Differential effects of AM fungal isolates on Medicago truncatula growth and metal uptake in a multimetallic (Cd, Zn, Pb) contaminated agricultural soil

Toxic metal accumulation in soils of agricultural interest is a serious problem needing more attention, and investigations on soil–plant metal transfer must be pursued to better understand the processes involved in metal uptake. Arbuscular mycorrhizal (AM) fungi are known to influence metal transfer in plants by increasing plant biomass and reducing metal toxicity to plants even if diverging results were reported. The effects of five AM fungi isolated from metal contaminated or non-contaminated soils on metal (Cd, Zn) uptake by plant and transfer to leachates was assessed with Medicago truncatula grown in a multimetallic contaminated agricultural soil. Fungi isolated from metal-contaminated soils were more effective to reduce shoot Cd concentration. Metal uptake capacity differed between AM fungi and depended on the origin of the isolate. Not only fungal tolerance and ability to reduce metal concentrations in plant but also interactions with rhizobacteria affected heavy metal transfer and plant growth. Indeed, thanks to association with nodulating rhizobacteria, one Glomus intraradices inoculum increased particularly plant biomass which allowed exporting twofold more Cd and Zn in shoots as compared to non-mycorrhizal treatment. Cd concentrations in leachates were variable among fungal treatments, but can be significantly influenced by AM inoculation. The differential strategies of AM fungal colonisation in metal stress conditions are also discussed.     

Heavy metal biosorption by fungal mycelial by-products: mechanisms and influence of pH

Summary Mycelial wastes of Rhizopus arrhizus, used in fermentation industries to produce lipases, were studied for their ability to absorb various heavy metal ions (Ni, Zn, Cd and Pb). Chelation of all these ions occurs by a chemical, equilibrated and saturatable mechanism, following the Langmuir adsorption model. Data transformation allowed us to calculate maximum uptake and dissociation constants of the sorption reaction. We also investigated the influence of pH on metal accumulation. Sorption capacity variations between different biosorbent types (Rhizopus, Mucor, Penicillium, and Aspergillus), could be related to their acidity. pH neutralisation during the sorption reaction considerably enhanced zinc chelation (up to 56 mg/g). Previous NaOH treatment of mycelial wastes also increased their capacity for metal sorption. We report R. arrhizus metal uptake curves versus pH, using a pH-stat system. Optimal adsorption was achieved at neutral pH for nickel and zinc, pH 5.0 for lead, and inhibition of chelation was observed when the pH decreased. These results illustrate the importance of pH during the adsorption process, indicating a competitive mechanism for chelation between heavy metal ions and protons at cell wall adsorption sites. Correspondence to: J.-C. Roux     

丛枝菌根真菌菌丝体吸附重金属的潜力及特征

应用玻璃珠分室培养系统获得丛枝菌根真菌材料,研究了离体真菌菌丝体对pH缓冲体系中Zn、Cd和Mn等金属离子的吸附特征。试验结果表明,真菌菌丝体对各金属离子吸附能力差异显著,对Cd最强,Zn次之,Mn最弱。试验条件下,菌体可分别吸附相当于自身干物重1.6%的Mn、2.8%的Zn和13.3%的Cdo吸附于菌丝体的Cd2+绝大部分可以被Ca2+交换吸附。另外研究了宿主植物根系对Cd的吸附作用,证实菌根真菌侵染改变了根系的吸附特性,相对于非菌根根系,菌根的CEC较高,对Cd的吸附能力较强。试验结果为重金属污染条件下丛枝菌根强化根系的屏障作用提供了直接证据。     

