根际圈在污染土壤修复中的作用与机理分析

根际圈以植物根系为中心聚集了大量的生命物质及其分泌物,构成了极为独特的“生态修复单元”。本文叙述了根在根际圈污染土壤修复中的生理生态作用,富集、固定重金属,吸收、降解有机污染物等功能;菌根真菌对根际圈内重金属的吸收、屏障及螯合作用,对有机污染物的降解作用;根际圈内细菌对重金属的吸附与固定,对有机污染物的降解作用以及根际圈真菌和细菌的联合修复作用等,同时对可能存在的机理进行了分析,认为根际圈对污染土壤的修复作用是植物修复的重要组成部分和主要理论基础之一,并指出利用重金属超富集植物修复重金属污染土壤具有广阔的应用前景;筛选对水溶性有机污染物高吸收富集及其根 发泌能力强的特异植物,同时接种利于有机污染物降解的专性或非专性真菌和细菌可能会成为有机污染土壤植物修复研究的重要方向之一。     

解磷微生物修复土壤重金属污染研究进展

土壤重金属污染问题日益严重,具有普遍性、隐蔽性、表聚性、不可逆性等特点,已经成为环境污染治理中的热点、难点问题。解磷微生物能够依靠自身的代谢产物或通过与其他生物的协同作用,将土壤中的难溶性磷转化为可供植物吸收利用的磷,具有多重植物促生长功能和重金属解毒能力,可在重金属毒害水平下,促进植物生长、提高植物抗病能力、克服重金属对植物生长的不利影响,从而增强重金属修复植物的生存竞争力。从解磷微生物的研究现状入手,介绍了解磷微生物对土壤重金属污染的修复能力,综述了解磷微生物对土壤重金属污染修复的作用机制,分析了目前解磷微生物在重金属修复过程中存在的问题,并提出了今后研究的方向,为重金属污染土壤的修复提供了新思路。     

Red mud (RM)-Induced enhancement of iron plaque formation reduces arsenic and metal accumulation in two wetland plant species

Human activities have resulted in arsenic (As) and heavy metals accumulation in paddy soils in China. Phytoremediation has been suggested as an effective and low-cost method to clean up contaminated soils. A combined soil-sand pot experiment was conducted to investigate the influence of red mud (RM) supply on iron plaque formation and As and heavy metal accumulation in two wetland plant species (Cyperus alternifolius Rottb., Echinodorus amazonicus Rataj), using As and heavy metals polluted paddy soil combined with three rates of RM application (0, 2%, 5%). The results showed that RM supply significantly decreased As and heavy metals accumulation in shoots of the two plants due to the decrease of As and heavy metal availability and the enhancement of the formation of iron plaque on the root surface and in the rhizosphere. Both wetland plants supplied with RM tended to have more Fe plaque, higher As and heavy metals on roots and in their rhizospheres, and were more tolerant of As and heavy metal toxicity. The results suggest that RM-induced enhancement of the formation of iron plaque on the root surface and in the rhizosphere of wetland plants may be significant for remediation of soils contaminated with As and heavy metals.     

用转基因植物修复重金属污染的土壤

将新的性状转入高生物量植物中,以此开发高效的转基因植物修复系统,用于重金属污染的土壤修复是一项具有广阔应用前景的技术.大量实验表明,将细菌、真菌、动物、人类及植物本身与重金属脱毒相关的基因转入高生物量植物,异源表达产物可介导转基因植物耐受和高积累重金属及类似物.综述了这方面的研究进展.     

