Beneficial effects of earthworms and arbuscular mycorrhizal fungi on establishment of leguminous trees on Pb/Zn mine tailings

Planting trees to stabilize metalliferous mine tailings is a widely used form of land reclamation although substantial soil amendment is invariably required, both to improve the physico-chemical status of the tailings and to ameliorate toxicity prior to planting. Here, we report a glasshouse study of the combined effects of burrowing earthworms (Pheretima guillelmi) and arbuscular mycorrhizal fungi (Glomus spp., AMF) on establishment of a naturally invasive, woody, nitrogen-fixing legume, Leucaena leucocephala, on topsoil-amended Pb/Zn mine tailings. AMF provided the most effective preliminary inoculant, improving N, P and K uptake, but earthworms had more influence improving N nutrition. In most cases, the combined effects of AMF and earthworms were additive and proved to be beneficial to plant growth, plant nutrition and for protection against uptake of toxic metals. AMF influenced metal uptake more than earthworms, but together they reduced mobility of Pb and Zn in soil by as much as 25%. Some minor but significant negative interactions were also evident; for example, earthworms enhanced soil microbial activity but inhibited the beneficial effects of AMF on N₂-fixation. We argue that increased attention to ecological interactions in soil could reduce costs and improve the efficacy of restoring a vegetation cover to land impacted by contaminated spoils.     

Toxicity of Pb/Zn mine tailings to the earthworm <Emphasis Type="Italic">Pheretima</Emphasis> and the effects of burrowing on metal availability

Lead and zinc mine tailings from Guangdong, China were found to be toxic to two common species of the earthworm Pheretima, unless the spoil was diluted by at least 20% with an artificial uncontaminated soil. With different soil dilutions, there were significant differences in mortality, growth and Zn uptake between the two species. Zinc and arsenic were principally responsible for the toxicity of the tailings. LC₅₀ values for Zn, Pb, Cu and As for Pheretima were similar to those reported in the literature for Eisenia fetida. Following inoculation with the earthworms, spoil pH, EC and available metals increased; available-Pb and -Zn concentrations increased by up to 48.2% and 24.8% respectively. The findings suggest that earthworms may play an important role in reclamation of mining spoils to achieve a healthy soil supporting sustainable vegetation. Potentially increased toxicity of metals to plants and animals, through increased bioavailability in the presence of earthworms, is discussed in the context of their role in modifying the efficiency of phytoremediation treatments.     

Digestion and residue stabilization of bacterial and fungal cells,protein, peptidoglycan,and chitin by the geophagous earthworm Metaphire guillelmi

Microbial biomass is an important source of soil organic matter, which plays crucial roles in the maintenance of soil fertility and food security. However, the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using ¹⁴C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells, fungal (Penicillium chrysogenum) cells, protein, peptidoglycan, and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil, the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil, indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction, which were attributed to the passage of the microbial biomass through the earthworm gut, and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with ¹⁴C-lablled microbial cells and cell components provided direct evidence that microbial biomass is a food source for geophagous earthworm and fungal biomass is likely a more important food source for earthworms than bacterial biomass. Findings of this study have important implications for the roles of geophagous earthworms in the fate of microbial biomass in soil.     

Soil properties and metal accumulation by earthworms in the Siena urban area (Italy)

This paper reports the results of a study focused on the metal (Cd, Co, Cr, Cu, Ni, Pb, Sb, U and Zn) distribution in soils and uptake and accumulation by earthworms Nicodrilus caliginosus (Savigny) from urban, peri-urban, green-urban and non-urban zones of Siena municipality (central Italy). The main goal was to define the influence of soil properties and metal soil contents on the uptake of these contaminants by earthworms. Data indicated that Cd, Cu, Pb, Sb and Zn soil contents increased in the following order: non-urban < green-urban < peri-urban < urban soils, suggesting that vehicular traffic affects the distribution of these metals. Pb and Sb were the main soil contaminants and their highest enrichments were found in urban sites where stop-and-go traffic occurs. Concentrations of these traffic-related metals in earthworms showed a distribution pattern similar to that in soil, suggesting that soil contamination influenced the uptake of Cd, Cu, Pb, Sb and Zn by N. caliginosus. There were significant positive correlations between Cd, Pb and Sb earthworm concentrations and their soil contents. The lack of correlation for Cu and Zn could be due to the physiological regulation of these elements by earthworms. Statistical analysis pointed out that the uptake and accumulation of Cd, Cu, Pb, Sb and Zn by earthworms were affected by some soil physicochemical properties such as the organic carbon and carbonate contents that are able to rule the bioavailability of metals in soils.     

