Metal Accumulation In Plant Tissues Research Articles

Physiological responses of the nickel hyperaccumulator Bornmuellera emarginata under varying nickel dose levels and pH in hydroponics

Abstract Background and aims The nickel hyperaccumulator Bornmuellera emarginata (Brassicaceae) is a species adapted to thrive on naturally nickel-enriched ultramafic soils in the Balkans and a promising candidate for use in nickel agromining. The main aim of this study was to provide insight into the physiological mechanisms of nickel hyperaccumulation in B. emarginata. Methods Bornmuellera emarginata was cultivated under various nickel exposure concentrations (control, 1, 10, and 100 µM nickel in solution), and different pH levels of the hydroponic solution for four weeks. During this period, the plants underwent assessment for various physiological parameters, including photosynthetic pigments, leaf relative water content, tolerance index, and metal accumulation in plant tissues. Results The results show that the translocation factors and bioconcentration factors were > 1 even at 1 µM nickel in solution. This confirms the ability of B. emarginata to hyperaccumulate nickel (up to 6600 mg kg−1) over a wide range of nickel concentrations in hydroponics. Nickel at 100 µM (a concentration that is an order of magnitude higher than the highest soil solution nickel concentration found in ultramafic soils) induced only mild physiological stress symptoms (e.g. a minor proline response). Alterations in the solution pH did not cause any significant effect on nickel accumulation in the plants. Conclusions Bornmuellera emarginata is a highly adapted nickel-tolerant and nickel hyperaccumulating species that shows very little stress responses even to extreme nickel exposure concentrations in hydroponics. This species shows interesting trade-off responses between nickel and other metals, including non-competitive uptake of zinc. The potential for this species to accumulate zinc should therefore be further explored.

Sheep manure and sewage sludge boost biofortification of barley and restricts heavy metal accumulation in plant tissues

In recent centuries, micronutrient deficiencies are considered a major challenge for human health. Biofortification of principal crops has been broadly accepted as a sustainable scenario to overcome this limitation. The experiment was carried out in a completely randomized factorial design with three replications during the 2007–2008 and 2008–2009 growing seasons. Four fertilizers and two doses of humic acid were used in the experiment. Analysis of variance indicated that humic acid, fertilizer type, and growing season caused statistically significant differences in macro and micronutrient content and heavy metal concentrations of shoot and seed in plants. Results also denoted that organic material amendment improved macro and micronutrient content of barley plants compared with IF in which SS treatment increased Ca, Mg, Mn, Fe, Zn, and Ni concentrations in shoot/seed while SM treatment enhanced N, P, and K concentration of plants. Moreover, IF-treated plants increased heavy metal accumulation in shoot and seed tissues whereas organic amendments reduced heavy metal uptake such that the lowest Pb and Cd were determined in SM-treated plants, and the lowest Ni content was measured in W-treated samples. HA application promoted Zn, Mg, and Cu accumulation in plants, however, individual or combined with fertilizers reduced other micro and macronutrient uptake. In conclusion, the amendment of 40 tons ha−1 of sheep manure and sewage sludge is an improving and beneficial practice in barley cultivation for the biofortification of crops. However, HA treatment did not form a meaningful whole in the experiment but promoted Zn, Mg, and Cu concentrations in plant tissues.

Micro- and nano-plastics in agricultural soils: A critical meta-analysis of their impact on plant growth, nutrition, metal accumulation in plant tissues and crop yield

