水稻土砷形态转化的生物学机理与调控措施

Paddy rice is efficient at arsenic (As) accumulation due to a combination of the specific As biogeochemical cycle under the flooded environment and the plant physiological characteristics of rice. Rice is the most important contributor to the intake of inorganic As for the general population in China. Some paddy areas in Southern China have been seriously contaminated by As, threatening agricultural production, food safety and human health. Flooding of paddy soil leads to a massive increase in the reductive dissolution of As and a significant enhancement of As biomethylation and volatilization; however, the underlying biological mechanisms remain poorly understood. In this proposal, a suite of modern analytical techniques and soil microbial molecular methodologies will be combined to probe the key mechanisms and factors controlling As species transformation in the soil solid and solution phases. The relationship between As mobilization, iron and sulphur reduction and complexation with soil organic matter will be examined. The biomethylation and volatilization of As will be quantified. The data will be used to establish a predictive model for As mobilization in paddy soils. The abundance, diversity and expression of key microbial functional genes controlling As transformation in paddy soils will be determined. Furthermore, oxidizers of arsenite and/or ferrous iron will be isolated from paddy soils or from the rice rhizosphere. The effect of bioaugmenting arsenite or ferrous iron oxidizers in the rhizosphere on As bioavailability will be investigated. The project will provide a theoretical basis for developing practical measures to reduce As accumulation by rice.

由于水稻土生物地球化学过程和水稻特有的生理特性，水稻具有较强的砷累积能力，稻米是我国人口无机砷摄入的最主要来源。我国南方部分稻区受砷污染较为严重，危害粮食生产、农产品安全和人体健康。水稻土淹水后砷还原性溶解大幅度增强、砷甲基化和挥发显著增加，但其生物学机理仍不清楚。本项目申请通过现代分析化学和土壤微生物分子技术相结合，系统深入地研究水稻土固相和液相砷化学形态转化的关键机理和影响因子，探讨砷活化与铁、硫还原及与有机质结合的关系，定量测定砷甲基化和挥发通量， 建立预测水稻土砷活化的模型，揭示影响水稻土砷形态转化的关键微生物功能基因丰度、多样性和活性，分离水稻土或水稻根际亚砷酸和亚铁氧化细菌，探讨通过强化水稻根际亚砷酸和亚铁氧化过程降低砷的生物有效性，为提出减少水稻砷累积的实用措施提供理论指导。

我国南方部分地区土壤受砷污染较为严重，由于水稻土特殊的生物地球化学过程，水稻积累较多的砷，危害农产品安全和人体健康。水稻土淹水后砷还原性溶解大幅度增强、砷的甲基化和挥发显著增加，但其生物学机理仍不清楚。本项目采用现代分析化学和土壤微生物分子技术相结合，研究了水稻土淹水后砷形态转化的关键化学与生物学过程与机理、及调控水稻土砷生物有效性的措施。通过一系列室内培养、温室盆栽和大田试验，得到如下主要结果：1）无定型铁氧化物吸附的砷是水稻土淹水后砷释放的主要来源；2）土壤锰氧化物对砷的释放起重要调控作用，而硫对砷有效性的影响取决于还原条件下亚铁的释放量；3）淹水条件下水稻土中三价砷的厌氧氧化与反硝化过程存在偶联关系，反硝化菌是驱动砷厌氧氧化的主要微生物；4）淹水条件下水稻土中的硫酸盐还原菌对砷甲基化起主要作用，而甲烷产生菌则对甲基砷起脱甲基的作用；5）从南方砷污染水稻土中分离筛选到多株厌氧砷氧化菌和砷甲基化菌，证明了AioA介导厌氧砷氧化和ArsM 介导砷甲基化的功能；6) 水稻土中存在独立于砷甲基化的微生物砷挥发途径；7) 添加锰氧化物、施用硅肥及稻田水分管理可降低水稻砷积累，而秸秆还田促进砷甲基化和挥发、促进水稻砷积累。通过本项目研究，初步建立了水稻土砷转化的生物地球化学模型，并提出了阻控水稻砷吸收的一些有效措施。