Impacts of ozone on the biomass and yield of rice in open-top chambers

The impacts of different O3 concentration on the biomass and yield of rice were studied by using OTC-1 open-top chambers. Experimental treatments included the activated charcoal-filtered air (CFA), 50 nl/L (CF50), 100 nl/L (CF100) and 200 nl/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 50 nl/L or 100 nl/L O3 exposure, but reduced by 17.0% and 4.8% by 200 nl/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 7 h-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 46.9 nl/L O3 for 7 h-daily mean O3 concentration exposure or at 12930 nl/(L.h) O3 for AOT40.