Screening of sunflower cultivars for metal phytoextraction in a contaminated field prior to mutagenesis

Sunflower can be used for the remediation of metal-contaminated soils. Its high biomass production makes this plant species interestingfor phytoextraction and using sunflower oil for a technical purpose may improve the economic balance of phytoremediation. The aim of the present field study was to screen 15 commercial cultivars of Helianthus annuus L. grown on metal-contaminated soil, to find out the variety with the highest metal extraction, which can be further improved by mutation or in vitro breeding procedures. Two different fertilizers (ammonium sulphate and ammonium nitrate) were also used to enhance the bioavailability of metals in soil Highly significant differences were observed within tested varieties for metal accumulation and extraction efficiency. Furthermore, ammonium nitrate increased cadmium extraction, whereas ammonium sulphate enhanced zinc and lead uptake in most tested cultivars. In this field-based sunflower screening, we found enhanced cumulative Cd, Zn, and Pb extraction efficiency by a factor 4.4 for Salut cultivar. We therefore emphasize that prior to any classical breeding or genetic engineering enhancing metal uptake potential, a careful screening of various genotypes should be done to select the cultivar with the naturally highest metal uptake and to start the genetic improvement with the best available plant material.     

Cs phytoremediation by Sorghum bicolor cultivated in soil and in hydroponic system

Cs accumulation characteristics by Sorghum bicolor were investigated in hydroponic system (Cs level at 50–1000 μmol/L) and in soil (Cs-spiked concentration was 100 and 400 mg/kg soil). Two varieties of S. bicolor Cowly and Nengsi 2# grown on pot soil during the entire growth period (100 days) did not show significant differences on the height, dry weight (DW), and Cs accumulation. S. bicolor showed the potential phytoextraction ability for Cs-contaminated soil with the bioaccumulation factor (BCF) and the translocation factor (TF) values usually higher than 1 in soil system and in hydroponic system. The aerial parts of S. bicolor contributed to 86–92% of the total removed amounts of Cs from soil. Cs level in solution at 100 μmol/L gave the highest BCF and TF values of S. bicolor. Cs at low level tended to transfer to the aerial parts, whereas Cs at high level decreased the transfer ratio from root to shoot. In soil, the plant grew well when Cs spiked level was 100 mg/kg soil, but was inhibited by Cs at 400 mg/kg soil with Cs content in sorghum reaching 1147 mg/kg (roots), 2473 mg/kg (stems), and 2939 mg/kg (leaves). In hydroponic system, average Cs level in sorghum reached 5270 mg/kg (roots) and 4513 mg/kg (aerial parts), without significant damages to its biomass at 30 days after starting Cs treatment. Cs accumulation in sorghum tissues was positively correlated with the metal concentration in medium.     

Effect of thallium fractions in the soil and pollution origins on Tl uptake by hyperaccumulator plants: a key factor for the assessment of phytoextraction

Phytoremediation is often discussed as a means of extracting trace metals in excess in the soil, but to increase its efficiency a better understanding of the factors controlling plant uptake is required. The main objective of this study was to examine the effect of origin (anthropogenic vs. geogenic) and mobility of thallium (Tl) in the rhizosphere on Tl uptake. Two Tl-hyperaccumulating Brassicaceae species, kale (Brassica oleracea acephala L. cv. Winterbor F1) and candytuft (Iberis intermedia Guers.), were grown in a rhizobox system to investigate the dynamics of Tl in the rhizosphere soil. Four different soils were used. Two soils contained high Tl amounts due to anthropogenic sources (emissions from a cement plant and mining activities). High Tl content in the two other soils was due to a high rock content (geogenic origin). On completion of growth in the rhizoboxes, the depletion of Tl in seven different chemical fractions, determined by sequential extraction, was compared to the plant uptake. Most of the Tl taken up was derived from the so-called "easily accessible" fractions in both soils with geogenic Tl as well as in the soils polluted by mining activities. Due to the small amounts of easily accessible Tl in the geogenic soils, Tl uptake by Brassicaceae was low. On the other hand, for the air emission-polluted soil, a high depletion of Tl from "less accessible" fractions was observed in addition to depletion of the easily accessible fractions. Hence, the latter soil demonstrated the highest potential for effective soil decontamination by phytoextraction within an appropriate time frame.     

