Genotype-density interactions in a clonal, rosette-forming plant: cost of increased height growth?

Game theoretical models predict that plants growing in dense stands invest so much biomass in height growth that it trades-off with investment in other organs such as the leaves, leading to decreased plant production. Using the stoloniferous plant Potentilla reptans, we tested the hypothesis that genotypes investing more in the petioles in response to increased density show a greater decrease in total plant mass. We also tested whether a greater increase in mother ramet investment would lead to a greater decrease in investment in vegetative propagation. To uncouple costs and benefits of investments in petioles, ten genotypes that were known to differ in their response to shading signals were grown in monogenotypic stands at two different densities. Genotypes differed in their increase in petiole investment in response to an increase in density, but not in their decrease in total plant mass or root mass. Total lamina area per plant did not differ significantly between the densities, nor did the mass invested in the laminae per unit of total plant mass. Genotypes differed considerably in the change in vegetation height and petiole investment, but this was not significantly negatively correlated with the change in total plant mass. The genotypes did differ in the change of mass investment in the mother ramet: a greater increase in investment in the mother ramet was correlated to a greater decrease in vegetative propagation. While a greater increase in height investment did not lead to a greater decrease in biomass production, it did lead to a decrease in vegetative propagation. This ability to change allocation towards the mother ramets may imply that competition within a stand of stoloniferous plants does not necessarily result in lower total biomass production due to increased height investment.