Heavy-Metal Stress and Developmental Patterns of Arbuscular Mycorrhizal Fungi

The rate of global deposition of Cd, Pb, and Zn has decreased over the past few decades, but heavy metals already in the soil may be mobilized by local and global changes in soil conditions and exert toxic effects on soil microorganisms. We examined in vitro effects of Cd, Pb, and Zn on critical life stages in metal-sensitive ecotypes of arbuscular mycorrhizal (AM) fungi, including spore germination, presymbiotic hyphal extension, presymbiotic sporulation, symbiotic extraradical mycelium expansion, and symbiotic sporulation. Despite long-term culturing under the same low-metal conditions, two species, Glomus etunicatum and Glomus intraradices, had different levels of sensitivity to metal stress. G. etunicatum was more sensitive to all three metals than was G. intraradices. A unique response of increased presymbiotic hyphal extension occurred in G. intraradices exposed to Cd and Pb. Presymbiotic hyphae of G. intraradices formed presymbiotic spores, whose initiation was more affected by heavy metals than was presymbiotic hyphal extension. In G. intraradices grown in compartmentalized habitats with only a portion of the extraradical mycelium exposed to metal stress, inhibitory effects of elevated metal concentrations on symbiotic mycelial expansion and symbiotic sporulation were limited to the metal-enriched compartment. Symbiotic sporulation was more sensitive to metal exposure than symbiotic mycelium expansion. Patterns exhibited by G. intraradices spore germination, presymbiotic hyphal extension, symbiotic extraradical mycelium expansion, and sporulation under elevated metal concentrations suggest that AM fungi may be able to survive in heavy metal-contaminated environments by using a metal avoidance strategy.     

Assessment of arbuscular mycorrhizal fungi diversity in the rhizosphere of <Emphasis Type="Italic">Viola calaminaria</Emphasis> and effect of these fungi on heavy metal uptake by clover

 The ability of arbuscular mycorrhizal (AM) fungi from a metal-tolerant plant (Viola calaminaria, violet) to colonise and reduce metal uptake by a non-tolerant plant (Trifolium subterraneum, subterranean clover) in comparison to a metal-tolerant AM fungus isolated from a non-tolerant plant was studied. AM spores from the violet rhizosphere and from violet roots were characterised by polymerase chain reaction (PCR) amplification of the SSU rDNA, and sequencing. Subterranean clover was grown in pots containing a soil supplemented with Cd and Zn salts and inoculated either with a mixture of spores extracted from the violet rhizosphere or with spores of a Cd-tolerant Glomus mosseae P2 (BEG 69), or non-inoculated. The diversity of fungi, including AM fungi, colonising clover roots was assessed and analysed using terminal-restriction fragment length polymorphism. At least four different Glomus species were found in the violet rhizosphere. After 8 weeks in a growth chamber, colonisation of clover roots with spores from the violet rhizosphere increased Cd and Zn concentrations in clover roots without significantly affecting the concentrations of metals in the shoot and plant growth. G. mosseae P2 reduced plant growth and slightly increased the Cd concentration. Only one AM fungus (Glomus b) from the violet rhizosphere colonised clover roots, but other fungi were present. AM fungi from heavy metal-contaminated soils and associated with metal-tolerant plants may be effective in accumulating heavy metals in roots in a non-toxic form. Accepted: 7 July 2000     

Strategies of cadmium and zinc resistance in willow by regulation of net accumulation

This work was performed to find out if metal resistant clones of Salix viminalis L. are capable to achieve high resistance to the metals by regulating their net accumulation. Salix clones with low or high resistance in combination with low or high accumulation capacity of either Zn or Cd were cultivated from cuttings in nutrient solution. The investigation included leakage and uptake experiments using ⁶⁵Zn or ¹⁰⁹Cd and analysis of root cation exchange capacity (CEC). Some plants were pre-treated with unlabeled 0.5 μM Cd or 2.5 μM Zn 24 h prior to the experiments to induce possible tolerance mechanisms. To find out if the regulation was a metabolic process, experiments were also performed with 2,4-dinitrophenol (DNP). Clones with high resistance and low Cd accumulation had higher efflux of Cd compared to the other clones, in both untreated and Cd pre-treated plants. This indicates a constitutive property to lower Cd accumulation by high Cd leakage. Pre-treatment with 0.5 μM Cd diminished the Cd net uptake to a level near zero in all clones, likely to be due to decreased the Cd uptake. In contrast, resistant clones with high Cd accumulation had the highest root CEC, which may be used to bind up Cd in the free space. No clear regulation of Zn net uptake was found in Zn-resistant clones. Pre-treatment with Zn decreased the uptake of Zn into the free space in Zn-resistant clones. The resistant high-accumulating clones, however, showed the highest leakage of Zn in both untreated and pre-treated plants, a constitutive process not related to high accumulation. Neither the influx nor the efflux of Cd or Zn was affected by DNP indicating passive transport across the plasma membrane.     

