水稻土厌氧砷氧化效应的母质分异规律与机制

The water management of rice fields makes the oxidation and reduction of arsenic active in paddy soils. Arsenic reduction enhances its toxicity and mobility, while oxidation is the opposite. The mechanism of anaerobic arsenic oxidation is the theoretical basis for controlling arsenic pollution in rice fields. Paddy soils are widely distributed from south to north in China, with different types of parent materials. The scientific hypothesis of the project is that anaerobic arsenic oxidation is significantly influenced by the parent-material-induced differentiation of soil physicochemical properties and indigenous microorganisms. To illustrate how different parent materials affect arsenic translation in paddy soils, the research program will investigate the relationship of arsenic species/valence states as well as the diversity and abundance of arsenic-oxidizing bacteria with parent material characteristics. Further, we will examine the process of anaerobic arsenic oxidation coupled with nitrate reduction using soil microcosms. We will investigate the difference in arsenic oxidation dynamics and mineralization products as well as the community composition and activity of arsenic-oxidizing bacteria in soils with different parent materials. The objectives are to (1) explain how parent material influence the process of anaerobic arsenic oxidation coupled with nitrates reduction and (2) find the key physicochemical factors and microbial groups. The innovation of this project is to preliminarily illustrate the mechanism of anaerobic arsenic oxidation and fixation in paddy soils with different parent materials. We expect the results of this study can provide theoretical basis for regulating the anaerobic arsenic oxidation and fixation process in paddy soils.

稻田淹水环境使得砷的氧化还原活跃，砷还原增加其毒性与移动性，氧化则反之。阐明厌氧砷氧化机制是控制稻田砷污染的理论基础。我国稻田从南到北广泛分布，母质发育类型多。该项目的科学假设是：母质分异造成的土壤理化性质及土著砷氧化菌群的差异，显著影响稻田厌氧砷氧化过程。以我国主要母质发育的砷污染稻田为研究对象，重点研究不同母质发育水稻土的特征理化指标与砷价态及形态、砷氧化菌群多样性及丰度的关系，阐明其砷氧化的母质分异规律；在此基础上，进一步以厌氧硝酸盐还原驱动的砷氧化为主要过程，构建微宇宙实验体系，研究其砷氧化动力学、成矿产物、砷氧化群落组成与活性差异，阐明硝酸盐还原耦合砷氧化的母质分异规律；确定影响厌氧砷氧化的关键理化因子及重要微生物类群。其主要创新在于：阐明不同母质发育水稻土中厌氧砷氧化固定机制。预期成果可为稻田砷氧化过程调控提供理论依据。

我国稻田砷污染问题严重，影响到农产品安全，是涉及民生的重大问题，亟待解决。厌氧条件下，微生物驱动的硝酸盐还原与砷氧化过程之间存在着密切的联系，是影响砷迁移转化和生物有效性的关键因素。探明不同母质发育水稻土中厌氧砷氧化固定机制，可为稻田砷氧化过程调控提供理论依据。本项目研究了硝酸盐还原和砷氧化在水稻土中的普遍性和特性。实验结果表明，添加硝酸盐（NO3-）后，99.8%的水溶态As（III）在2-8天内转化为溶解的As（V），As（V）与Fe结合，砷的移动性降低。此外，硝酸盐的添加也显著地诱导了五种水稻土中16S rRNA和As（III）氧化酶（aioA）基因的表达，特别是紫砂土石和第四纪红粘土发育的水稻土，NO3-处理分别增加了10倍和3-5倍；此外，通过宏基因组分析还发现了一系列的新型硝酸盐依赖性As（III）氧化细菌，主要包括Aromatoleum、类芽孢杆菌属（Paenibacillus）、微小杆菌属（Microvirga）、草螺菌属（Herbaspirillum）、慢生根瘤菌（Bradyrhizobium）、固氮螺菌属（Azospirillum）。另外，土壤有机质含量、pH、养分状况、矿物组成等土壤特性显著影响了微生物的相对丰度以及多样性及其介导的砷的生物化学转化过程。总之，以上研究表明，硝酸盐还原耦合砷氧化是在稻田环境中普遍存在的重要的氮砷耦合过程，拓展了稻田Fe、N、As耦合转化过程的微生物理论机制，证实了稻田施加硝态氮肥是一种行之有效的降低砷移动性的措施。