shade composition of the litter assemblage, which mimics a natural fossil assemblage. Of the variables measured, the UI for the top-side (adaxial) epidermal cells and leaf mass per area (LMA) have the strongest correlation to light environment. The 2019 time series then determines when UI is set as leaves grow to maturity, and it determines this separately for leaves grown in natural, bright sun and deep shade, something which has not yet been studied in woody dicots.