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

An isolated Dunaliella salina (D. salina) 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_v/F_m) under different NaH₂PO₄ concentrations were studied. Based on the results, the growth kinetics of D. salina 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 NaH₂PO₄ concentration improved the biomass, the total chlorophyll and beta-carotene content, retarded the decrease of F_v/F_m value. The optimal phosphate concentration for the growth of D. salina KU XI was above 72.6 μM. The maximum biomass and beta-carotene were 0.24 g L^-1 and 17.4 mg L^-1 respectively when NaH₂PO₄ was 290.4 μM. The algae growth was restrained by phosphate or nitrate when NaH₂PO₄ 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.