Plastics have found widespread use in the contemporary world due to their numerous benefits. However, approximately 99 % of them are estimated to be discarded in the environment. Following various weathering processes, they break into smaller particles forming micro (MPs) and nano (NPs) plastics, which can accumulate in the ecosystems and persist for decades. Thus, pollution from plastics has emerged as one of the most pressing global environmental concerns. MPs and NPs effects have been extensively studied in aquatic ecosystems. However, research about their impact on terrestrial ecosystems is still insufficient. Recent estimates suggest that MPs and NPs content could be up to twenty-three times higher in soils than in aquatic environments. For that reason, their diffusion and biological effects on terrestrial ecosystems have attracted the attention of the scientific community in recent years. MPs quantity appears to be higher in agricultural soils, where they may affect the health, quality, and functionality of soils, putting crops and, therefore, humans at serious risk from potential food chain spread. Thus, the investigation of MPs behaviour in soils and their impact on crops is crucial due to the hazards that may arise. In the present study, bibliometric research and statistical meta-analysis were used to explore the current research progress and acquire a more comprehensive knowledge of crops' responses to MPs and NPs exposure. Four crops (Triticum aestivum L., Zea mays L., Oryza sativa L., and Lactuca sativa L.) with the highest data availability were selected for further evaluation. Among them, Lactuca sativa L. appears to be the most sensitive crop, maintaining the highest rates of decline in terms of plants' growth and development, in contrast to Triticum aestivum L., which exhibits the highest level of resistance. Substantial effects have been observed in Oryza sativa L. plants, while the response of Zea mays L. is generally negative, though to a lesser extent. Exposure to different polymer types, particle sizes, and contamination doses causes diverse effects on crops. However, adjustments in the roots and shoots of each studied crop separately appear to follow a similar pattern, indicating significant alterations in nutrient uptake and metal accumulation.

Screening of new native metallophytes from copper abandoned mining site: Promising tool for phytoremediation

AbstractA field survey on abandoned mining site ‘Bir Nehass‐Morocco’ was conducted to identify new native metallophytes as a promising tool for phytoremediation. The spatial distribution of metals in tailings and mining soils was investigated and metal accumulation in plant tissues was analyzed and compared. The results indicated that the studied area was polluted by Cu, Zn, Pb and Cd Cadmium with maximum values of 2892, 27868.3, 6982 and 63.03 mg.kg−1, respectively, which are higher than background levels for agricultural soils. The concentrations of Cu, Zn, Pb and Cd decreased with the distance from the mine tailings. Thirteen species (11 families) were identified and mainly native and therophyte plants. Significant difference (p < 0.05) was observed among the average concentrations of metals in plant tissues and most values exceeded the normal concentration range. Based on the comparative analysis of heavy metals content, translocation and bioconcentration factors in plants, Aizoon canariense L, Hirschfeldia incana (L.) L. Fossat, Citrullus colocynthis (L.) Schrader and Peganum harmala L had a high accumulation ability and showed a remarkable phytoremediation potential which could be identified as promising candidates for phytoremediation techniques.

Effect of copper ions on the associations of Azospirillum bacteria with wheat seedlings (Triticum aestivum L.).

The physiological and biochemical activity of plant–microbial associations enables them to determine the mobility, bioavailability, and accumulation of heavy metals in plant tissues. These abilities are the basis for the use of plants and their associated microorganisms in the development of approaches that ensure both the prevention of the ingress of toxic metals into food crops and the extraction of pollutants from polluted soils by using phytoremediation technologies. Whether plant–microbial complexes are used successfully depends on the knowledge of how specific organisms interact with heavy metals. We evaluated the effect of copper ions on common wheat (Triticum aestivum L.) inoculated with three plant-growth-promoting rhizobacteria (PGPR) of the genus Azospirillum. We analyzed the growth variables of 14-day-old wheat seedlings, the content of photosynthesis pigments, the activity of plant oxidoreductases, and the accumulation of copper by plant tissues. All strains more or less compensated for copper toxicity to seedling development and increased metal accumulation in roots and shoots. Copper affected the photosynthetic apparatus of the inoculated plants, primarily by decreasing the content of chlorophyll b. An analysis of the activity of plant oxidoreductases (peroxidases and phenoloxidases), which are involved in the physiological responses of plants to pollutant stress, showed strain-specific dependence and a significant effect of copper on the inoculated plants. Overall, the obtained results clearly show that the effect of Azospirillum on the physiological and biochemical status of wheat is diverse. The compensatory effect of bacteria on copper toxicity and the simultaneous increase in metal accumulation in plant tissues can be considered as mutually exclusive crop-production aspects associated with the growing of food plants in heavy-metal-polluted areas.