Potential for phytoremediation of polychlorinated biphenyl-(PCB-)contaminated soil

Weathered soils contaminated with commercial-grade Aroclor 1260 from three sites in Canada were used to investigate the polychlorinated biphenyl (PCB) phytoextraction potential of nine plant species (Festuca arundinacea, Glycine max, Medicago sativa, Phalaris arundinacea, Lolium multiflorum, Carex normalis, and three varieties of Cucurbita pepo ssp. pepo) under controlled greenhouse conditions. The soils used varied in PCB concentration (90-4200 microg/g) and total organic content (0.06-2.02%). Greenhouse experiments controlled for PCB volatilization through the use of a vented enclosure and by isolating the contaminated soils with parafilm. After 8 wks, PCB concentrations of 47-6700 microg/g were observed in root tissues. Although PCB concentrations in shoot tissues were lower (< 1-470 microg/g), the absolute amounts of PCBs observed in shoot tissue were significant (1.7-290 microg) once shoot biomass was accounted for. Congener signatures indicated that tetra- to hexa-chlorobiphenyls contributed the largest proportions to shoot tissues, but hepta-to nona-chorobiphenyls were also present in measurable amounts. Overall, the results indicate that varieties of C. pepo were more effective at extracting PCBs from soil than other plants screened The evidence suggests that this was mainly due to root uptake of PCBs and tranlocation to the shoots, rather than volatilization of PCBs from soil. All plants screened showed signs of stress in the most highly contaminated soil (4200 microg/g), but not in the two lower PCB contaminated soils (250 and 90 microg/g, respectively). No detectable decreases in soil PCB concentrations were observed in these short-term greenhouse experiments, but the results suggest that this may be achievable through multiple plantings.     

Cadmium and zinc in plants and soil solutions from contaminated soils

In an experiment using ten heavy metal-contaminated soils from six European countries, soil solution was sampled by water displacement before and after the growth of radish. Concentrations of Cd, Zn and other elements in solution (K, Ca, Mg, Mn) generally decreased during plant growth, probably because of uptake by plants and the subsequent redistribution of ions onto soil exchange sites at lower ionic strength. Speciation analysis by a resin exchange method showed that most Cd and Zn in non-rhizosphere solutions was present as Cd2+ and Zn2+, respectively. The proportion of free ions was slightly lower in rhizosphere solutions, mainly due to an increase in dissolved organic carbon during plant growth. Solution pH increased during plant growth, although the bulk soil pH generally remained constant. Cd concentrations in leaves and tubers were more closely correlated with their total or free ionic concentrations in rhizosphere solutions (adjusted R2 0.90) than with their concentrations in soils (adj. R2 0.79). Cd concentrations in non-rhizosphere solutions were only poorly correlated with Cd concentrations in leaves and tubers. In contrast to Cd, there were no soil parameters that individually predicted Zn concentrations in leaves and tubers closely. However, multiple correlation analysis (including Zn concentrations in rhizosphere solutions and in bulk soils) closely predicted Zn concentrations in leaves and tubers (adj. R2 = 0.85 and 0.70, respectively). This suggests that the great variability among soils in the solubility of Zn affected the rate of release of Zn into solution, and thus Zn uptake. There was no such effect for Cd, for which solubility varied much less. Furthermore, the plants may have partly controlled Zn uptake, as they took up relatively less at high solution concentrations of Zn.Free ionic concentrations in soil solution did not predict concentrations of Cd or Zn in plants better than their total concentrations in solution. This suggests that with these soils, analysis of Cd and Zn speciation is of little practical importance when their bioavailability is assessed.     

Long-term field phytoextraction of zinc/cadmium contaminated soil by Sedum plumbizincicola under different agronomic strategies

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment “S. plumbizincicola intercropped with maize” was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha^?1 gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.     

铜污染旱地红壤的络合诱导植物修复作用

研究EDTA和低分子量有机酸对污染旱地红壤Cu形态变化及金属忍耐－富集型植物印度芥菜生长和Cu吸收的影响,以探讨Cu污染土壤的有机络合诱导植物吸取修复作用,结果表明,在芥菜营养生长旺盛期施用EDTA可显著提高土壤Cu的活性,土壤水浸提态Cu和交换态Cu均显著上升;这种活化效应随外加Cu浓度的上升和EDTA用量的增加而增大;柠檬酸和酸对土壤Cu的活化效应小,只对水浸提态Cu略有影响;EDTA可显著增加芥菜茎叶、根的Cu浓度和吸收量,等摩尔量柠檬酸和苹果酸对土壤铜形态变化和芥菜Cu吸收没有显著作用。     

The analysis of coefficient of 137Cs transfer from soil into potato in relationship with 137Cs content in soil and plant mineral feed

The soil-potato transfer factor for 137Cs (TF) was estimated by using results of 137Cs activity concentration measurements in 214 samples of soil and potato taken at fields with various level of contamination with 137Cs. The relationships between the coefficient TF and soil characteristics (acidity pH (KCl), content of K2O, P2O5, CaO and MgO in soil) and soil contamination with 137Cs have been analysed. The results show that the TF values tend to decrease with increasing concentration of 137Cs, K2O, P2O5, and CaO in considered sod-podsolic sandyloam soil. The regression function describing the TF dependence of 137Cs, K2O, P2O5, and CaO content in soil has been derived.     

