轮作作物与丛枝菌根真菌互作及其影响土壤镉形态的根际过程与机理

Crop rotation has a remarkable effect on accumulation of heavy metals in crops that associated with arbuscular mycorrhizal fungi (AMF) in farmlands. However, little is known about the rhizosphere processes and mechanisms for the interaction between rotation crop and AMF and its impact on speciation of heavy metals in soils, which constrain our knowledge on the rotation modes accumulating fewer heavy metals. Thus in this project, pot and field studies will be conducted to assess the rhizosphere processes in the farmlands around a lead and zinc mine site in Huize County, Yunnan Province. The study will focus mainly on two most common crop rotation modes (canola - maize and fababean - maize) and one main pollution element (cadmium) using high-throughput sequencing, Tessier sequential extraction, and high performance liquid chromatography. The research objects include: (1) To investigate the interaction between rotation crops and AMF based on analyzing effects of rotation on community ecology of AMF in farmlands and feedback effects of AMF community on the growth, mineral nutrition and cadmium accumulation of rotational crops. (2) To illustrate the changes in composition and content of rhizosphere exudates, including low molecular weight organic acids, glomalin related soil protein, soluble sugars, amino acids, and it mediates the transfer on rhizosphere cadmium speciation, during the course of interaction between rotation crops and AMF. (3) To reveal the differences and mechanisms on rhizosphere processes for transforming cadmium speciation in different rotational modes. The results will enrich the theory of the rhizosphere pollution ecology, and provide a new understanding on regulating indigenous AMF community and its ecological functions in farmlands by rotation.

轮作对农田土壤重金属形态、作物累积重金属的影响与丛枝菌根真菌（AMF）密切相关，但目前对轮作作物与AMF间的互作及其影响土壤重金属形态的根际过程与机理认识有限，制约了对重金属低富集轮作模式的理解。本项目拟在云南铅锌矿区周边农田，选取油菜-玉米和蚕豆-玉米两个最普遍的轮作模式，选择主要的污染元素镉，以根际过程为切入点，通过大田和盆栽试验，采用高通量测序、Tessier连续提取、高效液相色谱等技术，分析轮作对农田AMF群落生态的影响，及AMF 群落对轮作作物生长、矿质营养与镉累积的反馈影响，阐明轮作作物与AMF的互作效应；解析轮作作物与AMF互作的根际分泌物（低分子量有机酸、球囊霉素相关土壤蛋白、可溶性糖、氨基酸等）成分与含量的变化及其介导根际土壤镉形态的转化，揭示不同轮作模式根际镉形态转化过程的差异与机理。研究结果能丰富根际污染生态学的理论，为轮作调控农田AMF的群落与生态功能提供新的认识。

云南铅锌矿产资源丰富，长期的矿产开采与冶炼，导致矿区周边农田镉（Cd）污染严重。蚕豆—玉米和油菜—玉米是云南铅锌矿周边两种主要的轮作模式，其重金属累积存在的差异。轮作对农田土壤重金属形态、作物累积重金属的影响与丛枝菌根真菌（AMF）密切相关，但目前对轮作作物与 AMF 间的互作及其影响土壤重金属形态的根际过程与机理认识有限，制约了对重金属低富集轮作模式的理解。项目以蚕豆—玉米、油菜—玉米2种轮作模式为研究对象，选择主要的污染元素镉，以根际过程为切入点，采用高通量测序、Tessier连续提取、高效液相色谱等技术，在云南铅锌矿区周边农田开展大田试验，分析轮作作物根系分泌、Cd累积特征，及轮作对农田AMF群落生态的影响。通过盆栽试验，研究AMF对作物生长、矿质营养与Cd累积的反馈影响，解析AMF改变作物根际分泌物成分与含量，进而导致根际土壤Cd形态的转化，揭示这2种轮作模式根际镉形态转化过程的差异与机理。结果表明：（1）轮作改变作物根际低分子量有机酸的含量，影响根际Cd的化学形态和生物有效性，进而影响轮作作物植株Cd的含量与累积量。（2）轮作影响矿区周边农田AMF的物种组成。农田存在球囊霉属（Glomus）、原囊霉属（Archaeospora）、巨孢囊霉属(Gigaspora)等AMF种群，Glomus为优势的AMF。（3）Cd胁迫下，接种Glomus mosseae 和土著AMF显著增加玉米的株高和生物量，提高土壤速效养分和植株养分的含量，显著降低土壤中有效态Cd含量和玉米植株Cd含量。（4）接种AMF显著增加玉米根系酒石酸、苹果酸和琥珀酸的分泌量，减少柠檬酸的分泌量；导致玉米根际有机结合态Cd含量下降，铁锰氧化态Cd含量增加，进而减少玉米植株的Cd含量。因此，AMF通过改变作物根系分泌物的含量，影响土壤Cd的形态和生物有效性，在轮作作物Cd累积中起着一定的调节作用，对于构建重金属低富集的作物轮作模式，具有重要的理论与实践意义。