Assessment of edibility and effect of arbuscular mycorrhizal fungi on Solanum melongena L. grown under heavy metal(loid) contaminated soil

Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste

BACKGROUND

This study aimed to investigate the alterations in biochemical and physiological responses of oat plants exposed to antimony (Sb) contamination in soil. Specifically, we evaluated the effectiveness of an arbuscular mycorrhizal fungus (AMF) and olive mill waste (OMW) in mitigating the effects of Sb contamination. The soil was treated with a commercial strain of AMF (Rhizophagus irregularis) and OMW (4% w/w) under two different levels of Sb (0 and 1500 mg kg-1 soil).

RESULTS

The combined treatment (OMW + AMF) enhanced the photosynthetic rate (+ 40%) and chlorophyll a (+ 91%) and chlorophyll b (+ 50%) content under Sb condition, which in turn induced more biomass production (+ 67-78%) compared to the contaminated control plants. More photosynthesis in OMW + AMF-treated plants gives a route for phenylalanine amino acid synthesis (+ 69%), which is used as a precursor for the biosynthesis of secondary metabolites, including flavonoids (+ 110%), polyphenols (+ 26%), and anthocyanins (+ 63%) compared to control plants. More activation of phenylalanine ammonia-lyase (+ 38%) and chalcone synthase (+ 26%) enzymes in OMW + AMF-treated plants under Sb stress indicated the activation of phenylpropanoid pathways in antioxidant metabolites biosynthesis. There was also improved shifting of antioxidant enzyme activities in the ASC/GSH and catalytic pathways in plants in response to OMW + AMF and Sb contamination, remarkably reducing oxidative damage markers.

CONCLUSIONS

While individual applications of OMW and AMF also demonstrated some degree of plant tolerance induction, the combined presence of AMF with OMW supplementation significantly enhanced plant biomass production and adaptability to oxidative stress induced by soil Sb contamination.

Influence of bioaugmented fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora Sw. DC in heavy metal-polluted landfill soil

The research aimed to determine the influence of endophytic fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora in heavy metal-polluted landfill soil. A consortium of 13 fungal isolates as well as Prosopis juliflora Sw. DC was used to decontaminate heavy metal-polluted landfill soil. Enhanced plant growth (biomass and root and shoot lengths) and production of carotenoids, chlorophyll and amino acids L-phenylalanine and L-leucine that are known to enhance growth were found in the treated P. juliflora. Better accumulations of heavy metals were observed in fungi-treated P. juliflora over the untreated one. An upregulated activity of peroxidase, catalase and ascorbate peroxidase was recorded in fungi-treated P. juliflora. Additionally, other metabolites, such as glutathione, 3,5,7,2',5'-pentahydroxyflavone, 5,2'-dihydroxyflavone and 5,7,2',3'-tetrahydroxyflavone, and small peptides, which include Lys Gln Ile, Ser Arg Ala, Asp Arg Gly, Arg Ser Ser, His His Arg, Arg Thr Glu, Thr Arg Asp and Ser Pro Arg, were also detected. These provide defence supports to P. juliflora against toxic metals. Inoculating the plant with the fungi improved its growth, metal accumulation as well as tolerance against heavy metal toxicity. Such a combination can be used as an effective strategy for the bioremediation of metal-polluted soil.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Revealing the effects and mechanisms of arbuscular mycorrhizal fungi on manganese uptake and detoxification in Rhus chinensis

Arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal phytotoxicity and promote plant growth, while the underlying mechanisms of AMF symbiosis with host plants under manganese (Mn) stress remain elusive. A pot experiment was carried out to investigate the plant growth, micro-structure, Mn accumulation, subcellular distribution, chemical forms, and physiological and biochemical response of Rhus chinensis inoculated with Funneliformis mosseae (FM) under different Mn treatments. The results showed that compared with plants without FM, FM-associated plants exhibited higher growth status, photosynthetic pigments, and photosynthesis under Mn stress. FM-associated plants were able to maintain greater integrity in mesophyll structure, higher thickness of leaf, upper epidermis, and lower epidermis under Mn treatment, and promote leaf growth. Mn accumulation in leaves (258.67-2230.50 mg kg-1), stems (132.67-1160.00 mg kg-1), and roots (360.92-2446.04 mg kg-1) of the seedlings inoculated with FM was higher than non-inoculated ones. FM-associated plants exhibited higher osmotic regulating substances and antioxidant enzymes' activities under Mn exposure, suggesting lower Mn toxicity in FM inoculated seedlings, despite the augment in Mn accumulation. After FM inoculation, Mn concentration (151.04-1211.32 mg kg-1) and percentage (64.41-78.55%) enhanced in the cell wall, whilst the transport of Mn to aerial plant organs decreased. Furthermore, FM symbiosis favored the conversion of Mn from high toxic forms (2.17-15.68% in FEthanol, 11.37-24.52% in Fdeionized water) to inactive forms (28.30-38.15% in FNaCl, 18.07-28.59% in FHAc, 4.41-17.99% in FHCl) with low phytotoxicity. Our study offers a theoretical basis for remediation of the FM- R. chinensis symbiotic system in Mn-contaminated environments.

AMF Inoculation Alleviates Molybdenum Toxicity to Maize by Protecting Leaf Performance

The use of arbuscular mycorrhizal fungi (AMF) is a vital strategy for enhancing the phytoremediation of heavy metals. However, the role of AMF under molybdenum (Mo) stress is elusive. A pot culture experiment was conducted to explore the effects of AMF (Claroideoglomus etunicatum and Rhizophagus intraradices) inoculation on the uptake and transport of Mo and the physiological growth of maize plants under different levels of Mo addition (0, 100, 1000, and 2000 mg/kg). AMF inoculation significantly increased the biomass of maize plants, and the mycorrhizal dependency reached 222% at the Mo addition level of 1000 mg/kg. Additionally, AMF inoculation could induce different growth allocation strategies in response to Mo stress. Inoculation significantly reduced Mo transport, and the active accumulation of Mo in the roots reached 80% after inoculation at the high Mo concentration of 2000 mg/kg. In addition to enhancing the net photosynthetic and pigment content, inoculation also increased the biomass by enhancing the uptake of nutrients, including P, K, Zn, and Cu, to resist Mo stress. In conclusion, C. etunicatum and R. intraradices were tolerant to the Mo stress and could alleviate the Mo-induced phytotoxicity by regulating the allocation of Mo in plants and improving photosynthetic leaf pigment contents and the uptake of nutrition. Compared with C. etunicatum, R. intraradices showed a stronger tolerance to Mo, which was manifested by a stronger inhibition of Mo transport and a higher uptake of nutrient elements. Accordingly, AMF show potential for the bioremediation of Mo-polluted soil.

Arbuscular Mycorrhizal Fungi Enhance Biomass Growth, Mineral Content, and Antioxidant Activity in Tomato Plants under Drought Stress

Arbuscular mycorrhizal fungi (AMF) are symbiotically associated with crops. They increase biomass production, nutritional elements, and antioxidant activities in food and vegetable crops grown in soil under stress conditions. The present study focused on the effects of AMF (Acaulospora morrowiae, Paraglomus occultum, Funneliformis mosseae, Rhizophagus clarus, and Rhizophagus intraradices) on biomass growth and yield, contents of chlorophyll and carotenoids, activities of catalase (CAT) and ascorbate peroxidase (APX), and contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and minerals (Na, K, Ca, Mg, and Fe) in Unnayan, LT896, and Minto super tomato (Solanum lycopersicum L.) varieties grown in soil under drought stress (<10% moisture). The results showed that root length and shoot mass in plants treated with R. clarus and P. occultum were significantly higher than those of the control (non-AMF) in Minto super tomato. Compared to the control, the shoot’s dry weight and yield were enhanced by 28% and 20% with AMF-treated tomatoes. The CAT activity in P. occultum-treated plants was statistically higher than that of the control in Unnayan tomatoes. H2O2 content was detected higher in the control than R. clarus-treated LT896 tomatoes. In plants treated with A. morrowiae and R. clarus, APX activity was significantly higher than that of the control in the Unnayan tomatoes. CAT and APX activity increased by 42% and 66% in AMF-treated leaves of tomatoes compared to non-AMF. Treatment with AMF reduced the content of MDA and H2O2 (ROS) in the leaves of tomato plants by 50% and 2% compared to the control, respectively. Potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) of tomato fruits increased by 2%, 13%, 24%, and 37% with AMF treatment compared to the control. These results suggested that biomass growth, yield, photosynthetic pigments, antioxidant enzyme activity, and mineral contents could be enhanced by AMF in food crops grown under drought stress. It is concluded that AMF might be used for the development of AMF-enriched biofertilizers that will improve the nutritional quality of food crops grown under stress conditions.

