红壤水稻土干湿交替作用下的2,4-D迁移转化及微生物学机理

Widely distributed in southern China, red paddy soils are facing potential ecological risks associated with large-scale use of herbicides and pesticides. The migration and transformation of chlorinated organic pollutants in agricultural soils has been a great concern in the field of soil environmental chemistry. In this project, the natural attenuation of 2,4-dichlorophenoxyacetic acid (2,4-D), a typical chlorinated acid herbicide, in paddy soils, will be investigated. The microbial driving force will be focused on, and the two important natural attenuation processes, i.e., the anaerobic reductive transformation under water-logged conditions and the aerobic mineralization and detoxification under drying processes will be studied dependently. The migration and transformation kinetics of 2,4-D with the wetting/drying cycles in red paddy soils and the underlying microbiological mechanism will be investigated. We will focus on aggregate reconstruction, changes of iron species, and the response of microbial communities, and their impacts on the mode of occurrence and the pathways of migration and transformation of 2,4-D in the wetting/drying cycles. By simulating typical agronomic practices in southern China, the differences in migration and transformation kinetics of 2,4-D will be demonstrated for soils with different organic matter contents and different pH. The dominant soil microbial community composition and the dynamic changes of oxidation-reduction potentials will also be evaluated. Results from this project are expected to reveal the inherent nature of the migration and transformation of 2,4-D in wetting/drying cycles and to enrich the environmental behavior theory of chlorinated organic matter in red paddy soils.

红壤水稻土在我国南方广泛分布，但面临除草剂等农药大量使用带来的潜在生态环境风险，而农田土壤氯代有机污染物的迁移转化，在土壤环境化学领域一直受到强烈关注。项目以典型氯代苯氧乙酸类除草剂2,4-D为目标物，以微生物驱动力为核心，将水稻土2,4-D自然衰减的两个重要过程，即淹水厌氧还原转化、落干好氧矿化脱毒耦联进行研究，探讨在干湿交替循环作用下，南方红壤水稻土2,4-D迁移转化动力学及微生物学机理。重点研究不同周期"淹水-落干"过程中，水稻土团聚体组成重构、铁物质形态变化、微生物群落响应机制，及其对2,4-D赋存状态和迁移转化途径等影响的作用机理。通过模拟南方典型农艺措施，考察土壤不同有机质含量和pH条件下，2,4-D迁移转化动力学差异，结合土壤优势微生物群落组成及氧化还原电位动态变化等分析，揭示南方红壤水稻土干湿交替作用下的2,4-D迁移转化内在本质,以期丰富水稻土氯代有机物环境行为研究理论。

红壤水稻土在我国南方广泛分布，但面临除草剂等农药大量使用带来的潜在生态环境风险，农田土壤氯代有机污染物的迁移转化受到强烈关注。项目以典型氯代苯氧乙酸类除草剂2,4-二氯苯氧乙酸（2,4-D）作为模型污染物，富含铁的南方红壤水稻土为研究对象，构建了“土壤-腐殖质/电子供体/电子受体/Fe(III)-2,4-D”厌氧反应体系，研究南方红壤水稻土2,4-D的厌氧转化动力学与微生物群落结构变化，探讨不同外源物质对2,4-D降解转化的影响，揭示水稻土中2,4-D还原转化的微生物机制。研究结果表明：灭菌土壤没有铁还原作用，2,4-D未发生降解；而活性土壤中Fe(III)还原生成Fe(II)，2,4-D发生厌氧转化，表明微生物活性是铁还原与2,4-D降解转化主要驱动力。土壤中2,4-D发生厌氧降解，生成中间产物2,4-DCP、4-CPA和4-CP，最终产物4-CP浓度持续升高后保持恒定。AQDS轻微促进土壤中2,4-D微生物还原脱氯，可能是由于AQDS还原过程使得细胞增殖，促进直接脱氯转化过程。此外，还原产物AHQDS对2,4-D具有还原能力。乳酸钠和葡萄糖可作为碳源和电子供体被土著微生物利用，促进微生物生长和铁还原，从而加快2,4-D的还原转化。硝酸根极易被微生物利用而最先被还原，但很快消耗完，故硝酸钠对2,4-D及硫酸根的还原转化稍有抑制。硫酸钠抑制铁还原过程，同时硫酸根作为电子受体较2,4-D更易得到电子而被还原，因此显著抑制2,4-D的还原转化。土壤中变形菌门为最优势门类，乳酸和葡萄糖组中微生物群落结构与原土组存在显著差异。原土组中具有2,4-D降解活性属水平微生物的相对丰度的最高值出现在40 d，而乳酸和葡萄糖组的均出现在20 d，并且20 d时乳酸和葡萄糖组的相对丰度显著高于原土组（p < 0.05），这很好的解释了添加乳酸或者葡萄糖能促进土壤中2,4-D发生微生物降解。本项目共发表SCI论文1篇，联合培养硕士研究生1人。