Abstract:

Arsenic pollution in paddy fields is a serious problem in China. Pentavalent arsenic is reduced by microorganisms to highly active trivalent arsenic under flooded anaerobic conditions, becoming easy to be absorbed and accumulated by rice, thus threatening human health. On the other hand, rice production requires a large amount of nitrogen fertilizer, and the redox activity of nitrogen in paddy soil is high, which has an important impact on arsenic speciation transformation in paddy field. Based on the summary of the main processes of nitrogen cycling in paddy soils and the characteristics of functional microorganisms, arsenic speciation transformation and related functional microorganisms in paddy soils, the effects of nitrogen cycling processes in paddy soils (nitrification, denitrification, anammox, Feammox and dissimilatory nitrate reduction to ammonium, etc.) on arsenic migration and transformation in paddy soil and the key environmental factors were analyzed in depth. It was concluded that nitrification and denitrification are beneficial to arsenic adsorption and fixation, while anammox, Feammox and dissimilatory nitrate reduction to ammonium can promote the reduction and release of arsenic. In addition, denitrification can be coupled with arsenic demethylation, thus enhancing arsenic toxicity. Among them, the redox process of iron in paddy soil plays an important role, which can be used as a bridge between nitrogen cycle and arsenic migration and transformation. For example, the inhibition of iron reduction by nitrate is beneficial to arsenic adsorption; iron minerals formed by nitrate reduction coupled with iron oxidation promote arsenic adsorption and fixation; Feammox promotes iron reduction, which is beneficial to the reduction and release of adsorbed arsenic. Based on the above summary, it is suggested that the nitrogen cycle process in soil under different redox conditions and its coupling mechanism with arsenic speciation transformation, the main functional microorganisms of Feammox reaction in paddy soil and their contribution to arsenic migration and transformation, and how to directionally regulate the coupling process of nitrogen cycling and arsenic transformation are important scientific issues and main development trends in this field in the future. The solution of the above scientific problems can provide important theoretical support for the research and development of arsenic pollution control technology in paddy fields, and provide a scientific basis for rational nitrogen application in paddy fields to reduce arsenic risk in rice.

Key words: paddy field, nitrogen cycle, arsenic transformation, microorganism, coupling mechanism

摘要：

中国稻田砷污染问题突出。淹水厌氧条件下，五价砷被微生物还原为活性较高的三价砷，易于被水稻吸收积累，从而威胁人类健康。另一方面，水稻生产需要施用大量的氮肥，水稻土中氮素氧化还原活性高，对稻田砷形态转化具有重要影响。文章在系统总结稻田土壤氮循环主要过程及功能微生物特征、稻田干湿交替条件下砷形态转化及相关功能微生物等国内外研究现状的基础上，深入分析了稻田土壤氮循环过程（硝化作用、反硝化作用、厌氧氨氧化、铁氨氧化以及硝酸盐异化还原成铵等）对水稻土砷迁移转化的影响及关键环境因子，总结出硝化和反硝化作用有利于砷的吸附固定；而厌氧氨氧化、铁氨氧化及硝酸盐异化还原成铵，可促进砷的还原释放。此外，反硝化作用可耦合砷脱甲基化过程，从而提高砷的毒性。其中，水稻土中铁氧化还原过程扮演重要角色，其可作为氮循环影响砷迁移转化的桥梁。比如，硝酸盐抑制铁还原有利于砷的吸附；硝酸盐还原耦合亚铁氧化生成氧化铁矿物，促进砷的吸附固定；铁氨氧化促进铁还原有利于吸附态砷的还原释放。基于以上的总结，认为不同氧化还原条件下土壤氮循环过程及其与砷形态转化的耦合机理，水稻土中铁氨氧化反应的主要功能微生物及该过程对砷迁移转化的贡献，以及如何定向调控氮循环耦合砷转化过程，是今后该领域需要关注的重要科学问题和主要发展趋势。以上科学问题的解决，可为稻田砷污染控制技术的研发提供重要理论支撑，同时为稻田合理施氮降低稻米砷风险提供科学依据。

关键词: 稻田, 氮循环, 砷转化, 微生物, 耦合机理