Effects of increased atmospheric CO2and 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 CO2 concentration 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 molmol-1, and two NO-3 levels which was added 0, 500 molL-1 NaNO3 in seawater. The algae cultured under non-N-enriched seawater, elevated CO2 concentration had no significant effects on growth and biochemical traits. However, the algae cultured under N-enriched seawater, elevated CO2 could 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 NO-2，and elevated CO2 concentration caused pH value to decrease. This condition was well to form HNO2, which is toxic effect on H.fusiformis.