Effect of earthworms on the phytoremediation of zinc-polluted soil by ryegrass and Indian mustard

In this paper, the effects of earthworms on the growth and Zn uptake of ryegrass and Indian mustard in artificially Zn-contaminated soils were studied. Earthworm inoculation increased plant shoot biomass by 29–83% for ryegrass and by 11–42% for Indian mustard, respectively, as compared to the treatments without earthworms, while the roots’ biomass of both plants were increased much more than their corresponding shoots. Earthworms also increased shoot Zn concentrations in both ryegrass and Indian mustard, although the increases in ryegrass did not show significant difference. Except for soil without Zn contamination, the Zn contents of both ryegrass and Indian mustard roots were significantly increased by earthworm addition. Generally, Zn contents of roots were relatively higher than those of shoots for both plants, which were independent of earthworms inoculation. Earthworm increased soil bioavailable metal (diethylenetriamine-pentaacetic acid–Zn) (DTPA-Zn) concentrations, which resulted in a direct increase in Zn uptake by the plants, since a significant correlation was observed between the DTPA–Zn contents and plant Zn uptake. However, the main reason for the increase in plant Zn uptake under earthworm inoculation was probably the increase in dry matter production stimulated by earthworms.     

Lethal critical body residues as measures of Cd,Pb, and Zn bioavailability and toxicity in the earthworm<Emphasis Type="Italic">Eisenia fetida</Emphasis>

Background. Earthworm heavy metal concentrations (critical body residues, CBRs) may be the most relevant measures of heavy metal bioavailability in soils and may be linkable to toxic effects in order to better assess soil ecotoxicity. However, as earthworms possess physiological mechanisms to secrete and/or sequester absorbed metals as toxicologically inactive forms, total earthworm metal concentrations may not relate well with toxicity. Objective  The objectives of this research were to: i) develop LD₅₀s (total earthworm metal concentration associated with 50% mortality) for Cd, Pb, and Zn; ii) evaluate the LD₅₀ for Zn in a lethal Zn-smelter soil; iii) evaluate the lethal mixture toxicity of Cd, Pb, and Zn using earthworm metal concentrations and the toxic unit (TU) approach; and iv) evaluate total and fractionated earthworm concentrations as indicators of sublethal exposure. Methods  Earthworms (Eisenia fetida (Savigny)) were exposed to artificial soils spiked with Cd, Pb, Zn, and a Cd-Pb-Zn equitoxic mixture to estimate lethal CBRs and mixture toxicity. To evaluate the CBR developed for Zn, earthworms were also exposed to Zn-contaminated field soils receiving three different remediation treatments. Earthworm metal concentrations were measured using a procedure devised to isolate toxicologically active metal burdens via separation into cytosolic and pellet fractions. Results and Discussion  Lethal CBRs inducing 50% mortality (LD₅₀, 95% CI) were calculated to be 5.72 (3.54-7.31), 3.33 (2.97-3.69), and 8.19 (4.78-11.6) mmol/kg for Cd, Pb, and Zn, respectively. Zn concentrations of dead earthworms exposed to a lethal remediated Zn-smelter soil were 3-fold above the LD₅₀ for Zn and comparable to earthworm concentrations in lethal Zn-spiked artificial soils, despite a 14-fold difference in total soil Zn concentration between lethal field and artificial soils. An evaluation of the acute mixture toxicity of Cd, Pb, and Zn in artificial soils using the Toxic Unit (TU) approach revealed an LD₅₀ (95% CI) of 0.99 (0.57-1.41) TU, indicating additive toxicity. Conclusions  Total Cd, Pb, and Zn concentrations in earthworms were good indicators of lethal metal exposure, and enabled the calculation at LD₅₀s for lethality. The Zn-LD₅₀ developed in artificial soil was applicable to earthworms exposed to remediated Zn-smelter soil, despite a 14-fold difference in total soil Zn concentrations. Mixture toxicity evaluated using LD₅₀s from each single metal test indicated additive mixture toxicity among Cd, Pb, and Zn. Fractionation of earth worm tissues into cytosolic and pellet digests yielded mixed results for detecting differences in exposure at the sublethal level Recommendation and Outlook  CBRs are useful in describing acute Cd, Pb, and Zn toxicity in earthworms, but linking sublethal exposure to total and/or fractionated residues may be more difficult. More research on detoxification, regulation, and tissue and subcellular partitioning of heavy metals in earthworms and other invertebrates is needed to establish the link between body residue and sublethal exposure and toxicity. Keywords: Bioavailability; Cd; critical body residues; earthworms; metals; Pb; soil; Zn An erratum to this article is available at .     