Rhizostabilization of metals in soils using Lupinus luteus inoculated with the metal resistant rhizobacterium Serratia sp. MSMC541

The aim of this work was to test Lupinus luteus plants, inoculated with metal resistant rhizobacteria, in order to phytostabilise metals in contaminated soils. The resistance to heavy metals of strains isolated from nodules of Lupinus plants was evaluated. The strain MSMC541 showed multi-resistance to several metals (up to 13.3 mM As, 2.2 mM Cd, 2.3 mM Cu, 9 mM Pb and 30 mM Zn), and it was selected for further characterization. Furthermore, this strain was able to biosorb great amounts of metals in cell biomass. 16S rDNA sequencing positioned this strain within the genus Serratia. The presence of arsenic resistance genes was confirmed by southern blot and PCR amplification. A rhizoremediation pot experiment was conducted using Lupinus luteus grown on sand supplemented with heavy metals and inoculated with MSMC541. Plant growth parameters and metal accumulation were determined in inoculated vs. non-inoculated Lupinus luteus plants. The results showed that inoculation with MSMC541 improved the plant tolerance to metals. At the same time, metal translocation to the shoot was significantly reduced upon inoculation. These results suggest that Lupinus luteus plants, inoculated with the metal resistant strain Serratia sp. MSMC541, have a great potential for phytostabilization of metal contaminated soils.     

用转基因植物修复重金属污染的土壤

将新的性状转入高生物量植物中,以此开发高效的转基因植物修复系统,用于重金属污染的土壤修复是一项具有广阔应用前景的技术。大量实验表明,将细菌、真菌、动物、人类及植物本身与重金属脱毒相关的基因转入高生物量植物,异源表达产物可介导转基因植物耐受和高积累重金属及类似物。综述了这方面的研究进展。     

Enhancing Degradation of Total Petroleum Hydrocarbons and Uptake of Heavy Metals in a Wetland Microcosm Planted with Phragmites Communis by Humic Acids Addition

The effects of humic acid (HA) on heavy-metal uptake by plants and degradation of total petroleum hydrocarbons (TPHs) in a wetland microcosm planted with Phragmites communis were evaluated by comparing waterlogged soils and water-drained upland soils. Experiments were conducted on soils artificially contaminated with heavy metals (Pb, Cu, Cd, Ni) and diesel fuel. HA showed a positive influence on biomass increase for all conditions, but more for belowground than aboveground biomass, and lower in contaminated than uncontaminated soil. The bioavailability and leachability factor (BLF) for all heavy metals except Ni increased with HA addition in both the control and the P. communis planted microcosms, suggesting that more heavy metals could be potentially phytoavailable for plant uptake. Microbial activities were not affected by both heavy metals and TPH contamination, and HA effects on stimulating microbial activities were much greater in the contaminated soil than under uncontaminated conditions. HA addition enhanced the degradation of TPH and n-alkane in waterlogged conditions. The results show that HA can increase the remedial performance in P. communis dominated wetlands simultaneously contaminated with heavy metals and petroleum hydrocarbons and thus prevent contamination of groundwater or other adjacent ecosystems.     

Abiotic stress leads to somatic and heritable changes in homologous recombination frequency, point mutation frequency and microsatellite stability in Arabidopsis plants

In earlier studies, we showed that abiotic stresses, such as ionizing radiation, heavy metals, temperature and water, trigger an increase in homologous recombination frequency (HRF). We also demonstrated that many of these stresses led to inheritance of high-frequency homologous recombination, HRF. Although an increase in recombination frequency is an important indicator of genome rearrangements, it only represents a minor portion of possible stress-induced mutations. Here, we analyzed the influence of heat, cold, drought, flood and UVC abiotic stresses on two major types of mutations in the genome, point mutations and small deletions/insertions. We used two transgenic lines of Arabidopsis thaliana, one allowing an analysis of reversions in a stop codon-containing inactivated β-glucuronidase transgene and another one allowing an analysis of repeat stability in a microsatellite-interrupted β-glucuronidase transgene. The transgenic Arabidopsis line carrying the β-glucuronidase-based homologous recombination substrate was used as a positive control. We showed that the majority of stresses increased the frequency of point mutations, homologous recombination and microsatellite instability in somatic cells, with the frequency of homologous recombination being affected the most. The analysis of transgenerational changes showed an increase in HRF to be the most prominent effect observed in progeny. Significant changes in recombination frequency were observed upon exposure to all types of stress except drought, whereas changes in microsatellite instability were observed upon exposure to UVC, heat and cold. The frequency of point mutations in the progeny of stress-exposed plants was the least affected; an increase in mutation frequency was observed only in the progeny of plants exposed to UVC. We thus conclude that transgenerational changes in genome stability in response to stress primarily involve an increase in recombination frequency.     