Mycorrhizal and Endophytic Fungal Colonization in Arrhenatherum elatius L. Roots According to the Soil Contamination in Heavy Metals

The aim of this work was to jointly study non-mycorrhizal (dark septate fungi) and mycorrhizal (arbuscular mycorrhizae) colonization along a large range of heavy metal pollution in soil in order to determine the effective contribution of each type of endophytes in relation to heavy metal uptake and tolerance. Hence, eight sites were chosen in the mining area of northern France with respect both to a large range of heavy metal contamination (Cd, Pb, Zn) and monospecific colonization by Arrhenatherum elatius. Root colonization with both arbuscular mycorrhizae (AM) and dark septate fungi (DSF) as well as spore density in rhizospheric soil were estimated in relation to soil characteristics. Mycorrhizal infestation (hyphae, arbuscules and vesicles) was adversely affected by soil pollution almost to exclusion. The intensity of colonization with DSF was very low in presence of AM in non-contaminated soils but higher in polluted soils. The effect of the fungal colonization on the heavy metal tolerance of Arrhenatherum elatius is discussed.     

Heavy metal uptake by arbuscular mycorrhizas of Elsholtzia splendens and the potential for phytoremediation of contaminated soil

A pot culture experiment and a field experiment were carried out separately to study heavy metal (HM) uptake from soil contaminated with Cu, Zn, Pb and Cd by Elsholtzia splendens Nakai ex F. Maekawa inoculated with arbuscular mycorrhizal (AM) fungi and the potential for phytoremediation. The HM-contaminated soil in the pot experiment was collected from the field experiment site. Two AM fungal inocula, MI containing only one AM fungal strain, Glomus caledonium 90036, and M II consisting of Gigaspora margarita ZJ37, Gigaspora decipens ZJ38, Scutellospora gilmori ZJ39, Acaulospora spp. andGlomus spp., were applied to the soil under unsterilized conditions. In the pot experiment, the plants were harvested after 24 weeks of growth. Mycorrhizal colonization rate, plant dry weight (DW) and P, Cu, Zn, Pb, Cd concentrations were determined. MI-treated plants had higher mycorrhizal colonization rates than MII-treated plants. Both MI and MII increased shoot and root DW, and MII was more effective than MI. In shoots, the highest P, Cu, Zn and Pb concentrations were all observed in the plants treated with MII, while MI decreased Zn and Pb concentrations and increased P but did not alter Cu, and Cd concentrations were not affected by either of two inocula. In roots, MII increased P, Zn, Pb concentrations but did not alter Cu and Cd, and MI did not affect P, Cu, Zn, Pb, Cd concentrations. Cu, Zn, Pb, Cd uptake into shoots and roots all increased in MII-treated plants, while in MI-treated plants, Cu and Zn uptake into shoots and Cu, Zn, Pb, Cd into roots increased but Pb and Cd uptake into shoots decreased. In general, MII was more effective than MI in promoting plant growth and HM uptake. The field experiment following the pot experiment was carried out to investigate the effects of MII under field conditions. The 45-day-old nonmycorrhizal and MII-colonized seedlings of E. splendens were transplanted to HM-contaminated plots and harvested after 5 months. MII-inoculation increased shoot DW and shoot P, Cu, Zn, Pb concentrations significantly but did not alter shoot Cd concentrations, which led to higher uptake of Cu, Zn, Pb, Cd by E. splendens shoots. These results indicate that the AM fungal consortium represented by MII can benefit phytoextraction of HMs and therefore play a role in phytoremediation of HM-contaminated soils.     

