【作者】 刘春英；

【导师】 弓晓峰；

【作者基本信息】 南昌大学 ， 环境科学与工程， 2015， 博士

【摘要】 湿地植物根表铁膜是污染物进入植物体内的门户,对植物消减污染物起着重要作用。铁膜的形成不仅影响植物对营养元素的吸收利用,而且影响根际土壤中重金属的迁移和转化。因此,研究湿地植物根表铁膜对重金属的生物有效性、迁移、转化及其影响,对深入了解湿地植物净化土壤中重金属的内在机理有着积极的意义。为探索湖泊湿地植物根表铁膜对湿地植物富集重金属的作用,本研究以典型淡水湖泊湿地——鄱阳湖湿地为例,采用溶液培养和土-砂联合培养的试验方法,结合扫描电镜-能量色散谱(SEM-EDX)以及化学提取法(DCB法),研究鄱阳湖湿地植物根表铁膜的形成以及对铅在植物体内累积和迁移转化的影响。主要结果如下:(1)鄱阳湖湿地植物根表铁膜的含量为禾本科>莎草科>蓼科>菊科。不同植物种类根表铁膜的含量具有显著性差异,即使是同属一科的湿地植物,其根表铁膜的含量也存在差异,如同属于莎草科的苔草根表铁膜的含量是刚毛荸荠的6倍;不同生境中,活性铁含量高的南矶山湿地植物根表铁膜量普遍高于吴城;不同季节采集三种鄱阳湖优势种群湿地植物的根表铁膜量也存在差异,11月份植物根表铁膜的含量高于4月份。(2)植物根系氧化力、溶液pH值、Fe2+浓度、培养时间、水位变化以及根系分泌物等对根表铁膜的形成具有显著影响。根系氧化力高的苔草根表铁膜的含量高于根系氧化力弱的虉草;当pH为5.5~6时,两种湿地植物铁膜含量均达到最高值;两种植物的根表铁膜都随溶液中Fe2+浓度的增加而增加,根表铁膜的量与溶液中Fe2+浓度具有显著的正相关;苔草根表铁膜的含量随诱导时间的增加呈现先升高后变缓的趋势,7 d作为苔草根表铁膜含量的最佳形成时间;随着淹水水位的增加,苔草和虉草根表铁膜的含量均有所增长,在淹水2~3 cm前根表铁膜的含量随土壤水分含量的增加而增加;根系分泌物中的草酸、苹果酸和柠檬酸等能与溶液中的Fe2+发生螯合从而降低了溶液中Fe2+浓度,减少了铁膜的含量。(3)培养时间对苔草的生长、根系氧化力、根表铁膜的含量以及铁膜的活性具有影响。苔草根表铁膜的含量随培养时间的增加呈现先上升后降低的趋势,第一周根表铁膜的生成速率最大,第三周趋于平衡,第四周开始铁膜的生成速率开始出现负值,铁膜的含量开始下降;苔草根系氧化力随培养时间呈现出先增加后降低的趋势,且低浓度的铁可以促进苔草的根系氧化力;苔草根表铁膜无定形态的铁只占铁氧化物总量的6%~18%,大部分的铁为结晶态的铁氧化物。从第五周开始,苔草根表铁膜开始出现老化现象。(4)通过电镜扫描(SEM)观察可知,苔草根表面有一层非结晶态的颗粒物沉积在表皮细胞外,但分布并不均匀。不同铁浓度水平下,铁膜的紧密程度也不一致,不加铁处理的根表铁膜比较稀疏,加铁处理的苔草,根表铁膜更密实。由能谱分析(EDX)分析得出,苔草根表铁膜主要含有C、O、Al、K、Si、Ca、Fe等,有铁膜的根表铁的含量高于无铁膜的植物根表。通过XRD分析得出,根表铁膜主要是结晶态的铁α-Fe2O3(赤铁矿)。(5)鄱阳湖湿地植物苔草和虉草根表铁膜对溶液中的铅具有吸附作用。铅在苔草和虉草中的分配为铁膜>根内>地上部分,约有50%~60%累积在根表铁膜中,根表提取的铅含量与根内铅含量具有显著的相关性。约90%的铅累积在根内,说明根表铁膜能够吸附铅,且在一定程度上可以抑制铅由根内向地上部分迁移。(6)鄱阳湖湿地植物苔草根表铁膜对土壤中的铅具有富集作用。苔草根表铁膜的含量受土壤中Fe2+添加量以及铁、铅交互作用的影响,但铅的添加对根表铁膜含量的影响并不显著。在铅浓度为0~100 mg·kg-1(处于鄱阳湖湿地土壤目前实际的铅浓度范围内)时,添加500 mg·kg-1的铁,苔草根表铁膜的含量可达到13.63 g·kg-1,根部铅的百分含量提高了14.95%,苔草根表铁膜促进了铅在根部的累积。苔草铅的TFroot和TFshoot在不同处理中分别为0.61~3.32和0.17~0.90,加铁处理可增加苔草铅的TFroot,降低TFshoot,铅在苔草中的DC随着铁浓度的提高而显著降低。苔草根表铁膜的存在促进了铅从苔草根表向根内迁移,而且大量富集在根内。对于鄱阳湖湿地这种低铅污染的土壤,可添加铁来增强根表对土壤中铅的吸附,促进铅由湿地土壤向苔草根系的迁移,起到净化湿地土壤重金属的作用。从而避免了湿地土壤中的重金属通过“土壤-水生生物-候鸟”生物链间接被候鸟吸收。更多还原

【Abstract】 Waterlogged soils are frequently anaerobic, with low partial pressure of oxygen. To acclimate to an anaerobic condition when submerged in water, wetland plants must allow aerenchyma to transfer oxygen from aerial parts to the rhizosphere, which is termed radial oxygen loss. Radial oxygen loss also causes the oxidation of ferrous iron to ferric iron and the precipitation of iron oxides or hydroxides on the root surface. This material is termed “iron plaque”. Iron plaque is a mixture of crystalline and amorphous iron oxide or hydroxide, and is mainly composed of ferric hydroxides, goethite and lepidocrocite. Given the high adsorption capacity of functional groups on iron oxides or hydroxides, iron plaque can influence the chemical behavior and bioavailability of heavy metals and nutrient elements in the rhizosphere. Iron plaque is the portal of the pollutants into the plant body, and it plays an important role in pollutants reducing. In order to explore the effect of iron plaque on the roots of Lake Wetland plants on heavy metals uptake, Poyang Lake wetland was taken as research object. Solution culture experiment and pot experiment were conducted to investigate the information of iron plaque on the root surfaces of wetland plants from Poyang Lake, and the effects of iron plaque on translocation of Pb in soil- Carex cinerascens Kukenth. System, using Scanning Electron Microscopy(SEM) and Energy Dispersive X-Ray Spectrometry(EDX).