The Relationship between Soil Fertility and Fire-Stimulated Floral Induction in Two Populations of Grass-Leaved Golden Aster, Pityopsis graminifolia

Abstract

Classic life-history theories of reproductive strategies ignore the relationship between the cost of reproduction and reproductive plasticity. In this study, I examined the extent to which two populations of a perennial plant (Pityopsis graminifolia) differed in their floral induction responses to manipulation of fire, clipping, and fertilization regimes. I also measured site differences in soil concentrations of several mineral nutrients. The two populations differed dramatically in their observed patterns of reproduction ; the north Florida population substantially increased rates of bolting in response to fire, clipping and litter removal, and nutrient addition, whereas the central Florida population did not. Soils at the central Florida site contained over three times the concentration of phosphorus compared to soils at the north Florida site. Soil phosphorus levels were significantly (albeit slightly) increased by fire at the north Florida site but not at the central Florida site. Results of a field experiment using clonal transplants indicated that the population differences in reproductive sensitivity to fire-related environmental changes were associated with genetic differences. A May fire was more effective at stimulating floral induction in clonal fragments from the north Florida site than from the central Florida site. The results of this study were consistent with the prediction that selection pressure for fire-stimulated flowering is most intense in habitats in which flowering is highly resource (e.g., phosphorus) limited. I hypothesize that fire-stimulated flowering may be a means of reducing the direct resource costs of reproduction.