Characterization of Heavy Metals in Soil by High Gradient Magnetic Separation

In recent years forecasting soil cleaning efficiencies of polluted soil, especially those contaminated with heavy metals, has become an important issue. Failure of the methods to predict the right efficiency has resulted in financial losses and penalties. This article describes an addition to the traditional characterization methods for soils contaminated by heavy metals, improving the quality of the basic decisions to be made. The method is based on magnetic separation using a Frantz Isodynamic Separator (FIS) for this study. The FIS isolates soil particles containing heavy metals so that these particles, which are relevant for soil cleaning, can be studied in more detail. Four contaminated soils were tested, for example, soils that were a problem for the soil-cleaning industry. The experiments indicate that each soil has its own magnetic properties that should be regarded as a fingerprint. Density measurements of two soils show that densities approach the quartz density separated at moderate and high magnetic fields suggesting that some of the heavy metals cannot be removed by density separation techniques. A pilot plant scale test supports this conclusion. It also shows that a part of the heavy metals are found in particles lighter than quartz. Based on the results, a qualitative model is proposed to account for the presence of the heavy metals in soil.     

Employment of associative bacteria for the inoculation of barley plants cultivated in soil contaminated with lead and cadmium

In laboratory experiments, the rhizobacteria Azospirillum lipoferum 137, Arthrobacter mysorens 7, Agrobacterium radiobacter 10, and Flavobacterium sp. L30 were found to have a relatively high resistance to the toxic heavy metals lead and cadmium (except that strain L30 was found to be sensitive to Cd). When introduced by means of seed bacterization, the heavy metal-resistant strains actively colonized the rhizosphere of barley plants cultivated in uncontaminated and contaminated soils. In both pot and field experiments, seed bacterization improved the growth of barley plants and the uptake of nutrient elements from soil contaminated with Pb and Cd. The bacterization also prevented the accumulation of Pb and Cd in barley plants, thereby mitigating the toxic effect of these heavy metals on the plants.     

Investigating the Effect of Heavy Metals on Developmental Stages of Anther and Pollen in <Emphasis Type="Italic">Chenopodium botrys</Emphasis> L. (Chenopodiaceae)

Excessive amounts of heavy metals adversely affect plant growth and development. Whereas some regions naturally contain high levels of heavy metals, anthropogenic release of heavy metals into the environment continuously increases soil contamination. Preliminary studies have shown that Chenopodium botrys can grow in some heavy metal contaminated soils and is a high accumulator plant species for Cu and moderately accumulator plant species for Fe, Mn, and Zn, thus, was considered as an important species in this study. Based on that, in this species, we studied the individual effects of heavy metals on the formation, development, and structure of anther and pollen. To achieve this purpose, surrounding area of Hame-Kasi iron and copper mine (Hamedan, Iran) was chosen as a polluted area where the amount of some heavy metals was several times higher than the natural soils. Flowers and young pods were removed from non-polluted and polluted plants, fixed in FAA 70, and subjected to developmental studies. Analysis of anther development in plants from contaminated sites showed general similarities in the pattern of pollen formation with those from non-polluted ones, but also deviation from typical form of major stages of anther and pollen development was seen in plants from polluted ones. Stabilizing of tapetum layer, increasing in tapetum layer numbers, thickening callose wall in the microspore mother cell stage, changing the anther shape, and decreasing the size of anther were the effects of heavy metals. Reduction of pollen number was also seen in the plants collected from polluted area.     