Effects of Arbuscular Mycorrhizal Fungi on the Growth and Root Cell Ultrastructure of Eucalyptus grandis under Cadmium Stress

Eucalyptus grandis (E. grandis) has been reported to form a symbiosis with arbuscular mycorrhizal fungi (AMF), which plays an important role in improving plant tolerance of heavy metal. However, the mechanism of how AMF intercept and transport cadmium (Cd) at the subcellular level in E. grandis still remains to be researched. In this study, a pot experiment was conducted to investigate the growth performance of E. grandis under Cd stress and Cd absorption resistance of AMF and explored the Cd localization in the root by using transmission electron microscopy and energy dispersive X-ray spectroscopy. The results showed that AMF colonization could enhance plant growth and photosynthetic efficiency of E. grandis and reduce the translocation factor of Cd under Cd stress. After being treated with 50, 150, 300, and 500 μM Cd, the translocation factor of Cd in E. grandis with AMF colonization decreased by 56.41%, 62.89%, 66.67%, and 42.79%, respectively. However, the mycorrhizal efficiency was significant only at low Cd concentrations (50, 150, and 300 μM). Under 500 μM Cd concentration condition, the colonization of AMF in roots decreased, and the alleviating effect of AMF was not significant. Ultrastructural observations showed that Cd is abundant in regular lumps and strips in the cross-section of E. grandis root cell. AMF protected plant cells by retaining Cd in the fungal structure. Our results suggested that AMF alleviated Cd toxicity by regulating plant physiology and altering the distribution of Cd in different cell sites.

Safety assessment and sustainability of consuming eggplant (Solanum melongena L.) grown in wastewater-contaminated agricultural soils

Vegetables cultivated on contaminated agricultural soils are being consumed by the public, and consequently cause serious health concerns due to contaminants' dietary intake. The current study examines the safety and sustainability of eating eggplant (Solanum melongena) by looking into the possibility of heavy metals translocation from polluted soils to the edible sections, as well as the health hazards that come with it. Soil and eggplant samples were taken from three contaminated and other three uncontaminated farms to estimate their chemical constituents and plant growth properties. Based on the pollution load index data, the contaminated soils were highly polluted with Fe, Cu, Pb, and Zn; and relatively polluted with Cr, Mn, Cd, Mn, Co, and V. Under contamination stress, the fresh biomass, dry biomass, and production of eggplant were significantly reduced by 41.2, 44.6, and 52.1%, respectively. Likewise, chlorophyll a and b were significantly reduced from 1.51 to 0.69 mg g⁻¹ and 1.36 to 0.64 mg g⁻¹, respectively. The uncontaminated plant shoots had the highest quantities of N, P, and proteins (1.98, 2.08, and 12.40%, respectively), while the roots of the same plants had the highest K content (44.70 mg kg⁻¹). Because eggplant maintained most tested heavy elements (excluding Zn and Pb) in the root, it is a good candidate for these metals' phytostabilization. However, it had the potential to translocate Mn and Zn to its shoot and Pb, Cr, Mn, and Zn to the edible fruits indicating its possibility to be a phytoextractor and accumulator of these metals. Cd, Cu, Ni, Pb, Mn, and Co quantity in the edible sections of eggplant grown in contaminated soils exceeded the permissible level for normal plants, posing health hazards to adults and children. For safety issues and food sustainability, our investigation strongly recommends avoiding, possibly, the cultivation of eggplant in contaminated agricultural lands due to their toxic effects even in the long run.

