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The impacts of different O3 concentration on the biomass andyield of rice were studied by using OTC-1 open-top chambers. Experimental treatments included the activated charcoal-filtered air (CFA), 50nl/L (CF50), 100nl/L (CF100) and 200nl/L (CF200) concentrations of O3. The O3 treatments significantly decreased the total biomass per plant. The elevated O3 exposure resulted in a more decrease in the root growth than in the shoot growth. Assessments of yield characteristics at the final harvest revealed an O3 - induced decrease in the number of grains per plant, resulting from fewer ears per plant, fewer grains per ear and more unfilled grains per ear. The 1000 grain dry weight and the harvest index (HI) were not changed significantly under 50nL/L or 100nL/L O3 exposure, but reduced by 17.0% and 4.8% by 200nL/L O3 treatment, respectively. Compared to the CFA treatment, CF50, CF100 and CF200 treatments caused a 8.2%, 26.1%, 49.1% decrease of the grain yield per plant, and a 14.2%, 31.7%, 51.7% decrease of the total biomass per plant, respectively. Linear regression showed that the 7h-daily mean O3 concentration exposure for 3 months (July-September) and AOT40 (cumulative exposure accumulation over threshold 40 nL/L) were well correlated with the relative grain yield. A yield loss of 10% was estimated to be at 46.9nL/L O3 for 7h-daily mean O3 concentration exposure or at 12930 nL/(L.h )O3 for AOT40.