Soil cadmium stress reduced host plant odor selection and oviposition preference of leaf herbivores through the changes in leaf volatile emissions

The Elemental defense hypothesis suggested that metal accumulation in plant tissues could serve as direct defense to reduce herbivore feeding preference as metals are toxic to phytophagous insects. However, the indirectly defensive role of heavy metals on host plant odor selection and oviposition preference of leaf herbivores through the changes in leaf volatile organic compounds (VOCs) is still unknown. In this study, we used a local woody plant species, Populus yunnanensis, to investigate whether soil cadmium (Cd) stress could affect plant VOC production and whether Cd-mediated changes in leaf VOC emissions will further influence the host plant odor and oviposition preferences of female adults of a specialist and a generalist herbivore species. The results clearly showed that the soil Cd stress could prominently induce leaf total VOC emissions of P. yunnanensis and such induction was positively correlated with leaf Cd accumulation. Herbivore olfactometer bioassays further demonstrated that the VOCs released by P. yunnanensis under Cd exposure are far less attractive to both of the specialist and generalist female adults compared to control plants, leading to significant reduction in oviposition on Cd-treated plants. Moreover, the host plant odor selection and oviposition preference of the two herbivore species were all negatively correlated with leaf total VOC emissions, which confirmed the defensive role of Cd-induced VOCs for deterring the female insects. The result will extend the existing knowledge of the Elemental defense hypothesis and provide new insight into predicting the herbivore damage level of poplar species that naturally occurred in metal-polluted habitats.

Influence of sawdust addition on the toxic effects of cadmium and copper oxide nanoparticles on Vigna radiata seeds

Studies in the literature concern the toxicity of nanoparticles either in a Petri dish or in agar media-based tests. Therefore, for environmental relevance, individual and binary mixtures of metal oxide nanoparticles (M-NPs) cadmium oxide (CdO-NP) and copper oxide (CuO-NP) were tested in this study for their effect on Vigna radiata in soil with and without the addition of sawdust. Seed germination was 67% in 100 mg CuO-NP in soil without sawdust. Seeds failed to germinate in 100 mg CdO +100 mg CuO-NPs in soil without the addition of sawdust and germination was 83% at the same concentration in soil with sawdust. In sawdust added to soil, when compared with control (soil without M-NPs), the maximum reduction in shoot (82%) and root (80%) length and wet (61%) and dry (54%) weight of plant was recorded in CdO-NP treated soil. Similarly, compared with control (soil without sawdust and M-NPs), the percent reduction in shoot (61%) and root (70%) length and wet (44%) and dry (48%) weight was highest in CdO-NP treated soil not supplemented with sawdust. In a binary mixture test (CdO-NP + CuO-NP), the addition of sawdust promoted the above plant growth parameters compared with individual CdO-NP and CuO-NP tests. Cadmium (511 mg kg−1 for individual and 303 mg kg−1 for binary mixture tests) and Cu (953 mg kg−1 for individual and 2954 mg kg−1 for binary mixture tests) accumulation was higher in plants grown in soil without sawdust. The beneficial effect of sawdust addition was observed in seed germination, plant growth, and metal accumulation. With or without sawdust, the binary mixture of CdO and CuO was antagonistic. These results indicate that sawdust can prevent M-NP-induced toxicity and reduce metal accumulation in plant tissues.

Effects of exogenous spermidine on poplar resistance to leaf and root herbivory as affected by soil cadmium stress

Elemental defense hypothesis (EDH) proposed that metal accumulation in plants could increase plant resistance to herbivores. However, the over-accumulation of metals in low-accumulators such as woody plants will cause adverse effects on plant health. Thus, the application of EDH on low-accumulators in metal contaminated areas is strongly limited. Since the supplement of exogenous spermidine (Spd) was reported to alleviate metal-induced toxicity in plants while stimulating metal accumulation in plant tissues, we hypothesized that such application will further improve plant resistance to herbivores. In this study, we employed a woody plant species, Populus yunnanensis, to test this hypothesis. We first tested a Spd concentration series applied on plants subjected to soil cadmium (Cd) stress and found that the 1 mM Spd strongly promoted plant growth while stimulated Cd accumulation in plant leaves and roots. We further conducted herbivore bioassays to test the growth performance and feeding preference of two leaf herbivore species and a root herbivore species that fed on plants from different treatments. The results showed that the inhibition effect of Cd stressed-plants on herbivore growth was significantly magnified by the addition of Spd. The growth weight of all the three tested herbivores were negatively correlated with increased Cd concentrations in plant tissues. In addition, the feeding preferences of the two leaf herbivore species were strongly repelled by leaf discs from Cd-treated plants with Spd supplement. The results suggested that the application of exogenous Spd at a certain dose could enhance elemental defense of plants against herbivory.

