生物质炭负载菌协同鼠尾草根际去除土壤重金属的耦合机制

The efficient and safe utilization of heavy metal contaminated soil is a major agricultural, ecological and environmental problem that urgently needs to be solved presently in China. Based on the previously selected heavy metal tolerance plant growth promoting bacteria (PGPB) isolated from hyperaccumulator rhizosphere and essential oil aromatic plant, this study aimed at use the biochar immobilized PGPB associate with sage root exudates, to establish rhizosphere functional microorganisms network, and achieve higher biomass, essential oil production and heavy metal removal efficiency, ultimately. Through monitoring the formation of biochar immobilized bacteria biofilm, counting of living cells and the survival of immobilized PGPB in soil, the most suitable carrier for PGPB would be selected and characterized. To illustrate the interaction between PGPB and root exudates, and their synergistic effect on heavy metal accessibility, components of sage root exudates with and without the best immobilized PGPB under different heavy metal concentrations, survival and migration of labeled PGPB under different root exudates component, and heavy metal speciation in the cultured soil would be investigated. Finally, through a multiple layer rhizobox potting experiment inoculating with and without biochar immobilized PGPB, sage biomass, essential oil production and components, and heavy metal removal efficiency, the physiological and biochemical responses of sage to heavy metal stress, root-soil interface effect, and the microbial community structure would be studied. Based on these research contents, the biochemical coupling remediation mechanism of heavy metal in aromatic plant rhizosphere inoculating with biochar immobilized PGPB would be illustrated. The results of this project will provide theoretical basis and technical support for high value, high efficient in-situ remediation of heavy metal contaminated agricultural soil.

重金属污染土壤的高效、安全利用是我国目前亟需解决的重大农业、生态和环境问题。本项目拟在前期耐性促生菌株和产精油芳香植物筛选基础上，以生物质炭为细菌固定化载体，在根系分泌物驱动下，构建根际有益功能微生物网络，以提高产量和重金属吸取修复效率。拟通过研究载体上生物膜的形成、固定化活细胞量和固定化菌株在土壤中的存活能力，筛选出最佳载体生物质炭；通过研究根系分泌物组成、促生菌繁殖与释放、重金属形态变化，阐明固定化促生菌与鼠尾草根系(分泌物)相互作用及其协同调控土壤重金属生物有效性的机制；通过温室盆栽实验，评价精油成分和产量、重金属去除率，明确鼠尾草对重金属胁迫的生理生化响应、根-土界面效应以及根际微生物群落特征。通过以上研究揭示生物质炭负载促生菌协同植物根际强化重金属去除的生化耦合机制。研究结果为我国大面积重金属污染土壤的高值、高效原位修复提供理论依据和技术支撑。

植物根际促生菌协同植物联合修复是目前金属污染土壤治理和安全利用最为重要且可行的技术方法之一。但由于游离菌直接加入土壤中难以与土著微生物竞争等，往往达不到预期的效果。此外，实际土壤污染情况复杂，呈现多金属复合污染现状，现有超积累植物大多受限于元素选择性、经济效益低等，制约了其大规模推广应用。因此，筛选优质植物和微生物资源，以生物质炭为载体，构建生物质炭负载菌-经济植物联合的“边生产边修复”技术，对我国重金属污染土壤安全生产和高效利用具有重要意义。本项目从我国长期受重金属污染土壤中分离筛选出了2株具有多种金属耐受性、且对鼠尾草具有促生功能的细菌，并通过吸附固定将其负载于生物质炭上，明确了生物质炭吸附固定活细胞的条件。分析了实验室制备的20余种生物质炭固定活细胞数量以及生物质炭基本理化性质，结果表明生物质炭中挥发性物质含量、生物质炭孔隙体积及比表面积与其载菌能力呈显著相关关系。批处理结果表明，金属耐性细菌TS8Y负载于生物质炭上后，可提高生物质炭对溶液中Cd的吸附量30-80%以上，FTIR结果表明，负载金属耐性细菌TS8Y增加了生物质炭表面吸附位点。盆栽实验研究发现，国产红花和兰花鼠尾草品种对重金属重度污染土壤的修复能力远高于国外引进品种，施用生物质炭可以显著提高鼠尾草生物量，提高鼠尾草对重金属的提取修复效率；高通量测序结果表明生物质炭负载菌可改变土壤微生物群落，增加金属耐性促生菌在土壤中的存活率，重建根际功能微生物群落，进而促进植物生长。以上结果对我国复合污染土壤植物-微生物联合修复研究和应用具有借鉴和指导意义。