| Selenium(Se)and zinc(Zn)biofortification of wheat grains is a key strategy to combat the human Se and Zn malnutrition,and the foliar application method has been proved highly effective.Meanwhile,incorporating such approach into already existed pesticide management or into foliar Zn spray would be greatly cost-effective and support the biofortification of wheat with Se and Zn in practice.Two field experiments and one pot experiment were conducted in the present study.The following three studies were investigated:(a)the effectiveness of grain Se biofortification through combined foliar application of selenite and pesticides or phosphorus;(b)the Se and Zn accumulation and partitioning in wheat organs and grain Se and Zn enrichment under simultaneous foliar application of zinc sulfate and low to high rates of selenite;(c)the comparison between Se and Zn uptake,accumulation and partitioning,and the possible reasons of Zn and Se interactions in these processes in wheat with foliar application of selenite and Zn under different N regimes.The main results were as follows:(1)Grain Se can be over-riched(0.25～0.3 mg/kg)through combined foliar application of selenite and pesticides(imidacloprid and triazolone)or phosphorus at the early milk stage of wheat without any yield losses.Compared to the foliar Se spray alone,the Se plus pesticides treatments significantly increased grain Se distribution,but has no impacts on grain Se concentration.The addition of phosphorus further increased grain Se concentration by 74%-87%.The combination of selenite,pesticides and phosphorus had limited impacts on the concentrations of N,K,Fe,Mn,Cu and Zn in grain relative to the solely spray of selenite with few exceptions of grain P concentration.(2)Grain Zn and Se can be simultaneously enriched through foliar application of zinc sulfate and low to high rates of selenite,as well as their bioavailability.There were no significant changes in Zn concentrations of grain,bran and flour between treatments of Zn spray alone and Zn plus Se.However,compared to the foliar Se application alone,Se concentration decreased by 40% in grain and its milling fractions in the combined applications(the first year).In treatments with combined Zn and Se application,grain Se concentrations markedly increased with the Se application rate,while the Se distr ibution in each organ kept relatively constant.(3)The magnitude of grain Se enrichment,but not grain Zn enrichment,was significantly reduced by Zn plus Se application relative to the solely spray of Se or Zn.Compared to the foliar Se spray alone,the combined application caused 52%～56%,35%～45% and 32～38% reduction of Se concentrations in grain,bran and flour under nil N or optimum N levels in the field,and 76%～77% reduction of grain Se concentration in pot experiment.However,there were no differences in Se concentration between these two treatments when applying manures to the optimum N treatment.Nitrogen supply contributed to the grain Zn enrichment to some extent,while the Se concentrations in grain,flour and bran decreased by 40%～66%,32%～48% and 35%～45% in all Se spray treatment under optimum N vs.zero N level in the field.In addition,the reduction of Se concentrations in grain and flour in treatments of Zn plus Se relative to Se spray alone might be associated with the changes of Asp,Ser,Gly and Ala(7%～14%),and thus storage protein fractions in these tissues.Take together,Grain Se and Zn can be enriched simultaneously through combined foliar application of selenite and zinc sulfate and pesticides or phosphorus at the early milk stage of wheat without any sacrifices of grain yield.Nonetheless,the addition of zinc sulfate to selenite spray reduced the magnitude of grain Se enrichment,which depended on the N regimes in the field.Overall,such knowledge is valuable for deepening the theoretical basis for optimizing the agronomic strategies of grain zinc bio-fortification and quality improvement via optimizing the nutrient management in wheat production. |
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