Poster

         Paleobotany

Insights into Climate Reconstruction From Palm Leaf Traits

Presenting Author
Michael Machesky
Description
In order to mitigate the impacts of anthropogenic climate change on extant organisms and modern ecosystems, it is important to understand how life responded to past changes in climate. Plants are of specific interest to global change scientists, as their leaves interact directly with the atmosphere via photosynthesis and transpiration. Certain traits of plants are sensitive to environmental, climatic, and ecological factors and thus create a record of the plant’s local environment through its leaf morphology and chemistry. Presently, the majority of paleoclimate reconstruction using plant fossils has been applied at mid to high-latitudes, leaving a gap in the tropics and sub-tropics for paleoclimate reconstruction analyses. Arecaceae (palms) are particularly promising for low-latitude paleoclimate study because of their worldwide low-latitude distribution and persistence in extreme climatic conditions, their commercial and agricultural importance, and their extensive fossil record dating from the Late Cretaceous through the entirety of the Cenozoic. This study investigates how palm leaf traits record climate changes both geographically (across ~7.5° latitude gradient and ~12° longitude gradient) and temporally (1864-present) with implications for tracing (sub)tropical paleoclimatic conditions. Models combining leaf traits such as stomatal density and size with leaf carbon isotope discrimination (Δleaf) yield reliable pCO2 estimates, but could potentially be further constrained with vein density, measured as vein length per area (VLA), by refining mesophyll conductance estimates. We measured each of these traits on leaves from the palm species Sabal palmetto (n=184), Caryota urens (n=32), and Phoenix dactylifera (n=25) collected both from living plants across the Southeastern United States (n=149) and from worldwide historical collections housed in herbaria dating back as far as 1864 (n=92). Climate data were compiled for each collection location and analyzed for their relationship to individual leaf traits from PRISM Climate Group and WorldClim2; these climate variables included mean annual temperature (MAT), mean annual precipitation (MAP), and vapor pressure deficit. While the average Δleaf of each species fell within the expected range of C3 plants (~18.00–22.00‰), S. palmetto and C. urens showed much greater ranges in Δleaf values with maxima above the expected range (17.49–25.98‰ and 18.02–28.07‰, respectively) and showed higher discrimination overall than P. dactylifera (17.44–21.95‰). This difference suggests that P. dactylifera and its fossil relative Phoenicites is the best candidate for paleoclimatic reconstruction, as its isotopic behavior is most similar to that of plants currently applied to existing models.