Effects of ozone on growth of rice and prevention of exogenous ascorbic acid.

The ozone is the primary gaseous pollutant with significant adverse effects on vegetation.Those effects include visible leaf injury, growth and yield reductions,accelerated senescence and altering sensitivity to biotic and abiotic stresses.Reductions in photosynthesis rate, stomata conductance,and root/shoot ratio,increasing in respiration,and changing in crop quality has also been observed in many crops.With fast industrial development,tropospheric ozone in the Yangtze River Delta,in Eastern China,as risen since the later of the last century.The elevated ozone has became a prominent environmental and economic issue in this region. In order to alleviate the phytotoxin of elevated level O3 to crops,the prevention of exogenous ascorbic acid(ExAsA)on growth of rice(Oryza sativa L.)was investigated.Rice was grown in open top chambers(OTCs)under field conditions and exposed to four levels of O3:NF(No-Filter)with a daily average of 20~50 nL·L-1; CF(Charcoal-Filter)with an 8 h average of 5~15 nL·L-1; OzoneⅠwith an 8 h average of 100 nL·L-1; Ozone Ⅱwith an 8 h average of 200 nL·L-1. The concentration of exogenous ascorbic acid was 0.1%(m/V). The results showed that compared to CF, the chlorophyll a content of rice leaves, the plant height of rice, leaves area, per panicle total grain and weight decreased under the treatment of high ozone concentration (200 nL· L-1), 47.9%, 17.8%, 31.6%, 45.7% and 42.9% respectively. But with exogenous ascorbic acid spraying, there was a rising trend in the chlorophyll a content of rice leaves, the plant height of rice , leaves area , per panicle total grain and weight, 11.6%,7.7%,17.4%,5.6%, 11.1% respectively. From these results, it can thought that ExAsA defers leaf senescence, increases the tolerance ability of rice under elevated O3 and improved effectively rice growth.