Abstract: The toxicity of 1-octyl-3-methyimidazolium bromide (\[OMIm\]Br) ionic liquid on Chlorella pyrenoidosa was investigated by acute toxicity tests The results showed that under \[OMIm\] Br stress for 96 h, algal biomass (algal cell density, chlorophyll and protein contents) changed with the \[OMIm\]Br dosage in a positive correlation. The concentration for 50% of maximal effect (EC₅₀) of \[OMIm\]Br to C. pyrenoidosa was 14.95 mg·L^-1. The activities of superoxide dismutase (SOD) and peroxidase (POD) decreased, whereas the malondialdehyde (MDA) content increased with the increasing \[OMIm\]Br dosage. The direct harm of \[OMIm\]Br to protein and antioxidant system was the main cause of toxicity to C. pyrenoidosa. It was proved that, owing to the damage of \[OMIm\]Br revealed by flow cytometry (FCM) detection, C. pyrenoidosa cell cycle stopped at S phase and G₂/M phase, and ［OMIm］Br resulting in necrosis. The degree of cell retardation and necrosis was positively correlated with the \[OMIm\]Br dosage.

Key words: continuous cropping obstacle, soil enzyme, p-hydroxy benzoic acid, cinnamic acid, peanut, yield., soil available nutrients