汞污染土壤植物修复技术研究进展

汞是一种全球性污染物,汞污染土壤的修复问题,一直倍受各国科学工作者关注,土壤汞污染的植物修复技术是近年来发展起来的新兴技术.其中,汞污染土壤的植物提取技术是最有发展前途的一种汞污染土壤植物修复技术.本文对国内外有关汞污染土壤的植物修复技术进行了系统分析,对有关汞污染土壤的植物修复应用技术,如植物挥发、固化及提取等修复方法进行了评述,探讨了植物修复技术在汞污染土壤修复中的应用前景.加快对汞超积累植物的筛选和植物体对重金属耐性机制的研究,对今后开展汞污染土壤的植物修复工作具有重要的现实意义.     

The optimization of the soil acidity of agrocenosis contaminated 137Cs and 90Sr: threshold parameters

During the field researches were determined the differences between agrochemical optimum of the acidity of the Sod-podzol loamy sand soil, which provides high productivity of the crops and the pH-value, which provides the minimal accumulation of 137Cs and of 90Sr by the biomass (the ecological optimum). On the average for the majority of the agricultural plants the minimal accumulations of 137Cs and of 90Sr are noticed under pHKCl 6.7, which is higher than agrochemical optimum on 0.7. The efficiency of liming under the discrimination of 137Cs and of 90Sr is much higher in soils with low values of pH. On the average, in crop rotation due to decreasing of the acidity in the soil from 4.9 to 5.9 pHKCl, the crop yield has grown on 9%, 137Cs contents has decreased on 16.7%, 90Sr--on 23.7%. The further decreasing of the soil acidity (from 5.9 to 6.8 pHKCl) was poorly effective: the productivity didn't change essentially. The transfer of 137Cs decreased on 8.9% and of 90Sr on 8.4%.     

Effect of biotite,zeolite, heavy clay,bentonite and apatite on the uptake of radiocesium by grass from peat soil

Biotite is a potassium rich mineral, which is used as a fertilizer in organic farming and as a soil amendment in conventional farming. Its ability to reduce ¹³⁴Cs uptake by ryegrass from peat soil was studied in pot experiments and compared with zeolite, heavy clay, bentonite and apatite. In addition, the long-term effect of biotite on ¹³⁷Cs uptake from peat soil was studied in the peat field. In the pot experiments in the first cut of ryegrass, the minerals decreased ¹³⁴Cs uptake by plants in the following order: zeolite > heavy clay > bentonite > biotite > apatite. Apatite did not have any effect on the plant ¹³⁴Cs level. In the later cuts, the uptake of ¹³⁴Cs from biotite-treated soil decreased further while that from soils treated with other minerals remained unchanged or even increased. In general, ¹³⁴Cs uptake by plants decreased with increasing mineral level. The decrease of ¹³⁴Cs uptake became more efficient, especially at the early growth stage, by mixing small amounts of zeolite in biotite. The results of the field experiment indicated the long-term effect of biotite on reducing ¹³⁴Cs uptake by plants. Biotite application rate was 30 t ha-1. The five-year mean of the plant/soil concentration ratio of ¹³⁷Cs was 0.05 for biotite-treated soil, in contrast to 0.14 for the control soil. On the whole, biotite reduced considerably the ¹³⁷Cs level of plants on peat soil and this effect was long-lasting. For an effective reduction of plant radiocesium a great quantity of biotite is needed and therefore it is most suitable for greenhouse cultivation where contaminated slightly decomposed peat is used as a growing medium.     

Phytoextraction and Accumulation of Mercury in Three Plant Species: Indian Mustard (Brassica Juncea), Beard Grass (Polypogon monospeliensis), and Chinese Brake Fern (Pteris vittata)

The objective of this research was to screen and search for suitable plant species to phytoextract mercury-contaminated soil. Our effort focused on using some of the known metal-accumulating wild-type plants since no natural plant species with mercury-hyperaccumulat ing properties has yet been identified. Three plant species were evaluated for their uptake efficiency for mercury: Indian mustard (Brassica juncea), beard grass (Polypogon monospeliensis), and Chinese brake fern (Pteris vittata). Four sets of experiments were conducted to evaluate the phytoremediation potential of these three plant species: a pot study with potting mix where mercury was provided daily as HgCl₂ solution; experiments with freshly mercury-spiked soil; and a study with aged soils contaminated with different mercury sources (HgCl₂, Hg(NO₃)₂, and HgS). Homemade sunlit chambers were also used to study foliar uptake of Hg from ambient air. Among the three plant species, Chinese brake fern showed the least stress symptoms resulting from mercury exposure and had the highest mercury accumulation. Our results indicate that Chinese brake fern may be a potential candidate for mercury phytoextraction. We found that mercury contamination is biologically available for plant uptake and accumulation, even if the original and predominating mercury form is HgS, and also after multiple phytoremediation cycles.     