Exogenous nitrogen enhances poplar resistance to leaf herbivory and pathogen infection after exposure to soil cadmium stress

Elemental defense hypothesis suggests that toxic metals accumulated in plant tissues could enhance plant defense against herbivores and pathogens. Since over-accumulation of metals in plant organs will pose negative effects on plant health, it is necessary to find a way to alleviate metal-induced toxicity in plants while keeping or even improving plant resistance. Exogenous nitrogen (N) application was reported to have such alleviation effect while stimulating metal accumulation in plant tissues. In this study, we examined whether soil N addition in three different doses to a poplar species under cadmium (Cd) stress can simultaneously improve plant growth and resistance to four herbivorous insects and a leaf pathogen. The results showed that N application to Cd-amended soil prominently enhanced plant growth and leaf Cd accumulation. While N addition in three doses all remarkably reduced herbivore growth than control plants, only the highest N dose exerted stronger inhibition than the sole Cd-treated plants. In the paired-choice experiment, plants supplied with the highest N dose showed an enhanced deterrent effect on herbivore preference than plants exposed to sole Cd. Furthermore, plant resistance to the leaf pathogen infection was strongly enhanced as the levels of N addition increased. Leaf sugar and three main defensive chemicals were not affected by N application implied that such enhanced effect of N on plant resistance was due to increased leaf Cd accumulation. Our results suggested that the application of exogenous N over a certain amount could enhance the resistance of Cd-treated plants to leaf herbivory and pathogen infection.

English

This study was carried out to determine the heavy metal accumulation of Juncus rigidus Desfontaines, 1798 from three different regions of the Basrah Province in Southern of Iraq. Specifically, the concentrations of lead, nickel, and cadmium were determined in the roots, culms and leaves of the plant. The results indicated that the highest accumulation of the heavy metal was recorded in lead (Pb) 12.50± 3.58 mg kg-1and then in nickel ( 1 used to the ability of J. rigidus for both phytoextraction and phytostabilization. The anatomical analysis showed that heavy metal accumulation in plant tissues led to a reduction in root and culm thickness; in polluted area it has been found that cortex and intercellular spaces in aerenchyma layers were deceased in size, whereas high pollution levels were observed in vascular bundles, which were smaller, and had increased sclerenchyma, as well as appeared more black or dark color compared to the specimens grown in the control area

Exploring the phytoremediation potential of water hyacinth by FTIR Spectroscopy and ICP-OES for treatment of heavy metal contaminated water

Toxic heavy metal pollution of water is a major environmental problem and the current remediation approaches are not optimal as they are non-eco-friendly and lacking in efficiency. As such phytoremediation, a green remediation technology is recognized as a better approach. In this study, both Fourier Transform Infrared (FTIR) Spectroscopy and Inductive Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) were used to investigate the capability of an aquatic plant, water hyacinth (Eichhornia crassipes) to remove heavy metals of lead, copper, cadmium and arsenic from aqueous solution at concentrations of 2 mg/L and 8 mg/L. Overall, the results showed that the uptake was rapid with the plants removing >80% of all the heavy metals at both concentrations. This uptake was proven by the detection of metal accumulation in plant tissues. Roots proved to be better accumulator than leaves. Maximum bioconcentration factor values indicating that the plant is a hyperaccumulator for lead and a moderate accumulator for the other heavy metals. Ligands such as O–H, C–O, C–C and C–H were found to aid the plant in accumulating heavy metal in its tissues. This study concludes that water hyacinth can be utilized as a phytoremediation agent to clean up heavy metal polluted water.

Combined use of companion planting and PGPR for the assisted phytoextraction of trace metals (Zn, Pb, Cd)

Biomass production and metal accumulation in plant tissue (bioconcentration) are two critical factors limiting the phytoextraction rate. Metal translocation to aboveground organs should be accounted for as the third most important factor, as harvesting of the plant roots is usually economically disadvantageous. These three parameters could be potentially increased with the use of companion planting, a well-known agricultural technique, and inoculation with plant growth–promoting bacteria (PGPB). The aim of the study was to determine whether intercropping and inoculation with endophytic PGPB (Burkholderia phytofirmans PsJNT) can increase the efficiency of phytoextraction of Zn, Pb, and Cd. The study was conducted on Brassica juncea (L.) Czern. “Małopolska” grown in a monoculture or co-planted with Zea mays L. “Codimon” and Medicago sativa L. “Sanditi.” Results show that companion planting and inoculation with rhizobacteria can increase the efficiency of metal phytoextraction, mainly by increasing the yield of dry biomass and the survival rate of plants grown on contaminated soil. We have shown that the simultaneous planting of B. juncea with M. sativa and inoculation with PGPB were the most efficient variants of assisted phytoextraction reaching a recovery of 95% Zn, 90% Cd, and on average about 160% Pb compared with control B. juncea plants grown in monoculture.