Reduction of Pb and Zn bioavailable forms in metal polluted soils due to paper mill sludge addition. Effects on Pb and Zn transferability to barley

In the last few years solidification/stabilisation of acidic soils polluted by heavy metals with low-cost sorbents has been investigated. Paper mill sludges are produced in large amounts and their disposal is a serious environmental problem. The possibility was therefore studied of using paper mill sludge as a stabilizer to reduce the bioavailable metal forms in polluted soils and thus the transferability of metals to plants (barley). We first investigated the sorbing properties of paper mill sludge for Zn(II) and Pb(II) and then their fractionation both in a polluted soil and in the same soil amended with paper mill sludge in order to check the decrease in mobile forms. Finally in both soils we tested the uptake of two metals by common barley in order to assess the performance of soil remediation from an ecological point of view. The addition of paper mill sludge to a soil contaminated by lead and zinc induces a decrease in the mobile forms of both metals, probably due to the presence in sludge of organic matter and kaolinite, which are able to bind the metals very strongly. The decrease in the mobile forms, which are the most readily available for uptake by plants, corresponds to a decrease in plant uptake.     

The potential of phytoremediation using hyperaccumulator plants: a case study at a lead-zinc mine site

Contamination with heavy metals is one of the most pressing threats to water and soil resources, as well as human health. Phytoremediation might potentially be used to remediate metal-contaminated sites. A major advance in the development of phytoremediation for heavy metal affected soils was the discovery of heavy metal hyperaccumulation in plants. This study applied several established criteria to identify hyperaccumulator plants. A case study was conducted at a mining area in the Hamedan province in the west central region of Iran. The results indicated that plant metal accumulation differed among species and plant parts. Plant species grown in substrata with elevated metal levels contained significantly higher metal levels. Using the most common criteria, Euphorbia macroclada and Centaurea virgata can be classified as hyperaccumulators of specific heavy metals measured in this study and they might potentially be used for the phytoremediation of contaminated soils.     

Understanding molecular mechanisms for improving phytoremediation of heavy metal-contaminated soils

Heavy metal pollution of soil is a significant environmental problem with a negative potential impact on human health and agriculture. Rhizosphere, as an important interface of soil and plants, plays a significant role in phytoremediation of contaminated soil by heavy metals, in which, microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes, and therefore, have potential to enhance phytoremediation processes. Phytoremediation strategies with appropriate heavy metal-adapted rhizobacteria or mycorrhizas have received more and more attention. In addition, some plants possess a range of potential mechanisms that may be involved in the detoxification of heavy metals, and they manage to survive under metal stresses. High tolerance to heavy metal toxicity could rely either on reduced uptake or increased plant internal sequestration, which is manifested by an interaction between a genotype and its environment.A coordinated network of molecular processes provides plants with multiple metal-detoxifying mechanisms and repair capabilities. The growing application of molecular genetic technologies has led to an increased understanding of mechanisms of heavy metal tolerance/accumulation in plants and, subsequently, many transgenic plants with increased heavy metal resistance, as well as increased uptake of heavy metals, have been developed for the purpose of phytoremediation. This article reviews advantages, possible mechanisms, current status and future direction of phytoremediation for heavy-metal–contaminated soils.     

Employment of Rhizobacteria for the Inoculation of Barley Plants Cultivated in Soil Contaminated with Lead and Cadmium

In laboratory experiments, the rhizobacteria Azospirillum lipoferum 137, Arthrobacter mysorens7, Agrobacterium radiobacter 10, and Flavobacterium sp. L30 were found to have a relatively high resistance to the toxic heavy metals lead and cadmium (except that strain L30 was found to be sensitive to Cd). When introduced by means of seed bacterization, the heavy metal–resistant strains actively colonized the rhizosphere of barley plants cultivated in uncontaminated and contaminated soils. In both pot and field experiments, seed bacterization improved the growth of barley plants and the uptake of nutrient elements from soil contaminated with Pb and Cd. The bacterization also prevented the accumulation of Pb and Cd in barley plants, thereby mitigating the toxic effect of these heavy metals on the plants.     