Effects of arbuscular mycorrhizal fungi on frond antimony enrichment, morphology, and proteomics in Pteris cretica var. nervosa during antimony phytoremediation

Pteris cretica var. nervosa is a dominant fern species found in antimony (Sb) mining areas, capable of forming symbiosis with arbuscular mycorrhizal fungi (AMF), especially with those members of the Glomus genus. Despite this fern's relevance and the potential contribution of mycorrhizal symbiosis to phytoremediation, the AMF's impact on P. var. nervosa phytoremediation of Sb remains unknown. Here, we exposed P. var. nervosa to different concentrations of Sb for 6 months. Our results showed that Sb reduced shoot biomass, enlarged the root/shoot ratio, and disrupted the fronds' intracellular structure. AMF inoculation, however, was able to moderate these phenotypic changes and increased the accumulation level of Sb in plants. From a proteomics analysis of this plant's fronds, a total of 283 proteins were identified. Notably, those proteins with catalytic function, carbon fixing and ATP metabolic function were highly enriched. K-means clustering demonstrated protein-changing patterns involved in multiple metabolic pathways during exposure to Sb. Further, these patterns can be moderated by AMF inoculation. Pearson correlations were used to assess the plant biomarkers-soil Sb relationships; This revealed a strong correlation between ribosome alteration and the root/shoot ratio when inoculated with AMF, and a positive correlation between photosynthesis proteins and chlorophyll (SPAD value). Our results indicate AMF could moderate the fronds impairment by maintaining the sufficient protein levels for ribosomal functioning, photosynthesis activity and to counter ROS production. We demonstrate the effective use of AMF associated with P. cretica var. nervosa for Sb phytoremediation and the potential of applying proteomics to better understand the mechanism behind this symbiotic plant physiological response.

The intercropping and arbuscular mycorrhizal fungus decrease Cd accumulation in upland rice and improve phytoremediation of Cd-contaminated soil by Sphagneticola calendulacea (L.) Pruski

Little is known about the impact of the combined application of intercropping and arbuscular mycorrhizal fungus (AMF) on the plant growth and Cd accumulation in the two intercropped plants. A greenhouse pot experiment was performed to investigate the effects of intercropping (IC) and AMF-Glomus versiforme (GV) on the growth, photosynthesis, Cd accumulation and antioxidant activities in the two intercropped plants-upland rice and Cd hyperaccumulator Sphagneticola calendulacea (L.) Pruski in the soils added with 5 mg Cd kg^-1. It was found that the GV inoculation and the combined treatment of IC and GV (IC + GV) significantly (p < 0.05) increased the biomasses and the P contents of upland rice and S. calendulacea. In addition, the Cd concentrations and uptakes of plants in IC, GV and IC + GV treatments were significantly (p < 0.05) dropped in upland rice but increased in S. calendulacea compared with the monocropping control, and the compound treatment showed better effect on decreasing Cd accumulation in upland rice (especially grains) and increasing Cd uptake by S. calendulacea compared with the single intercropping or AMF treatment. Moreover, IC, GV and IC + GV treatments significantly (p < 0.05) improved the net photosynthetic rate, stomatal conductance and transpiration rate of the two intercropped plants. Finally, IC, GV and IC + GV treatments all significantly increased the catalase activities and total antioxidant capacities, while decreased the malondialdehyde contents in upland rice and S. calendulacea. The present work could provide a feasible strategy for safe production of upland rice and phytoremediation of Cd contaminated soils.

Arbuscular mycorrhizal fungi, a key symbiosis in the development of quality traits in crop production, alone or combined with plant growth-promoting bacteria

Modern agriculture is currently undergoing rapid changes in the face of the continuing growth of world population and many ensuing environmental challenges. Crop quality is becoming as important as crop yield and can be characterised by several parameters. For fruits and vegetables, quality descriptors can concern production cycle (e.g. conventional or organic farming), organoleptic qualities (e.g. sweet taste, sugar content, acidity) and nutritional qualities (e.g. mineral content, vitamins). For other crops, however, the presence of secondary metabolites such as anthocyanins or certain terpenes in the targeted tissues is of interest as well, especially for their human health properties. All plants are constantly interacting with microorganisms. These microorganisms include arbuscular mycorrhizal fungi as well as certain soil bacteria that provide ecosystem services related to plant growth, nutrition and quality parameters. This review is an update of current research on the single and combined (co-inoculation) use of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria in crop production, with a focus on their positive impacts on crop quality traits (e.g. nutritional value, organoleptic properties). We also highlight the need to dissect mechanisms regulating plant-symbionts and symbiont-symbiont interactions, to develop farming practices and to study a broad range of interactions to optimize the symbiotic potential of root-associated microorganisms.

