Effects of carbon dioxide and bisulphite solution on species composition, density and cells characteristics of terrestrial microalgae / Ummi Masyitah Abdul Razak

Microalgae are known to have high tolerance to environmental changes particularly of atmospheric pollutants. The effects of elevated CO2 on the density and chlorophyll-a content of the most dominant terrestrial microalgae (Chlorococcum sp.) has been investigated in the laboratory. The treatments involved were CO2 concentration at 450 ppm, 750 ppm and control. The experiment was conducted in a CO2 growth chamber. The effects of elevated bisulphite (HSO3") on the density and chlorophyll-a content of the Chlorococcum sp. was investigated by exposing the microalgae to HSO3" solutions (0 mM to 1.2 mM). HSO3" solution is the closest representative to SO2 in the atmosphere. The density of microalgae exposed to the pollutant was measured on a weekly basis until week 12. In addition to that, chlorophyll-a content was measured at the beginning and at the end of the experiment using a spectrophotometer. The results showed that Chlorococcum sp. was the most dominant species in both polluted and less polluted areas followed with Trebouxia sp. and Trentepohlia sp. 1. Average microalgal density in polluted area (954.4 ± 27.6 x 103 cells/cm2 ) is significantly higher as compared to the less polluted area (122.1 ± 9.4 x 103 cells/cm2 ) (p < 0.05). Chlorococcum sp. treated with elevated CO2 showed that higher concentration resulted in higher microalgal density and chlorophyll-a content. CO2 concentration at 750 ppm demonstrated the highest microalgal density (729.1 ±21.3 x 104 cells/mL) and the chlorophyll-a content (7.7 ± 0.004 p.g/mL). Chlorococcum sp. exposed to HSO3" showed that higher concentration resulted in higher inhibition in microalgal density and chlorophyll-a content where 1.2mM bisulphite recorded the lowest microalgal density (77.7 ± 0.1 x 104 cells/mL) and chlorophyll-a content (0.4 ± 0.005 ug/mL) as compared to other HSO3" concentrations. In conclusion, this study concluded that the growth of terrestrial microalgae was triggered by high CO2 content but inhibited by high HSO3" content.