A Laboratory Study on Revegetation and Metal Uptake in Native Plant Species from Neutral Mine Tailings

Lygeum spartum, Zygophyllum fabago and Piptatherum miliaceum are typical plant species that grow in mine tailings in semiarid Mediterranean areas. The aim of this work was to investigate metal uptake of these species growing on neutral mine tailings under controlled conditions and their response to fertilizer additions. A neutral mine tailing (pH of soil solution of 7.1–7.2) with high total metal concentrations (9,100 and 5,200 mg kg^?1 Zn and Pb, respectively) from Southern Spain was used. Soluble Zn and Pb were low (0.5 and <0.1 mg l^?1, respectively) but the major cations and anions reached relatively high levels (e.g. 2,600 and 1,400 mg l^?1 Cl and Na). Fertilization caused a significant increase of the plant weight for the three species and decreased metal accumulation with the exception of Cd. Roots accumulated much higher metal concentrations for the three plants than shoots, except Cd in L. spartum. Shoot concentrations for the three plants were 3–14 mg kg^?1 Cd, 150–300 mg kg^?1 Zn, 4–11 mg kg^?1 Cu, and 1–10 mg kg^?1 As, and 6–110 mg kg^?1 Pb. The results indicate that neutral pH mine tailings present a suitable substrate for establishment of these native plants species and fertilizer favors this establishment. Metal accumulation in plants is relatively low despite high total soil concentrations.     

The significant contribution of mycorrhizal fungi and earthworms to maize protection and phytoremediation in Cd-polluted soils

Mycorrhizal fungi and earthworms can individually or interactively influence plant growth and heavy metal uptake. The influence of earthworms and arbuscular mycorrhizal (AM) fungi either alone or in combination on maize (Zea mays L.) growth and cadmium (Cd) uptake was investigated in a calcareous soil artificially spiked with Cd. Soils were contaminated with Cd (10 and 20 mg Cd kg⁻¹), inoculated or un-inoculated with the epigeic earthworm Lumbricus rubellus and two AM fungal species (Rhizophagus irregularis and Funneliformis mosseae) for two months of growth under greenhouse conditions. Generally, earthworms alone increased both shoot P uptake and biomass but decreased shoot Cd concentration and root Cd uptake. AM fungi individually often increased total maize P uptake, declined shoot Cd concentration, and consequently produced higher total biomass. However, R. irregularis enhanced shoot Cd uptake at low Cd level and root Cd uptake at high Cd level. In plants inoculated with F. mosseae species, earthworms increased shoot biomass and Cd uptake, decreased root biomass and Cd uptake at all Cd levels, and increased shoot Cd concentration at low Cd level. In plants colonized by R. irregularis species, however, earthworm addition decreased maize biomass only at high Cd level and root Cd concentration and total maize Cd uptake at both Cd levels. Earthworm activity decreased Cd transfer from the soil to maize roots at low Cd level, but this was counterbalanced in the presence of F. mosseae. Mycorrhizal symbiosis significantly reduced the transfer of Cd from roots to shoots, independence of earthworm effect. Overall, it is concluded that L. rubellus and AM fungi, in particular F. mosseae isolate, improved maize tolerance to Cd toxicity both individually and interactively by increasing plant growth and P nutrition, and restricting Cd transfer to the aboveground biomass. Consequently, the single and interactive effects of the two soil organisms might potentially be important not only in protecting maize plants against Cd toxicity, but also in Cd phytostabilization in soils polluted by this highly toxic metal.     

