| Ozone (O3) is currently the most important air pollutant that negatively affects growth and yield of agricultural crops. Rice is arguably the most important food crops in the world. The process of spikelet formation directly determined the final number of spikelets per panicle, which plays a critical role in securing a sufficient number of spikelets per unit area for a higher yield. Therefore it is very important to accurately assess the impact of increasing surface O3 concentration ([O3]) on spikelet formation and grain yield of rice. In order to investigate the effects of high [O3] on the number of differentiated spikelets, degenerated spikelets, and surviving spikelets, as well as grain yield of different rice cultivars, we conducted an experiment for the first time in the world with rice using unique FACE system from 2007 to 2009, at Xiaoji town, Jiangdu Country, Jiangsu Province, China (119°42′0″E,32°35′5″N). Two Chinese rice cultivars: Yangdao 6 (inbred indica cultivar), Liangyoupeijiu (two-line hybrid rice cultivar), were grown at ambient or elevated (target at ca. 50% above ambient) [O3]. Results showed as follows:1. Averaged across the two cultivars, rice plants grown in the E-O3 plots produced 15 fewer surviving spikelets per panicle (relative decrease of 8%, P < 0.01), compared with the plants grown in the ambient plots. With respect to different cultivars that were investigated, E-O3 decreased the number of surviving spikelets per panicle by 6% and 9%, for Yangdao 6 and Liangyoupeijiu, respectively. As for different years, the average number of surviving spikelets per panicle decreased by 9%, 7% and 6% in 2007, 2008 and 2009 rice growing seasons, respectively. On average, elevated [O3] reduced the number of surviving spikelets on primary (PB) and secondary rachis branches (SB) per panicle by 2% (P < 0.05) and 11% (P < 0.01), respectively. E-[O3] had no effect on the number of surviving PB, but it significantly decreased the number of surviving SB by 7%.The proportion of SB spikelets was significantly reduced, while the proportion of PB spikelets showed the opposite response to elevated [O3]. The number of surviving spikelets on each SB was significantly reduced by E-[O3] (-3%) , while no ozone impact was detected on the number of surviving spikelets on each PB. Statistical analysis of variance (ANOVA) indicated a significant ozone by cultivar interaction for the number of surviving SB spikelets per SB, and a significant O3×year interaction with respect to the number of PB and the number of surviving PB spikelets per PB.2. Across cultivars, rice plants grown in the E-O3 plots differentiated 18 fewer spikelets per panicle (relative decrease of 7%, P < 0.01), compared with the plants grown in the ambient plots. With respect to different cultivars, E-O3 decreased the number of differentiated spikelets per panicle by 3% and 9%, for Yangdao 6 and Liangyoupeijiu, respectively. As for different years, the average number of differentiated spikelets per panicle decreased by 6%, 7% and 6% in 2007, 2008 and 2009, respectively. On average, elevated [O3] reduced the number of differentiated PB and SB spikelets per panicle by 2% (P < 0.01) and 8% (P < 0.01), respectively. E-[O3] had no effect on the number of differentiated PB, but it significantly decreased the number of differentiated SB by 5% across the two cultivars (P < 0.01). The number of differentiated SB spikelets on each SB was significantly reduced by E-[O3] (-3%; P < 0.01), while no effect was detected on the number of differentiated PB spikelets on each PB. ANOVA indicated a significant ozone by cultivar interaction for the number of differentiated spikelets, the number of differentiated SB spikelets and the number of differentiated SB spikelets per SB, and a significant O3×year interaction with respect to the number of differentiated PB and the number of differentiated PB spikelets per PB.3. On average, rice plants grown in the E-O3 plots degenerated 2 fewer spikelets per panicle (relative decrease of 3%, P > 0.1), compared with ambient grown plants. With respect to different cultivars, E-O3 increased the number of degenerated spikelets per panicle by 9% for Yangdao 6, but decreased by 9% for Liangyoupeijiu. As for different years, the average number of degenerated spikelets per panicle increased by 6% in 2007, but decreased by 7% and 5% in 2008 and 2009, respectively. On average, elevated [O3] had no effect on the number of degenerated PB and SB per panicle, as well as the number of degenerated PB and SB spikelets per panicle. E-[O3] had no effect on percentage of degenerated PB, but it significantly increased percentage of degenerated SB. There was a significant ozone by cultivar interaction observed for the total number of degenerated spikelets per panicle and the number of generated SB spikelets per panicle, but no interaction between O3×year was detected for all the parameters regarding degeneration.4. The number of surviving spikelet per panicle can be divided into two factors: shoot dry weight (SDW) and the ratio of surviving spikelets to SDW. Averaged across the cultivars grown, SDW significantly decreased by 8% under elevated [O3], while no O3 effect was detected for the ratio of surviving spikelets to SDW. Thus, the reduction in the number of surviving spikelets per panicle by elevation in [O3] could be ascribed for the limitations in assimilate supply to the developing panicles.5. The number of surviving spikelets per panicle is also a function of nitrogen (N) absorption per stem at heading and the ratio of surviving spikelet to N. On average, N absorption at heading significantly reduced by 9% under elevated [O3], while no effect of ozone was observed for the ratio of surviving spikelet to N. Thus, the reduction in the number of surviving spikelets per panicle under elevated [O3] also contributed to the reduction in N accumulation through heading.6. Elevated [O3] had no effect on the concentration of soluble sugar, starch and soluble carbohydrates in stem at heading.7. Averaged across all cultivars, elevated [O3] significantly reduced the grain yield of rice by 114 g m-2 (relative decrease of 13%). Concerning different cultivars, the yield decreased by 9% and 16%, for Yangdao 6 and Liangyoupeijiu, respectively. As for different years, grain yield decrease by 10%, 10% and 19% under elevated [O3] in 2007, 2008 and 2009, respectively. Ozone-induced yield loss of hybrid rice cultivar Shanyou 63 may relate to suppression of spikelet formation, and hybrid Liangyoupeijiu appear to be more sensitive to elevated [O3] as compared with inbred Yangdao 6 with respect to spilelet formation and grain yield.
|
PDF Full Text Request