| Rice is one of the most important food crops in China. Lodging is the commen problem in rice production, which causes great losses in both grain quantity and quality. Furthermore, it also causes difficulties in harvest operations, and consequently results in increased production cost. Ozone (O3) is currently one of the most important air pollutant that negatively affects growth and yield of crops. The objective of the present study was to answer the following questions:Does elevated ozone concentration ([O3]) increase the risk of lodging in rice? How different rice cultivars respond to elevated [O3] and the mechanisms responsible for genotypic differences? An FACE (Free Air gas Concentration Enrichment) experiment was conducted in a rice field (119■42’0"E,32°35’5"N) using unique FACE system in the world. Two Chinese rice cultivars, Wuyunjing21(inbred japonica cultivar) and Liangyoupeijiu (two-line hybrid rice cultivar), were grown at ambient (A-O3) or elevated [O3](target at ca.50%above ambient, E-O3). The effects of elevated [O3] on lodging-related traits of rice were investigated, including lodging index, bending moment, breaking-resistant strength, culm diameter, the fresh and dry weight per unit length, the concentration of soluble carbohydrates and starch of different internodes.1. Averaged across the two cultivars, elevated [O3] increased lodging index of the fifth, forth and third internodes from the top at heading by4%,11%, and6%respectively, at maturity by5%,11%and6%respectively. For both growth stages, the effect of E-O3on the forth internode from the top showed the biggest response to elevated [O3] among all investigated internodes and the effects was statistically significant. In general, the lodging index of Liangyoupeijiu was more sensitive to E-O3than Wuyunjing21.2. The bending moment of the fifth, forth and third internodes from the top was decreased by elevated [O3] at heading,20days after heading and maturity. However, the effect was only significant at20days after heading among the three growth stages. The decrease of bending moment by O3stress of Liangyoupeijiu is greater than that of Wuyunjing21.3. Averaged across the two cultivars, elevated [O3] decreased breaking-resisitant strength of the fifth, forth and third internodes from the top at heading by4%,11%and6%respectively, at20days after heading by15%,6%and3%respectively, at maturity by5%,11%and6%respectively. Among all investigated internodes, the forth internodes from the top showed significant responses to elevated [O3] at heading and maturity. Compared with Wuyunjing21, Liangyoupeijiu was more sensitive to E-O3in terms of breaking-resistant strength. The increase of lodging index of rice internodes under ozone stress could be attributed to the decrease of breaking-resistant strength of internodes, rather than the change of bending moment. 4. Compared with A-O3, elevated [O3] reduced the fresh weight per unit length of the fifth, forth, third, second and first internodes from the top at heading,20days after heading, and maturity.The significant effects of elevated [O3] on the fresh weight per unit length of internodes were observed at heading. For the majority of internodes, the03-induced reduction in the fresh weight per unit length was greater in Liangyoupeijiu than Wuyunjing21.5. Compared with A-O3,elevated [O3] reduced the dry weight per unit length of the fifth, forth, third, second and first internodes from the top at heading,20days after heading and maturity. For the majority of internodes, the effect of O3on the dry weight per unit length was statistically significant. The03-induced reduction in the dry weight per unit length of internodes was greater in Liangyoupeijiu than Wuyunjing21at heading and20days after heading.6. Compared with A-O3, E-O3slightly reduced the culm diameter of the fifth, forth, third, second and first internodes from the top at maturity., but the effects were not statistically significant. There was no significant difference between two cultivars.7. Elevated [O3] reduced the concentration of soluble carbohydrates of the fifth, forth, third, second and first internodes from the top of two rice cultivars at heading,20days after heading and maturity. The significant O3effects were found for the majority of internodes investigated. The03-induced reduction in the concentration of soluble carbohydrates was greater in Liangyoupeijiu than Wuyunjing21at20days after heading and maturity.8. Elevated [O3] decreased the concentration of starch of the fifth, forth, third, second and first internodes from the top at heading by6%,4%,16%,23%and5%respectively, at maturity by30%,20%,23%,15%and18%respectively. The significant O3effects were observed on all investigated internodes except the first internodes from the top at heading. The interactions between O3and cultivars varied among different growth stages or different internodes. |
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