Effects of blue light on the vertical colonization of space by white clover and their consequences for dry matter distribution

The morphology of white clover is very sensitive to the light environment, especially to the ratio of red:far-red light and to photon irradiance. However, less is known about the effects of blue light on clover morphogenesis. Cuttings of white clover were grown for 56 d in two controlled chambers receiving light with similar photosynthetic efficiency and phytochrome photoequilibrium state but different levels of blue light: some plants were grown under orange light (very low blue light, 0.02 mu mol m(-2) s(-1)) or under white light containing blue light (83 mu mol m(-2) s(-1)). Other plants were switched from white light to orange light or vice versa, after 30 d. The absence of blue light modified the growth habit of clover and raised the laminae in the upper layer of the canopy by increasing petiole length, and petiole angle from the horizontal, and by raising stolons above the ground surface. Moreover, the absence of blue light had no effect on total leaf area and total dry weight per plant, but increased the leaf area and biomass of petioles of the main axis. Larger petioles and laminae were associated with the allocation of more dry weight to the petiole at the same petiole thickness but with thinner laminae. These results indicate that a decrease in blue light is involved in the perception of, and adaptation to, shading by the plant. (C) 1997 Annals of Botany Company.