Heavy-metal stress and developmental patterns of arbuscular mycorrhizal fungi

The rate of global deposition of Cd, Pb, and Zn has decreased over the past few decades, but heavy metals already in the soil may be mobilized by local and global changes in soil conditions and exert toxic effects on soil microorganisms. We examined in vitro effects of Cd, Pb, and Zn on critical life stages in metal-sensitive ecotypes of arbuscular mycorrhizal (AM) fungi, including spore germination, presymbiotic hyphal extension, presymbiotic sporulation, symbiotic extraradical mycelium expansion, and symbiotic sporulation. Despite long-term culturing under the same low-metal conditions, two species, Glomus etunicatum and Glomus intraradices, had different levels of sensitivity to metal stress. G. etunicatum was more sensitive to all three metals than was G. intraradices. A unique response of increased presymbiotic hyphal extension occurred in G. intraradices exposed to Cd and Pb. Presymbiotic hyphae of G. intraradices formed presymbiotic spores, whose initiation was more affected by heavy metals than was presymbiotic hyphal extension. In G. intraradices grown in compartmentalized habitats with only a portion of the extraradical mycelium exposed to metal stress, inhibitory effects of elevated metal concentrations on symbiotic mycelial expansion and symbiotic sporulation were limited to the metal-enriched compartment. Symbiotic sporulation was more sensitive to metal exposure than symbiotic mycelium expansion. Patterns exhibited by G. intraradices spore germination, presymbiotic hyphal extension, symbiotic extraradical mycelium expansion, and sporulation under elevated metal concentrations suggest that AM fungi may be able to survive in heavy metal-contaminated environments by using a metal avoidance strategy.     

Equilibrium and kinetic studies on biosorption potential of charophyte biomass to remove heavy metals from synthetic metal solution and municipal wastewater

The risk of heavy metal contamination in domestic water causes serious health and environmental problems. Biosorption has been considered as an efficient and alternative way for treatment of heavy metal–contaminated wastewater. The potentials of dried charophytes, Chara aculeolata and Nitella opaca, to biosorb lead (Pb), cadmium (Cd), and zinc (Zn) from synthetic solutions and municipal wastewater were investigated. The efficiency of metal removal was studied under varied conditions in different sorbent dosages, pH, and contact times. Biosorption isotherm and kinetics were used to clarify heavy metal preference and biosorption mechanism. C. aculeolata and N. opaca performed well in the biosorption of all three metal ions, with preference towards Pb, followed by Cd and Zn, in the single-metal solutions. Pb adsorption onto algal biomass followed first-order rate kinetics (N. opaca) and intraparticle diffusion (C. aculeolata and N. opaca). These results indicated physical adsorption process between Pb ions and both algal biomasses. Cd and Zn biosorption kinetics fitted the second-order rate model, indicating chemical adsorption between metal ions and both algae. The experimental data of three-metal biosorption fitted well to Langmuir isotherm model, suggesting that the metal ion adsorption occurred in a monolayer pattern on a homogeneous surface. C. aculeolata exhibited slightly higher maximum uptake of Pb, Cd, and Zn (105.3 mgPb/g, 23.0 mgCd/g, 15.2 mgZn/g) than did N. opaca (104.2 mgPb/g, 20.5 mgCd/g, 13.4 mgZn/g). In multi-metal solutions, antagonistic effect by metal competition was observed. The ability of charophytes to remove Pb and Zn was high in real municipal water (81–100%). Thus, the charophytic biomass may be considered for the treatment of metal contamination in municipal wastewater.     

