红萍调控土壤镉/砷生物有效性的机理研究

In recent years, the severe issue of food safety caused by heavy metal in farmland soil in China has attracted much attention. In this research, the status of Azolla related to the morphological transformation and bioavailability of heave metals such as cadmium, arsenic were detected. The chemical and microbiological mechanisms of Azolla in Eh in soil were clarified by analyzing physical and chemical properties of soil solution (pH, Eh, DOM and the forms of Cd/As/Fe/S) in situ status. qPCR was used to analyze the functional microbial abundance changes involved in oxidation-reduction functional microorganism (microorganisms for arsenic oxidation/reduction, sulfur-oxidizing/reducing bacteria and iron-oxidizing/reducing bacteria) in soil, and Illumina Hiseq was used to clarify the microbial response process. Aiming at the pollution of cadmium or arsenic, the different “Rice-Azolla” model and water management was put forward. The bioavailability of heavy metals in soil and accumulation in rice was reduced without affecting the extraction of heavy metals in the next crop in the normal production process of rice, which provide a new biological control technology for safe production of rice.

我国耕地土壤镉/砷污染状况日益严重，其导致的粮食安全问题已引起国家高度重视。土壤氧化还原性状是影响土壤镉/砷化学行为的关键因素之一，但目前有效控制土壤氧化还原电位的生物学手段较为缺乏。本项目研究红萍不同生长状态（水面生长、土面生长、土面腐解）对镉或砷形态转化和生物有效性的影响。通过原位测定土壤溶液氧化还原电位、pH、可溶性有机物、镉/砷/铁/硫氧化-还原状态；分析参与氧化-还原微生物（砷氧化/还原微生物、硫氧化/还原菌和铁氧化/还原菌）的丰度变化；并利用高通量测序技术（Illumina Hiseq）明确上述微生物群落结构和多样性的响应过程；阐明红萍生长状态加剧土壤氧化/还原程度的化学与微生物学机制。在此基础上，分别针对镉、砷污染，提出相应的稻萍共育技术策略降低土壤镉/砷活性并抑制稻米镉/砷累积，为水稻的安全生产提供新的生物学治理技术。

本项目从土壤化学、微生物学角度，研究淹水条件下，施用红萍后土壤根际Eh、pH、DOC、DON的动态变化，以及对硫循环及Cd、As有效性的影响；同时研究了介导铁、硫还原的功能微生物种群，阐明了红萍翻埋的微生物驱动机制；通过水稻盆栽试验验证了红萍翻埋后可以减少水稻中Cd的吸收，但会增加土壤中As的有效性，导致水稻中As的吸收增加。主要结果及数据如下：.（1）淹水条件下，不同有机物料的添加显著降低土壤氧化还原电位，且随着时间的增加氧化还原电位随时间呈下降的趋势，添加外源有机物提高了土壤可溶性有机质和还原铁的含量，但降低了硫酸根的浓度，进而能够显著降低土壤溶液中Cd含量，相比其他有机物，红萍处理下降速度最快。.（2）添加红萍后，土壤氧化还原电位改变导致土壤微生物群落组成、多样性、功能基因构成都发生显著变化，主要是影响了硫还原的功能微生物种群，增加了Geobacter, Anaeromyxobacter和Desulfovirga，增加了soxZ、soxX功能基因的比例，从而显著降低土壤中Cd的有效性。.（3）红萍和淹水处理协同降低了土壤中Cd的有效性和稻米中Cd的含量，但会促进土壤中As的有效性和稻米中As的含量。红萍翻埋可作为减少水稻籽粒中Cd积累的绿色途径，同时还可以实现增产，可在双季稻田中广泛应用。