First Name:
Kristin
Last Name:
Buchner
Major Department:
Biology
Thesis Director:
Ray Williams
Date of Thesis:
May 2009
Two studies were conducted to better understand the role of defensive plant chemicals in mediating plant-insect interactions. First, to address how multiple, interacting climate drivers may affect terpene content in Solidago canadensis, leaf specimens were sampled from an old-field plant community grown for over three years under simultaneous carbon dioxide (CO2), temperature, and water manipulation. The goal was to determine which climate variable, or combination of variables, may affect plant terpenes. Terpenes are compounds that are known to play a role as defensive allelochemicals in plants. Plant tissue was sampled in June 2008 and terpenes were quantified using gas chromatography. Results show that a reduction in available water had a significant effect on total plant terpenes, as the average terpene concentrations increased from 0.168 mg/g to 3.353 mg/g. Likewise, the combination of water reduction and increased atmospheric CO2 variables significantly increased terpene concentrations. No significant increases were observed for raised temperature or CO2 concentrations alone. For the four individual terpene compounds identified, the interaction of all three climate variables produced a significant effect on the area of one compound. This effect was also seen when temperature increases and water restrictions were present, or with increases in CO2 concentrations and water restrictions. Reduced water supply alone had a significant effect on the area of a second identified terpene compound. These data demonstrate that principal climate drivers, especially soil water, may alter important chemical constituents in some plant species.
The second study on defensive plant chemicals was in collaboration with the local North Carolina Agricultural Extension. This study was designed to quantify the terpene levels in Fraser Fir, Abies fraseri, which had been either attacked by pests or unaffected. Terpenes were sampled from healthy and insect infested areas of the same tree to see if localized variation in terpene concentrations occurred. We found that there were, on average, more terpenes present in healthy, uninfested areas of the trees versus insect infested areas. This localized variation suggests the firs are allocating carbon differently in certain parts of the tree. In summary, data from both theSolidago and the Abies studies suggest that the terpene content of various plant species may be altered by environmental factors such as climate variation or pest infestation.