| Zinc, as an essentiall trace element, plays an important role in human health. Zinc deficiency has been considered as the major healthy problem in the world. In China, wheat, as the main food source for the north people, is mainly grown on calcareous soil which is classificated as potentially Zn deficient soil. However, Zn concentration in wheat grains was low. In this present days, Zn fertilization of soil and foliar spray of Zn could increase grain Zn concentrations. However, previous researches had focused on extremely Zn deficient soil, little information was known about Zn fertilization on potentially Zn deficient soil. Therefore, a two-year field experiment and a sand culture experiment was conducted to investigate the mechanim of wheat absorb Zn when Zn was supplied through root or leaf. The main conclusions are as below:(1)A sand culture experiment was conducted to investigate the effect of Zn supplied to root and foliar spray of Zn on Zn concentrations in wheat tissues. A factorial design was conducted with three factors (Zn supplied to root, foliar spray of Zn and growth stagte). Results showed that there was no significant effect of Zn fertilization methods on wheat biomass. Compared to the control, Zinc concentration in root, stem, leaf, gume and grain was 15.68,3.91,3.60,1.90 and 2.11 times higher in the Zn supplied to root treatment compared to the control. Foliar spray of Zn only significantly increased Zn concentration in leaf, glume and grain, with 1.85,2.67 and 1.11 times higher compared to the control. Zinc supplied to root significantly increased Zn content by 18.4,3.98,3.71,1.58 and 1.90 times in wheat root, stem, leaf, glume and grain, respectively. Zinc content in glume and grain was increased by 1.58 and 2.08 times compared to the control, respectively. Zinc content in wheat tissues decreased in the order: leaf>root>glume>stem>grain. Overall, when root was provided with sufficient Zn, grain Zn was mainly from the root absorption Zn. When Zn was deficient in medium, grain Zn was from other organs, such as leaves. However, most of Zn was rent in root when Zn was supplied to roots. Therefore, to increase grain Zn concentration could be through increasing the re-translocation of Zn from root to shoot.(2)A two-year field experiment was conduceted to investigate the effect of different Zn fertilization method on increasing grain Zn nutritional quality of wheat grown on calcareous soil which is potentially Zn deficient soil. A split-plot design was conducted combined with four Zn levels and five wheat cultivars. Results showed that on calcareous soil (potentially Zn deficient soil), foliar spray of Zn increased grian Zn concentration by 61% and grain Zn bioavailability was relatively increased by 35.5%. However, Zn fertilization of soil had no significant effect on grain Zn concentration. Soil DTPA-Zn content was increased by 167% and 231% in the Zn fertilization of soil treatment in the two cropping, respectively. Phytic acid content of wheat cultivars showed significant variation. Furthermore, phytic acid content in wheat grain was mainly controlled by environmental factors, such as year and Zn fertilization had no significant effect on grain phytic acid content. Overall, on potentially Zn deficient soil, to increase grain Zn bioavailability was through foliar spray of Zn. Low Zn absorption of wheat root may be due to the low soil DTPA-Zn concent in wheat roots.(3)A sand culture experiment was conducted to investigate the different Zn fertilization methods on Zn, Fe, Cu and Mn concentration and uptake in wheat plants. The experiment used a factorial design with three factors (Zn supplied to root, foliar spray of Zn and growth stage). Results showed that Zn supplied to root significantly increased Zn concentration and uptake in root, stem, leaf, glume and grain. Foliar spray of Zn significantly increased leaf-, glume- and grain-Zn concentration and uptake. However, foliar spray of Zn had no significant effect on root- and stem-Zn concentration and uptake. Zinc concentration in root, stem, leaf, glume and grain was 1.02,1.18,1.85,2.67 and 1.11 times higher in foliar spray of Zn treatment compared to the control. Stem-Fe concentration and uptake averagely reduced by 38% in the Zn supplied to root treatment compared to the control. Meanwhile, foliar spray of Zn reduced root-Fe concentration and uptake by 11% and 33%, respectively. On the other hand, Zn supplied to root resulted in a reduse in stem-Mn concentration and uptake, by 166% and 216%, respectively. Furthermore, stem-Mn concentration was also reduced by 202% in the foliar spray of Zn. However, foliar spray of Zn had no significant effect on root, leaf, glume and grain Mn concentration and uptake. Root Cu concentration and uptake was increased by 37% and 38% in the Zn supplied to root treatment compared to the control. In contrast, foliar spray of Zn reduced root Cu concentration and uptake, averagely being 14%. The effect of foliar spray of Zn at different growth stage on the concentration of trace elements in wheat plants was dependent on wheat tissues and the types of elements. Analysis of the step regression of micronutrients, there was a significant interaction between grain micornutrients concentration and Zn concentration in wheat tissues, root-Mn concentration and root-Fe concentration. So, to increase grain micronutrient concentrations, it is reasonable to increase Zn concentration in tissue, Mn and Fe concentrations in roots. Grain Zn concentration was primarily from Zn absorption from medium; when Zn supply was deficient, Zn in other organs (such as leaf) could be transported into grains. On potentially Zn deficient soil, Zn fertilization of soil had no significant effect on grain Zn nutritional quality; however, foliar spray of Zn could be effectively increased grain Zn nutritional quality... |
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