Selective digestion of the proteinaceous component of humic substances by the geophagous earthworms Metaphire guillelmi and Amynthas corrugatus

Humic substances play a key role in the global carbon cycling and the sequestration of micropollutants in soil. The transformation of these substances by earthworms, the dominant soil macroinvertebrates of many terrestrial ecosystems, and the mechanisms involved are still obscure. We prepared two chemically identical humic model compounds that were specifically ¹⁴C-labeled either in the aromatic or the proteinaceous component, and added them to soil incubated with the geophagous earthworm species Metaphire guillelmi (anecic) and Amynthas corrugatus (endogeic). In the absence of the earthworms, both the aromatic and the proteinaceous components were mineralized at similarly low rates (5−8% after 9 days of incubation). In the presence of the earthworms, mineralization rate of the proteinaceous component was strongly stimulated (2-fold by M. guillelmi and 1.4-fold by A. corrugatus). The mineralization rate of the aromatic component was (slightly) stimulated (1.2-fold; P < 0.05) only by A. corrugatus. In all cases, the stimulated mineralization was accompanied by a transformation of radiolabeled humic acids to fulvic acids within the earthworm guts and by an incorporation of radiolabel into the earthworm tissues. Digestion of the proteinaceous component of humic acids by the earthworms was corroborated also by a decrease of extractable humic acids in fresh cast and a stimulated mineralization of soil nitrogen; in the case of M. guillelmi, the fresh cast contained sixfold more NH₄⁺ than the non-ingested soil. Our study provides direct evidence for the selective digestion of humic components by earthworms. Considering the ubiquity of geophagous earthworms and their large biomass, the alteration of the chemical structure of humic substances by the earthworms through their selective digestion of peptidic components may have significant impacts on the stability of humic substances and the bioavailability of micropollutants in soil.     

Effects of earthworm activity and P‐solubilizing bacteria on P availability in soil

The effects of phosphate solubilizing bacteria (Bacillus megateriumi) (PSB) and earthworms (Pheretima guillelmi and Eisenia fetida) on phosphorus (P) turnover and transformation in soil were investigated in a laboratory experiment lasting for 21 days. The treatments included soil + P. guillelmi (SW1), soil + E. fetida (SW2), soil + B. megaterium (SB), soil + P. guillelmi + B. megaterium (SBW1), soil + E. fetida + B. megaterium (SBW2), and the control with sterilized soil (control) only. The results showed that the number of B. megaterium. was enhanced in all treatments especially those with earthworms added when compared with the control. Activities of acid phosphatase (pH = 6.5) increased in all treatments, especially in the presence of P. guillelmi with or without PSB (64 % and 38 %, respectively). Significant increases in both inorganic P and water‐soluble P were observed in treatments involving B. megaterium. and earthworms when compared with the control. Inoculation of both earthworms and PSB had significant effects on microbial growth, enzymatic activity, and thus enhanced the release of available P. The dual inoculation of earthworms and bacteria further accelerated P transformation. Different performances observed for the earthworm species were probably due to their different feeding habits and physiology.     

Oral sealing using glue: a new method to distinguish between intestinal and dermal uptake of metals in earthworms

Earthworms may take up chemicals from soil and pore water, both through their skin (dermal) and by ingestion (oral). It remains unclear, however, what the relative importance of these pathways is. To assess bioavailability of pollutants in soil to earthworms, it is necessary that the contribution of each pathway is known. Lumbricus rubellus were sealed by means of medical histoacryl glue, to block ingestion of soil particles and pore water. For 6 d, these earthworms showed good survival and vitality and no soil ingestion was found. Equal metal uptake was found by sealed and unsealed earthworms exposed to an inert sand matrix continuously flushed with contaminated water. Therefore, pore water uptake via ingestion contributes little to metal accumulation. Uptake rates of Cd, Cu and Pb in sealed and unsealed earthworms exposed to two contaminated field soils were similar. Uptake and elimination kinetics of Zn were significantly lower in sealed earthworms exposed to one of the two field soils. Body concentrations of Cu and Pb could be completely attributed to the dermal route. For internal Cd and Zn concentrations, however, 0-17 and 21-30%, respectively, were derived from ingestion. It is concluded that for metals the dermal route is the uptake route of importance. The sealing method described here may be useful in a variety of earthworm nutrition and contamination-effect studies.     

