Intraspecific chemical variation ofTanacetum vulgareaffects plant growth and reproductive traits in field plant communities

Intraspecific plant chemodiversity plays a fundamental role in interactions between plants and their interaction partners. However, how chemodiversity at the stand level (plant communities that vary in the number and type of plant chemotypes that grow in them, i.e., chemotype richness) affects ecosystem functioning is not fully understood. We describe a biodiversity experiment using six chemotypes of common tansy ( Tanacetum vulgare L., Asteraceae) to manipulate intraspecific plant chemodiversity at the plot level. We tested the effects of chemotype identity and plot-level chemotype richness (1-6) on plant growth and reproductive traits at plant and plot levels. We found that chemotypes differed in growth and reproductive traits and that traits were affected by the plot-level chemotype richness. Although morphological differences became less pronounced over time, reproductive phenology patterns persisted. It suggests that chemotypes initially adopted different growth strategies, which may facilitate their establishment in nature. Although chemotype richness did not lead to overyielding effects, plot-level trait means were affected by the presence or absence of certain chemotypes in a plot, and the direction of the effect depended on the chemotype. We analyzed plot-level headspace emissions and found that blends released from plant communities were neither richer nor more diverse with increasing plot-level chemotype richness. However, we found that plots became more dissimilar in their headspace terpenoids as they were more dissimilar in their leaf-terpenoid profiles. This long-term field experiment will allow further investigation into plant-insect interactions and insect community assembly in response to intraspecific chemodiversity.