Effects of Developmental Light Level on Photosynthesis and Biomass Production in Echinacea laevigata, a Federally Listed Endangered Species

Echinacea laevigata (Boyton & Beadle) Blake, or smooth coneflower, is an herbaceous perennial native to the piedmont of the southeastern United States. Of the 57 known historical populations, 21 (36%) remained at the time of its federal listing as endangered in 1992. It is thought that smooth coneflower populations benefit from disturbance and that suppression of fire is a significant cause for their decline. In order to effectively manage E. laevigata populations, it is important to understand how this species responds to changes in the light environment. While it is generally agreed that the species requires early successional habitats, the extent to which light limits plant development has not been quantified. We compare the effects of high, medium, and low developmental light levels on biomass allocation and photosynthetic performance as described by photosynthetic light response curves. Plants were raised under three light regimes (18%, 43%, and 100% of full sunlight) for approximately six months. Using a segregated experimental design, we found no significant difference in photosynthetic light response among plants grown at different light levels; quantum yield, maximum rate of photosynthesis, light saturation point, light compensation point, and dark respiration rates were not significantly different among the light treatments. This suggests that E. laevigata retains photosynthetic characteristics of sun-grown plants even when leaves develop in low or medium light. However, plants grown under low light (18% of full sun) had significantly lower root and flowering stem dry weight and number of flower heads than plants grown in full sun or moderate shade (43% of full sun). Therefore, in order to optimize biomass and flower production, important factors in population persistence, we recommend that light levels be maintained at or above 40% of full sun for E. laevigata populations.