石灰性土壤锌扩散对外源施锌的响应及小麦根系锌吸收的调控机制

Zn deficiency-related health problems take place worldwide among people who rely on the single wheat-based diets. However, on the potentially Zn-deficient calcareous soils that is the major wheat growing areas in northern China, zinc application does not effectively increase the concentration of Zn in wheat grain. It is well known diffusion is the dominant approach of Zn movement in soil. We hypothesize that the poor Zn uptake by crops results from the low diffusive transfer of Zn in soil caused by the transformation of the added Zn into the less available forms, but amendment of organic materials is expected to enhance the diffusive transfer of exogenous Zn in soil. In view of this hypothesis, winter wheat will be used as research objective and the incubation and field experiments will be conducted as research methods. Meanwhile, some techniques will be adopted such as diffusive gradients in thin films, simulation of roots uptake, and chemical fractionation of Zn. This project aims to investigate: (1) the response of Zn diffusive transfer in soil to the inorganic and organic Zn fertilizers and its regulating mechanism for Zn uptake by roots; (2) the interaction of organic materials and Zn fertilizer and its improvement mechanism for Zn diffusive transfer and uptake by roots; and (3) the influence of Zn diffusive transfer in soil and uptake by roots on Zn biofortification of wheat grain. These results from the project will reveal the obstacle and regulating mechanism of Zn diffusive transfer and uptake by wheat roots and give a guidance for increasing Zn concentration of wheat grain through Zn application on calcareous soil.

在膳食结构单一且以小麦为主食的人群中人体缺Zn问题十分严重，但在我国北方麦田的主体土壤类型-潜在缺锌石灰性土壤采用土施锌肥措施，其对小麦籽粒Zn含量提升效果并不理想。土壤锌向作物根系的主导迁移方式是扩散，据推测，外源锌进入土壤后向难利用态组分转化可能是导致锌扩散能力差进而限制作物吸收的主因，而锌与有机物料配施有望有效促进Zn扩散能力。基于此，本项目以冬小麦为研究对象，拟通过土培和田间试验方法，采用DGT、根系吸收模拟和土壤锌分组等技术开展研究：一是探讨土壤锌扩散对不同形态锌肥（无机盐态和螯合态）的响应及根系锌吸收的调控机制，二是揭示有机物料与外源锌在土壤中的互作机制及提高锌扩散和小麦锌吸收的机理，三是阐明外源施锌条件下土壤锌扩散和根系锌吸收对籽粒富锌的影响。研究结果为深入揭示外源锌在石灰性土壤中扩散和根系吸收过程的障碍因子及调控机制，进而通过施锌措施提高小麦籽粒Zn含量提供科学依据。

在发展中和不发达国家，锌摄入不足是导致人体缺锌根本原因，而通过施用锌肥提高主食作物锌含量是缓解人体缺锌的有效途径。在我国主食作物小麦广泛分布在北方石灰性土壤上，但外源施锌对小麦籽粒锌含量的提升效果却非常有限。因此，查明石灰性土壤上小麦根系对外源锌的吸收障碍及提高机制，对于改善小麦籽粒锌含量进而缓解以小麦为主食人群缺锌问题意义重大。基于此，本项目通过土培和大田试验，结合梯度薄膜扩散、根系模拟和锌化学分组等技术探究了：不同锌源在土壤中的迁移转化规律及对根系自由空间锌累积和跨膜吸收的影响机制；有机物料与锌肥配施土壤锌迁移转化规律及对根系自由空间锌累积和跨膜吸收的影响；不同锌源单施及与有机物料配施土壤锌迁移转化对小麦籽粒富锌的影响机制。结果表明：（1）相较于梯度薄膜扩散和提取技术，根系模拟技术测得土壤有效锌含量与小麦锌吸收和含量均具有较高的拟合度；土施ZnEDTA可显著增加土壤锌向有效态组分转化，从而提高小麦根系自由空间锌的累积和跨膜吸收；（2）添加有机物料降低了土壤对外源锌的吸附容量，提高了锌的吸附强度和解吸能力；有机物料与锌肥配施展示出了较高的扩散迁移能力，从而增加了小麦根系自由空间锌的累积和跨膜吸收；（3）相较于小麦根系自由空间锌的累积和跨膜吸收，土壤锌扩散迁移是限制石灰行土壤小麦籽粒富锌的核心因素。因此，通过农艺措施提高外源锌在土壤的扩散迁移（如施螯合锌肥、硫酸锌配合施有机物料等）可能是强化小麦籽粒富锌，进而改善人体锌营养的有效措施。