Heavy Metal Stress, Signaling, and Tolerance Due to Plant-Associated Microbes: An Overview.

Several anthropogenic activities including mining, modern agricultural practices, and industrialization have long-term detrimental effect on our environment. All these factors lead to increase in heavy metal concentration in soil, water, and air. Soil contamination with heavy metals cause several environmental problems and imparts toxic effect on plant as well as animals. In response to these adverse conditions, plants evolve complex molecular and physiological mechanisms for better adaptability, tolerance, and survival. Nowadays conventional breeding and transgenic technology are being used for development of metal stress resistant varieties which, however, are time consuming and labor intensive. Interestingly the use of microbes as an alternate technology for improving metal tolerance of plants is gaining momentum recently. The use of these beneficial microorganisms is considered as one of the most promising methods for safe crop-management practices. Interaction of plants with soil microorganisms can play a vital role in acclimatizing plants to metalliferous environments, and can thus be explored to improve microbe-assisted metal tolerance. Plant-associated microbes decrease metal accumulation in plant tissues and also help to reduce metal bioavailability in soil through various mechanisms. Nowadays, a novel phytobacterial strategy, i.e., genetically transformed bacteria has been used to increase remediation of heavy metals and stress tolerance in plants. This review takes into account our current state of knowledge of the harmful effects of heavy metal stress, the signaling responses to metal stress, and the role of plant-associated microbes in metal stress tolerance. The review also highlights the challenges and opportunities in this continued area of research on plant–microbe–metal interaction.

BIOLOGICAL FERTILIZER EFFECT OF HEAVY METAL ABSORPTION OF COPPER AND LEAD TO BABY CORN CROP

Absorption of heavy metals by plants is influenced by soil and plant biology. Heavy metals are absorbed into plant tissues through the root, then enter the food chain cycle. Metal will accumulate in body tissues and can have negative impacts for humans, animals, and plants when exceeding the limit of tolerance. Heavy metal accumulation in plant tissues can directly affect plant growth and production, can indirectly affect human health when consuming food contaminated heavy metals. The research objective was to determine the ability of biological fertilizers containing bacteria Azotobacter sp. and Pseudomonas sp., in absorbing heavy metals (Cu and Pb) contained in landfill waste compost, which is used to fertilize crops corn (baby corn). The research methodologyuses a split plot design arranged in Completely Randomized Design with 3 blocks as replicates. The first factor that serves as the main plot of the biological fertilizer, consisting of two cedars, namely: no biological fertilizers and biological fertilizers. The second factor that functions as a sub plot that is a combination of landfill waste compost with NPK fertilizer, consisting of four treatments, namely: Compost waste landfill: no fertilizer NPK = 1: 0; compost waste landfill: NPK = 2/3 : 1/3; compost waste landfill: fertilizer NPK = 1/3: 2/3Without landfill waste compost: NPK = 0: 1. The results showed that administration of biological fertilizers in combination with compost waste landfill is more dominant for increasing and improving soil physical chemistry, such as increasing soil pH, nutrients nitrogen, phosphorus and potassium and cation exchange capacity (KPK). Biological fertilizer containing bacteria Azotobacter sp. and Pseudomonas sp. may reduce the uptake of heavy metals Cu to below the threshold of 2.526 to 15.79 ppm, the maximum content of Cu ranges between 20-100 ppm. The mean content of Pb in tissues and cobs of corn is above the maximum limit of 29.80 to 42.69 ppm, which is still allowed Pb content between 0.1 to 10 ppm. Means baby corn crop is not safe for consumption.key words: compost from the landfill, heavy metals, biological fertilizer

Phytoremediation potential of rhizobacterial isolates from Kans grass (Saccharum spontaneum) of fly ash ponds