Improvement of heavy metal biosorption by mycelial dead biomasses (Rhizopus arrhizus, Mucor miehei and Penicillium chrysogenum): pH control and cationic activation

Abstract: Fungal mycelial by-products from fermentation industries present a considerable affinity for soluble metal ions (e.g. Zn, Cd, Ni, Pb, Cr, Ag) and could be used in biosorption processes for purification of contaminated effluents. In this work the influence of pH on sorption parameters is characterized by measuring the isotherms of five heavy metals (Ni, Zn, Cd, Ag and Pb) with Rhizopus arrhizus biomass under pH-controlled conditions. The maximum sorption capacity for lead was observed at pH 7.0 (200 mg g^-l), while silver uptake was weakly affected. The stability of metal-biosorbent complexes is regularly enhanced by pH neutralization, except for lead. A transition in sorption mechanism was observed above pH 6.0. In addition, comparison of various industrial fungal biomasses ( R. arrhizus, Mucor miehei and Penicillium chrysogenum indicated important variations in zinc-binding and buffering properties (0.24, 0.08 and 0.05 mmol g^−l, respectively). Without control, the equilibrium pH (5.8, 3.9 and 4.0) is shown to be related to the initial calcium content of the biosorbent, pH neutralization during metal adsorption increases zinc sorption in all fungi (0.57, 0.52 and 0.33 mmol g-l) but an improvement was also obtained (0.34, 0.33 and 0.10 mmol g⁻¹) by calcium saturation of the biomass before heavy metal accumulation. Breakthrough curves of fixed bed biosorbent columns demonstrated the capacity of the biosorbent process to purify zinc and lead solutions in continuous-flow systems, and confirmed the necessity for cationic activation of the biosorbent before contact with the heavy-metal solution.     

Alleviation of Cadmium Toxicity to <i>Medicago Truncatula</i> by AMF Involves the Changes of Cd Speciation in Rhizosphere Soil and Subcellular Distribution

Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to several abiotic stresses, including heavy metals, drought or salinity exposure. However, the role of AMF in alleviation of soil cadmium (Cd)-induced toxicity to plants is still largely unknown. In this study, Cd speciation in soil and subcellular distribution of Cd were used to characterize the roles of application AM fungi in the alleviation of Cd toxicity in alfalfa plants. Our results showed that the addition of Glomus mosseae in Cd contaminated soil (10 mg/Kg) significantly increased soil pH, cation exchange capacity (CEC) and organic matter in rhizosphere soil with Medicago truncatula L., and then account for significantly decreased contents of exchangeable and carbonate-bounded Cd speciation in rhizosphere soil, indicating alleviation of plant toxicity by reduction of bioavailable fractions of Cd. Although there is no significant difference found in Cd accumulation by roots and shoots respectively between Cd and AM-Cd treatments, more portion of Cd was recorded compartmentalization in cell wall fraction of both root and shoot in treatment of Cd with AM application, indicating alleviation of Cd toxicity to plant cell. Herein, application of AM fungi in Cd treatments performed to inhibit the appearance of Cd toxicity symptoms, including the improvement of leaf electrolyte leakage, root elongation, seedling growth and biomass. This information provides a clearer understanding of detoxification strategy of AM fungi on Cd behavior with development and stabilization of soil structure and subcellular distribution of plant.     

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was -irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.     

Litter N retention over winter for a low and a high phenolic species in the alpine tundra

Mycorrhizal fungus colonization of roots may modify plant metal acquisition and tolerance. In the present study, the contribution of the extraradical mycelium of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae (BEG 107), to the uptake of metal cations (Cu, Zn, Cd and Ni) by cucumber (Cucumis sativus) plants was determined. The influence of the amount of P supplied to the hyphae on the acquisition and partitioning of metal cations in the mycorrhizal plants was also investigated. Pots with three compartments were used to separate root and root-free hyphal growing zones. The shoot concentration of Cd and Ni was decreased in mycorrhizal plants compared to non-mycorrhizal plants. In contrast, shoot Zn and Cu concentrations were increased in mycorrhizal plants. High P supply to hyphae resulted in decreased root Cu concentrations and shoot Cd and Ni concentrations in mycorrhizal plants. These results confirm that some elements required for plant growth (P, Zn, Cu) are taken up by mycorrhizal hyphae and are then transported to the plants. Conversely, Cd and Ni were transported in much smaller amounts by hyphae to the plant, so that arbuscular mycorrhizal fungus colonization could partly protect plants from toxic effects of these elements. Selective uptake and transport of plant essential elements over non-essential elements by AM hyphae, increased growth of mycorrhizal plants, and metal accumulation in the root may all contribute to the successful growth of mycorrhizal plants on metal-rich substrates. These effects are stimulated when hyphae can access sufficient P in soil.     

