Two types of growth pattern of the five microalgal species under different nitrogen supplies

Abstract

Manipulation of nitrogen levels is a viable strategy to improve microalgal biomass production. Here, nitrogen uptake and biochemical characteristics of the five microalgal strains were studied with high and low nitrogen concentrations. Two types of growth pattern were observed, non-influencing growth (type Ⅰ, Nannochloropsis gaditana and Kirchneriella sp.) and inhibitory growth (type Ⅱ, Scenedesmus acuminatus, Scenedesmus obliquus and Chlorella vulgaris). The highest biomass of the type Ⅰ microalgae was obtained with higher nitrogen supply (≥18 mM), whereas type Ⅱ microalgae reached highest biomass under nitrogen-limited conditions (7.2–10.8mM). Type Ⅰ microalgae had the highest nitrogen uptake capacity (N. gaditana) and nitrate reductase (NR) activity (Kirchneriella sp. 3.67 U g−1, 10.8 mM). The lower the nitrogen concentration, the higher the NR activity measured in type Ⅱ microalgae on day 1. The nitrogen replete group (21.6mM) of the type Ⅱ microalgae decreased the nitrogen uptake. The NR activity of S. acuminatus was positively associated with the initial nitrogen supply, and an NR activity threshold effect was observed in S. obliquus and C. vulgaris. The amount of nitrite released by the type Ⅱ microalgae was one order magnitude higher than those released by the type Ⅰ microalgae. In nitrogen-limited conditions, the five microalgae species shifted the photosynthetic carbon partitioning into lipid accumulation. The difference in growth patterns was mainly due to nitrogen uptake capacity, activity of nitrate reductase and the amount of nitrite released.