刺槐-根瘤菌共生体系对铅锌矿区污染土壤生物修复过程氮循环相关的微生物驱动机制

Heavy metal pollution in soil is one of the serious ecological and environmental problems and a high incidence of heavy metal pollution has been found in the industrial and mining areas. The way by using phytoremediation technology to restore heavy metal contaminated soil in mining areas has become a research hotspot. However, the soil nitrogen deficiency in the polluted mining areas restricts the vegetation restoration. It is urgent to carry out the research on the mechanism of microbial community related to the nitrogen cycle in the heavy metal contaminated soil in the process of vegetation restoration. In this study, we take Robinia pseudoacacia-rhizobia symbiotic system as the research object, and barren soil polluted by heavy metals in lead and zinc mining areas was collected to carry out continuous indoor potted restoration experiment. Technologies such as the amplicon sequencing and fluorescence quantitative PCR would be used in this study. By continuously monitoring the dynamic change of the biological and non-biological factors in this symbiotic system, we would clarify microbial community structure and function genes involving nitrogen cycle in the phytoremediation of heavy metal contaminated soils; explore the effect of environmental factors on microbial community and function genes involving nitrogen cycle; and understand the relationship among microbial community structure and function genes involving nitrogen cycle, root exudates and heavy metal bioavailability during the phytoremediation by the R. pseudoacacia-rhizobia symbiotic system. Therefore, this study will reveal the microbial driving mechanism of soil nitrogen cycle in the R. pseudoacacia-rhizobia symbiotic system grown in heavy metal contaminated soil, and illuminate the process of soil nitrogen transformation in the symbiotic system and the feedback regulating mechanism of nitrogen cycle in the heavy metal contaminated soil ecosystem. It provides a theoretical basis for the nitrogen cycle in the process of vegetation restoration under the background of polluted soil in mining area.

土壤重金属污染是当前面临的严峻的生态环境问题之一，工矿区是重金属污染的高发地。利用植物修复技术修复矿区重金属污染土壤已成为研究热点；而矿区污染地土壤氮素的亏缺制约了该区域的植被恢复，因此研究植物修复过程中土壤氮循环相关的微生物学驱动机制，对探究矿区污染植被恢复过程中氮循环过程有着重要意义。本研究以刺槐-根瘤菌共生体系为研究对象，采集铅锌矿区不同程度重金属污染的贫瘠土壤，开展室内盆栽连续修复实验，采用扩增子测序及荧光定量PCR等技术手段，通过连续监测共生体系对污染土壤修复过程中生物与非生物因子动态变化，以期阐明共生体系修复下根际氮循环相关微生物群落和功能基因的变化特征，探讨修复过程中微生物群落和功能基因、根系分泌物、重金属生物有效性三者之间的相互作用关系，揭示刺槐-根瘤菌共生体系修复重金属污染土壤过程中参与氮循环的微生物驱动机制，为明确矿区污染土壤背景下植被恢复过程中氮循环过程提供理论依据。

矿区污染土壤氮素的亏缺制约了该区域的植被恢复。研究植物修复过程中土壤氮循环相关的微生物驱动机制，对探索矿区污染植被恢复过程中氮循环过程有着重要意义。本项目以刺槐-根瘤菌共生体系为研究对象，分析了共生体系修复不同污染程度土壤的差异，同时利用高通量扩增子测序和qPCR技术探讨了共生体系修复下根际氮循环相关微生物群落和功能基因的变化特征。研究结果表明，接种根瘤菌可提高土壤全氮和有机质含量，促进植物组织中Cd的积累，尤其是对低镉污染土壤。高通量测序结果表明，接种根瘤菌对稀有和丰富的微生物亚群落的多样性影响很小，但却改变了微生物群落的组成和功能基因的丰度。接种后，丰富物种门（如Proteobacteria和Glomeromycota）相对丰度增加；而Firmicutes和Ascomycota等稀有物种门的相对丰度较未接种时有所下降。实时定量PCR结果表明，接种后nifH基因（固氮）丰度增加，amoA、amoB、nirS、nirK、nosZ、napA和narG基因（硝化和反硝化）丰度降低。网络分析表明，接种后微生物共生网络的复杂性降低，核心类群介导了氮循环（如细菌：Bacteroidetes, Proteobacteria和Gemmatimonadetes；真菌：Ascomycotes和Basidiomycetes）。此外，随着修复时间的延长，细菌群落结构发生了明显的变化，在30-60 d期间alpha多样性下降，而在90 d恢复。根际土壤细菌群落丰度在接种初期（30 d）变化最为显著。特别是在低镉污染水平下，接种根际土壤中富集了Microvirga和Psychroglaciecola等33个属。镉污染土壤共生网络在后期（90 d）比前期（30 d和60 d）更为稳定。与氮循环（Rhizobacter, Mesorhizobium, Burkholderia, Nitrospira和Steroidobacter）和碳循环（Solirubrobacter和Brevundimonas）有关的功能细菌可被鉴定为核心类群。在项目执行期间，发表论文4篇，其中3篇被SCI收录，主要发表在Land Degradation & Development，Applied Soil Ecology，陕西林业科技（1篇）期刊上，参加全国性学术研讨会8人（次），培养研究生4名，其博士研究生1名。

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