利用铁同位素制约水稻耕作对江西鹰潭红壤铁循环的影响

Iron is one of the important elements in the paddy soils. It is not only an essential element for the growth of rice, but is also closely related to the organic carbon cycles and nitrogen fixation in the soils. It is critical to investigate the impact of rice cultivation on iron cycles in the soil, in order to obtain a comprehensive understanding on the nutrient cycles in the paddy soils. We choose a study site in the red soil zone of Southern China, and focus on the flooding-drainage alternation of rice cultivation, a key factor that control iron cycles in paddy soils. We propose to investigate two vertical profiles of long-term cultivation and newly cultivated paddy fields, with the new technology of iron stable isotopes, as well as element geochemistry and physical parameters in the soils at high spatial resolution. The impact of rice cultivation on iron cycles in the red soils will be discussed with emphasis on stable isotope fractionation. We try to shed new light on the fractionation mechanisms of iron stable isotopes in paddy soils, and understand the impact of rice cultivation on iron cycles in the soils from a new aspect. The outcome of this study would also benefit research on the carbon and nitrogen cycles in paddy soils, and have potential in guiding agriculture.

铁元素是水稻土中的一种重要元素。它不仅是水稻生长必需的营养元素，也与有机碳循环和土壤中的固氮作用有密切的关系。认识水稻耕作对土壤铁循环的影响对全面理解水稻土中营养元素循环至关重要。本项目选取位于我国南方典型红壤带的研究区域，针对水稻耕作带来的淹水-落干循环这一控制铁循环的关键因素，采用铁同位素这一新兴技术手段，结合铁元素和土壤Eh、pH等参数，通过对比长期耕作和新近改种的两处水稻田垂直土壤剖面的高分辨率铁同位素分布，从稳定同位素分馏的角度探讨水稻耕作对红壤中铁循环的影响。通过本研究，有望深入探讨水稻田中铁同位素的分馏机理，从新的角度理解水稻耕作对土壤铁循环的影响。本项目的研究成果也将对水稻土中碳氮循环的研究提供重要理论支持，对指导农业生产具有潜在意义。

铁元素是水稻田生态系统中的重要元素，与水稻生长及水稻土有机碳循环息息相关。在水稻土的成土过程中，氧化还原状态的变化可以改变铁元素形态，并引起铁的垂向迁移。但之前并未有针对水稻土中铁同位素垂直分布和其中蕴含的铁循环机制的详细研究。本项目在前人初步工作的基础上，测定了鹰潭新老水稻田中高分辨率的铁含量和铁同位素垂直分布，以及苏州水稻田剖面中不同赋存形态的铁含量和铁同位素组成，发现水稻土耕作层和犁底层的铁在淹水期被还原为富集轻同位素的二价铁，并随土壤溶液向下迁移，在氧化性较高的层位迅速沉淀，形成以短程有序形态铁为主的铁富集层，且铁富集层的铁同位素明显偏轻。本项目为水稻土中铁元素循环提供了新的认识，并有助于指导水稻田土壤性质的科学管理。

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