Effects of Chemical Variation on Competition and Insect Communities Across Solidago altissima Genotypes

Individuals within a plant species can differ greatly from one another, especially regarding the range of chemical compounds produced. However, the functions of many of these chemicals are unknown, but likely include defenses against herbivores, attractants for pollinators and seed dispersers, as well as mechanisms for resource competition. To assess the effects of foliar chemical composition on interspecific plant competition and insect communities, I conducted a common garden and greenhouse experiment using 24 genotypes of the allelopathic species Solidago altissima for which the foliar chemistry had been characterized. Using these data and chemical profiles of S. altissima, I linked foliar chemistry to plant performance, competitive ability and the foliar/floral insect communities. The common garden experiment showed there was great variation in foliar chemistry between the genotypes. Ecological patterns existed between foliar chemistry and plant performance, as foliar chemistry was strongly related to most measures of plant performance across genotypes. Pollinator communities were found to relate with total aboveground biomass, proportion of flower mass, and % light transmittance as well as plant chemistry. The greenhouse experiment showed marked variation in both rhizome and above-ground biomass growth for S. altissima. The above-ground biomass of Abutilon theophrasti, S. scoparium, and S. integrifolium had their biomass significantly reduced via competition with S. altissima. Chemistry significantly affected the biomass of both A. theophrasti and S. scoparium, suggesting that chemistry is a critical driver of competition for S. altissima