优势植物-微生物协同修复海南农田土壤的重金属耗竭动态及农艺强化研究

Microbe-assisted phytoremediation is an environmentally friendly, low-cost, easily operated, and largely potential technology for in-situ remediation of heavy metals-contaminated soils. When compared with the selection of heavy metal hyperaccumulating plant species, it is particularly important to choose the appropriate metal-accumulating plants with strong adaptability to a wide range of soil types and a large plant biomass, which are compatible with regional climate, soil conditions and cultivation techniques. The aim of this project is to formulate a novel phytoremediation strategy by using Hainan's local metals-accumulating plants (Pennisetum americanum×P. purpureum, Agave sisalana Perrine, Tephrosia candida DC) coupled with metal-resistant microbes. Several methods including Chromatography-mass spectrometry(HPLC/GC-MS), diffusive gradients in thin-films (DGT), extended X-ray absorption fine structure (EXAFS) and GeoChip5.0-based functional gene array will be employed to determine: 1) the phytoextraction abilities of three metal-accumulating plants in Cd-Cr contaminated aged soils; 2) the dynamics of Cd and Cr partitioning between the rhizosphere and non-rhizosphere soil, and between soil solid and solution phases during phytoextraction; 3) the effects of microbe-assisted phytoremediation on the fixation and depletion of soil heavy-metal pools; 4) the dynamic relationship between rhizosphere environment factors (eg,root exudates, Eh, pH, soil nutrients, root system architecture,metal binding speciations to organic matter, root oxygenation,etc.) and spatial distribution of heavy metals in plants, which will be needed to elucidate the response mechanisms of both metal-accumulating plants and rhizosphere microorganisms on the dynamic variations of soil heavy metal availability; 5) rhizosphere mechanisms on the enhancement of metal bioavailability and plant uptake by different agronomic approaches. The final purpose of this project is to illuminate the mechanisms involved in the dynamic of Cd/Cr depletion at the root-soil interface and proposed enhancement countermeasures based on the changes of heavy metal fractions, partitioning, mobilization and uptake during phytoextraction, and to provide implications for long term plant-microbial remediation strategies especially after repeated cropping of metal-accumulating plants. Furthmore,it is important to provide more choices for choosing suitable metal-accumulating plants and metal-resistant microbes for bioemediation of metal-contaminated sites in Hainan.

植物-微生物协同修复是环境友好的低成本、易操作、潜力大的土壤原位治理技术。相对筛选重金属超积累植物，选择与区域气候、土壤条件、栽培技术协调的适应性强和生物量大的富集植物尤为关键。以海南的富集植物（王草、剑麻和灰叶豆）与耐重金属的微生物为对象，应用色谱-质谱、现代薄层凝胶梯度法、同步辐射及功能基因芯片等技术，比较重金属在富集植物体内的分布及其萃取效果，明确对土壤重金属库固定和耗竭的影响；揭示根际环境（如分泌物、Eh、pH、土壤养分、根系构型、金属结合形态、根系泌氧等）与重金属在植物体内分配的动态关系，探索富集植物和根际微生物对土壤重金属有效性变化的响应规律；探明农艺措施强化生物修复污染土壤的重金属吸收、转运的根际效应。以期从富集植物对重金属活化与吸收、微生物协同、重金属形态与分配变化及农艺强化等角度阐明根-土界面重金属耗竭动态和调控机制，为海南重金属污染土壤的生物修复提供材料和强化措施选择。

本项目针对我国耕地土壤中重金属复合污染普遍存在的状况，以镉(Cd)-铬(Cr)为研究对象，选择与区域气候和土壤条件的适应性强和生物量大的富集植物王草，协同耐重金属的印度梨形孢(Piriformospora indica)进行修复，本研究运用气相-质谱联用、凝胶色谱-电感耦合等离子体质谱联用、同步辐射、高通量测序等技术，测定了5种海南本地富集植物(王草、李氏禾、印度芥菜、蓖麻和木薯)接种P.indica后吸收重金属的情况，筛选出了一套高效的富集植物与微生物组合(王草-印度梨形孢)；明晰了Cd/Cr在王草内的微区分布特征，王草根系中维管柱是吸收Cd的主要通道，王草叶片是Cd/Cr主要富集部位，接钟P.indica显著增加了各部位对Cd/Cr的富集；接种P.indica对王草根际土壤中硫化合物的呼吸作用影响较大，不仅提高了微生物固氮能力，而且提高了化学异养功能和纤维素分解功能。EDTA、CA、EDDS和GLDA可作为Cd-Cr污染土壤中植物提取的良好候选螯合剂，能显著地增加土壤Cd-Cr流动性，并迁移转化到植物各组织部位，5mmol/kg的EDDS可强化P.indica-王草体系对Cd-Cr的提取，提高王草对重金属的富集系数和去除率。EDDS和P.indica的应用有效促进王草生长和根系形态结构，探明了农艺措施强化生物修复污染土壤的重金属吸收、转运的根际效应。本研究研发出植物根际和非根际土壤采集、植物根系分泌物原位收集、重金属在污染土壤中迁移模拟的土壤淋洗等装置6套，并获得了专利。总之，接种印度梨形孢后，主要通过影响王草根系分泌物组成和土壤微生物的群落结构，降低了土壤pH值，提高了土壤Cd/Cr的生物有效性，从而提高了土壤Cd/Cr修复效率。该研究成果从富集植物对重金属活化与吸收、微生物协同、重金属形态与分配变化及农艺强化等角度阐明根-土界面重金属耗竭动态和调控机制，为海南地区重金属污染土壤的生物修复提供材料和强化措施选择。