Effects of decapitated and root-pruned Sedum alfredii on the characterization of dissolved organic matter and enzymatic activity in rhizosphere soil during Cd phytoremediation

Decapitation and root pruning, can impact plant morphological and physiological characteristics, which may determine the efficiency of phytoremediation. However, the effects of decapitated and root-pruned plants on the characterization of dissolved organic matter (DOM) and enzymatic activity, which determine the bioavailability of soil pollutants, have rarely been reported. This study aims to characterize DOM and enzymatic activity in the rhizosphere soil of Sedum alfredii when treated by decapitation and root pruning. Decapitation, slight pruning (10% root cutting), and their combination stimulated S. alfredii to secrete more DOM in the rhizosphere soil compared with the control. Furthermore, the proportions of hydrophilic increased from 42.7% in the control to 57.1% in the decapitation and slight pruning combination. Soil urease, invertase, and neutral phosphatase activities were higher in the rhizosphere soil of decapitated and root-pruned S. alfredii, and the highest values were observed with their combination. DOM from the soils of decapitated and root-pruned S. alfredii had significantly higher Cd extraction ability compared with that of the untreated species. Based on the findings of this study, we suggest that decapitation and root pruning can improve the phytoremediation efficiency of S. alfredii by increasing the bioavailability of Cd in its rhizosphere.

Comparative transcriptome analysis reveals the differential response to cadmium stress of two Pleurotus fungi: Pleurotus cornucopiae and Pleurotus ostreatus

Pleurotus has great potential for heavy metal mycoremediation. Using comparative transcriptome analysis, the response of Pleurotus ostreatus and Pleurotus cornucopiae under Cd contamination was evaluated. P. ostreatus and P. cornucopia accumulated 0.34 and 0.46 mg/g Cd in mycelium, respectively. Cd removal elevated with its concentration elevation, which reached 56.47% and 54.60% for P. ostreatus and P. cornucopia with Cd at 20 mg/L. Low-level Cd (≤ 1 mg/L) had no significant influence on either fungus, while varied response was observed under high-level Cd. 705 differentially expressed genes (DEGs) were identified in P. cornucopia at Cd1 and Cd20, whereas 12,551 DEGs in P. ostreatus. Differentially regulated functional categories and pathways were also identified. ATP-binding cassette transporters were involved in Cd transport in P. cornucopia, whereas the endocytosis and phagosome pathways were more enhanced in P. ostreatus. 26 enzymes including peroxisomal enzymes catalase and superoxide dismutase were upregulated in P. ostreatus, whereas only cytosolic catalase was overexpressed in P. cornucopia, suggesting their different Cd detoxification pathways. Also, the mitogen-activated protein kinase signaling pathway involved in Cd resistance in both species instead of glutathione metabolism, although more active in P. ostreatus. These findings provided new insight into the molecular mechanism of mycoremediation and accumulator screening.

Mycorrhizal fungi and Pseudomonas fluorescens application reduces root-knot nematode (Meloidogyne javanica) infestation in eggplant

Eggplant cultivation is subjected to attacks by numbers of pests and diseases from the nursery stage until harvest. Root-knot nematode (M. javanica) is one of the most significant restrictions in the successful cultivation of eggplant as it damages the crop year-round. One of the most essential classes of plant symbionts is arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB), which significantly impact plant development, feeding, disease tolerance, and resistance to M. javanica. Eggplant seedlings were inoculated with two mycorrhizal fungi, Glomus mosseae (Gm) and Gigaspora gigantea (Gg), together with the phosphate-solubilizing bacteria (PSB) Pseudomonas fluorescens (Pf; ATCC-17400) under the presence of nematodes inoculation of Meloidogyne javanica as 1000 eggs of M. javanica in each pot. Observations were recorded for 9 morphological traits, 6 fruit morphometric traits using Tomato Analyzer (version 4) software program, and 4 fruit biochemical traits. Along with the data recorded for mycorrhization (%), number of galls and reaction to RKN. Plants inoculated with the consortium (Pf + Gm + Gg) performed substantially better for most traits. Furthermore, the eggplant plants treated with consortium developed the highest levels of fruit biochemical content along with the highest level of mycorrhization (68.20%). Except for certain fruit morphometric traits, the treatment containing Pf + Gg outperformed the treatment containing Pf + Gm. Overall, this research showed that AM fungi could be a sustainable solution to the eggplant RKN problem.

