Effects of phosphorus on the growth and chlorophyll fluorescence of a Dunaliella salina strain isolated from saline soil under nitrate limitation

Abstract

An isolated <em>Dunaliella salina</em> (<em>D. salina</em>) KU XI from saline soils in northeastern Thailand was cultured in f/2 medium in column photobioreactor. The variations of the growth, chlorophyll and beta-carotene content and the maximum quantum yield of PS II photochemistry (F<sub>v</sub>/F<sub>m</sub>) under different NaH<sub>2</sub>PO<sub>4</sub> concentrations were studied. Based on the results, the growth kinetics of <em>D. salina</em> KU XI was established, which could simulate the algae growth rate under different phosphate concentrations and temperatures. The phosphorus could significantly affect the growth and pigments accumulations of this isolated strain. Increasing NaH<sub>2</sub>PO<sub>4</sub> concentration improved the biomass, the total chlorophyll and beta-carotene content, retarded the decrease of F<sub>v</sub>/F<sub>m</sub> value. The optimal phosphate concentration for the growth of <em>D. salina</em> KU XI was above 72.6 μM. The maximum biomass and beta-carotene were 0.24 g L<sup>-1</sup> and 17.4 mg L<sup>-1</sup> respectively when NaH<sub>2</sub>PO<sub>4</sub> was 290.4 μM. The algae growth was restrained by phosphate or nitrate when NaH<sub>2</sub>PO<sub>4</sub> below 12.1 μM or above 72.6 μM. It indicated that properly supplementing nitrate in the late growth stage with high phosphate concentration was favored for enhancing the growth and biomass production.