Chemotype, maternal genotype, or field neighbors: what influences performance and resource allocation in a perennial plant species the most?

Plants have to allocate resources into their growth and reproduction but also in phytochemicals used in interactions with their environment. Some species display an extraordinarily high diversity of such phytochemicals, called chemodiversity. In stands with different neighbors, plot chemodiversity may be even higher and provide associational resistance. Little is known about trade-offs in investment into growth and reproduction versus chemodiversity in plant individuals growing in chemically different neighborhoods.We investigated such trade-offs using the perennial Tanacetum vulgare, which shows differences in leaf terpenoid composition, forming distinct chemotypes. We planted plots consisting of five plants of one of five chemotypes (homogenous neighborhoods) and plots consisting of five different chemotypes (heterogenous) in a field. Plants within each block were offspring from different mother plants (here called maternal genotypes). Over 2 years, plant performance traits related to growth and reproduction were recorded and the leaf terpenoid profiles were measured once. Depending on the chemotype, plants had significantly different chances of flowering. Plants in heterogenous plots produced a higher maximum number of flower heads than those in homogenous plots. The maternal genotype explained some of the variance in growth- and reproduction-related traits. No significant correlations were found between the terpenoid functional Hill diversity (FHD) or its components (terpenoid richness, evenness, and structural disparity) and growth- and reproduction-related plant traits. Our results suggest that both the terpenoid chemotype of an individual and the chemodiversity of its neighborhood can impact reproduction-related traits, possibly driven by interactions of the individual with the environment and different resource allocation.