Collaborative Research: Seeing the forest with the leaves--inferring plant habit and ecophysiology from leaf fossils

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COLLABORATIVE RESEARCH: SEEING THE FOREST WITH THE LEAVES--INFERRING PLANT HABIT AND ECOPHYSIOLOGY FROM LEAF FOSSILSC. Kevin Boyce1 & Maciej A Zwieniecki2 (PIs)1.-Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637.2. Arnold Arboretum of Harvard University, Cambridge, MA 02138.Detached leaves are among the most common of plant macrofossils. Because leaves are the primary interface between plant and environment, fossil leaf morphology has been widely proven to be a valuable source of information regarding past climates and atmospheric compositions. From the leaf's perspective, however, the plant to which the leaf is attached is as much a part of its environment as regional climate. Thus, fossil leaves may also preserve an untapped wealth of information concerning the habit and ecology of the parent plant as well as the vegetation structure of the landscape. The primary goal of this project is to develop anatomical proxies for interpreting three parameters of whole-plant ecophysiology from leaf fossils using the emerging mechanistic understanding of how leaf structure and physiology are linked. 1) Plant habit -tall tree or low shrub- is provided from variance in vein density between leaf compressions with similar total vein number. 2) Adaptation to water vapor pressure deficit -a sunny, exposed environment or a shaded, understory environment- is provided by the ratio of the vein-vein and vein-leaf surface distances in anatomically preserved leaf fossils. 3) Carbon assimilation and transpiration capacities are provided by the density of veins per leaf surface area in leaf compressions. These tools will be established with a phylogenetically and ecologically diverse series of field-based measurements in both tropical and temperate forests, as well as greenhouse and growth chamber experiments to simulate conditions that no longer exist in the modern world. First applications will focus on the ecophysiology of key fossils during the Cretaceous/Early Cenozoic diversification of flowering plants and the late Paleozoic diversification of seed plants - key topics in their own right, but also important for the introduction of these techniques to the larger paleontological community.A crucial point is that the proxies are based in understood physiological mechanisms, not just in statistical correlations. Thus, they will be available to all paleontologists interested in any period of plant evolution from the first leaves and forests in the Devonian through to the Recent. These tools will aid reconstruction of fossils and understanding of the evolution of physiology and ecology. More broadly, this work will provide a new approach for constraining past climates and the carbon and hydrological cycles of deep time.