Influence of sunlight and soil nutrients on clonal growth and sexual reproduction of the understory perennial herb Sanguinaria canadensis L

Sanguinaria canadensis L. is a rhizomatous understory perennial herb that varies considerably in clone size, leaf size and allocation to sexual reproduction among local populations. Permanent plots were established in a high-light site with large, many-leafed plants and a low-light site with small, few-leafed plants. Within these plots, a reciprocal transplant study was performed to separate local evolutionary differentiation from environmentally determined differentiation. Also, half the plots in each site were fertilized to explore effects of soil fertility on vegetative growth and sexual reproduction. Plants from a third high-light site were used in a potting study to explore combined influences of elevated sunlight and fertilization on vegetative growth and sexual reproduction. Fertilization resulted in plants with proportionally fewer small and more large leaves in high-light permanent plots and had no effect on plants growing in low-light permanent plots. Fertilization increased leaf number and total leaf area, but had no influence on seed production in the potting and reciprocal transplant studies. Unshaded plants had significantly more leaves and greater total leaf area in the potting study. Also, in the high-light site of the reciprocal transplant study, both fertilized and unfertilized plants (especially fertilized plants originating from the high-light site) had more leaves and a higher total leaf area per plant than plants growing in the low-light site. Light intensity did not influence seed production in the potting study; however, more seeds were produced on plants growing in the high-light site than in the low-light site. Mortality was high for plants transplanted into the low-light site and for fertilized plants growing in shade in the common garden study. Clonal growth as measured by leaf size and leaf number in S. canadensis is highly plastic and responds vigorously to increased sunlight and to fertilization when under high-light conditions. In contrast, sexual reproduction exhibits relatively little plasticity. We suggest that local populations of S. canadensis rapidly respond to increases in light and nutrients associated with disturbance through increased clonal growth. This rapid response to environmental variability may partly explain the patchy spatial distribution of S. canadensis populations.