Photosynthetic potential of sun and shade Viola species

Abstract

The photosynthetic responses of a forest floor violet (Viola blanda) and a related meadow species (Viola flmbriatula) grown under controlled conditions were measured to test the prediction that these two species were photosynthetically shade and sun adapted, respectively. Based on their low photosynthetic and dark respiration rates, and low light saturation and compensation points, both violets can be classified as shade-tolerant. The forest species was photosynthetically and morphologically inflexible when grown under high light conditions, which led to chlorosis and greatly decreased photosynthetic performance. Conversely, the meadow species was both photosynthetically and morphologically flexible; its photosynthetic performance allowed it to grow well under both high and low light regimes. As a consequence, morphological flexibility may play a greater role than physiological (i.e., photosynthetic) plasticity in regulating the distribution of these two violets under field conditions.