| Selenium(Se)is one of the essential trace elements for human health,sufficient Se intake is consequently of importance to for maintaining the function of human immune system and preventing the cancer.Rice,as one of the staple food in China,is an efficient carrier for Se biofortification in Soil-Rice system,to increase the Se content in rice grain,and thus,is the fundamental approach to improve the human Se balance and health.Therefore,our researches focused on the regulatory effects of Se biofortification in Soil-Rice system and the cost-effectiveness analysis of agronomic biofortification strategy,and attempted to improve the human Se level,especially those living in rural regions.The main results obtained in this thesis are displayed as follows:(1)In order to clarify the character of the absorption,translocation and accumulation of Se in different rice tissue under different growth periods as well as the effects of iron plaque on Se bioavailability,to lay the foundation for the follow-up Se nutrition research.The soil pot experiment was conducted under Se and non-Se treatments,and the sampling analysis was carried out under different growth stages.The results showed that about 50% of the selenium in the different tissues was absorbed by the plant at the jointing and booting stages,and 47.22% of the total Se in the spikelet was filled up at the booting stage.Se content in the iron plaque peaked at the seedling stage,accounting for 73.63% of the total in the plant,which was 4.87 times that(15.12%)in the stem.As the plant grew,Se content in the iron plaque declined significantly down to 20.02% in proportion at the maturing stage,while Se content in the stem reached 65.42%.Therefore,the jointing and booting stages are the two critical periods for the rice to absorb and accumulate Se in grain and the iron plaque plays a role of "buffer" in Se absorption and accumulation of rice.(2)In order to define the key physiological process for determining the level of Se content in rice grain and contribution of different growth period to the Se accumulation in rice grain,to provide reference for production practice of applying Se period.The sand culture experiment was conducted to grow Se-enrichment(Xiushui 48)and non-Se-enrichment(Bing 9652)rice,and the Se was supplied in different growth periods only for 7 days.The sampling analysis of different parts of rice plant was conducted after harvest.The results showed that the Se concentration in root of Xiushui 48 was significantly lower than that of Bing 9652,but the Se concentration in shoot,especially in stem and grain,of the former was significantly higher than that of the latter.The tendency of Se accumulation was the same as the Se concentration.The transfer coefficient of Se in shoot different parts of Xiushui 48 was significantly higher than that of Bing 9652,particularly,the transfer coefficient of Se in grain of the former was even 4 times as high as that of the latter.Similarly,the distribution of Se in shoot of Xiushui 48 was higher than that of Bing 9652.Besides,the Se accumulation in shoot under Se supply before the panicle initiation stage was markedly higher than that after it,and the Se transfer coefficient and distribution coefficient were both consistent with the rule of Se accumulation.Therefore,the Se transport of rice under the period between the jointing and panicle initiation stages is the most efficient.The key reason of the more Se accumulated in grain in Se-enrichment rice Xiushui 48 is that the process of Se transfer from root,especially from the leaf,to grain is more efficient.(3)In order to study the difference of Se biofortification and grain nutritional quality between different selenium absorption and transport pathways,and to provide references for the application of Se in the practical production,the soil pot experiment was conducted.There were two different Se fertilization pattern,the soil application(SA)and foliar spraying(FS),and all conditions were controlled strictly consistent,such as rice variety,soil type and Se dosage.The samplings were measured after harvest for the effects of different fertilization pattern on the absorption,translocation of Se and the grain nutritional quality in rice.The results displayed that these two fertilization pattern could both increase the Se content in rice shoot and grain significantly with the same Se dosage.However,the Se content in shoot and grain with SA was 8.9 and 5.3 times than that with FS,respectively,but the distribution coefficient of Se in grain with FS was 2 times more than that with SA.SA could significantly improve the content of other trace elements in rice grain,and the effect of FS on other nutrients was not significant.Compared with the control,the crude protein in rice grain with SA and FS could be increased by 8% and 4.5%,respectively.Meanwhile,the content of serine(Ser)and tyrosine(Tyr)with Se application were both higher than that with non-Se application,the Tyr content with SA was significantly higher than that with the FS,the former was 1.15 times of the latter.In conclusion,compared with FS,SA could increase the Se content and nutritional quality in rice grain more efficiently,while the less loss of Se in transportation with FS.(4)It is necessary to reduce the cost of this strategy,in order to promote agronomic biofortification measures in the poor rural areas in China.Therefore,the disability-adjusted life years(DALYs)framework was conducted to calculate the health burden caused by iron(Fe)and zinc(Zn)deficiency,to quantify the health impact of agronomic biofortification via a single,dual or triple foliar spray of Fe,Zn and/or pesticide in four(Northeast,Central China,Southeast,Southwest)major Chinese rice-based regions,and finally the cost-effectiveness analysis was conducted.The current health burden by Fe or Zn malnutrition was 0.45-1.45 or 0.14-0.84 million DALYs for these four regions.Compared to traditional rice diets,the daily Fe and/or Zn intake from Fe and/or Zn-biofortified rice increased,and the health burden of Fe and/or Zn deficiency decreased by 28 and 48 %.The cost of saving one DALYs ranged from US$376 to 4,989,US$194 to 2,730 and US$ 37.6 to 530.1 for the single,dual and triple foliar Fe,Zn and/or pesticide application,respectively,due to a substantial decrease of labor costs by the latter two applications.Therefore,Agronomic biofortification of rice with the triple foliar spray of Fe,Zn and pesticide is a rapidly effective and cost-effectiveness pathway to alleviate Fe and Zn deficiency status for rice-based dietary populations.In conclusion,this thesis focused on the soil-rice system,closely related to the practical production,to carry out the research based on the timeline and space.Firstly,based on the timeline,the adsorption-desorption effect of iron plaque during the whole growth period of rice and the key growth period of Se in rice was clarified.And then,spatially,the process of absorption and translocation of Se in rice and the key physiological process of Se biofortification was clarified.In the practical production,the SA selenate was recommended as the Se biofortification strategy to efficient increase the Se content and nutritional quality in rice grain.In addition,the strategy via foliar spray of micronutrients plus pesticide which could reduce the cost of production could also be an references for promoting the Se biofortification. |
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