Effects of increased atmospheric CO₂ and N supply on some physiological and biochemical traits in the economic brown seaweed, Hizikia fusiformis (Sargassaceae, Phaeophyta)

The marine macroalgae Hizikia fusiformis (Harvey) Okamura (Sargassaceae, Phaeophyta) was cultured under the condition of elevated atmospheric CO₂and increased N supply to investigate the effects of increased CO₂concentration and N supply on the growth, photosynthesis, and other related physiological and biochemical traits in this species. The experiment was designed for two CO₂ levels which was 350 and 700 mol · mol^-1, and two NO₃^-levels which was added 0, 500 mol · L^-1 NaNO₃in seawater. The algae cultured under non-N-enriched seawater, elevated CO₂concentration had no significant effects on growth and biochemical traits. However, the algae cultured under N-enriched seawater, elevated CO₂could effectively depress the growth.The ratio of fresh weight (FW)to dry weight (DW), the concentrations of soluble protein and soluble carbohydrate were decreased 4.5%, 15% and 32%. It suggested that increased N supply led to the accumulation of NO₂^-, and elevated CO₂concentration caused pH value to decrease. This condition was well to form HNO₂, which is toxic effect on H.fusiformis.