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 t hat varies considerably in clone size, leaf size and allocation to sex ual reproduction among local populations. Permanent plots were establi shed in a high-light site with large, many-leafed plants and a low-lig ht site with small, few-leafed plants. Within these plots, a reciproca l transplant study was performed to separate local evolutionary differ entiation from environmentally determined differentiation. Also, half the plots in each site were fertilized to explore effects of soil fert ility on vegetative growth and sexual reproduction. Plants from a thir d high-light site were used in a potting study to explore combined inf luences of elevated sunlight and fertilization on vegetative growth an d sexual reproduction. Fertilization resulted in plants with proportio nally fewer small and more large leaves in high-light permanent plots and had no effect on plants growing in low-light permanent plots. Fert ilization increased leaf number and total leaf area, but had no influe nce on seed production in the potting and reciprocal transplant studie s. Unshaded plants had significantly more leaves and greater total lea f area in the potting study. Also, in the high-light site of the recip rocal transplant study, both fertilized and unfertilized plants (espec ially 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 grow ing in the high-light site than in the low-light site. Mortality was h igh 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 plast ic and responds vigorously to increased sunlight and to fertilization when under high-light conditions. In contrast, sexual reproduction exh ibits relatively little plasticity. We suggest that local populations of S. canadensis rapidly respond to increases in light and nutrients a ssociated with disturbance through increased clonal growth. This rapid response to environmental variability may partly explain the patchy s patial distribution of S. canadensis populations.