Effects Of Ozone Pollution On Growth And Quality Of Different Rice Cultivars

The increase of tropospheric ozone concentration can inhibit leaf photosynthesis of rice,reduce plant growth and yield,and affect grain quality.However,the relationship between ozone response and rice cultivar or type,as well as agronomic measures(such as foliar zinc application)is rarely reported.Eight rice cultivars,HD5,WYJ27,GNZ,YD6,ZZ39,FYXZ,SLY136 and YY1540,were subjected to clean air(13 nL L-1)and ozone pollution(80 nL L-1)treatment throughout cropping season(from 20 days after transplanting to plant maturity)in natural-light climate chambers.Foliar zinc application(0.2%ZnSO4)started right after the heading stage for 3 times at an interval of every 5 days.Rice yield formation,grain quality traits,and physiological parameters associated with yield and quality response to ozone treatment were determined systematically.The study mainly focus on the effects of moderate ozone pollution on rice growth and development,leaf physiology,dry matter accumulation,grain yield and quality of different rice varieties.The response of grain zinc concentration and bioavailability to ozone pollution and its relationship with foliar zinc application or rice cultivars were studied.The main results showed as follows:1.Compared with clean air,ozone concentration of 80 nL L-1 reduced plant height and tiller number at each rice growth stage,and the decrease in the late growth stages was higher than that in the early growth stages.Significant ozone by cultivar interactions were detected on plant height or tiller number in most of growth stages.2.The symptoms of leaf injury by ozone gradually increased with the prolong of rice growth.Accordingly,leaf SPAD value and chlorophyll content decreased under ozone stress.The magnitude of decrease in SPAD value increased with time,and the lower leaves decreased more than the upper leaf.In most cases,ozone × cultivar,ozone × position,ozone × cultivar× position interactions were detected for leaf bronzing scores and SPAD value.3.When rice grown under ozone stress,a trend of increase in leaf ascorbic acid and total phenol was found at tillering and heading stage,while carotenoids showed an opposite trend.Ozone pollution increased the activity of POD and GSH at tillering and heading stage,while CAT activity decreased,and the response of SOD activity varied with growth stage.Significant ozone by cultivar interaction was found for SOD,CAT activity,reduced ascorbic acid content,total phenol content of leaves.Ozone by growth stage interaction was found for SOD activity,total ascorbic acid,reduced ascorbic acid and malondialdehyde content.4.Ozone pollution reduced the aboveground dry weight by 6.2%,19.6%,26.8%and 17.8%at tillering,heading,20 days after heading and plant maturity,respectively,but only the reduction at heading and 20 days after heading was statistically significant.Ozone pollution reduced the dry weight of stem,leaf and panicle,and the reduction of leaf was the smallest among three plant organs.Ozone pollution had no significant effect on the ratio of panicle to above-ground dry weight at heading,20 days after heading and plant maturity,but reduced the ratio of stem to above-ground dry weight by 9.4%,11.9%and 12.4%,respectively.Ozone pollution increased the ratio of leaf to above-ground dry weight by 18.6%,23.0%and 25.3%,respectively.All changes of dry matter distribution in response to ozone pollution were statistically significant,except for the ratio of leaf to above-ground dry weight at heading Significant ozone by cultivar interaction was detected for stem dry weight and the ratio of leaf to above-ground dry weight.Significant ozone by growth stage interaction was detected for stem dry weight and the ratio of stem to above-ground dry weight.The significant interaction of ozone × cultivar × growth stage was found for the ratio of leaf to above-ground dry weight and the ratio of panicle to above-ground dry weight.5.Ozone pollution reduced the grain yield on average by 19.3%(P<0.1),which was mainly related to the decrease of spikelets per panicle(-9.1%),fulfilled grain percentage(-4.4%)and fulfilled grain weight(-7.7%).Different degree of interaction between ozone and cultivar was detected for yield,spikelets