Effects of mycorrhizal colonisation on<Emphasis Type="Italic"> Thymus polytrichus</Emphasis> from heavy-metal-contaminated sites in northern England

A study was performed to establish whether colonisation with arbuscular mycorrhizal (AM) fungi is beneficial to wild thyme [Thymus polytrichus A. Kerner ex Borbás ssp. britannicus (Ronn.) Kerguelen (Lamiaceae)] growing in the heavy-metal-contaminated soils along the River South Tyne, United Kingdom. T. polytrichus plants of the same genotype were grown under controlled conditions with and without Zn contamination, and differences between AM-colonised and -uncolonised plants in mean shoot and root growth (dry weight) and Zn concentration were assessed. When grown in the heavy-metal-contaminated, low-P soil from one of the South Tyne sites, AM-colonised plants grew significantly larger than uncolonised plants; however, there was no significant difference in growth between AM and non-AM plants grown in an artificial substrate with a larger available P concentration, with or without Zn contamination. Mycorrhizal colonisation increased tissue Zn concentrations during the experiments. It is concluded that AM fungi are beneficial, if not essential, to T. polytrichus growing in the low-nutrient soils along the River South Tyne, because of their role in enhancing plant uptake of P (and possibly other nutrients). There was no evidence from this study that the fungi reduce plant uptake of heavy metals at these sites, but rather increase Zn uptake. However, the resulting tissue metal concentrations do not appear to be large enough to be detrimental to plant growth.     

Influence of zinc on cadmium-induced toxicity in nodules of pigeonpea (Cajanus cajan L. Millsp.) inoculated with arbuscular mycorrhizal (AM) fungi

Arbuscular mycorrhizal (AM) fungi are known to alleviate heavy-metal stress in plants. The intent of the present work was to analyze accumulation of heavy metals (Cd and Zn) in nodules of two Cajanus cajan (L.) Millsp. genotypes and their subsequent impact on nitrogen fixation, oxidative stress, and non-protein thiols (glutathione and phytochelatins) with and without AM fungus Glomus mosseae. Accumulation of Cd and Zn in nodules resulted in sharp reduction in nodule number, nodule dry mass as well as nitrogen fixation (leghemoglobin and nitrogenase (N₂ase)), although Cd had more pronounced effects than Zn. Cd-induced lipid peroxidation, H₂O₂ accumulation, and electrolyte leakage were largely reversed by Zn supplementation. Zn application significantly altered the negative effects of Cd on the synthesis of non-protein thiols, suggesting antagonistic behaviour of Zn. Higher concentration of Zn was more effective in lessening the negative effects of Cd than its lower concentration. Remarkable genotypic variation was found, with more severe effects of both the metals in P792 than Sel 85N. Glomus mosseae attenuated the phytotoxic effects of metals in nodules by decreasing metal uptake, oxidative stress, and by enhancing defense system ultimately leading to better nitrogen-fixing potential of pigeonpea nodules.     

EFFECTS OF INOCULATION WITH ARBUSCULAR MYCORRHIZAL FUNGI ON MAIZE GROWN IN MULTI-METAL CONTAMINATED SOILS

Pot culture experiments were established to determine the effects of colonization by arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. sp) on maize (Zea mays L.) grown in Pb, Zn, and Cd complex contaminated soils. AMF and non-AMF inoculated maize were grown in sterilized substrates and subjected to different soil heavy metal (Pb, Zn, Cd) concentrations. The root and shoot biomasses of inoculated maize were significantly higher than those of non-inoculated maize. Pb, Zn, and Cd concentrations in roots were significantly higher than those in shoots in both the inoculated and non-inoculated maize, indicating the heavy metals mostly accumulated in the roots of maize. The translocation rates of Pb, Zn, and Cd from roots to shoots were not significantly difference between inoculated and non-inoculated maize. However, at high soil heavy metal concentrations, Pb, Zn, and Cd in the shoots and Pb in the roots of inoculated maize were significantly reduced by about 50% compared to the non-inoculated maize. These results indicated that AMF could promote maize growth and decrease the uptake of these heavy metals at higher soil concentrations, thus protecting their hosts from the toxicity of heavy metals in Pb, Zn, and Cd complex contaminated soils.     