(1) The amount of iron plaque on the root surfaces of different wetland plants from Poyang Lake showed significant difference. It was the order: Grass family > Cyperaceae > Polygonaceae > Composite family. Even belong to the same family of the wetland plants, the amount of iron plaque also existed difference, Carex cinerascens Kukenth. and Heleocharis belonged to Cyperaceae and had the same habitats, the amount of iron plaque on the root surfaces of Carex cinerascens Kukenth. was 6 times than that of Heleocharis. Habitats and season affected the amount of iron plaque on the root surfaces of wetland plants, the amount of iron plaque on the root surfaces of wetland plants in Nanjishan wetland which has high Fe concentration than that of other. The amount of iron plaque on the root surfaces of wetland plants collected on November was higher than that on April.(2) The formation of iron plaque was controlled by Fe2+ concentration in environment and the oxidizing capability of the root system. The effects of Fe2+ concentration, plant species, culture times, pH, variation of water level, root exudates on iron plaque were investigated by hydroponics condition and soil-sand pot experiment. Results showed that the amount of iron plaque increased as the Fe2+ concentration and culture times increased. Root exudates concentration was negatively correlated with the content of iron plaque. The amount of iron plaque first increased and then decreased with the increase of water level, the amount of iron plaque reached max when water level was 2-3cm and pH=5.5~6.(3) The amount of iron plaque on the root surfaces of Carex cinerascens Kukenth. increased and then decreased with increasing culture time. The generation rate of iron plaque was the largest in the first week, and treaded balance in the third week. But in the fourth week, the generation rate of iron plaque was negative, and the amount of iron plaque began to decline. The root activity of Carex cinerascens Kukenth. increased at first and then decreased with increasing culture time, the low concentration iron was contributed to promote the root activity. Fe0/Fed of iron plaque was 0.0667 to 0.2265, amorphous iron accounted for 6% to 18% of the total iron oxide, and most of iron oxide was crystalline. Fe0/Fed of iron plaque increased at first and then decreased with the extension of culture time. At the beginning of fifth week, the iron plaque began aging.(4) The physico-chemical properties of iron plaque were determined using Scanning Electron Microscopy(SEM) and Energy Dispersive X-Ray Spectrometry(EDX). The analysis of SEM-EDX showed that iron plaque was present as an amorphous coating which followed the contours of the cells. The coating was not uniform and plaque deposits were absent from large areas of the root surface. The plaque at 0 mg Fe·L-1 treatment appeared loose, and the plaque at 100 mg Fe·L-1 treatment was dense. The plaque formed on the root