Microbial communities in the rhizosphere of different willow genotypes affect phytoremediation potential in Cd contaminated soil

Plant-associated microorganisms play an important role in controlling heavy metal uptake and accumulation in aerial parts. The microbial community and its interaction with Cd accumulation by willow were assessed to explore the association of phytoextraction efficiency and rhizospheric microbial populations. Therefore, the rhizosphere microbial compositions of three willow genotypes grown in two Cd polluted sites were investigated, focusing on their interactions with phytoremediation potential. Principal coordinate analysis revealed a significant effect of genotype on the rhizosphere microbial communities. Distinct beneficial microorganisms, such as plant growth promoting bacteria (PGPB) and mycorrhizal fungi, were assembled in the rhizosphere of different willow genotypes. Linear mixed models showed that the relative abundance of PGPB was positively associated (p < 0.01) with Cd accumulation, since these microbes significantly increased willow growth. The higher abundance of arbuscular mycorrhizal fungi in the rhizosphere of Salix × aureo-pendula CL 'J1011' at the Kejing site, showed a negative correlation with the Cd content, but a positive correlation with biomass. Conversely, mycorrhizal fungi, were more abundant in the rhizosphere of S. × jiangsuensis CL. 'J2345' and positively correlated with the Cd content in willow tissues. This study provides new insights into the distinctive microbial communities in rhizosphere of different willow genotypes, which may be consistent with the phytoremediation potential.

Insights into nanomycoremediation: Secretomics and mycogenic biopolymer nanocomposites for heavy metal detoxification

Our environment thrives on the subtle balance achieved by the forever cyclical nature of building and rebuilding life through natural processes. Fungi, being the evident armor of bioremediation, is the indispensable element of the soil food web, contribute to be the nature's most dynamic arsenal with non-specific enzymes like peroxidase (POX), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), non-enzymatic compounds like thiol (-SH) groups and non-protein compounds such as glutathione (GSH) and metallothionein (MT). Recently, the area of nanomycoremediation has been gaining momentum as a powerful tool for environmental clean-up strategies with its ability to detoxify heavy metals with its unique characteristics to adapt mechanisms such as biosorption, bioconversion, and biodegradation to harmless end products. The insight into the elaborate secretomic processes provides us with huge opportunities for creating a magnificent living bioremediation apparatus. This review discusses the scope and recent advances in the lesser understood area, nanomycoremediation, the state-of-the-art, innovative, cost-effective and promising tool for detoxification of heavy metal pollutants and focuses on the metabolic capabilities and secretomics with nanobiotechnological interventions.

Mycorrhizal stress alleviation in Senecio bonariensis Hook & Arn growing in urban polluted soils

Loss of biodiversity and accumulation of contaminants in urban soils and water bodies cause serious issues in metropolitan areas. The Matanza-Riachuelo river basin (metropolitan area of Buenos Aires, Argentina) is one of the most environmentally degraded regions in the world. Senecio bonariensis Hook & Arn (Asteraceae) grows in the periodically flooded soils of this wetland. This plant concentrates potentially toxic trace elements (PTEs) in its tissues and establishes symbiosis with arbuscular mycorrhizal (AM) fungi that collaborate with PTE phytostabilization in soils. The objective of this work was to evaluate tolerance and stress alleviation of AM-colonized S. bonariensis when transplanting and exposing to highly polluted environmental conditions of the river basin. Plants were initially inoculated with different AM strains and maintained in greenhouse conditions. After 6 mo, they were transplanted to the field. These plants showed a more equal distribution between shoot and root biomass production in comparison to field spontaneous S. bonaerensis plants. Plants in earlier contact with native soil inoculum showed positive correlation with phosphorus content and a significant increase of vesicle frequency. Plants belatedly contacted with native inoculum in the field (control) showed a higher catalase level that was positively correlated with the total colonization frequency and chlorophyll content. The ability to establish symbiosis with Rhizophagus intraradices (strain GC3), commonly used in the formulation of biofertilizers, was also analyzed. Plants inoculated with GC3 at the beginning of the assay showed lower colonization and were less efficient in the field. The preservation of spontaneous native plants with ornamental value and bioaugmentation of their associated microbiome can contribute to the stabilization of contaminants in soils.

