Transformation and Immobilization of Chromium by Arbuscular Mycorrhizal Fungi as Revealed by SEM-EDS, TEM-EDS, and XAFS

Diversity of Arbuscular Mycorrhizal Fungi of the Rhizosphere of Lycium barbarum L. from Four Main Producing Areas in Northwest China and Their Effect on Plant Growth

Arbuscular mycorrhizal fungi (AMF) can help plants absorb more mineral nutrients after they colonize plant roots, and the mycelia harmonize the soil structure and physical and chemical properties by secreting compounds. AMF species co-evolve with their habitat's geographic conditions and hosts; this gradually causes differences in the AMF species. By using Melzer's reagent to analyze the morphology and using Illumina Miseq sequencing technology to perform the molecular identification of AMF communities among the four typical L. barbarum planting areas (Zhongning, Guyuan, Jinghe, and Dulan) investigated, the variety of L. barbarum roots and rhizosphere AMF communities was greater in the Zhongning area, and every region additionally had endemic species. The successfully amplified AMF was re-applied to the L. barbarum seedlings. We found that the total dry weight and accumulation of potassium increased significantly (p < 0.05), and the root volume and number of root branches were significantly higher in the plants that were inoculated with Paraglomus VTX00375 in the pot experiment, indicating that AMF improves root development and promotes plant growth. We have investigated AMF germplasm species in four regions, and we are committed to the development of native AMF resources. The multiplication and application of AMF will be conducive to realizing the potential role of biology in the maintenance of agroecology.

Arbuscular Mycorrhizal Fungus Alleviates Charged Nanoplastic Stress in Host Plants via Enhanced Defense-Related Gene Expressions and Hyphal Capture

Contamination of small-sized plastics is recognized as a factor of global change. Nanoplastics (NPs) can readily enter organisms and pose significant ecological risks. Arbuscular mycorrhizal (AM) fungi are the most ubiquitous and impactful plant symbiotic fungi, regulating essential ecological functions. Here, we first found that an AM fungus, Rhizophagus irregularis, increased lettuce shoot biomass by 25-100% when exposed to positively and negatively charged NPs vs control, although it did not increase that grown without NPs. The stress alleviation was attributed to the upregulation of gene expressions involving phytohormone signaling, cell wall metabolism, and oxidant scavenging. Using a root organ-fungus axenic growth system treated with fluorescence-labeled NPs, we subsequently revealed that the hyphae captured NPs and further delivered them to roots. NPs were observed at the hyphal cell walls, membranes, and spore walls. NPs mediated by the hyphae were localized at the root epidermis, cortex, and stele. Hyphal exudates aggregated positively charged NPs, thereby reducing their uptake due to NP aggregate formation (up to 5000 nm). This work demonstrates the critical roles of AM fungus in regulating NP behaviors and provides a potential strategy for NP risk mitigation in terrestrial ecosystems. Consequent NP-induced ecological impacts due to the affected AM fungi require further attention.

Integrated approaches for heavy metal-contaminated soil remediation: harnessing the potential of Paulownia elongata S. Y. Hu, Oscillatoria sp., arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices), and iron nanoparticles

In recent years, researchers have extensively investigated the remediation of heavy metal-contaminated soil using plants, microorganisms, and iron nanoparticles. The objective of this study was to investigate and compare the individual and simultaneous effects of Paulownia elongata S. Y. Hu, cyanobacteria (Oscillatoria sp.), arbuscular mycorrhizal fungi (AMF) including Glomus mosseae and Glomus intraradices, and zero-valent iron nanoparticles (nZVI) on the remediation of heavy metal-contaminated soil containing chromium (Cr VI and Cr III) and nickel (Ni). The study found significant variations in parameters such as pH (acidity), electrical conductivity (EC), nitrogen (N), phosphorus (P), potassium (K), and organic carbon (OC) among different treatments. The addition of cyanobacteria, AMF, and nZVI influenced these properties, resulting in both increases and decreases compared to the control treatment. The treatment involving a combination of cyanobacteria, AMF, and nZVI (CCAN25) exhibited the highest increase in growth parameters, such as total dry mass, root length, stem diameter, and leaf area, while other treatments showed varied effects on plant growth. Moreover, the CCAN25 treatment demonstrated the highest increase in chlorophyll a, chlorophyll b, and carotenoid levels, whereas other treatments displayed reductions in these pigments compared to the control. Moderate phytoaccumulation of Cr and Ni in P. elongata samples across all treatments was observed, as indicated by the bioconcentration factor and bioaccumulation coefficient values being less than 1.0 for both metals. The findings provide insights into the potential application of these treatments for soil remediation and plant growth enhancement in contaminated environments.

Performance and mechanism of SMX removal by an electrolysis-integrated ecological floating bed at low temperatures: A new perspective of plant activity, iron plaque, and microbial functions

Improvements in plant activity and functional microbial communities are important to ensure the stability and efficiency of pollutant removal measures in cold regions. Although electrochemistry is known to accelerate pollutant degradation, cold stress acclimation of plants and the stability and activity of plant-microbial synergism remain poorly understood. The sulfamethoxazole (SMX) removal, iron plaque morphology, plant activity, microbial community, and function responses were investigated in an electrolysis-integrated ecological floating bed (EFB) at 6 ± 2 ℃. