Effect of elevated carbon dioxide and phosphorus on nitrogen uptake, lipid content, and growth of <i>Tetraselmis sp.</i>

Abstract

Effect of elevated carbon dioxide (CO2) and phosphorus levels on nitrogen uptake, lipid content, and growth of <i>Tetraselmis sp.</i> were investigated. Cultures of <i>Tetraselmis sp.</i> were added with CO2 and phosphorus at concentrations above those currently used in aquaculture practices in a factorial experiment. Three levels of CO2 (no addition, 5% v/v, and 10% v/v of the incoming air for aeration) and three levels of phosphorus added as NaH2PO4 (5, 10, 20 mg L’1) in modified F medium with NH4+ as the primary nitrogen source were used. Optical density (680 nm) and residual NH3-N in the culture medium were monitored daily over a culture period of 6 days. Relative growth rate (k'), nitrogen uptake (pg NH3-N cell’1 day1), and lipid content (% dry weight) were calculated and determined at the end of the culture period. No interactive effect between phosphorus and CO2 levels was observed in all variables measured (p > 0.05). Highest growth rate (k = 1.82±0.04), nitrogen uptake (0.316±0.008 μg NH3-N cell1 day1), and lipid content (10.95±0.15 %DW) were exhibited at 10% CO2 supplementation. Growth and nitrogen uptake were similar in treatments with elevated levels of phosphorus, but lipid yield (9.41±0.27 %DW) was lowest at 20 mg L1 of phosphorus supplementation (p < 0.05). These results showed the critical role of CO2 in nitrogen uptake, lipid content, and growth of <i>Tetraselmis sp.</i> It also indicates the potential of this algal species for waste water remediation, biofuel production, and carbon sequestration.