园林树木和地被植物混种降低污泥重金属污染的根系作用机理

Recycling of sludge to landscape soils as fertilizer has become a viable option for sludge disposal which is an extremely difficult question all over the world. However, such application can lead to soil pollution because of its enrichment in heavy metals which are difficult to remove. How to reduce heavy metal pollution has become a key issue for the safe utilization of sludge on landscape soils. In our previous studies, we had analyzed the characteristic of heavy metal pollution in sludge-amended soil, the heavy metal accumulation capacity of different landscape plants and the root characteristics of these plants, and hypothesize that mixed planting of landscape tree and ground cover plant (MPTG) can reduce the heavy metal pollution of recycling sludge to landscape soils. In this proposed study, three landscape trees (Neolamarckia cadamba, Bischofia javangca, and Amygdalus communis) and three ground cover plants (Schefflera odorata, Aphelandra ruellia, and Syngonium podophyllum) are selected to construct MPTG. According to a pot experiment, we first evaluate the feasibility of MPTG under sludge application, and select an optimum MPTG that can effectively reduce heavy metal pollution. By using a disassembly rhizobox system and a split-spot rhizobox system, we further explore the physiological characteristics of root, root network, chemical properties of rhizosphere soil, and microbial diversity on the transportation and transformation of heavy metals, analyze the relationship among root physiological traits, root morphogenesis, and rhizosphere ecology in this process, and then reveal the root system mechanism of MPTG for reducing the heavy metal pollution of sludge. At last, we will establish a mixed planting root model of reducing heavy metal pollution. This study will not only provide a scientific basis for the safe utilization of sludge and using landscape plants for phytoremediation of heavy metal, but will also strength our understanding of the physiological and ecological characteristics of plant root in phytoremediation of heavy metal.

污泥作为肥料进行园林利用，被认为是解决合理处置污泥这个世界难题的重要途径。然而，污泥的重金属含量高且难清除，易产生土壤污染。降低重金属污染成为保障污泥在园林安全利用的关键问题。我们前期分析了污泥重金属污染特征、园林植物的重金属累积能力及其根系特征，推测园林树木与地被植物混种可有效降低污泥重金属污染。本研究将优选园林树木（黄梁木、秋枫和扁桃）和地被植物（花叶鹅掌柴、翠芦莉和合果芋），首先通过盆栽实验，评价污泥施用条件下这两种植物混种的可行性，优选降低重金属污染的混种组合。随后，借助观测根箱和裂区根箱，分析根系生理、根系网络、根际土壤化学性质和微生物多样性对重金属迁移转化的影响，探究根系生理、根系形态建成和根际生态三者关系，进而解析混种降低污泥重金属污染的根系作用机理，并建立相应的混种根系模型。这将为污泥安全利用和土壤重金属园林植物修复提供科学依据，也增强对重金属植物修复根系生理生态学的认识。

污泥作为肥料进行园林利用，被认为是解决合理处置污泥这个世界难题的重要途径。然而，污泥的重金属含量高且难清除，易产生土壤污染。降低重金属污染成为保障污泥在园林安全利用的关键问题。本项目先优选降低污泥重金属污染的园林树木和地被植物混种组合。随后，分别借助根箱实验和裂区实验，分析树木与地被植物混种的根系生理生态变化和根系网络构建对重金属迁移转化的影响。研究发现园林树木与地被植物混种，不同植物之间既存在竞争关系又存在相互促进作用。针对降低污泥施用土壤重金属污染风险目的，黄梁木与鹅掌柴混种组合表现出最好效果。两者混种可以缓解混施污泥对的根系生长抑制作用。混种鹅掌柴0~20 cm层的根系重金属含量显著高于不施污泥处理，而20~40 cm层的根系重金属含量差异不显著，并且根系镉、锌、铜和镍含量均与根长呈极显著的负相关。混种的污泥层、15 cm土层和35 cm土层细根分布较均匀，细根形成的网状结构密集。浅色根的根长与土壤EC值或镉含量呈较好的负线性相关关系，而深色根与土壤EC值或镉含量呈较好的正线性相关关系。混种提高了黄梁木叶片Cu含量，鹅掌柴不同土层根系的镉含量以及0-30 cm土层的铜和锌含量。混种没有影响鹅掌柴根际的细菌群落的香农指数，但变形菌门、芽单胞菌门和厚壁菌门的丰度显著升高；混种显著降低黄梁木根际香农指数，且PLAT13的等丰度显著高于单种处理。混种后鹅掌柴和黄梁木根际分别有115和139种代谢物产生差异，这些存在差异的代谢通路集中在碳转化、ABC转运蛋白、次生代谢物合成、氨基酸合成和有机酸合成等。项目初步探索了降低污泥重金属污染的园林植物混种途径和建立混种根系模型，从根系生理生态学角度解析园林植物混种降低污泥重金属污染机理，为污泥安全利用、城市土壤重金属修复以及重金属植物修复的根系生理生态研究提供借鉴。项目设计和制作了可拆解根系生长非扰动观测根箱和大型裂区根箱。项目产出研究论文10篇。此外，参加学术会议2次，培养研究生1名。