Regenwürmer als Bioindikatoren für Schwermetallbelastungen von Böden unter Freilandbedingungen

The use of earthworms in monitoring soil pollution by heavy metals Total heavy metal contents (HNO₃-soluble) and exchangeable fractions (Ca(NO₃)₂-soluble) of Pb, Zn and Cd were measured in soils, litter layers and earthworms (dry masses) from forest, arable and pasture sites in a transect of the main wind direction and varying distances (1.5, 5.4, 11.4, 15.6 km) to a lead smelter near Bad Ems, Germany. Additionally, cast materials of Lumbricus terrestris-individuals were collected from the surface of the pasture sites. In the observed area total soil contents of Pb and Cd exceeded the C-level and total contents of Zn the B-level of the “Netherland-list”. Heavy metal contents in soils and earthworms decreased with increasing distance to the smelter. Pb showed the best correlation. Correlation between total contents of Pb and Cd in soils and earthworms were significant (rs = 0.66; p < 0.05 and rs = 0.67; p < 0.01, respectively). The uptake of heavy metals by Lumbricus rubellus, L. terrestris and Aporrectodea caliginosa was metal specific rather than species specific with factors of accumulation being <1 (Pb), 2.7–7.6 (Zn) and 19.5–85.5 (Cd). The heavy metal contents of the observed cast materials signified the different transfer of elements from soil material via earthworm individuals to the faeces. In the cast materials the amounts of Pb were high and the amounts of Zn and Cd were low. This indicates a high accumulation rate for Zn and especially for Cd in the tissues of the observed earthworm individuals. The present data support the necessity of ecotoxicological threshold levels.     

Effects of earthworms on decomposition and metal availability in contaminated soil: Microcosm studies of populations with different exposure histories

Population-specific differences in the responses of earthworms to simultaneous exposure to Cu and Zn were studied in microcosm experiments. Two populations of Aporrectodea caliginosa tuberculata (Eisen) with different metal exposure histories were chosen for the studies. Microcosms were prepared containing either uncontaminated soil or soils with low or high combined Cu/Zn -concentrations (79/139 or 178/311 mg kg⁻¹ dry mass of soil, respectively). Earthworms from each population were introduced to the microcosm treatments with some microcosms serving as controls without earthworms. One series of microcosms was destructively sampled after 16 weeks incubation in a climate chamber. Survival, growth, reproduction and decomposition by earthworms in each treatment were measured. An additional microcosm series was sampled for soil and earthworm measurements at four weeks intervals to determine temporal changes in the availability of metals in the soils and their accumulation into earthworms. Cu and Zn were sequentially extracted from the soil samples of both microcosm series to estimate mobility and availability of the metals in the soil. Earthworms with long-term exposure history to metal-contaminated soil seemed to tolerate higher soil metal concentrations than earthworms without earlier exposure. Both earthworms and metals affected soil respiration (CO₂ production) and nitrogen mineralization. In addition, earthworms seemed to decrease the mobility and bioavailability of metals in the soil through their burrowing activity.     

Nutrient uptake in mycorrhizal plants – role of earthworms

Both arbuscular mycorrhizal fungi (AMF) and earthworms often coexist in agriculture ecosystems, but very little is known on the interactions between them. A two-compartment air gap-incorporating device was used to investigate the effects of three species of earthworm (epigeic Eisenia foetida, endogeic Aporrectodea trapezoide, and anecic Pheretima guillelmi) on AMF (Glomus intraradices) under the exclusion of plant roots, and then on maize (Zea mays L.) performance and nutrients uptake. Results showed a strong correlation between hyphal length density and subsequent plant growth and nutrient uptake. Earthworms improved soil nutrients availability in hyphal compartment (HC): E. foetida improved the concentration of soil inorganic N, A. trapezoide changed the concentration of available phosphate in the soil, and P. guillelmi changed the soil's physical properties. We found some indications that different species of earthworm and AMF might interact within the soil. Earthworms and AMF mainly acting on different nutrients create distinct niches for plants. The feeding and burrowing activities did not significantly destroy hyphal length density and made negative affect on plant performance.     

Influence of plant species and phosphorus amendments on metal speciation and bioavailability in a smelter impacted soil: a case study of food-chain contamination

Purpose

The present research aimed to assess the influence of two phosphorous (P) amendments on metal speciation in rhizosphere soil and the soil–plant transfer of metals.

Materials and methods

Complementary experiments were performed: field experiments on a contaminated cultivated soil and laboratory experiments on an uncultivated contaminated soil to highlight the mechanisms involved in metal-phosphorous interactions. In laboratory experiment, P amendments were added at 120 mg P/kg of soluble KH₂PO₄ amendment and 9,000 mg P/kg of solid Ca₅(PO₄)₃OH amendment.

