Semester

Spring

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Richard Thomas

Committee Co-Chair

William Peterjohn

Committee Member

Edward Brzostek

Committee Member

Jonathan Cumming

Committee Member

David Nelson

Abstract

The frequency and severity of extreme environmental conditions will continue to increase under global environmental change. How terrestrial plants respond to prolonged, and often novel environmental stressors, will have profound impacts on, and feedbacks with, the Earth climate system at local to continental scales. Central to these feedbacks are plant stomata, actively regulated pores on the leaves of plants that act as a control valve over the fluxes of carbon dioxide (CO2) into the leaf during photosynthesis and water vapor (H2O) out of the leaf during transpiration. Importantly, changes in stomatal aperture do not affect the fluxes of CO2 and H2O equally, tipping the balance between CO2 uptake and H2O loss, or water use efficiency (WUE), from the leaf to the canopy scale. Understanding the environmental factors driving changes in leaf physiology is of paramount concern under climate change as small changes in tree WUE can have major effects on biogeochemical processes over large geographical areas. In this dissertation, I use a dendroisotopic approach to investigate the drivers of tree growth and intrinsic water use efficiency (iWUE) over the twentieth century, a period of rapid environmental change. I begin by synthesizing tree ring carbon and oxygen isotope data from published literature to examine how changes in the underlying component parts, photosynthesis and stomatal conductance to water, have driven changes in iWUE since the early twentieth century. I then focus my analysis to the Central Appalachian Mountains in the eastern United States, where I investigate how moderate climate change, along with reductions in acidic air pollution, have affected the growth and physiology of red spruce, a tree species that has been historically sensitive to acidic pollution. Finally, I expand my analyses of the environmental drivers of growth and physiology to two of the most common broadleaf deciduous tree species in the eastern United States, northern red oak and tulip poplar. This research suggests at the global scale, most tree species have shown increasing iWUE since the early 1900s, which positively accelerated in 1963, and has largely been a result of stimulated photosynthesis. At a more local scale, I found reductions in acidic pollution, alongside increases in atmospheric CO2 concentrations, led to increased growth and iWUE of red spruce trees since ca. 1989. Lastly, I found the tree species studied exhibit a range of sensitivity to acidic pollution—while red spruce trees were highly sensitive, the two studied broadleaf deciduous trees were less so, highlighting the nuance and complexity behind tree responses to environmental change. Overall, these results showcase the active physiological response of trees to environmental change consistent with physiological theory and will help guide decisions regarding the importance of environmental factors in future model development and parameterization.

Embargo Reason

Publication Pending

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