Effect Of Silicon Application On Eco-physiological In Soybean Under Ozone Pollution

Ozone is believed to be an important environmental pollutant causing severe losses ofcrops production under global change scenarios. Technical countermeasures to alleviatingozone stress would help ensure food security, among which adding silicon might be one of thepractical approaches. Open top chambers （OTCs） were applied in determining the effects ofozone (ambient air,<40μg L^-1O₃or elevated O₃,80±5μg L^-1,7h·day-1) and silicon (Si-free,0μg g^-1or+Si,100μg g^-1) on plant growth and yield of soybean after anthesis. The mainresults are as follows:1Effects of different treatments on yield of soybeanCompared with the control treatments, O₃significantly decreased grain weight per plant（20%）（P<0.05），the main reason for lower grain weight per plant is the reduction of podsnumber and seeds per plant. However, the effect of O₃stress on100-grain weight was notsignificant （P>0.05）; against Si-free treatments, silicon application could significantlyincrease the grain weight per plant under either ambient air condition or elevated O₃environment （P<0.05）, however, the effects of O₃on pods number, seeds number and100-grain weight of soybean were not significantly （P>0.05）.2Effects of different treatments on agronomic characters of soybeanThe plant height of soybean under elevated O₃environment was largely lower than thatunder ambient air condition. During the24d to48d after treated by ozone, pods number perplant of soybean growing in+O₃treatments was significantly lower than that under of controltreatments （CK）（P<0.05）, but there was no significant difference against+Si+O₃treatments（P>0.05）; and there were no significant differences among CK,+Si,+Si+O₃treatments duringthe whole exposure period （P>0.05）. Under the elevated O₃environment, the number ofsoybean leaves was significantly reduced （P<0.01）, meanwhile under the elevated O₃environment, compared with Si-free treatments, silicon application could significantlyincrease the number of soybean leaves from24d to32d after treated by ozone （P<0.01）, andsignificantly reduce the rate of yellow leaves （P<0.01） during the whole exposure period.3Effects of different treatments on photosynthetic capability of soybeanUnder the elevated O₃environment, against that under ambient air condition, the contentof chlorophyll in leaves of soybean was decreased notably by large extent （P<0.01）, the effective photosynthetic area （10%¹9%）, stomatal conductance（8%⁴3%）, the netphotosynthetic rate （5%³3%）, maximum efficiency of PSII in the dark （Fv/Fm）（3%⁷%）,the electronic transportation rate （ETR）（5%¹8%） and photochemical quenching （qP）（3%³4%） were reduced, and non-photochemical quenching （NPQ）（37%⁷8%）wasincreased. While under the elevated O₃environment, against Si-free treatments, siliconapplication can significantly increase the chlorophyll content in leaves （4%⁹%）, thephotosynthetically active area （6%¹7%）, the stomatal conductance （7%⁶2%）, netphotosynthetic rate （4%³8%）, Fv/Fm （1%⁴%）, ETR （3%¹4%） and qP （4%²5%）, andreduce NPQ （14%²8%）. But there was little impact on soybean under ambient air condition,while silicon application, against Si-free treatments.4Effects of different treatments on antioxidant system and lipid peroxidation in leavesof soybeanUnder the elevated O₃environment, against Si-free treatments, silicon applicationsignificantly increased SOD （14%²1%）, POD （12%³3%）, CAT （11%¹7%） activity（P<0.05）, significantly reduced the MDA content in leaves of soybean （20%²6%）（P<0.01）,while reduced the peroxidation of membrane lipid of soybean leaves leading to improvingresistant ability of soybeans to O₃stress.Under the elevated O₃environment, the soluble protein content in leaves of soybean wassignificantly decreased （15%²6%）（P<0.01）. During the whole exposure period, against CKtreatments,+Si+O₃treatments notably reduced the soluble protein content in leaf of soybean（12%¹7%）（P<0.05）. While under the elevated O₃environment, against Si-free treatments,silicon application could increase the soluble protein content in leaves of soybean （4%¹9%）during the whole exposure period, and the soluble protein content in leaves of soybean wassignificantly increased （P<0.01） at24d and increased （P<0.05） at32d.Under ambient air condition, there was no difference （P>0.05） between siliconapplication treatments and Si-free treatments. While under the elevated O₃environment, thesoluble sugar content in leaves of soybean was significantly increased （11%²7%）（P<0.01）.Under the elevated O₃environment, silicon application treatments could notably reduce thesoluble sugar content in leaves of soybean （7%¹2%）（P<0.01） from24d to32d aftertreated by ozone.5Effects of different treatments on the mineral element content in organs of soybeanO₃stress significantly reduced nitrogen, phosphorus, potassium, calcium contents in root,stem, leaf and grain, the reduction of phosphorus and potassium is especially more significant.Under the elevated O₃environment, against Si-free treatments, silicon application could significantly improve the nitrogen, phosphorus, potassium, calcium contents in root, stem,leaf and grain of soybean. However, compared with Si-free treatments, there was little impacton the nitrogen, phosphorus, potassium, calcium contents in root, stem, leaf and grain ofsoybean with silicon application under ambient air condition.6Effects of different treatments on biomass and distribution of soybeanUnder the elevated O₃environment, the shoot biomass, root biomass, and total biomasswere significantly decreased, with the reduction of27%,37%and28%, respectively, at thefinal harvest. The reduction of root biomass was higher than shoot biomass, resulting inlowering root to shoot ratio. While under the elevated O₃environment, against Si-freetreatments, silicon application could effectively alleviate the reduction of shoot biomass, rootbiomass, and total biomass under O₃stress, and at the final harvest were increased by18%,29%and19%, respectively. Silicon application promoted the transport of assimilates to theroots, and improved the root to shoot ratio under the elevated O₃environment.