Effect of salinity, nitrogen and phosphorus stresses on growth and photosynthetic activity of the marine microalga Dunaliella parva

The growth of the marine green alga Dunaliella parva was studied and optimized under different salinity levels of NaCl (0.5, 1, 2, 2.5, and 3.5 M). The growth was monitored by cell number pigment content (Chl. a, Chl. b, and carotenoids). The grown alga, under the optimal conditions, was exposed to different stresses (nitrogen, phosphorus starvation, and salinity either singly or combined. Under nitrogen and phosphorus starvation, either singly or combined, the growth rate and the metabolic activities were decreased. Under salt stress (2.5 M NaCl) combined with N starvation and heavy metals stress, glycerol production increased, while glycerol synthesis decreased under salt stress of 1 M NaCl and P starvation. Also, free radicals (total antioxidant, reducing power, DPPH, and Lipid peroxidation), pigment content, and activity of antioxidant enzymes were recorded. D. parva grown under salinity level (2.5 M NaCl) combined with nutrient starvation correlated with more efficient enzymatic antioxidant activity accumulation. This study strongly suggested that the induction of antioxidant defense was one component of the tolerance mechanism of D. parva to salinity, as evidenced by its growth behavior.