内生真菌强化东南景天积累镉的机理研究

There are some critical problems in phytoextraction of cadmium (Cd) contaminated soil, such as low availability and limited contaminant uptake. Inoculation of endophytic fungi is an effective method for the enhancement of phytoextraction process. The Cd-phytoextraction efficiency of Sedum alfredii Hance has been reported to be enhanced by inoculating plants with Piriformospora indica but the mechanisms behind this process remain unclear. Thus, the overall objective of this project is to explore the mechanisms behind Piriformospora indica induced Sedum alfredii Cd accumulation. The effects of Piriformospora indica inoculation on the contents and components of root exudates will be determined by ion chromatography. Meanwhile, the effects of Piriformospora indica inoculation on the Cd mobilization ability of the root exudates will be evaluated by diffusive gradient in thin films technique. Then the mechanism of Cd mobilization in the rhizosphere induced by Piriformospora indica inoculation will be demonstrated. X-ray absorption spectroscopy will be performed to probe the effects of Piriformospora indica inoculation on the speciation of Cd in the roots of Sedum alfredii. Concentrations of non-protein thiols in the roots will be determined by traditional plant physiology methods. Then the mechanisms of the enhancement of transportation of Cd to the aerial part will be cleared. The mechanisms of Piriformospora indica inoculation enhances the accumulation of Cd by Sedum alfredii will be revealed by the changes of root exudates and Cd speciation in the roots. The results of this project are expected to provide new knowledge on the role of endophytic fungi in phytoextraction and to provide theoretical support for the microbe-assisted phytoextraction.

镉(Cd)污染土壤的植物提取存在Cd有效性差及地上部积累量低等技术瓶颈，接种内生真菌是强化植物提取的重要手段。内生真菌印度梨形孢已被证明能够增强超富集植物东南景天对Cd的积累，提高Cd的植物提取效率。然而其强化机理目前尚不清楚。本项目以东南景天根系分泌物为切入点，采用离子色谱等技术研究接种印度梨形孢对东南景天根系分泌物产生量及组成的影响，通过梯度薄膜扩散技术分析接种菌株对根系分泌物Cd活化能力的影响，明确接种菌株提高土壤Cd有效性的机理。结合X射线吸收光谱、传统植物生理学方法研究接种印度梨形孢对东南景天根部Cd结合形态和根系非蛋白巯基肽的影响，探明接种菌株增强Cd向植物地上部转运的机制。从根系分泌物影响和根部Cd结合形态角度揭示内生真菌印度梨形孢强化东南景天积累Cd的机理，为理解内生真菌在植物提取中的作用提供新认识，为开展Cd污染土壤的微生物强化修复提供理论基础。

东南景天是一种镉(Cd)超富集植物，具有修复Cd污染土壤的潜力。微生物强化是提高植物修复效率的有效手段，本项目研究了内生真菌Piriformospora indica对东南景天修复Cd污染土壤效率的影响，包括对Cd积累以及土壤微生态环境的改善，并探讨了Piriformospora indica影响植物提取效率的机理。结果显示，Piriformospora indica能够影响东南景天抗Cd胁迫生理指标，提高抗氧化酶活性（SOD和CAT），降低丙二醛含量，缓解东南景天Cd毒害。接种Piriformospora indica能够增强东南景天根系分泌作用，提高根系分泌有机酸含量（乳酸、酒石酸和草酸），且接种Piriformospora indica东南景天根系分泌物能够改变土壤Cd形态分级，提高交换态和弱酸提取态Cd含量。土培试验显示，接种Piriformospora indica 能够提高东南景天生物量，增大地上部Cd积累量，提高Cd提取效率。土壤分析显示，接种Piriformospora indica提高了根际土壤有效态Cd含量，从而促进东南景天的Cd吸收。接种Piriformospora indica显著提高了土壤微生物数量、基础呼吸以及酶活性（脲酶、磷酸酶和转化酶），提高了微生物群落多样性指数，改变了土壤细菌群落，提高了土壤中有益菌的丰度，在门水平，提高了Actinobacteria、Acidobacteria和Gemmatimonadetes的相对丰度；在纲水平，提高了Actinobacteria、Thermoleophilia和Gemmatimonadetes的相对丰度；在属水平，提高了Streptomyces、Kribbella的相对丰度，这些细菌群落丰度的提高反映出土壤微生态环境的改善。以上说明，Piriformospora indica促进东南景天吸收Cd的主要机理是增强东南景天根系有机酸分泌量，提高根际Cd有效性，同时根际有效养分的增加改善了土壤微生态环境。综上，接种 Piriformospora indica能促进东南景天提取Cd，改善土壤微生态环境，提高土壤微生物数量和活性，从而提高植物提取效率。本项目从不同角度揭示了Piriformospora indica 强化东南景天积累Cd的机制，为开展微生物联合东南景天植物修复污染土壤提供理论支持和指导。