Bacteria associated with yellow lupine grown on a metal‐contaminated soil: in vitro screening and in vivo evaluation for their potential to enhance Cd phytoextraction

In order to stimulate selection for plant‐associated bacteria with the potential to improve Cd phytoextraction, yellow lupine plants were grown on a metal‐contaminated field soil. It was hypothesised that growing these plants on this contaminated soil, which is a source of bacteria possessing different traits to cope with Cd, could enhance colonisation of lupine with potential plant‐associated bacteria that could then be inoculated in Cd‐exposed plants to reduce Cd phytotoxicity and enhance Cd uptake. All cultivable bacteria from rhizosphere, root and stem were isolated and genotypically and phenotypically characterised. Many of the rhizobacteria and root endophytes produce siderophores, organic acids, indole‐3‐acetic acid (IAA) and aminocyclopropane‐1‐carboxylate (ACC) deaminase, as well as being resistant to Cd and Zn. Most of the stem endophytes could produce organic acids (73.8%) and IAA (74.3%), however, only a minor fraction (up to 0.7%) were Cd or Zn resistant or could produce siderophores or ACC deaminase. A siderophore‐ and ACC deaminase‐producing, highly Cd‐resistant Rhizobium sp. from the rhizosphere, a siderophore‐, organic acid‐, IAA‐ and ACC deaminase‐producing highly Cd‐resistant Pseudomonas sp. colonising the roots, a highly Cd‐ and Zn‐resistant organic acid and IAA‐producing Clavibacter sp. present in the stem, and a consortium composed of these three strains were inoculated into non‐exposed and Cd‐exposed yellow lupine plants. Although all selected strains possessed promising in vitro characteristics to improve Cd phytoextraction, inoculation of none of the strains (i) reduced Cd phytotoxicity nor (ii) strongly affected plant Cd uptake. This work highlights that in vitro characterisation of bacteria is not sufficient to predict the in vivo behaviour of bacteria in interaction with their host plants.     

石油污染土壤修复植物的根-土界面微生物特征

选取沈抚灌区的主要修复植物蓖麻为实验材料,分析了蓖麻根区土壤、根际土壤、根面、根内4个层面上细菌和真菌的数量,优势菌种的生理生化特征,及细菌菌株生长营养类型,揭示了根-土界面微生物区系特征与石油污染土壤生物修复的关系.结果发现：修复植物根-土界面上,细菌数量为根际>根面>根内,真菌数量为根内>根面>根际,根面细菌与真菌数量均处于根际与根内区域微生物数量之间;修复植物蓖麻根面区域优势细菌种类最多,根内区域优势真菌种类最多;根际与根内的优势细菌具有较强的降解大分子物质的能力;根面细菌在营养需求分类上可归为氨基酸需求菌群.     

Phytoextraction capacity of trees growing on a metal contaminated soil

Phytoremediation is an innovative biological technique to reclaim land contaminated by heavy metals or organic pollutants. In the present work, we studied the ability of five woody species to extract heavy metal (copper, zinc or cadmium) from a polluted soil to their above-ground tissues. Metal content in leaves and twigs was determined. Salix and Betula transferred zinc and cadmium to leaves and twigs, but Alnus, Fraxinus and Sorbus excluded them from their above-ground tissues. None of the species considered transferred copper to the shoots.     

Nitrate accumulation in leaves of vegetation of a forested ecosystem receiving high amounts of atmospheric ammonium sulfate

Vegetation of an acid woodland, receiving an atmospheric ammonium input of about 3 kmol (40 kg N) per hectare per year, was analyzed on the content of organic nitrogen, ammonium and nitrate. A high nitrate content (50–320 μmol g⁻¹ dry weight) was found in bird-cherry, black-berry and bracken, whereas only low amounts (up to 2 μmol g⁻¹ dry weight) of nitrate were present in mountain-ash, hazel and the two dominant tree species oak and birch. The impact of this nitrate uptake and nitrate accumulation on soil pH and autotrophic nitrification is discussed.     

汞污染土壤植物修复中转基因技术的应用

汞是一种全球性污染物.随着工业的发展、汞矿开采的加速,土壤汞污染日益严峻,给生态环境和人类生活带来了严重的威胁.因此,汞污染土壤的修复问题受到了广大学者的关注.针对受污染的土壤修复问题,植物修复技术具有成本低和不会给环境带来新的危害等特点.本文对目前国内外汞污染土壤修复植物修复技术的研究进行了综述,介绍了转基因技术在汞污染土壤中的应用,探讨了转基因技术在环境治理和环境修复中潜在的应用价值.