原位研究有机质对水稻根际砷形态和有效性的影响及其微界面机理

Land application of organic fertilizer is encouraged by Chinese government to improve soil physicochemical properties as well as recycle the organic solid waste (such as animal manure) in rural areas. However, some agricultural soils are contaminated by arsenic (As) in China and the land application of organic fertilizer will greatly influence the arsenic uptake by rice, thus increasing the As exposure to human through rice consumption. Since the organic matter composition and content are different for organic fertilizers with various feedstocks, investigating the influence of different organic matter (such as humic substances, cellulose, polysaccharide etc.) on As bioavailability to rice is imperative to screen the appropriate type of organic fertilizer for marginally arsenic contaminated land. In this research, we first develop a DGT device to in-situ measure the labile concentrations of As(III) and As(V) in soils. Then, this DGT device was used to determine the change of As speciation and labile concentrations in rice rhizosphere and non-rhizosphere soils with application of various organic matter. The correlation between As(III), As(V) labile concentrations and organic matter parameters (such as polarity, aromaticity, function group distribution etc.) were analyzed to identify the crucial organic matter parameter influencing the As speciation and bioavailability. Finally, the bio-geochemical processes of As in the rhizosphere micro-niche was 2D-visualized using the high resolution method of coupling planar optode with DGT-LA-ICP-MS. Revealing the As speciation and labile in the rhizosphere micro-niche will help to elucidate the mechanism of organic matter impact on As uptake by rice.

落实有机肥替代化肥是国家“十三五”规划改善土壤肥力、治理农业面源污染的一项重要举措。我国耕地砷（As）污染情况严重，向农田施用有机肥将影响水稻对As的吸收。由于有机肥来源丰富，其含有的有机质类型及特性差别显著，因此，研究不同有机质对水稻根际As形态与有效性的影响程度及其微界面机理意义重大，将为筛选适用于轻度As污染农田的有机肥提供科学依据。本项目以轻度As污染农田土壤为研究对象，选取四种代表性的有机质（腐殖质类、纤维素类、糖类、蛋白质类），基于土壤中污染物有效性的原位分析方法-梯度扩散薄膜技术（DGT），定量考察水稻根际As形态、有效态浓度与有机质特性（如极性、可降解性等）及施用量的响应关系，同步表征根系-土壤微界面中物理、化学、生物过程，深入探讨在多因素共同作用下，有机质调控水稻根际As形态及有效性的微界面机理。

有机固废土地利用是一种资源循环与污染防治协同的处置方式。然而，我国耕地砷（As）污染情况严重，研究外源有机质施用对土壤As形态和有效性的影响意义重大，将为筛选适用于轻度As污染农田的有机肥提供科学依据。项目基于“原位方法构建-形态变化表征-微界面机理探究”的研究思路开展研究。在原位方法构建方面，开发了AsIII有效态浓度的原位选择性DGT监测装置，在常见环境条件（pH为5–9、离子强度为0–100 mmol L-1 NaNO3）下均可实现对AsIII的选择性测定；在形态变化表征方面，证明外源有机质的组成和类型是影响土壤As的形态和有效性的重要因素，易降解的有机质会促进As的释放，而芳香化程度高、稳定的有机质会降低As有效性；在微界面机理方面，揭示了水稻根际AsIII向AsV转化的高分辨规律。相关研究成果为指导有机固废的合理土地利用提供科学支撑。