To further study the effect of ozone stress on growth and yield formation of rice (Oryza sativa), we conducted an experiment with rice by using Free Air gas Concentration Enrichment (FACE) facility stored in paddy field in China. A conventional indica cultivar Yangdao 6 and a super hybrid indica cultivar II you 084 were grown at current or elevated ozone concentration (target at 50% above current, E-O-3) under low (LD, 16 hills m(-2)), medium (MD, 24 hills m(-2)) or high planting density (HD, 32 hills m(-2)) from tillering until maturity. The increase of O-3 had no significant effect on phenology and plant height of Yangdao 6, but greatly accelerated phenology development and reduced plant height of II you 084. Ozone stress significantly reduced dry matter production of rice in mid and late stage, and finally, decreased the biomass of Yangdao 6 and II you 084 by 17.6% and 25.4% respectively. Ozone stress had no significant effect on harvest index of Yangdao 6 but reduced it of II you 084 by 9.0%. The increase of O-3 had no significant effect on the panicle number per area of rice. Ozone stress had no significant effect on the spikelet number per panicle of Yangdao 6, but significantly reduced that of II you 084 by 22.0%. Ozone stress decreased spikelets per area, filled grain percentage, and filled grain weight of rice, and eventually reduced grain yield of Yangdao 6 and II you 084 by 15.9% and 27.3% respectively. Variance analysis showed that the impacts of ozone stress on II you 084 were bigger than Yangdao 6, which were proved by the significant ozone by cultivar interactions for biomass, harvest index, spikelet number per panicle, spikelet number per area, filled grain percentage, filled grain weight. Week interactions of ozone by cultivar by planting density were detected: The effects of ozone stress on biomass and grain yield of Yangdao 6 were decreased with the increase of planting density. The above results showed that the increase of O-3 depressed the dry matter production of rice, and then decreased the yield, and the response of super hybrid rice varieties to ozone is greater than that of conventional varieties. The selection of highyielding conventional varieties combined with relatively high planting density can minimize the yield loss in the future high ozone conditions.
