Effects of dissolved inorganic carbon availability on growth, nutrient uptake and chlorophyll fluorescence of two species of marine microalgae

Abstract

Growth of two species of marine microalgae, namely Nannochloropsis gaditana Lubián (Eustigmatophyceae) and Nannochloris maculata Butcher (Chlorophyceae), was investigated in cultures submitted to three different concentrations of dissolved inorganic carbon (DIC). Cultures of N. gaditana grown in the absence of DIC in the medium and aerated with less than 0.0001% (v/v) CO 2 in air (low DIC conditions) showed a reduction in final cell biomass of approximately 56% as compared with the biomass obtained in cultures grown under control conditions (2 mM DIC in the medium and aerated with air-equilibrated levels of CO 2, i.e. 0.03% (v/v) CO 2). Growth was not observed in N. maculata cultured under low DIC conditions. A concentration of 1% (v/v) CO 2 in air (high DIC conditions) did not modify growth of N. gaditana in relation to that in the control-culture but enhaced growth of N. maculata. Nutrient (NO 3 − and PO 4 3−) uptake was also analyzed under the different growth conditions. The uptake of NO 3 − and PO 4 3− by N. maculata was dependent on the inorganic carbon level; thus, whereas no nutrient absorption was observed in the low DIC-culture, growth at the highest inorganic carbon concentration caused an accelaration of the uptake. Capacity to use nitrate was restricted in N. gaditana cells under low DIC conditions, but nutrient uptake was similar in cultures adapted to air levels of CO 2 and to CO 2-enriched air. Chlorophyll fluorescence measurements were used to determine the photochemical efficiency of photosystem II and the non-photochemical quenching. A similar pattern of evolution of the actual quantum yield of photosystem II (φ PSII) was observed in all cultures of N. gaditana over the growth period, without development of non-photochemical quenching. In contrast, changes in φ PSII of N. maculata differed between treatments and were concurrent with carbon and nutrient availabilities. Non-photochemical quenching rose in this alga when carbon or phosphate limitation constrained proton dissipation from the lumen. Results are discussed in relation to the particular carbon uptake mechanism of each alga.