Results and discussion

Field-culture results showed the possible food-chain contamination due to Pb, Cd, Cu, and Zn phytoaccumulation by pea and mustard plants from a cultivated agricultural soil. Moreover, P-metal complexes were observed by microscopy in the rhizosphere soil. In laboratory experiments, the application of P amendments significantly increased Pb and Zn level in rhizosphere soil compared to control. Phosphate amendments significantly increased metal-P fraction and decreased “oxides” and “organic matter” fractions of Pb and Zn. Soluble-P amendment was more effective than solid P amendment in changing Pb and Zn speciation. The changes in metal speciation are higher in the rhizosphere soil of pea than tomato. Application of P amendments increased Pb and Zn TF root/soil but decreased TF shoot/root.

Conclusions

The effectiveness of in situ metal immobilization technique varies with the type and quantity of applied P amendment as well as plant and metal type.     

Uptake and bioaccumulation of heavy elements by two earthworm species from a smelter contaminated area in northern Kosovo

As, Cd, Cu, Pb, Sb and Zn concentrations were determined in two earthworm species (Allolobophora rosea and Nicodrilus caliginosus) from a mining and industrial area in northern Kosovo and compared with their contents in the bulk soil and the main soil fractions. Earthworm specimens were collected at fifteen sites located at different distances from a Pb–Zn smelter along a gradient of decreasing contamination. Individuals of A. rosea and N. caliginosus showed similar tissue levels of As, Cd, Cu, Pb, Sb and Zn, suggesting that earthworm species belonging to the same eco-physiological group have a similar propensity to uptake and bioaccumulate heavy elements. Cd, Pb, Sb and Zn concentrations in both earthworm species were positively correlated with the respective total soil contents and generally decreased with distance from the smelter. The bioaccumulation factor (BAF) revealed that Cd and Zn were the only elements bioaccumulated by earthworms. The rank order of BAF values for both species was as follows: Cd > > Zn > > Cu > As = Pb = Sb. The absorption of Cd, Pb, Sb and Zn by earthworms mostly depended on the extractable, reducible and oxidable soil fractions, suggesting that the intestine is likely the most important uptake route. The extractable soil fraction constantly influenced the uptake of these heavy elements, whereas the reducible fraction was important mainly for Pb and Zn. The water soluble fraction had an important role especially for the most mobile heavy elements such as Cd and Zn, suggesting that dermal uptake is not negligible. As a whole, the analytical data indicate that soil fractionation patterns influence the uptake of heavy elements by earthworms, and the extractable fraction is a good predictor of heavy element bioavailability to these invertebrates in soil.     

Effects of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal fungus (Glomus intraradices) on enzyme activities of a sterilized soil–sand mixture and nutrient uptake by maize

A pot experiment was conducted to investigate the effect of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal (AM) fungi (Glomus intraradices) on soil enzyme activities and nutrient uptake by maize, which was grown on a mixture of sterilized soil and sand. Maize plants were grown in pots inoculated or not inoculated with AMF, treated or not treated with earthworms. Wheat straw was added as a feed source for earthworms. Mycorrhizal colonization of maize was markedly increased in AM fungi inoculated pots and further increased by addition of epigeic earthworms. AM fungi and epigeic earthworms increased maize shoot and root biomass, respectively. Soil acid phosphatase activity was increased by both earthworms and mycorrhiza, while urease and cellulase activities were only affected by earthworms. Inoculation with AM fungi significantly (p?<?0.001) increased the activity of soil acid phosphatase but decreased soil available phosphorus (P) and potassium (K) concentrations at harvest. Addition of earthworms alone significantly (p?<?0.05) increased soil ammonium-N content, but decreased soil available P and K contents. AM fungi increased maize shoot weight and root P content, while earthworms improved N, P, and K contents in shoots. AM fungi and earthworm interactively increased maize shoot and root biomass through their regulation of soil enzyme activities and on the content of available soil N, P, and K.     

