植物-微生物联合修复镉-滴滴涕复合污染土壤的根际调控机理研究

Soil pollution caused by heavy metals and persistent organic pollutants (POPs) is widespread concerned due to the coexistence of old and new pollutants, as well as heavy metals (Cd) and pesticides (DDT). A plant-microbe remediation approach, such as Cd-hyperaccumulator Sedum alfredii and DDT-degrading microbes, can be adopted to remediate agricultural soils co-contaminated with Cd and DDTs. The previous research studies were focused mostly on the interaction between pollutants and pollutant removal efficiencies, rather than clarifying the mechanism for rhizosphere remediation of Cd-DDTs co-contaminated soils. The focus of the proposed research work is therefore to explore the mechanisms involved in regulation of rhizosphere remediation of Cd-DDT co-contaminated soils using the plant-microbe system. Pot, rhizobox and lab-culture experiments will be conducted in the proposed work. The application of advanced analysis techniques, such as synchrotron radiation X-ray absorption spectroscopy (XAS), FTIR, SE-HPLC combined with ICP-MS, confocal laser scanning microscopy (CLSM) and next generation sequencing (NGS), will be adopted in the research. The main objectives of the proposal are to reveal the speciation and distribution characteristics of Cd and DDTs at the root-soil interface，clarify the relationship between root exudates and bioavailability of Cd and DDTs，reveal colonization pattern of gfp-tagged DDT-1 strain at root-soil interface, analyze soil microbial community diversity, and identify the plasmid in DDT-1 strain encoding the degradation of DDTs. Results of the proposed research will help to elucidate the mechanisms for regulation of rhizosphere remediation of Cd-DDTs co-contaminated soils using the plant-microbe system, it can furtherly optimize and develop in situ remediation techniques for co-contaminated soils.

镉(Cd)-滴滴涕(DDT)复合污染是我国耕地土壤污染的普遍存在形式，深受土壤环境科学与修复领域的关注。利用东南景天-降解菌联合修复技术，可成功修复Cd-DDT复合污染农田土壤，前期的研究工作主要围绕污染物间的相互作用及其去除效率等方面,而缺乏根际修复机理的研究。本申请以植物-微生物联合修复的根际调控为核心，采用根箱试验、盆栽试验和室内培养实验三种手段相结合，综合应用X射线吸收光谱、红外光谱、凝胶色谱-电感耦合等离子体质谱联用、激光扫描共聚焦显微镜、高通量测序等先进技术，研究污染物在根-土-水界面的分布特征及其赋存形态、根系分泌物的组成及其与污染物生物有效性的关系、土壤微生物群落结构多样性、降解菌Pseudomonas sp.DDT-1的定殖动态及其降解功能的定位。该项目研究可揭示植物-微生物联合修复复合污染土壤的根际调控机制。预期成果可为植物-微生物联合修复的根际调控手段提供理论依据。

本项目针对我国耕地土壤中重金属-POPs复合污染普遍存在的状况，以镉(Cd)-滴滴涕(DDs)为研究对象，开展了王草-印度梨形孢联合修复Cd-DDs复合污染土壤的根际调控机制研究。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、高通量测序等先进技术，研究了污染物在根-土界面的分布特征及其赋存形态，接种印度梨形孢（Piriformospora indica）显著提高了王草的根系活力，增加了王草的生物量，提高了王草叶片中YUCCA基因的相对表达量和蔗糖转化酶活性，降低了NRR基因表达量。明晰了污染物的微区分布特征,王草根部Cd主要分布在表皮细胞壁和和维管束,而茎部Cd主要分布在纤维和液泡;根部DDs主要分布在中柱和吸附在根毛表面,而茎部DDs主要分布在维管束、液泡。采用王草与Piriformospora indica联合修复，降低了土壤pH、提高了土壤EC值，增加了污染物的生物有效性,在轻度Cd-DDs复合污染条件下,Cd和DDs的去除率分别达到了11.9%和51.0%。测定了王草根系分泌物的组成，研究了其与污染物生物有效性的关系，接种印度梨形孢显著影响了王草根系分泌物中肉豆蔻酸、羟基丁酸和蔗糖含量，同时发现污染物的浓度对甲基胺、氯乙酸、尸胺、羟基丁酸、油酸、硬脂酸具有显著影响。测定了土壤微生物群落结构及其多样性，发现细菌Firmicutes和真菌Glomeromycota的相对丰度与土壤pH及有效态DDs含量呈正相关。检测了印度梨形孢在王草根部的定殖情况、降解DDs的途径及其相关功能基因的定位，发现DDT经由DDD/DDE-DDMU-DDNS-DDA-DBP-羧基苯丙酸等一系列脱氯、加氢、加氧、脱羧羟化、苯环开裂等途径进行降解，并进行了印度梨形孢对DDs降解的功能基因定位。本研究研发出一种植物根际和非根际土壤采集装置、一种植物根系分泌物原位收集实验装置、一种土壤通气培养装置、一种修复中轻度重金属复合污染农田的土壤改良剂及其使用方法，并申请了专利。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的生物有效性和DDs的可降解性，从而提高了土壤Cd和DDs修复效率。该项目研究成果初步揭示了王草-印度梨形孢联合修复Cd-DDs复合污染土壤的根际调控机制，为植物-微生物联合修复提供了技术支撑。