The effects of reduced and elevated CO₂ and O₂ on the seaweed <i>Lomentaria articulata</i>

Abstract

ABSTRACT We grew a non‐bicarbonate using red seaweed, Lomentaria articulata (Huds.) Lyngb., in media aerated with four O 2 concentrations between 10 and 200% of current ambient [O 2 ] and four CO 2 concentrations between 67 and 500% of current ambient [CO 2 ], in a factorial design, to determine the effects of gas composition on growth and physiology. The relative growth rate of L. articulata increased with increasing [CO 2 ] up to 200% of current ambient [CO 2 ] but was unaffected by [O 2 ]. The relative growth enhancement, on a carbon basis, was 52% with a doubling of [CO 2 ] but fell to 23% under 5× ambient [CO 2 ]. Plants collected in winter responded more extremely to [CO 2 ] than did plants collected in the summer, although the overall pattern was the same. Discrimination between stable carbon isotopes (Δ 13 C) increased with increasing [CO 2 ] as would be expected for diffusive CO 2 acquisition. Tissue C and N were inversely related to [CO 2 ]. Growth in terms of biomass appeared to be limited by conversion of photosynthate to new biomass rather than simply by diffusion of CO 2 , 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.