植物促生菌通过改善根际微环境强化植物修复重金属污染土壤的机制

In recent years, heavy metal pollution incidents have occurred frequently in our country, and the pollution situation has becoming increasingly severe. It is very urgent to find ways to control and restore the heavy metal contaminated soils. Our previous studies indicated that plant growth-promoting bacteria (PGPB) could improve the growth and heavy metal tolerance of their associated plants, and also enhanced the nutrient status in rhizosphere and phytoremediation efficiency. Rhizosphere is an important ecological remediation location for treating contaminated soils. However, little work has been done on how rhizosphere environment affected by the addition of PGPB. This work intends to reveal microbial community and metabolic characteristics in the rhizosphere of Brassica juncea growing on heavy metals-contaminated soils collected from the wetland of Poyang Lake and Le’An River. This project aims to work on: 1) the effects of PGPB on root growth, root activity and root exudates; 2) the impacts of PGPB on the microbial biomass and rhizosphere-soil biochemistry activity (nutrients, respiration rate, enzyme activity, and heavy metal bioavailability); 3) the effects of PGPB on the community and metabolic characteristics in the rhizosphere using the Biolog Eco method, high-throughput sequencing technology, as well as the isolation and characterization of rhizobacteria; 4) the coupling mechanisms of plant growth, rhizosphere-soil biochemistry activity and the functional and molecular diversity of microbial community. This project will explore the mechanism of PGPB improving the rhizosphere environment to enhance phytoremediation efficiency and provide theoretical support for artificial controls of rhizosphere environment to further strengthen the potential use of bacteria-assisted phytoremediation technology in the recovery of heavy metal contaminated soils.

近年来，我国土壤重金属污染事件频发，防控与修复刻不容缓。我们研究表明，植物促生菌（PGPB）可促进植物生长及增强重金属耐受性，提高根际土壤养分，强化植物修复效应。根际是恢复土壤生态功能的重要场所，但PGPB在植物修复过程中对根际微环境的影响及作用机制尚不清楚。本项目拟以鄱阳湖-乐安河流域重金属污染土壤种植的印度芥菜为研究对象，研究：1）PGPB对植物根系生长特性、活力和分泌物的影响；2）PGPB对根际土壤微生物生物量和生化活性（土壤养分、酶活、基础呼吸率和重金属生物有效性）的影响；3）采用高通量测序技术和Biolog Eco，结合传统菌种分离筛选，研究PGPB对根际微生物群落结构与代谢功能的影响；4）探讨植物生长、根际土壤特性与根际微生物群落结构和代谢功能的偶联机制。本研究将探索PGPB通过改善根际微环境强化植物修复的机制，为人工调控根际环境促进植物修复重金属污染土壤的应用提供理论依据。

植物促生菌（Plant growth-promoting bacteria，PGPB）可促进植物生长，增强根部重金属耐受性，提高根际土壤养分，被广泛用于强化植物修复效应。目前利用PGPB强化植物修复重金属污染土壤的研究主要集中在修复效果的评价，但其作用机制尚不清楚。本项目从江西省红壤区重金属污染农田土壤中筛选鉴定出一批具有多重重金属抗性的土著PGPB，盆栽条件下验证其对植物生长及重金属吸收的促进作用，并从根际微生态的角度，揭示PGPB强化植物修复重金属污染土壤的作用机制。本项目从鄱阳湖-乐安河流域段重金污染农田土壤中共分离得到34株具有Cu（100mg/L）、Pb（1200mg/L）、Zn（3200mg/L）、As（800mg/L）抗性的土著PGPB。通过测定ACC 脱氨酶活性、IAA、铁载体、溶磷、产氨等促植物生长特性，并基于16S rRNA 基因进行分子鉴定，筛选出 Pseudomonas monteilii strain S2-3和Burkholderia anthina strain S6-1具有较好的植物促生特性。通过盆栽试验证实，P. monteilii S2-3和B. anthina S6-1对重金属污染土壤中种植的高粱株高、干重、总氮含量有显著促进作用。S6-1显著提高高粱对Pb的积累量和Zn的转运系数，菌株S2-3显著提高高粱对Cu、Zn的修复效果。此外，接种PGPB的土壤理化性质与重金属含量与不接菌对照相比，并未发生显著变化。PGPB在接种后1天显著改变了土壤细菌群落组成，但接种10天之后这种改变逐渐减小直至消失。由此说明，PGPB接种到土壤后没有竞争为土壤优势种，并未对土壤产生不良生态风险。分子生态网络分析表明，接种PGPB改变了细菌群落的共现网络模式、主要模块及OTU拓扑角色。接种PGPB 的细菌群落物种之间相互作用更加复杂和紧密，此外，PGPB提高了网络模块连接者（connector）的比例，使网络不同模块之间的联系更加紧密。由此推测，接种PGPB有利于整个微生物群落结构变得更加有序和稳定，物种之间增强的相互作用可能与PGPB促植物生长效应有关。