Intraspecific chemical variation of Tanacetum vulgare at plant and plot level affects plant growth and reproductive traits in field plant communities

Intraspecific plant chemodiversity plays a fundamental role in interactions between plants and their interaction partners. Individuals of a plant species can be clustered into chemotypes by dominant chemical compounds or their chemical composition. Intraspecific stands of plant communities can vary in the number and type of plant chemotypes that grow in them (i.e., chemotype richness). Chemotypic diversity at the stand level is a special case of intraspecific diversity that is predicted to increase stand-level ecosystem functioning. Here we describe a biodiversity experiment in which we manipulated intraspecific plant chemodiversity at the plot level using six different chemotypes of common tansy (Tanacetum vulgare L., Asteraceae). We tested the effects of chemotype identity and plot-level chemotype richness (1-6) on plant growth and reproductive traits under field conditions. We found that plant chemotypes differed in growth and reproductive traits, both at the plant level, and at the plot level, and that reproductive plant traits and plot-level trait means were affected by tansy chemodiversity. The plot-level trait means were influenced by the presence or absence of certain chemotypes in a plot. The community's headspace terpenoid blend minimally reflected plot-level leaf terpenoid compound blends. Although tradeoffs between chemodiversity and growth and reproductive traits were observed, the links between chemodiversity and traits expressed themselves in the early establishment but dissolved over time, suggesting that different chemotypes adopt different growth strategies, which may facilitate their establishment in nature. This long-term field experiment will allow for further investigation of the consequences of intraspecific chemodiversity for plant-insect interactions and insect community assembly.