中文摘要：

依托全球唯一的稻田开放式空气中臭氧浓度增高系统平台，以汕优63和两优培九为供试材料，设置大气背景臭氧浓度和高臭氧浓度（比大气背景臭氧浓度高50％）两个浓度水平，研究FACE条件下高O3浓度对杂交稻颖花形成的影响。结果表明：高O3浓度使汕优63和两优培九每穗颖花数分别减少28朵和34朵，下降幅度分别为15％和13％。从稻穗构成看，高O3浓度胁迫下杂交稻每穗颖花数减少主要与每穗2次枝梗颖花数明显减少有关，对每穗1次枝梗颖花数的影响较小，因此高O3浓度胁迫下水稻每穗1次枝梗颖花数占全穗的比率增加，每穗2次枝梗颖花数占全穗的比率降低．从颖花形成看，高O3浓度胁迫下杂交稻每穗颖花数下降主要是颖花（特别是2次颖花）的分化受到抑制所致，而颖花的退化数不增反降。上述结果表明，采取相应措施削弱高O3浓度胁迫对颖花分化的抑制作用可能是近地层高O3浓度条件下减少杂交稻产量损失的关键。

英文摘要：

To investigate the effects of high ozone concentration on spikelet formation of hybrid rice cuhivars, an experiment using a unique free air ozone concentration enrichment （ozone-FACE） system was conducted in 2007. Two hybrid rice cultivars, Shanyou 63 （SY63） and Liangyoupeijiu （LYPJ）, were grown at ambient and elevated （target at 50% above ambient） ozone concentration. The results showed that compared with ambient ozone concentration, elevated ozone reduced the spikelet number per panicle by 28 and 34 （ relative decrease of 15% and 13% ） for SY63 and LYPJ, respectively. This reduction in spikelet number per panicle was mainly contributed to the significant decrease in spikelet number on secondary branches （SB） , while only minor response was detected for the spikelet number on primary branches （PB）, resulting in an increase in percentage of primary branch spikelets and a decrease in percentage of secondary branch spikelets under ozone exposure. In terms of spikelet formation, the large ozone-induced reduction in spikelet number per panicle of the two hybrid cultivars was entirely due to the suppression of spikelet differentiation per panicle （ especially that on SB）, while the degenerated spikelets per panicle decreased rather than increased under ozone exposure. It was suggested that corresponding measures should be adopted to mitigate the detrimental effects of ozone on the spikelet differentiation to minimize yield loss under increasing surface ozone concentration.