硫素对水稻根际微域中砷形态转化的影响及其微生物作用机理

It is an important and difficult scientific problem to control and in-situ remediate the arsenic pollution in paddy soil. In this case, the research of microbial mechanisms of arsenic transformations affected by sulfur in the micro region of rhizosphere in paddy soil will be full of theoretical importance and practical value, since it will help to develop the in-situ remediation technologies for arsenic pollution in paddy soil based on sulfur fertilization combined the agronomic measures. Therefore, this project will firstly conduct a field investigation and several batches of greenhouse experiments with rhizobox. A key question that whether the effect of sulfur on arsenic transformations (oxidation, reduction and methylation) differs within different distances to the rice root will be discussed and answered. The arsenic transformation in the special and simultaneous/alternate anaerobic and aerobic region in the rhizosphere will also be characterized. Secondly, Real-time PCR, high-throughput sequencing technology and other molecular technologies will be used to identify the functional microorganisms and the genetic abundance and diversity involved in the arsenic transformation processes affected by sulfur in the rhizosphere and explore the interaction of those functional microorganisms. Further, the Fe-Mn plaque in the micro region of rhizosphere will be extracted and the functional microorganisms and the genetic abundance and diversity will also be characterized in order to illustrate the response and key role of plaque during the arsenic transformation affected by sulfur. On the basis of these, the response and microbial mechanisms of arsenic transformations affected by sulfur in the micro region of rhizosphere in paddy soil will be clearly and systematically presented.

如何原位调控水稻土砷污染风险是当前面临的重要难题，开展硫素对水稻根际微域中砷形态转化的影响及机制基础研究，有助于开发基于硫肥与农艺措施相结合的水稻土砷污染原位修复技术，理论意义与实践价值重大。本项目结合大范围野外水稻土微区采样以及多批次室内根际箱盆栽实验，探究硫素对水稻土中砷氧化、还原和甲基化转化过程的影响是否具有微域梯度效应，探清硫素影响下水稻根际同时或交替存在的特殊厌氧好氧微域中砷形态转化的规律。在此基础上，运用Real-time PCR、高通量测序等分子生物学技术，考察根际微域中砷氧化、还原、甲基化以及硫素转化等功能微生物的组成与基因丰度，明确根际微域中砷硫转化等功能微生物的交互作用。进一步，提取水稻根际微域中铁锰胶膜并分析胶膜表面的砷硫转化功能微生物，明确硫素影响下根际胶膜的响应及其在根际微域砷生物转化过程中的重要角色，最终系统阐述硫素影响水稻根际微域中砷形态转化的微生物作用机制。

如何原位调控水稻土砷污染风险是当前面临的重要难题，开展硫素对水稻根际微域中砷形态转化的影响及机制基础研究，有助于开发基于硫素与农艺措施相结合的水稻土砷污染原位修复技术，理论意义与实践价值重大。本项目结合大范围野外水稻土微区采样以及多批次室内根际箱盆栽实验，探究硫素对水稻土中砷氧化、还原和甲基化转化过程的影响是否具有微域梯度效应，探清硫素影响下水稻根际特殊厌氧好氧微域中砷形态转化的规律。在此基础上，运用荧光定量PCR、高通量测序等分子生物学技术，考察根际微域中砷氧化、还原、甲基化以及硫素转化等功能微生物的组成与基因丰度，明确根际微域中砷硫转化等功能微生物的交互作用。.野外调查试验中，初步发现在砷污染土壤中，根际砷含量在厘米级微域上随距离的增加呈上升趋势。通过盆栽试验发现，硫素添加降低了根际、非根际土壤溶液中砷和Fe(II)含量。相同硫含量的硫酸钠比单质硫效果更显著。硫素添加增加了水稻产量，同时降低了水稻地上部对砷的累积。硫素作用下根际与非根际土壤群落组成相似。硫素对砷循环功能基因影响较小。硫酸钠添加显著增加了根际土Fe(III)和硫酸盐还原相关的微生物。在此基础上我们进行根箱盆栽试验，结果显示，石膏复合物添加降低了土壤中砷的移动性，降低了土壤溶液中As(III)和As(V)的含量。从微域上看，由于水稻根系及其分泌物影响，土壤溶液砷含量随微域距离的增加呈上升趋势，近根区与远根区差异显著，且石膏复合物的处理促进了根际微域效应。此外，石膏复合物添加显著影响微生物群落结构，土壤中优势菌群如Firmicutes、Proteobacteria等相对丰度随微域距离的增加逐渐降低。石膏复合物添加促进了砷还原（arsC）和甲基化（arsM）功能基因，促进了硫酸盐还原基因（dsrA），一定程度抑制了铁还原基因（Geobacteraceae）。呼吸砷还原基因（arrA）随根际微域距离的增加呈一定下降趋势。硫素的添加可能通过影响砷还原、甲基化和硫酸盐还原过程影响根际微域砷形态转化。