不同改良剂对黑麦草在铜矿尾矿砂上生长的影响

Montmorillonite, rice straw, organic manure and chemical fertilizer were used as amendment materials for copper mine tailings, and their effects on mine tailing pH, nutrients and metal availability to ryegrass were investigated. Chemical fertilization was the most effective one in improving ryegrass growth in mine tailings among the amendment materials examined. It was found that montmorillonite raised biomass of ryegrass at the 1st and 2nd cuts, but it did not give further positive effects at the 3rd and 4th cuts. The effect of organic materials on ryegrass growth was not so good as expected, mainly due to their slow decomposition in mine tailings with less soil microorganisms. Available Cu and Zn contents in mine tailings decreased in the presence of montmorillonite but increased when rice straw and organic manure were used as amendments. Cu and Zn contents in ryegrass decreased with increasing the rate of montmorillonite application but increased with the rate of rice straw. Zn showed much stronger mobility from soil to ryegrass than Cu, and almost all the available N and P in mine tailings, except for the treatments with organic manure, were completely consumed after ryegrass had grown in mine tailings for more than four months and been harvested for four times. Owing to its large biomass and high metal uptake, ryegrass is a potential plant for remediation of metal contaminated soils in practice.     

Uptake and bioaccumulation of heavy elements by two earthworm species from a smelter contaminated area in northern Kosovo

As, Cd, Cu, Pb, Sb and Zn concentrations were determined in two earthworm species (Allolobophora rosea and Nicodrilus caliginosus) from a mining and industrial area in northern Kosovo and compared with their contents in the bulk soil and the main soil fractions. Earthworm specimens were collected at fifteen sites located at different distances from a Pb–Zn smelter along a gradient of decreasing contamination. Individuals of A. rosea and N. caliginosus showed similar tissue levels of As, Cd, Cu, Pb, Sb and Zn, suggesting that earthworm species belonging to the same eco-physiological group have a similar propensity to uptake and bioaccumulate heavy elements. Cd, Pb, Sb and Zn concentrations in both earthworm species were positively correlated with the respective total soil contents and generally decreased with distance from the smelter. The bioaccumulation factor (BAF) revealed that Cd and Zn were the only elements bioaccumulated by earthworms. The rank order of BAF values for both species was as follows: Cd > > Zn > > Cu > As = Pb = Sb. The absorption of Cd, Pb, Sb and Zn by earthworms mostly depended on the extractable, reducible and oxidable soil fractions, suggesting that the intestine is likely the most important uptake route. The extractable soil fraction constantly influenced the uptake of these heavy elements, whereas the reducible fraction was important mainly for Pb and Zn. The water soluble fraction had an important role especially for the most mobile heavy elements such as Cd and Zn, suggesting that dermal uptake is not negligible. As a whole, the analytical data indicate that soil fractionation patterns influence the uptake of heavy elements by earthworms, and the extractable fraction is a good predictor of heavy element bioavailability to these invertebrates in soil.     

Uptake pathways and toxicity of Cd and Zn in the earthworm Eisenia fetida

The uptake of Cd and Zn by the earthworm Eisenia fetida was determined at varying Ca concentrations and with pre-exposure to different metabolic inhibitors in simulated soil solutions over a 48-h period. The presence of Ca in the solution had complex actions on Cd uptake. At a low Cd concentration of 0.1 μM, Ca (0.1-1 mM) slightly but significantly stimulated Cd uptake, whereas it inhibited Cd uptake at a higher Cd level (10 μM). Pre-exposure to a Ca-channel blocker (Lanthanum) inhibited Cd uptake over a relatively wide range of Cd concentrations, but not Zn uptake, suggesting that the uptake of Zn was not exerted at a Ca channel. N-ethylmaleimide, which specifically binds to sulfhydryl groups, inhibited Zn uptake at both 0.1 and 10 μM, implying that the transport of Zn is carrier-mediated by proteins or other SH-containing compounds. The present study provides evidence that the mechanisms of Cd and Zn uptake in earthworms are pharmacologically different, although both metals have similar geochemical and environmental properties. After 24 h pre-exposure to a sublethal concentration (1.0 μM) of Cd, Zn toxicity for E. fetida was significantly reduced with 48-h LC₅₀ values (with 95% confidence interval) increasing from 145 (105-201) to 316 (212-470) μM Zn. Pre-exposure to Zn (1.0 μM) did not, however, affect Cd toxicity. Pre-exposure to Cd significantly changed the subcellular Zn distribution, with a decreasing fraction of Zn associated with Fraction B (associated with granules and cell membranes), which is believed to be most indicative of toxic pressure and an increased fraction associated with Fraction G (associated with cytosol). This most likely explains the observed Zn tolerance of E. fetida after low level Cd pre-exposure. These results help to understand the uptake mechanism and interactions of Zn and Cd in earthworms.