Photosynthetic responses of Ulva lactuca at very low light

Abstract

Changes in photosynthetic variables and dark respiration were measured in Ulva lactuca acchmated to continuous photon f l u densities between 0 and 55prnol n ~-~ s-' at ?OC for up to 80d. Photosynthetic light harvesting efficiency (a) was lughest in U. lactuca acclimated to intermedate light levels of 8.8 and 25 prnol m-2s-1 and was associated with maximum chlorophyll density and light absorptance. Below 2.5 pm01 m-'s-', energy capture was insufficient to maintan the maximum light harvesting apparatus and at 55 pm01 m-2s-i, light was no longer fully lirnihng to photosynthesis. The light harvesting efficiency (m) was linearly related to light absorptance (A). The quantum efficiency (0, = a ~-')