Relationship Between CO₂ Concentration And Growth Of Microcystis Aeruginosa

Water bloom, which occurred frequently and strongly, has been seriously affected people's life and its occurring mechanism & treatment methods were paid more attention by scholars in the world. Water bloom is a combined result of multiple factors such as temperature, light, nutrients, trace element, carbon dioxide, etc. As a substrate, carbon dioxide (CO₂) plays an important role in algae's photosynthesis. Atmospheric CO₂ has risen dramatically as a result of human activities such as fossil fuel burning and deforestation, it was estimated that the concentration of CO₂ in atmosphere will be doubled at the end of 21st century. Effects of elevated CO₂ on algae's photosynthesis were worth to be concerned.Seven different CO₂ concentrations were set in this experiment to study the effects of CO₂ on Microcystis aeruginosa's growth and physiological activity. Results showed that biomass and chlorophyll a content of Microcystis aeruginosa increased firstly and then decreased with the increase of atmospheric CO₂. Algal growth was promoted at the range of 400～6400μL/L CO₂ concentration, the optimum CO₂ concentration for growth of Microcystis aeruginosa was about 800μL/L. Under different CO₂ concentration, Microcystis aerugonisa's biomass, chlorophyll fluorescence and oxygen evolution rate were significantly different (P<0.05). High CO₂ provided sufficient carbon soure for algal photosynthesis, the carbon-concentrating mechanism (CCMs) weak down and energy required reduced so that the saturated light intensity decreased. By stress of high ,synthesis of chlorophyll a was blocked and limited light absorption, transmission & transformation especially, which would influence the electron-transfer process, leading to the lower of the maximum electron transport rate ETRmax. In addition, under high CO₂ condition, Microcytis aeruginosa's dark respiration rate increased, then energy needed to maintain algal physiological activity increased and there was little erergy used for cell growth and reproduction. Lack of energy maybe the main reseason for block of the biosynthesis of chlorophyll a. Compared with the control , Microcystis aeruginosa, which was under high CO₂ (25600μL/L) condition, its external structure has not changed, but inner structure of cell were significantly different from the control cells, the number of thylakoid reduced and arranged irregularly. It indicated that algal photosynthetic apparatus has been damaged.Appropriate increase of atmospheric CO₂ will promote algae growth, in contrast, excessively high CO₂ will cause inhibition. Effects of high CO₂ inhibited the growth of Microcystis aeruginosa mainly due to the damage of photosynthetic apparatus and block of chlorophyll a synthesis. The optimal CO₂ concentration (800μL/L) to the growth of Microcystis aeruginosa would be helpful to understanding the occurring mechanism of Microcystis aeruginosa bloom.