Abstract: In order to explore the response of microalga Haematococcus pluvialis to different CO₂ concentrations,the effects of two kinds of CO₂ concentrations on the algal growth,pigment content,chlorophyll fluorescence parameter and activities of two carbon metabolism-related enzymes,were investigated by the physiological and biochemical methods. Results showed that at the green stage,compared to the air CO₂,the growth rate of H. pluvialis increased 3.08 times（10 th）under quadruple air CO₂ condition;the chlorophyll and carotenoid content,and the extracellular carbonic anhydrase activity all decreased;non-photochemical quenching（NPQ）,most of quantum yield of photo-chemical electron transport_（Ф_PSII）,and maximal photo-chemical efficiency of PSII（F_v/F_m）almost significantly increased,whereas the photo-chemical quenching（qP）and activity of ribulose-1,5-bisphosphate carboxylase/oxygenase（Rubisco）differed insignificantly.At the red stage,the algae cultured with quadruple air CO₂ grew slower,however,their astaxanthin content increased by 20.23%（8 d）of that under air CO₂ condition. The study indicated that appropriately high CO₂ concentration promoted its growth rate and astaxanthin accumulation in H.pluvialis.

Key words: Haematococcus pluvialis, CO₂, algal cell density, pigment content, chlorophyll fluorescence parameter