Plastic Responses to Single and Combined Environmental Stresses in a Highly Chemodiverse Aromatic Plant Species.

Plants face various environmental stresses, to which they respond in different ways. Due to climate change, it is expected that plants will encounter increased phases of drought and changes in herbivory. This study thus aimed to evaluate the intra-individual variation in responses, that is phenotypic plasticity, to single and combined stresses, including drought and insect herbivory. We used plants of the aromatic species Tanacetum vulgare, which are characterized by distinct terpenoid chemotypes and metabolic fingerprints shaped by maternal origin. Clones were exposed to no stress, drought, herbivory, or a combination of both. The impacts of these treatments were determined in terms of aboveground biomass as well as emission rates or concentrations, richness, and functional Hill diversity (FHD) of volatile organic compounds (VOCs), stored leaf and root terpenoids, and leaf metabolic fingerprints. Drought resulted in lower plant aboveground biomass, VOC richness, and VOC FHD. Herbivory had no effect on biomass, but increased the VOC emission rates and richness, also in combination with drought. The treatment significantly affected the phenotypic plasticity of the aboveground biomass and VOC emission. Our findings highlight the importance of studying intra-individual variation in plant responses to different stresses and their combinations to fully comprehend the finely tuned chemodiversity.