Effects of arbuscular mycorrhizal fungi on the growth and toxic element uptake of Phragmites australis (Cav.) Trin. ex Steud under zinc/cadmium stress

Arbuscular mycorrhizal fungi (AMF) play an important role in improving plant tolerance and accumulation of zinc (Zn) and cadmium (Cd). The growth, physiology and absorption of elements and transport in Phragmites australis (P. australis) were investigated under Zn and Cd stress to identify the transport mechanisms of toxic trace elements (TE) under the influence of AMF. Thus, AMF were observed to alleviate the toxic effects of Zn and Cd on P. australis by increasing plant biomass and through different regulatory patterns under different TE concentrations. The activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased under Zn stress, and the activities of SOD, catalase (CAT), peroxidase (POD), and APX significantly increased under high concentrations of Cd. AMF differ in their strategies of regulating the transport of different metals under TE stress. Under Zn stress, the concentration of Zn in P. australis decreased by 10-57%, and the effect on Zn translocation factor (TF_Zn) was concentration-dependent. AMF increased the TF_Zn under low concentration stress, but decreased under high concentration stress. Under Cd stress, the concentration of Cd increased by as much as 17-40%, and the TF_Cd decreased. AMF were also found to change the interaction of Zn×Cd. In the absence of AMF, Cd exposure decreased the Zn concentrations in P. australis at Zn_100 mg/L and Zn_300 mg/L, while it increased the contents of Zn at Zn_700 mg/L. The opposite trend was observed following treatment with AMF. However, regardless of the concentration of Cd, the addition of Zn decreased the concentration of Cd in both treatments in both the presence and absence of AMF. Under different TE stress conditions, the regulation of metal elements by AMF in host plants does not follow a single strategy but a trade-off between different trends of transportations. The findings of our study are important for applying AMF-P. australis systems in the phytoremediation of Zn-Cd co-contaminated ecosystems.

Arbuscular mycorrhizal fungi-induced mitigation of heavy metal phytotoxicity in metal contaminated soils: A critical review

The heavy metal pollution is a worldwide problem and has received a serious concern for the ecosystem and human health. In the last decade, remediation of the agricultural polluted soil has attracted great attention. Phytoremediation is one of the technologies that effectively alleviate heavy metal toxicity, however, this technique is limited to many factors contributing to low plant growth rate and nature of metal toxicities. Arbuscular mycorrhizal fungi (AMF) assisted alleviation of heavy metal phytotoxicity is a cost-effective and environment-friendly strategy. AMF have a symbiotic relationship with the host plant. The bidirectional exchange of resources is a hallmark and also a functional necessity in mycorrhizal symbiosis. During the last few years, a significant progress in both physiological and molecular mechanisms regarding roles of AMF in the alleviation of heavy metals (HMs) toxicities in plants, acquisition of nutrients, and improving plant performance under toxic conditions of HMs has been well studied. This review summarized the current knowledge regarding AMF assisted remediation of heavy metals and some of the strategies used by mycorrhizal fungi to cope with stressful environments. Moreover, this review provides the information of both molecular and physiological responses of mycorrhizal plants as well as AMF to heavy metal stress which could be helpful for exploring new insight into the mechanisms of HMs remediation by utilizing AMF.

The effect of arbuscular mycorrhizal fungi and biochar on the growth and Cd/Pb accumulation in Zea mays

A greenhouse pot experiment was conducted to assess the effects of biochar (BC) and arbuscular mycorrhizal fungus (AMF)-Funneliformis mosseae (Fm), Glomus versiforme (Gv) and Rhizophagus intraradices (Ri) on the plant growth and Cd/Pb accumulation by corn grown in the soils artificially contaminated with 5 mg Cd and 300 mg Pb kg^-1 soil. The single AMF inoculation and combined usage of AMF and BC evidently improved the P contents of maize. Furthermore, the combined use of AMF and BC produced pronounced positive effect on corn growth, and the shoot biomass in Gv + BC group was 9.85-fold higher than that of the control. Meanwhile, the single BC addition and combined utilization of AMF and BC significantly reduced Cd and Pb concentrations in maize, and the greater reduces were found in the combined utilization, and the lowest Cd concentration of shoot was appeared in Gv + BC group. The single BC addition and combined application of AMF and BC significantly increased soil pH, and reduced soil diethylenetriaminepentaacetic acid (DTPA)-extractable Cd/Pb. This study demonstrated a synergistic effect between AMF (Gv, Fm, Ri) and BC on improving maize growth and decreasing Cd/Pb accumulation in maize, and the combined use of Gv and BC brought the most pronounced effect, which could provide a feasible strategy for safe production of maize from Cd/Pb-polluted soils.

