Leaf shape can change in response to environmental cues and this plasticity is thought to allow the plant to maximize fitness in variable conditions. Carnivorous plants often have highly unusual leaves, as leaf function includes both light and prey capture. Leaves of the purple pitcher plant, Sarracenia purpureahave been shown to be narrower and flatter in response to nitrogen addition, potentially to maximize light uptake when nutrients are no longer limiting. We conducted studies to understand how pitcher plant leaves might vary in response to environmental variables. Sarracenia purpurea leaves were collected from a transect across a savannah near Sumatra, Florida. Soil conditions and light levels were determined near each collected leaf. Standardized measures were then taken for each leaf, and ordination (PCA) used to quantify shape variation. This shape variation was then correlated with the light availability and soil moisture. A greenhouse experiment was then used to quantify effects of light and nutrients on leaf shape. Replicate plants were grown for three months in a factorial design using 3 levels each of shade cloth and fertilizer “sticks”. Leaves were harvested, and ordination again used to analyze treatment effects on leaf shape.
Results/Conclusions
Leaves from the field exhibited significant variation in size and shape. The first PCA axis was related to size, the second axis identified variation in the narrowness of the tube and size of the dorsal leaf blade, and the third axis was correlated with the shape of the leaf opening. Increases in light and soil moisture were correlated with the third axis, producing with wider leaves in wetter, more open habitats. The greenhouse experiment found that the highest levels produced more tubular leaves with narrower hoods but proportionally wider blades. Nutrient addition had no significant effects on leaf shape, which is surprising as carnivory is thought to be an adaptation to low nutrient conditions. The effects of light were also surprising, because of the potentially conflicting effects of smaller blades, but wider hoods in low light. We suggest that that broader hoods can maximize light capture without loss of prey capture. Overall, the observed leaf variation may be useful for identifying environmental stressors both within and among populations in this wide-spread species and contributes to a growing literature on how leaf shape may serve as a bioindicator for climate change.