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Gowton, Chelsea Megan

University of British Columbia

Plant allocation of resources to defenses can impact their success in reducing herbivore damage. Of particular interest are indirect defenses, traits which recruit natural enemies, like predacious insects or parasitoids, which deter or kill herbivores. Indirect defenses are often phenotypically plastic and highly context specific, making it difficult to predict how they vary with biotic and abiotic factors. This thesis examines how biotic factors, such as rhizobia colonization, and abiotic factors, including elevated CO₂, nitrogen availability, and silicon accumulation, influence resource allocation to extrafloral nectar (EFN) production in Vicia faba. Using a series of growth chamber experiments, I examined the independent and interactive effects of biotic (rhizobia), and abiotic (atmospheric CO₂, nitrogen fertilization, and silicon) factors on plant allocation to EFN production. I hypothesized that increasing resource availability and reducing potential competition for carbohydrates will increase the amount of sugar in EFN. Across this series of experiments, I found elevated CO₂ on its own increased photosynthesis and foliar carbohydrates but did not increase EFN sugar content. Elevated CO₂ increased the proportion of active nectaries, suggesting its potential to influence predator foraging behavior. Rhizobia inoculation increased EFN sugar content, and nitrogen decreased rhizobia colonization of plant roots, but EFN sugar content was independent of nitrogen fertilization, indicating that while nitrogen availability influences rhizobia colonization, it does not directly affect EFN sugar content. In silicon rich environments, V. faba accumulated more silicon, which has been associated with heightened direct defense against herbivores, but simulated herbivory did not induce silicon or EFN defenses. Simulated herbivory, however, interacted with leaf silicon concentration to increase EFN sugar content. These findings demonstrate context dependency in plant allocation to indirect defense, with the induction of EFN under some conditions but not others. I did not detect clear tradeoffs between EFN and other traits, indicating EFN sugar content may not be reliant on limited resources. This research highlights the potential for unpredictability in multi-trophic interactions under global environmental change, particularly those reliant on plant allocation of carbon.

Text

2024-12-09

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89808

Plant Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/