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Dissertation/Thesis Abstract

The effects of atmospheric composition, climate, and herbivory on plant secondary metabolism and volatile organic carbon emissions
by Trowbridge, Amy Marie, Ph.D., University of Colorado at Boulder, 2012, 164; 3527408
Abstract (Summary)

Quantifying the biosynthesis and emission of terpenes by plants is necessary to understand ecological interactions and improve global atmospheric models. Many studies have addressed the importance of individual factors influencing terpene production and release into the atmosphere, but few have investigated complex interactions between multiple variables and the resulting chemistry's effects on interactions between organisms across multiple trophic levels. To address this gap in our knowledge, I conducted a series of experiments to examine abiotic and biotic controls over terpene synthesis and emission in Poplar x canescens and Pinus edulis, in which terpenes play prominent roles in plant physiological protection (isoprene) and defense (monoterpenes). Increases in atmospheric CO2 resulted in a smaller contribution of stored extra-chloroplastic carbon towards isoprene biosynthesis and a larger investment from recently assimilated carbon in poplar. In addition to climate change scenarios, it is also critical to understand how abiotic and biotic processes affect terpene concentrations and emissions in situ. Tiger moth herbivory increased pinyon pine monoterpene fluxes three to six fold during spring feeding, but summer drought decreased emissions while maintaining high levels of foliar concentrations. Following a release from drought stress, previously damaged pinyon pines exhibited significantly higher emission rates, potentially due to a drought delayed stimulation of induced monoterpene synthesis. I then performed a series of artificial diet experiments investigating how herbivore-induced monoterpenes observed in the field influences insect performance. While the synergistic effect of all monoterpenes present resulted in a trade-off between investment in immunity and growth, diets containing monoterpene levels mimicking herbivore damage encouraged further herbivory with no increase in growth but enhanced immunity to parasitoid infection. To further isolate temperature versus water status controls on monoterpene dynamics, I conducted a pinyon pine transplant experiment. Drought had little influence over the production of foliar monoterpenes, which is largely under genetic control. However, observed stomatal control over emission rates suggests that plant ecophysiology plays a much larger role in controlling monoterpene fluxes than previously thought. Together, my research provides novel insights into the underestimated contribution of ecophysiology in understanding the role of terpenes in higher trophic level interactions and coevolutionary processes.

Indexing (document details)
Advisor: Monson, Russell K.
Commitee: Bowers, Deane, Seastedt, Timothy R., Smith, Dena M., Townsend, Alan R.
School: University of Colorado at Boulder
Department: Ecology and Evolutionary Biology
School Location: United States -- Colorado
Source: DAI-B 74/02(E), Dissertation Abstracts International
Subjects: Botany, Ecology, Entomology, Climate Change
Keywords: Herbivory, Isoprene, Monoterpenes, Plant defenses, Plant secondary metabolism, Tritrophic interactions, Volatile organic carbon emissions, Volatile organic compounds
Publication Number: 3527408
ISBN: 978-1-267-61675-3
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