9306637 Schmitt Many plants display striking stem elongation and other morphological responses to the reduced ratio of red to far red light (R:FR) characteristic of vegetation shade; recent physiological studies have shown that these responses can be induced by the R:FR of light reflected onto plant stems by neighbors. Plant physiologists have suggested that shoot elongation in response to reduced R:FR is advantageous because it enables plants to sense and avoid competition for light. On the other hand, shoot elongation is thought to be disadvantageous at low density. The study proposed here will provide the first test of these predictions in an evolutionary context. By examining the relationship between elongation and fitness at manipulated densities in natural populations of the common native annual Impatiens capensis (jewelweed or touch me not), Dr. Schmitt will determine whether elongation in response to low R:FR is favored in crowded stands, but disadvantageous at low density. Moreover, by using R:FR to induce or inhibit elongation, the performance of experimental plants with "appropriate" and "inappropriate" morphologies can be compared both at low density and in dense canopies. Dr. Schmitt will also examine genetic variation in response to R:FR within and between natural populations to determine the potential for this trait to evolve and test for adaptive differentiation in response to light quality among pop ulations. The integration of quantitative genetic analysis, studies of population differentiation and adaptation, and direct measurement of selection in different environments will provide valuable information about the evolution of an ecologically important functional trait. This research will integrate genetic, physiological, and population biology approaches to the study of adaptive plasticity, and will introduce physiological methods for using R:FR to manipulate morphology to plant population biologists. %%% The results will contribute to understanding how plants interact in natural communities and will provide an ecological and evolutionary context for current research on the molecular genetics and physiology of plant responses to light spectral quality. This work will also be relevant to agriculture and forestry because it will provide useful information about how response to R:FR affects performance and yield in dense stands.
