Mechanisms and traits associated with compensation for defoliation in Ruellia nudiflora

A full understanding of the ecology and evolution of plant tolerance to damage requires the measurement of a diversity of traits (including multiple fitness-correlates) and underlying mechanisms. Here, we address the compensatory response to defoliation in the perennial herb Ruellia nudiflora, measure biomass allocation patterns and relate them to compensation, and address multiple mechanisms and traits that determine compensatory ability. We used maternal full-sib lines of R. nudiflora and conducted a defoliation experiment in which half the plants of each line were subjected to removal of 40% of leaf area (the other half remained undamaged). Fitness-correlated traits, physiological traits, and leaf longevity were measured during a 2-month period after defoliation. Using another set of plants, we conducted a second defoliation experiment and measured the concentration of non-structural carbohydrates to test for root-to-shoot carbon mobilization as a compensatory mechanism. R. nudiflora showed full compensation in terms of fruit output, and compensatory ability was positively correlated with investment in root biomass in the absence of damage. In addition, defoliated plants produced shorter-lived leaves and had a greater concentration of starch in roots, suggesting that reduced leaf longevity and accumulation of below-ground carbon reserves act as compensatory mechanisms. By measuring multiple fitness-correlates and induced traits, we provide a comprehensive evaluation of R. nudiflora compensatory responses to herbivory.