Growth, photosynthesis and nutrient uptake by Grateloupia livida (Halymeniales, Rhodophyta) in response to different carbon levels

Abstract

:Grateloupia livida is a commercially important red macroalgal species. In the present study, thalli of G. livida, collected from Nan'ao Island, China, were cultured at different levels of CO2 (c. 1000, 390 and 50 ppm) to examine the growth and physiology and how its plasticity may affect photosynthesis at different carbon levels. The pH-drift experiments showed that G. livida could reach a final pH value of 9.75. Carbonic anhydrase (CA) activity was detected potentiometrically with both thalli and homogenates of G. livida. These implied that G. livida used HCO3− as a source of inorganic carbon for photosynthesis and that this was mediated by extracellular CA activity. Thalli of G. livida grown at low CO2 reduced the relative growth rate (RGR), both the PO43− and NO3− uptake rates, nitrate reductase activity and photochemical activity compared with the algae grown at ambient CO2. Moreover, the RGR and the initial slope of the rapid light curves (α) were inhibited by the high CO2 level in the seawater. The results indicated that either raised or lowered CO2 in culture were unfavourable environmental factors for growth and photosynthesis of G. livida.