Assessment of sunflower germplasm for phytoremediation of lead-polluted soil and production of seed oil and seed meal for human and animal consumption

Phytoremediation is a valuable technology for mitigating soil contamination in agricultural lands, but phytoremediation without economic revenue is unfeasible for land owners and farmers. The use of crops with high biomass and bioenergy for phytoremediation is a unique strategy to derive supplementary benefits along with remediation activities. Sunflower (Helianthus annuus L.) is a high-biomass crop that can be used for the phytoremediation of polluted lands with additional advantages (biomass and oil). In this study, 40 germplasms of sunflower were screened in field conditions for phytoremediation with the possibility for oil and meal production. The study was carried out to the physiological maturity stage. All studied germplasms mopped up substantial concentrations of Pb, with maximum amounts in shoot > root > seed respectively. The phytoextraction efficiency of the germplasm was assessed in terms of the Transfer factor (TF), Metal removal efficiency (MRE) and Metal extraction ratio (MER). Among all assessed criteria, GP.8585 was found to be most appropriate for restoring moderately Pb-contaminated soil accompanied with providing high biomass and high yield production. The Pb content in the oil of GP.8585 was below the Food safety standard of China, with 59.5% oleic acid and 32.1% linoleic acid. Moreover, amino acid analysis in meal illustrated significant differences among essential and non-essential amino acids. Glutamic acid was found in the highest percentage (22.4%), whereas cysteine in the lowest percentage (1.3%). Therefore, its efficient phytoextraction ability and good quality edible oil and meal production makes GP.8585 the most convenient sunflower germplasm for phytoremediation of moderately Pb-contaminated soil, with fringe benefits to farmers and landowners.

Enhanced phytoremediation of uranium-contaminated soils by arbuscular mycorrhiza and rhizobium

Uranium phytoextraction is a promising technology, however, facing difficult that limited plant biomass due to nutrient deficiency in the contaminated sites. The aim of this study is to evaluate the potential of a symbiotic associations of a legume Sesbania rostrata, rhizobia and arbuscular mycorrhiza fungi (AMF) for reclamation of uranium contaminated soils. Results showed AMF and rhizobia had a mutual beneficial relations in the triple symbiosis, which significantly increased plant biomass and uranium accumulation in S. rostrata plant. The highest uranium removal rates was observed in plant-AMF-rhizobia treated soils, in which 50.5-73.2% had been extracted, whereas 7.2-23.3% had been extracted in plant-treated soil. Also, the S. rostrata phytochelatin synthase (PCS) genes expression were increased in AMF and rhizobia plants compared with the plants. Meantime, content of malic acid, succinic acid and citric acid were elevated in S. rostrata root exudates of AMF and rhizobia inoculated plants. The facts suggest that the mutual interactions in the triple symbiosis help to improve phytoremediation efficiency of uranium by S. rostrata.

The concentration data of heavy metals in vegetables of Guilan province, Iran

Food safety is a major problem currently facing the world and food consumption has been identified as the major pathway for human exposure to hazardous pollutants such as heavy metals. These datasets include the concentration of heavy metals like Cd, Pb, Cu, Ba, Co and Sn in selected vegetables in Guilan province and estimate daily intake of metals. The results of this dataset showed that the average concentration of heavy metals including Cd, Pb, Cu, Ba, Co and Sn in total vegetables were 0.55, 1.098, 4.095, 5.98, 0.69, and 0.2 mg/kg, respectively. The mint showed higher levels of Pb, Cu and Co contamination compared to other vegetables. The estimated daily intakes of Cd, Pb, Cu, Ba, Co and Sn for children were 0.311, 0.622, 2.320, 3.388, 0.391, 0.119 µg/day, whereas for adults were 0.182, 0.363, 1.357, 1.98, 0.228, 0.069 mg/kg, respectively. The present data highlights that both adults and children consuming vegetables ingest significant amount of these metals.