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.