Kans grass (Saccharum spontaneum) is a weed species that is frequently found in many heavy metal-enriched waste dumps including fly ash pond sites. In this study, among a collection of phosphate-solubilizing bacterial strains isolated from the rhizosphere of Saccharum spontaneum present in the abandoned ash pond site of Mejia Thermal Power Station (MTPS-DVC), three strains were characterized for their plant growth-promoting abilities. The isolates identified as Bacillus anthracis strain MHR2, Staphylococcus sp. strain MHR3 and Bacillus sp. strain MHR4 had phosphate solubilization indices of 2.86, 2.31 and 2.40 and they produced soluble phosphates of 700, 600 and 640 mg l−1, respectively, in 4 days. In all the PSBs, pH significantly decreased, indicating the production of various organic acids. They showed other plant growth-promoting features like production of ammonia, siderophore, hydrocyanide and IAA. All of them were resistant to multiple heavy metals and antibiotics. Dry and fresh weight and shoot and root lengths of Brassica juncea L. increased in the presence of these isolates in pot cultures. The strains also increased phytoextraction ability of plants by enhancing the metal accumulation in plant tissues. Thus, the isolated indigenous and stress-adapted rhizobacteria may serve as potential biotechnological tool for the successful ecorestoration of various metal-contaminated sites.

Soil Metals and Ectomycorrhizal Fungi Associated with American Chestnut Hybrids as Reclamation Trees on Formerly Coal Mined Land

Hybrid chestnut(Castanea dentata×C. mollissima)has the potential to provide a valuable agroforestry crop on formerly coal mined landscapes. However, the soil interactions of mycorrhizal fungi and buried metals associated with mining are not known. This study examined soil, plant tissue, and ectomycorrhizal (ECM) root colonization on eight-year-old hybrid (BC1F3and BC2F3) and American chestnuts on a reclaimed coal mine in Ohio, USA. Chestnut trees were measured and ECM colonization on roots was quantified. Leaves, flowers, and soil were analyzed for heavy metals. Differences were not detected among tree types regarding metal accumulation in plant tissue or ECM colonization. BC2F3hybrids had greater survival and less cankers than American chestnuts (P= 0.006 and <0.0001). Taller trees were associated with greater ECM root colonization and correlated with an increase in Al uptake (P= 0.02 and 0.01). When comparing tissue, manganese and aluminum were in higher concentrations in leaves than flowers, where copper and selenium were significantly higher in floral tissue (P< 0.05). All trees were flowering at this time meriting further examination in nut tissue. Block effects for selenium and zinc indicate the variability in reclaimed soils requiring further monitoring for possible elemental transfer to nut and wood tissue.

Changes in the heavy metal solubility of two contaminated soils after heavy metals phytoextraction with Noccaea caerulescens

Hyperacumulator plant species, such as Noccaea caerulescens, have been deeply studied due to their use in phytoextraction techniques, although the fate of the metals remaining in the roots at the end of the remediation process is still uncertain. Here, germination and growth, metal accumulation in plant tissues and degradation of roots remaining in the soil after harvest have been studied in two contaminated soils from an area affected by a toxic pyritic sludge spillage. Specially designed pots allowed the separation of the bulk soil and rhizosphere, where heavy metals fractionation in soil was determined at the end of the growing period. High Cd and, especially, Zn concentrations in the aerial parts of the plants were found, although the bio-concentration factors (BCF) were higher for Cd (13–34) than for Zn (2.37–4.34). For both soils, the soluble and exchangeable (CaCl2-extractable) concentrations of Fe and Mn were higher in the rhizosphere than in the bulk soil, while Zn and Cd concentrations were greater in the bulk soil. After plant harvesting, the degradation of heavy metal enriched roots in the soil was studied as well as the effect of this process on soil metal solubility. The soluble concentrations of Cu and Mn were higher in the soils with roots that in the corresponding soils without roots. Nevertheless, the amount of heavy metals released to the soil after root degradation (8–14% of their organic C was decomposed) was rather low (below 0.1μgg−1), showing the feasibility of the use of N. caerulescens for phytoextraction.

Growth and photosynthetic responses of Lemna minor L. exposed to cadmium in combination with zinc or copper.