Cadmium immobilization in the rhizosphere of arbuscular mycorrhizal plants by the fungal extraradical mycelium

The aim of the study was to assess how the extraradical mycelium (ERM) of arbuscular mycorrhizal (AM) fungi contributes to Cd immobilization in the rhizosphere. Substrates prepared by cultivation of AM and non-mycorrhizal tobacco (Nicotiana tabacum L.) in quartz sand in two experiments were amended with Cd in a range of concentrations and Cd immobilization was assessed as Cd toxicity using root growth tests. Split-root plants, inoculated at one part of the root system, and hyphal compartments colonized by ERM only were used to separate the effects of ERM from plant-mediated effects of mycorrhiza and from the effects of roots. AM decreased Cd toxicity in the substrates obtained by 12 weeks of cultivation (Experiment 1), while the effect was less clear after 8 weeks (Experiment 2). No indication was found for an involvement of plant-mediated effects; in contrast, the effect of ERM could be clearly demonstrated. Lower Cd toxicity in the substrates colonized by ERM was related to ERM-induced alkalinization, but not directly to ERM density. It is concluded that the ERM of AM fungi may enhance Cd immobilisation in soil not only due to its high Cd sorption capacity but also by its activity.     

Effects of leached alginate on metal biosorption

The Cu, Cd and Zn sorption capacity of formaldehyde-crosslinked seaweed biomass (Ascophyllum nodosum : FCAN) was studied using equilibrium methodology. The shape of sorption isotherms and biosorbent mass losses indicated that in the first uptake cycle the biosorbent leached cellular polysaccharides that formed precipitate with metal solutions influencing the sorption study and application. However, since the sorption levels of washed and non-washed biosorbents were comparable, the leached cell wall polysaccharide(s) (alginate) could not be the main component responsible for metal sorption in this case.on leave from Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil     

Identification of arbuscular mycorrhizal fungi in soils and roots of plants colonizing zinc wastes in southern Poland

 Analysis of the community of arbuscular mycorrhizal (AM) fungi in roots of Fragaria vesca growing in a heavy metal contaminated site was carried out on a Zn waste site near Chrzanow (southern Poland). The waste substratum was characterized by high contents of Pb, Zn, Cd, Cu and As, and by low levels of N, P and organic matter. Spores of Glomales were isolated by wet sieving and DNA was isolated from individual spores. Nested polymerase chain reaction (PCR) with taxon-specific primers was used to identify the species Glomus mosseae, Glomus intraradices and Glomus claroideum. Spores of other fungi were morphologically characterized and new taxon-discriminating molecular probes were developed for two of them (Glomus sp. HM-CL4 and HM-CL5) based on variations in the large ribosomal subunit (25S rDNA). High sequence similarities were found between Glomus sp. HM-CL4 and Glomus gerdemanii, and between Glomus sp. HM-CL5 and Glomus occultum. The designed primers were used to characterize the population of AM fungi colonizing the roots of F. vesca collected from the Zn waste site. The analysis, carried out on roots stained with trypan blue, showed that the most effective colonizer was closely related to G. gerdemannii. G. claroideum and the G. occultum-like fungus were slightly less common whilst frequencies of G. intraradices and G. mosseae in roots were much lower. The analysis of mycorrhiza stained with rhodizoniate to localize heavy metal accumulation showed that the stain does not influence the PCR reaction. Seventy percent of the root samples containing positively stained fungal hyphae were found to be colonized by G. mosseae. The data obtained demonstrate the usefulness of nested PCR for studies carried out in polluted areas. It will enable selection of AM fungi which are able to colonize plant roots under heavy metal stress conditions, as well as the identification of fungi showing high in situ accumulation of potentially toxic elements. Accepted: 7 July 2000