铜尾矿污染区土壤酶活性研究

对浙江省哩浦铜尾矿污染区土壤酶活性进行了研究,结果表明,尾矿区及其周边土壤环境受到不同程度的Cu、Zn、Pb、Cd污染,从尾矿库中心到外围重金属污染程度逐渐减轻,而土壤酶活性则不断提高,其中以脱氢酶和脲酶活性增加最明显,回归分析表明,单一脱氢酶、脲酶、酸性磷酸酶以及蛋白酶活性与重金属复合元素含量之间存在显著线性关系,主成分分析结果显示,尾矿区土壤酶信息系统的第一、二主成分方差贡献率之和达98．24％,以第一、二主成分建立了两个土壤总体酶活性指标,并用此指标对各供试样本进行空间分类,其结果与以重金属含量为依据的划分结果基本吻合,可见,采用酶活性构筑的土壤信息系统的总体酶活性来表征矿区土壤的重金属污染状况是可行的。     

Development and application of novel constructs to score C:G-to-T:A transitions and homologous recombination in Arabidopsis

We report on the development of five missense mutants and one recombination substrate of the beta-glucuronidase (GUS)-encoding gene of Escherichia coli and their use for detecting mutation and recombination events in transgenic Arabidopsis (Arabidopsis thaliana) plants by reactivation of GUS activity in clonal sectors. The missense mutants were designed to find C:G-to-T:A transitions in a symmetrical sequence context and are in that respect complementary to previously published GUS point mutants. Small peptide tags (hemagglutinin tag and Strep tag II) and green fluorescent protein were translationally fused to GUS, which offers possibilities to check for mutant GUS production levels. We show that spontaneous mutation and recombination events took place. Mutagenic treatment of the plants with ethyl methanesulfonate and ultraviolet-C increased the number of mutations, validating the use of these constructs to measure mutation and recombination frequencies in plants exposed to biotic or abiotic stress conditions, or in response to different genetic backgrounds. Plants were also subjected to heavy metals, methyl jasmonate, salicylic acid, and heat stress, for which no effect could be seen. Together with an ethyl methanesulfonate mutation induction level much higher than previously described, the need is illustrated for many available scoring systems in parallel. Because all GUS missense mutants were cloned in a bacterial expression vector, they can also be used to score mutation events in E. coli.     

Metal accumulation and response of antioxidant enzymes in seedlings and adult sunflower mutants with improved metal removal traits on a metal-contaminated soil

Sunflower mutant lines with an enhanced tolerance and metal accumulation capacity obtained by mutation breeding have been proposed for Zn, Cd and Cu removal from metal-contaminated soils in previous studies. However, soils contaminated with trace elements induce various biochemical alterations in plants leading to oxidative stress. There is a lack of knowledge concerning the metal accumulation and antioxidant responses during the growth and development of sunflowers. This study, therefore, aimed to characterise metal accumulation and possible metal detoxification mechanisms in young seedlings and adult sunflowers. Beside the inbred line, two mutant lines with an improved growth and enhanced metal uptake capacity on a metal contaminated soil were investigated in more detail.Sunflowers cultivated on a metal-contaminated soil in the greenhouse showed a decrease in shoot biomass and chlorophyll concentration in two different developmental stages. Adult sunflowers showed a lower sensitivity to metal toxicity than young seedlings, whereas mutant lines were more tolerant to metal stress than the control. Mutant lines also produced a higher amount of carotenoids on a metal-contaminated soil than on the control soil, indicating a possible protective mechanism of sunflower mutants against oxidative stress caused by Cd and excess Zn.Heavy metals primarily increased the activity of antioxidant enzymes involved in the ascorbate–glutathione cycle in sunflower leaves. Activity of dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) was strongly increased in young seedlings exposed to heavy metals. The enzyme activities were even more pronounced in mutant lines. A significantly increased ascorbate peroxidase (APOX) activity in adult sunflowers exposed to heavy metals indicated an elevated use of ascorbate after a longer exposure to metal stress.An increased antioxidant level corresponded to a high Cd and Zn accumulation in young and adult sunflowers. Metal distribution, zinc translocation in particular, from the root into the shoot tissue obviously increased during sunflower growth and ripening. Altogether, these results suggest that sunflower plants, primarily the mutant lines, possess an efficient defence mechanism against oxidative stress caused by metal toxicity. A good tolerance of sunflowers toward heavy metals coupled with an increased metal accumulation capacity might contribute to an efficient removal of heavy metals from a polluted area.     