Metals have a variety of negative outcomes on plants, essential components of any ecosystem. The effects of CdCl2 (5 μmol L-1), ZnCl2 (25 or 50 μmol L-1), and CuCl2 (2.5 or 5 μmol L-1) and combinations of CdCl2 with either ZnCl2 or CuCl2 on the growth, photosynthetic pigments, and photosystem II (PSII) efficiency of duckweed (Lemna minor L.) were investigated. All of the treatments caused growth inhibition and remarkable metal accumulation in plant tissue after 4 and 7 days. In the combined treatments, the accumulation of each metal applied was lesser in comparison to treatments with single metals. After 4 days, all of the treatments generally diminished chlorophyll a content and decreased the maximum quantum yield (Fv/Fm) and effective quantum yield (ΔF/F'm) of PSII. However, after 7 days of exposure to a combination of Cd and Zn, pigment content and PSII activity recovered to control levels. A higher concentration of Cu (5 μmol L-1) as well as Cd in combination with Cu had a prolonged inhibitory effect on photosynthetic features. Our results suggest that growth inhibition was due to the toxic effect of absolute metal quantity in plant tissue. Zn counteracted Cd uptake, as seen from the recovery of pigment content and PSII efficiency in plants exposed for 7 days to the Cd and Zn combination. Cu-induced oxidative stress led to a prolonged inhibitory effect in plants treated both with a higher concentration of Cu (5 μmol L-1) and simultaneously with Cd and Cu. Our findings could contribute to general knowledge on anthropogenic and environmental contaminants that endanger plant communities and significantly disrupt the sensitive balance of an ecosystem by influencing photosynthetic mechanisms.

Heavy metal accumulation in vegetables grown in urban gardens

Urban agriculture is increasingly popular for social and economical benefits. However, edible crops grown in cities can be contaminated by airborne pollutants, thus leading to serious health risks. Therefore, we need a better understanding of contamination risks of urban cultivation to define safe practices. Here we study heavy metal risk in horticultural crops grown in urban gardens of Bologna, Italy. We investigated the effect of proximity to different pollution sources such as roads and railways, and the effect of the growing system used, that is soil versus soilless cultivation. We compared heavy metal concentration in urban and rural crops. We focused on surface deposition and tissue accumulation of pollutants during 3 years. Results show that in the city, crops near the road were polluted by heavy metals, with up to 160 mg per kilogram of dry weight for lettuce and 210 mg/kg for basil. The highest Cd accumulation of up to 1.2 mg/kg was found in rural tomato. Soilless planting systems enabled a reduction of heavy metal accumulation in plant tissue, of up to −71 % for rosemary leaves.

Assessment of arbuscular mycorrhizal fungi status and heavy metal accumulation characteristics of tree species in a lead–zinc mine area: potential applications for phytoremediation

To select suitable tree species associated with arbuscular mycorrhizal fungi (AMF) for phytoremediation of heavy metal (HM) contaminated area, we measured the AMF status and heavy metal accumulation in plant tissues in a lead-zinc mine area, Northwest China. All 15 tree species were colonized by AM fungi in our investigation. The mycorrhizal frequency (F%), mycorrhizal colonization intensity (M%) and spore density (SP) reduced concomitantly with increasing Pb and Zn levels; however, positive correlations were found between arbuscule density (A%) and soil total/DTPA-extractable Pb concentrations. The average concentrations of Pb, Zn, Cu and Cd in plant samples were 168.21, 96.61, 41.06, and 0.79mg/kg, respectively. Populus purdomii Rehd. accumulated the highest concentrations of Zn (432.08mg/kg) and Cu (140.85mg/kg) in its leaves. Considerable amount of Pb (712.37mg/kg) and Cd (3.86mg/kg) were concentrated in the roots of Robinia pseudoacacia Linn. and Populus simonii Carr., respectively. Plants developed different strategies to survive in HM stress environment: translocating more essential metals (Zn and Cu) into the aerial parts, while retaining more toxic heavy metals (Pb and Cd) in the roots to protect the above-ground parts from damage. According to the translocation factor (TF), bioconcentration factor (BCF), growth rate and biomass production, five tree species (Ailanthus altissima (Mill.) Swingle, Cotinus coggygria Scop., P. simonii, P. purdomii, and R. pseudoacacia) were considered to be the most suitable candidates for phytoextraction and/or phytostabilization purposes. Redundancy analysis (RDA) showed that the efficiency of phytoremediation was enhanced by AM symbioses, and soil pH, Pb, Zn, and Cd levels were the main factors influencing the HM accumulation characteristics of plants.