The effects of reduced and elevated CO2 and O-2 on the seaweed Lomentaria articulata

We grew a non-bicarbonate using red seaweed, Lomentaria articulata (Huds,) Lyngb., in media aerated,vith four O-2 concentrations between 10 and 200% o f current ambient [O-2] and four CO2 concentrations between 67 and 500% of current ambient [CO2], in a factorial design, to determine the effects of g as composition on growth and physiology, The relative growth rate of L. art iculata increased with increasing [CO2] up to 200% of current ambient [CO2] but was unaffected by [O-2]. The relative growth enhancement, on a carbon basis, was 52% with a doubling of [CO2] but fell to 23% under 5x ambient [C O2], Plants collected in winter responded more extremely to [CO2] than did plants collected in the summer, although the overall pattern was the same. Discrimination between stable carbon isotopes (Delta(13)C) increased with i ncreasing [CO2] as would be expected for diffusive CO2 acquisition. Tissue C and N were inversely related to [CO2], Growth in terms of biomass appeare d to be limited by conversion of photosynthate to new biomass rather than s imply by diffusion of CO2, suggesting that non-bicarbonate-using macroalgae , such as L. articulata, may not be directly analogous to C3 higher plants in terms of their responses to changing gas composition.