Consequences of light limitation for carbon acquisition in three rhodophytes

Abstract

We investigated the consequences of growth at Limiting photon flux density (PFD) for the uptake of inorganic carbon by 2 species of red seaweed which are able to use H C 0 3 for photosynthesis [Palmaria palmata (Huds.) Larnour and Laurencia pinnatifida (L.) Kuntze] and one which is dependent on diffusive uptake of bulk CO, [Lomentaria articulata (Huds.) Lyngb.] We attempted to induce energetic limitation of plants and/or reduce their demand for inorganic carbon by growing them at a low PFD and comparing their carbon use characteristics with those of plants grown at high PFD. There were significant increases in the carbon isotope discrimination (more negative delta values relative to the PDB standard) when the 3 species were grown at 25 relative to 75 pm01 photons m-2 S-'. In the 2 species which are able to use bicarbonate, the decreased SI3c was associated with lower initial slopes of inorganic carbon uptake curves. Taken together, the changes in 6I3C and dissolved organic carbon uptake indicated that light-limited P. palmata and L. pinnatifjda were not using low concentrations of inorganic carbon as efficiently as were plants grown at high PFD. This hypothesis was further supported by evidence that light limitation also caused a reduction in C:N ratio and in the % dry matter made up of carbon in those species. In contrast, growth of L. articulata, which is dependent on diffusive uptake of CO, for photosynthesis, was inhibited by the higher PFD and there were no significant effects of growth PFD on inorganic carbon uptake efficiency, C:N ratio or % C in this species. KEY WORDS: Laurencja pinnatifida-Lomentaria articulata. Palmaria palmata. CO2-HCO,-. Light limitation. Photosynthesis. Stable carbon isotope ratios 0 Inter-Research 1994 Resale of full article not permitted

Inorganic carbon acquisition by red seaweeds grown under dynamic light regimes

“…The effects of fluctuating light relative to constant light were similar to those described previously for these species when grown under light-limitation (Kubler &Raven, 1994) . Palmaria palmata which has an active uptake system for inorganic carbon was more severely affected by the temporal pattern of light supply, in terms of the effectiveness of inorganic carbon uptake and the stable carbon isotope discrimination than was Lomentaria articulata, which relies on diffusive uptake of inorganic carbon .…”

“…were collected from Fife Ness, East Neuk of Fife, UK (2'35'W, 56'l 7' N) . Seaweeds were maintained in enriched sea water media at 10 °C, air equilibrium DIC, as described previously (KUbler & Raven, 1994) .…”

“…In the intertidal, these variations are compounded by the exposure of plants to unfiltered sunlight when emersed . The importance of light quantity for active inorganic carbon acquisition has been identified previously (Beardall, 1991 ;Johnston et al ., 1992 ;Kubler & Raven, 1994) . All of those studies compared carbon acquisition under continuous exposure to light of different photon flux densities (PFD) .…”

Phytoplankton and macrophyte contributions to littoral food webs in the Galician upwelling estimated from stable isotopes

“…Among the former, the higher δ 13 C values of macrophytes compared to those of phytoplankton were related to the thickness of the boundary water layer, which affects the diffusion of nutrients into the cells and causes fractionation of heavy isotopes (France 1995, Raven et al 2002. Low growth rates, typical of plants living in low light, subtidal environments (such as most rhodophyta) also cause characteristically low δ 13 C values because of a reduction in the active uptake of inorganic carbon (Kübler & Raven 1994). In addition, seagrasses have higher δ 13 C values than those of phytoplankton and macrophytes (McClelland & Valiela 1998).…”

The hydrodynamic effects of shape and size change during reconfiguration of a flexible macroalga

“…Realignment in response to the oscillatory flow typical of the intertidal zone (Denny, 1988) may increase photosynthetic rates by allowing alternate sides of the alga to be exposed to light. Such posture changes may also reduce self shading (Koehl and Alberte, 1988) and light competition among individuals in an algal canopy (Greene and Gerard, 1990;Kübler and Raven, 1994). At higher velocities, where forces approach those required to dislodge individuals in the field (Carrington et al, 2001), greater compression results in lower drag.…”