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Ozone is believed to be an important environmental pollutant causing severe losses of crops production under global change scenarios.Technical countermeasures to easing ozone stress would help ensure food security,among which adding silicon might be one of the practical approaches.Open-top chambers(OTCs) were applied in determining the effects of ozone(normal air,40 μg/kg O3 or elevated O3,(80±5) μg/kg,7 h/d) and silicon(Si-free,0 mg/kg or +Si,100 μg/g) on plant height,leaf area,chlorophyll content,antioxidant system and yield of soybean after anthesis.Our results indicated that,under normal air condition,compared with Si-free treatments,+Si significantly increased the amount of biomass of soybean roots,total biomass and grain weight per plant(14%,5% and 20%)(P0.05).While under the elevated O3 environment,against Si-free treatments,silicon application could maintain a high leaf area of soybean.Use of silicon also significantly increased chlorophyll content and SOD,POD,CAT activity,while decreased MDA content.The biomass of soybean roots,shoot,root-shoot ratio and yield of per plant were further improved by 29%,18%,19%,9% and 17%,respectively(P0.05).Our findings might provide theoretical support for the reasonable soybean cultivation and management in alleviating the damage of ozone pollution.

The elemental cycling of nitrogen plays a key role in agricultural ecosystem to ensure either food security or environmental sustainability.Bases on the premise of grain yield stability,cutting down proper part of N fertilizer application would largely decrease environmental pollution and significantly promote greenhouse gas emission reduction.In recent years,because of climate change,improvements of varieties,water conservation,delay of maize harvest and other factors,the area of late-sowing winter wheat increases continually.A reasonable field management of nitrogen fertilizer is therefore considered as an important measure to improve the yield of late-sowing winter wheat.Appropriate late sowing of winter wheat could extend growth period of previous maize,and reduce the consumption of water and fertilizer in winter wheat at early stage.In the Huanghuai Plain,seedtime postponing to mid-late October in winter wheat could mitigate the damage of frost on winter wheat to a certain extent.There are many researches which document the effects of temperature,light,moisture,density and other factors on carbon and nitrogen metabolism,yield and quality in late-sowing winter wheat.However,the influence of fertilizer management on nutrition absorption and dry matter accumulation in late-sowing winter wheat has been rarely reported.Meanwhile,no final conclusion has yet been reached on nitrogen application strategy in late-sowing winter wheat.Under field conditions,we here designed four treatments of nitrogen fertilizer application: 0 kg/hm2(N0),168.75 kg/hm2(N1),225 kg/hm2(N2),and 281.25 kg/hm2(N3),at two topdressing stages: jointing stage(S1),jointing and anthesis stage(S2).We found that that regulation effect of nitrogen application rate on dry matter accumulation changes due to nitrogen application time.The accumulation and transportation of dry matter and nitrogen,as well as nitrogen use efficiency of late-sowing winter wheat were carefully investigated.We also noted that elevating 25% nitrogen fertilizer rate on the basis of 225 kg/hm2(N2) had no significant influence on either the total nitrogen accumulation at anthesis or nitrogen transportation amount in vegetative organs when nitrogen fertilizer topdressed at jointing stage(S1).However,those variables increased when nitrogen fertilizer topdressed at jointing and anthesis stages(S2).Compared with treatment S1,nitrogen accumulation amount in grain and vegetative organs,nitrogen accumulation amount after anthesis and nitrogen distribution proportion were much higher in treatment S2.At the same nirogen fertilizer rate,the dry matter accumulation at maturity,dry matter accumulation intensity from anthesis to maturity and dry matter amount of grain were higher in treatment S2 than those in S1.While at the same nitrogen fertilizer topdressing stage,grain yield has no significant difference between treatment N2 and N3,but nitrogen fertilizer partial factor productivity declined after nitrogen fertilizer rate increased.Grain yield and nitrogen fertilizer recovery efficiency were higher in S2 than those in S1 when nitrogen fertilizer rate was identical.We therefore reasonably drew the conclusion that topdressing nitrogen fertilizer at jointing and anthesis stages with total nitrogen fertilizer application rate at 225 kg/hm2 was the optimal nitrogen fertilizer management mode which could not only achieve high yield but also obtain high nitrogen fertilizer use efficiency in late-sowing winter wheat.