surfaces of Carex cinerascens Kukenth. had a very specific chemical signature and was composed of C, O, K, Si, Al, Fe, together with lesser amounts of Ca and Cl. The weight percentage of Fe was 40.35% in plaqued root and 4.92% in unplaqued root. The weight percentage of Fe was 18.78% in plaqued root without Fe addition, and the weight percentage of Fe was 38.29% in plaqued root at 100 mg Fe·L-1 treatment. This showed that the amount of iron plaque increased with Fe additions. The analysis of XRD showed that iron plaque was α-Fe2O3.(5) A hydroponic experiment was conducted to investigate whether iron plaque could affect the uptake and translocation of lead by two dominant wetland plants, Carex cinerascens Kukenth. and Phalaris arundinacea Linn., growing in Poyang Lake, Jiangxi Province, China. After iron plaque on plant roots was induced by growing plants in solution containing 0, 30, 60, 100, 150, or 210 mg·L-1 Fe2+ for 7 days, plants were transferred to nutrient solution containing 10 mg·L-1 Pb2+ for 5 days. The amount of iron plaque formed on the root surfaces of Carex cinerascens Kukenth. was slightly higher than that of Phalaris arundinacea Linn. A significant positive correlation was observed between the amount of iron plaque and Fe2+ concentration in the solution for both the species. The Pb concentrations and percentage distribution in different matrices were in the order iron plaque > root > shoot. We observed that 50 – 60% of the total Pb accumulated in iron plaque and nearly 90% of the total Pb accumulated in iron plaque and roots. Iron plaque on the root surface increases sequestration of Pb in the root and inhibits the translocation Pb from root to shoot under hydroponic conditions to some extent.(6) Carex cinerascens Kukenth. from Poyang Lake wetland was taken as a case study. A pot experiment was conducted to investigate the effect of iron plaque on Pb uptake by and translocation in Carex cinerascens Kukenth. grown under open-air conditions. The Fe concentrations increased significantly with increasing Fe supply regardless of Pb additions. The most beneficial condition for the formation of iron plaque was 500 mg·kg-1 of Fe addition, which was under the condition that the concentration of Pb was from 0 mg·kg-1 to 100 mg·kg-1. The presence of iron plaque on the root surfaces of Carex cinerascens Kukenth. increased the concentrations of Pb adsorbed by iron plaque. Compared with 0 mg·kg-1 Fe treatment, the percentage of Pb in roots increased by 14.52% at 500 mg·kg-1 Fe treatment, and the distribution coefficient(DC) of Pb in Carex cinerascens Kukenth. was significantly decreased from 0.39 to 0.13. It was found that translocation factor(TF) root increased with Fe additions, but translocation factor(TF) shoot decreased with Fe additions. Our results suggested that iron plaque could promote the translocation of Pb from soil to roots to some extent, it not only played a role to reduce heavy metals pollution of Poyang Lake wetland, and prevented migratory birds from indirectly adsorbing heavy metals by the way of "soil- aquatic organism-migratory birds" to a certain extent as well.更多还原