per panicle,fulfilled grain weight and fulfilled grain percentage.6.Ozone pollution significantly reduced the rough rice weight,brown rice weight,rough rice volume and brown rice volume by 7.1%,5.3%,6.4%and 6.0%,respectively,but had no effect on grain density.Under ozone stress,the length,width and thickness of rough rice and brown rice decreased(about 1～3%),while the ratio of length to width of rough rice and brown rice increased significantly(about 2.5%),the density of rough rice and brown rice did not change.On average,the chalkiness rate and chalkiness degree of head rice had no significant response to ozone pollution.Except for the length and density of brown rice,significant ozone by cultivar interactions were found for all the other grain morphology indexes.7.When rice was exposed to ozone pollution from 20 days after transplanting to plant maturity,the green grain percentage of brown rice increased by 68.6%,perfect grain percentage decreased by 2.4%,while damaged grain percentage was unchanged.Significant ozone by cultivar interaction was found for green grain percentage and perfect grain percentage of brown rice8.Ozone pollution reduced amylose content of brown rice and head rice by 3.0%on average,and gel consistency of head rice by 13.0%.Starch RVA spectrum of brown rice showed that the peak viscosity and breakdown decreased by 4.4%and 12.4%on average,while the setback,peak time and gelatinization temperature increased by 69.4%.1.1%and 3.4%,respectively.The ozone response of starch RVA spectrum of head rice was similar to that of brown rice.In terms of taste index,the appearance.viscosity.balance.mouthfeel and taste value of rice decreased by 30.7%,30.6%,31.8%,9.7%and 11.8%respectively,while the hardness increased by 5.7%.Significant ozone by cultivar interaction was found for amylose.gel consistency,taste value and most indexes of starch RVA spectrum.9.Ozone pollution significantly increased the protein concentration of brown rice by 15.6%.Glutenin concentration significantly increased by 19.6%in response to ozone pollution,and the concentrations of albumin,globulin and gliadin also showed a trend of increase.The concentrations of Ca,K,Mg,P,Cu and Mn in rice increased in response to ozone pollution The concentrations of K,Cu in brown rice and K,Mg,P,Cu and Mn in head rice increased significantly.In general,the magnitude of increase in head rice was higher than that in brown rice.On the contrary.the elements accumulation in brown rice and milled rice decreased by ozone pollution(except Cu in milled rice),but only Fe accumulation in brown rice decreased significantly.Ozone by cultivar interaction was found for protein concentration,macroelement concentration of brown rice and microelement concentration of head rice.Ozone by cultivar interaction was also found for elements accumulation of brown rice and milled rice10.Ozone pollution increased the zinc concentration in brown rice and head rice by 2.8%and 3.6%,respectively.While the concentration of phytic acid in head rice increased by 10.7%under ozone pollution,no change was found for brown rice.Foliar zinc application after flowering increased zinc concentration of brown rice and head rice by 23.7%and 18.1%,respectively,and reduced the molar ratio of phytic acid to zinc by 16.9%and 16.9%,respectively,but there was no significant change in the concentration of phytic acid in both parts.Significant interaction of ozone × cultivar,ozone × cultivar × part were found for zinc concentration.In conclusion,ozone pollution inhibited the rice growth,as indicated by leaf yellowing and injury symptoms,resulted in biomass decrease and lower yield.Ozone pollution on rice growth parameters displayed cumulative damage over time.Ozone pollution deteriorated rice processing quality,cooking and eating quality,but grain element concentration tended to increase.In most cases,the effects of ozone pollution on the rice growth,yield and quality varied with rice cultivars.Among the eight rice varieties,Yangdao 6 and Shenliangyou 136 are the most sensitive to ozone pollution,while Wuyunjing 27 and Huaidao 5 are the resistant varieties..Foliar zinc application after flowering significantly increased the zinc nutrition level of rice,but the increase was not affected by ozone pollution.