Toward re-scaffolding the Phanerozoic : an improved representation of plants in the Late Paleozoic Ice Age.


Plants have served as the scaffolding of terrestrial ecosystems for hundreds of millions of years. Era-appropriate vegetation function and distribution are critical to resolve Earth’s natural history and potential future climates. However, plants have evolved and functioned differently across the Phanerozoic. This work aims to clarify plant function and ecosystem impacts in the Late Paleozoic Ice Age (LPIA, Pennsylvanian Subperiod), a representative time period and the most recent Icehouse before the present one. Pursuant to this aim I present: (Chapter Two) the first process-based global vegetation cover estimate for the LPIA, (Chapter Three) the first fossil-derived simulations of sapwood dysfunction in a paleo-ecosystem model, and (Chapter Four) an approach to stomatal pore measurement to allow resolution of lineage functional differences. In Chapter Two, I use GENESIS v3 global climate model data, and fossil-derived plant traits to parameterize the paleo-ecosystem model Paleo-BGC. Simulation results corroborate near-global vegetation cover based on leaf water balance. However, vegetation cover was limited by freezing temperatures, affecting surface runoff and mineral transport. Stem properties likely also limited Pennsylvanian plants. In Chapter Three, I expand Paleo-BGC to explore the importance of stem hydraulic properties of plants to ecosystem processes as an intersection of climate and natural selection associated with anatomical constraints on water supply. The limited ability of ancient plant stems to tolerate water stress suggests that even subhumid conditions certain plant types may have been water limited. These modeling approaches are based on incomplete plant physiological information due to open topics in that field regarding differences in stomatal function, which may have distinguished plant groups and their role in ecosystems for hundreds of millions of years. Toward the resolution of functional differences, I present (Chapter Four), an improved method for measuring stomatal pores in vivo that: 1) allows the characterization of additional pore dimensions (i.e., pore depth), 2) avoids artifacts of previously described methods, and 3) is applicable across a range of experimental conditions. Reconciling the details of extinct plant function by combining inferences from models, natural history, and Plant Physiology will allow improved predictions of future climate change impacts on ecosystems.



Modeling. Carboniferous. Freezing. Forest cover. Runoff. Sapwood. Leaves. Allometry. Cavitation. Xylem. Tracheids. Guard cells. Stomata. Scanning electron microscopy. Light microscopy. Imaging equipment.