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ABSTRACT Unexpected Environmental Conditions Suggest Paleozoic Plant Morphological Gas Conductance Models Christopher J. A. Skrodzki Director: Joseph D. White The importance of plants in regulating and defining Earth’s greenhouse gas and water vapor composition has been previously demonstrated. This study addresses the relationship between the morphological and physiological response of paleo-plants to changing atmospheric gas compositions, which in turn lead to changes in atmospheric pressures. Higher atmospheric pressures are here suggested to alter plant gas exchange dynamics and Photosystem II activation. These effects increases plant bulk carbon dioxide, an important greenhouse gas, and water vapor transport leading to changes in Earth’s climate through alterations in the carbon cycle and hydrological balance. To elucidate this relationship, the response of two extant lycopod species, Selaginella kraussiana and Lycopodium lucidulum, was measured in response to an atmospheric pressure of 5kPa over current conditions. Results show that L. lucidiulum changed leaf shape, decreasing in stomatal density but increasing in stomatal index, in response to higher pressures and harbors a closer correlation with stomatal conductance values in response to stomatal index over maximal stomatal aperture values. S. kraussiana, exhibited an increase in stomatal density and index values in response to increased pressures and that its stomatal conductance values are more dependent on maximal stomatal aperture values than stomatal index This research demonstrates that paleo-plant stomatal indices are by themselves not accurate measures of atmospheric carbon dioxide or water vapor values as two extant paleo-plants of closely related phyla exhibit confounding results. These results suggest a reexamination of geological atmospheric conditions by showing that paleo-plant gas exchange can be influenced by atmospheric conditions other than carbon dioxide composition. APPROVED BY DIRECTOR OF HONORS THESIS: ______________________________________________________ Dr. Joseph D. White, Department of Biology: Baylor University APPROVED BY HONORS PROGRAM: ______________________________________________________ Dr. Andrew Wisely, Director DATE: ____________________________ UNEXPECTED ENVIRONMENTAL CONDITIONS SUGGEST PALEOZOIC PLANT MORPHOLOGICAL GAS CONDUCTANCE MODELS A Thesis Summited to the Faculty of Baylor University In Partial Fulfilment of the Requirements for the Honors Program By Christopher J. A. Skrodzki Waco, Texas May 2015 TABLE OF CONTENTS List of Figures ........................................................................................................................pg. iv List of Tables .........................................................................................................................pg. v Abbreviations ........................................................................................................................pg. vi Acknowledgments..................................................................................................................pg. vii Dedication ..............................................................................................................................pg. viii Chapter One: Introduction .....................................................................................................pg. 1 Background ................................................................................................................pg. 1 Hypotheses .................................................................................................................pg. 3 Chapter Two: Materials and Methods....................................................................................pg. 5 Experimental Design ..................................................................................................pg. 5 Morphological Effects ...............................................................................................pg. 6 Gas Exchange Rates ...................................................................................................pg. 6 Photosystem II Activation ..........................................................................................pg. 8 Chapter Three: Results ...........................................................................................................pg. 9 Morphological Effects ...............................................................................................pg. 9 Gas Exchange Rates ...................................................................................................pg. 11 Photosystem II Activation ..........................................................................................pg. 16 ii TABLE OF CONTENTS Chapter Four: Discussion .......................................................................................................pg. 17 Morphological Effects ...............................................................................................pg. 17 Gas Exchange Rates ...................................................................................................pg. 18 Photosystem II Activation ..........................................................................................pg. 19 Concluding Remarks ..................................................................................................pg. 20 Future Directions .......................................................................................................pg. 21 Appendices .............................................................................................................................pg. 23 Appendix A – Global climate change over geological time .....................................pg. 24 Appendix B – Modern angiosperm leaf morphology and gas exchange ...................pg. 25 Appendix C – Model of used pressure chambers of this study ..................................pg. 26 Appendix D – Model of pressure chamber for proposed further studies ...................pg. 27 Appendix E – Full data table of morphological effects .............................................pg. 28 Appendix F – Full data table of gas exchange rates ..................................................pg. 29 Appendix G – Full data table of Photosystem II Activation ......................................pg. 30 References and Suggested Reading .......................................................................................pg. 31 iii LIST OF FIGURES Figure 1 – A L. lucidulum enamel impression after treatment of ≈105kPa at 100X. ...........pg. 11 Figure 2 – CO2 Conductance vs. Stomatal Index ..................................................................pg. 14 Figure 3 – CO2 Conductance vs. Maximal Stomatal Aperture Area .....................................pg. 15 iv LIST OF TABLES Table 1 – Morphological Effects of Different Atmospheric Conditions ...............................pg. 10 Table 2 –Gas Exchange Rates in Response to Different Atmospheric Conditions, part 1 ....pg. 13 Table 3 – Photosystem II Activation in Response to Different Atmospheric Conditions pg. 16 v ABBREVIATIONS Amax – Maximal Stomatal Aperture Area CO2 – Carbon dioxide ETR – Linear Electron Transport Rate GCO2 – Carbon dioxide gas Conductance GH2O – Water vapor Conductance GL – Leaf carbon dioxide Conductance GS – Stomatal carbon dioxide Conductance Ha – Alternate Hypothesis Ho – Null Hypothesis Index – Stomatal Index KP – leaf water Conductivity Mya – Million years ago PAR – Photosynthecially Active Radiation Pn. – Photosynthesis ΦPSII – PhotoSystem II Quantum Yield RuBisCO – Ribulose-1,5-Bisphosphate Carboxylate Trans. – Water Vapor Transpiration VPD – Vapor Pressure Deficit VPS – Saturated Vapor Pressure WUE - Water Use Efficiency vi ACKNOWLEDGEMENTS I would like to first and foremost sincerely thank Dr. White for helping me maintain a clear sense of focus for this thesis work, his honest critic and assistance editing this work, and for his inexorable patience in assisting me through this entire process. As well, I would find it wrong to not extend another thank you to all of the professors here at Baylor that have been a part of my personal journey in quenching my thirst for knowledge and introducing me to the world of real scientific research. Lastly, without the administrative support and opportunity of the Honor’s Program, none of this would have been written before you. vii Dedicated to A. C. M. For inspiring me to keep working, even when I know you will probably never read this. ~Thank you. viii CHAPTER ONE Introduction Background Lycophytes, also known as lycopsids, are the basal extant lineage of all vascular plants, of which the genera Selaginella (spike moss) and Lycopodium (club moss) are representative of a pre-transitional early-late phase of the Pennsylvanian epoch (Dimichele et al., 2009). The phylum Traecheophyte is considered polyphyletic with the genera Selaginella and Lycopodium representing distinctly derived orders of Sellaginales and Lycopidiales, respectively, with Lycopodium being the most basal (Bateman, 1990; Wikström and Kenrick, 2001). Two extant species, Selaginella kraussiana and Lycopodium lucidulum, contain tracheid structures which are representative of the flora dominating this time period (Bierhorst, 1971; Chu, 1974; Friedman and Cook, 2000). The adaptations of these organisms to effectively react quickly to periods of drought allowed survival through the arid late Devonian (Arrigo et al., 2013; Gueidan et al., 2011).
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