芦竹对不同重金属耐性的研究

研究芦竹(Arundo donax)在不同重金属污染湿地中的耐毒性能,测定了不同生长时段芦竹的生物性状和叶绿素含量,以及土壤中重金属含量的变化.结果表明,芦竹分别在浓度为100 mg·kg^-1左右的CuCu²⁺、Pb²⁺、Cd²⁺、Zn²⁺、Ni²⁺、Hg²⁺和50 mg·kg^-1以下的Cr⁶⁺污染环境中能正常成活,在40 d的生长期内,植物体内叶绿素有不同程度降低,下降比率在20%～56%,植物出现叶片软化,叶尖枯黄等症状,但植株仍呈现增长趋势.与对照植物相比较,在重金属胁迫下,植株细长,茎、叶呈黄绿色,除Cr⁶⁺、Hg²⁺外,植物高度基本不受重金属胁迫的影响.芦竹在高浓度(100mg·kg^-1)Cr⁶⁺污染环境中耐性较弱,表现出生长缓慢,部分地下茎腐烂,叶片短时间内出现枯萎等症状.结果还表明,土壤中重金属浓度随植物生长期增长而降低,除被植物吸收,植物挥发外,还存在着重金属向根际圈环境迁移的趋势,根周边湿土中重金属含量,明显高于试验缸外围湿土中重金属含量.可以认为,芦竹具有生物量大,根系发达,适应性强等特点,对修复湿地重金属污染蕴藏着巨大潜力,研究芦竹在植物修复技术中的应用,具有一定的现实意义.     

磷酸盐修复重金属污染土壤的研究进展

从研究方法、反应机理以及风险评价等方面综述了磷酸盐修复重金属污染土壤的研究进展,分析和讨论了其中存在的问题和不足,提出了今后加强研究的重点。目前磷酸盐修复重金属污染土壤时,使用的主要研究方法有化学形态提取法、化学平衡形态模型法和光谱及显微镜技术,各个方法都有其优缺点,应该结合使用并探索新方法。磷酸盐稳定重金属的作用机理主要有3个:磷酸盐诱导重金属吸附、磷酸盐和重金属生成沉淀或矿物和磷酸盐表面吸附重金属,但磷酸盐与重金属反应的机理十分复杂,人们尚不完全清楚,因此难以有效区分和评价诱导吸附机理和沉淀机理或其它固定机理,相应地对磷酸盐修复重金属的长期稳定性难以预测。磷酸盐修复重金属污染土壤时由于其较高的施用量可能会造成磷的积聚从而引发一些环境风险,如磷淋失造成水体富营养化,营养失衡造成作物必需的中量和微量元素缺乏以及土壤酸化等。所以应该谨慎选择磷肥种类和用量,最好是水溶性磷肥和难溶性磷肥配合、磷肥与石灰物质等配合施用。今后应着重研究磷酸盐与重金属相互作用的机理区分和评价;关注磷酸盐修复重金属污染土壤时存在的潜在风险,特别是加强植物长期不断吸收磷或其它环境条件变化致使土壤磷素持续减少过程中稳定的重金属溶解性和移动性的研究,磷酸盐修复重金属污染土壤的长期田间实践等。