Volatiles, Plant-Plant Interactions And Insect Herbivory: Lessons From Old-Field Communities That Inform Community Ecology

Abstract

Plants interact with numerous organisms in their communities, including neighboring plants. In large part, these interactions are mediated by blends of volatile organic compounds (VOCs) that plants emit into their headspaces, which may inform other organisms by reflecting plants' physiologies and the biotic and abiotic stresses they are experiencing. However, while the ubiquity of VOC-mediated plant-plant interactions is well established, their mechanisms, ecological outcomes and evolutionary trajectories remain largely uncharacterized. Collectively, these experiments seek to close some of these knowledge gaps, using tall goldenrod (Solidago altissima) and its diverse herbivore community as a model system. Chapter 1 reviews the literature on plants' responses to herbivores and VOCs from neighboring plants - highlighting numerous parallels between the molecular mechanisms and ecological outcomes underlying induced responses to herbivores and VOC-mediated plant-plant interactions. We emphasize the need to conduct mechanistic and ecological studies that directly compare plants' responses to VOCs vis-à-vis herbivory. Chapter 2 examines the effects of VOC-mediated plant-plant interactions on herbivore performance and behavior. It reveals that these interactions may result in VOC-exposed and herbivore-damaged plants becoming of equally bad food quality for subsequent herbivores - reducing feeding and increasing between-host movement - in spite of the fact that induced leaf chemistry of damaged and exposed plants is not identical. Chapter 3 explores whether VOC-mediated plant-plant interactions have specific effects on different herbivores. We demonstrate that herbivore-induced VOCs elicit specific chemical changes in exposed plants, and that these chemical changes have specific effects - making VOC-exposed plants more or less resistant to subsequent herbivores. Chapter 4 explores whether VOC emission and perception vary across plant genotypes. We find that genotypes vary in their abilities to emit and perceive VOCs, and that receivers may induce resistance or susceptibility to subsequent herbivores, or not respond, depending on the genotypes of VOC-emitting plants. Collectively, these experiments reveal that the identity of a plant's neighbors affects available information and its resistance state in its community. The observed specificity and genotypic variation in VOC-mediated plant-plant interactions suggests that it is worth exploring the costs and benefits of these interactions in the context of the genetic structure of plant populations, and the diversity/composition of the herbivore community.