Red alga Palmaria palmata—growth rate and photosynthetic performance under elevated CO₂ treatment

Abstract

Marine macroalgae offer a feasible solution for reducing CO₂ emissions by fixing CO₂ as algal biomass and thus providing a source of renewable energy. The perennial red alga Palmaria palmata was cultivated and supplied with increased CO₂ concentrations starting with 22 μmol kg⁻¹ (pH 8.53) to 9770 μmol kg⁻¹ (pH 6.04). Experiments covered test periods of 28 days, 7 days, and 2 h to examine the possible influence of different treatment durations. Biomass productivity over 28 days showed an increased production rate, which continuously declined with increasing CO₂ concentration. After 7 days, the productivity was below the controls, suggesting a lag phase or necessary adaptation period to elevated CO₂ concentrations of more than 7 days. Concerning the effects on maximum electron transport rate (ETR_max), light-harvesting efficiency (alpha), and light saturation of the photosynthetic electron transport (E _k ), a stimulating influence was identified with the effect becoming more significant the shorter the test period was. The treatment with elevated CO₂ concentrations for 28 days led to a decrease in photochemical efficiency (Y(II)) and regulated nonphotochemical energy dissipation (Y(NPQ)). In contrast, the treatment duration of 7 days predominantly increased photochemical quenching whereas the 2-h treatment resulted in a significant increase in photochemical quenching and in a significant decrease in nonregulated nonphotochemical energy dissipation. Hence, elevated CO₂ concentrations over a prolonged time period interfered more distinctively with the fluorescence quenching ability of P. palmata.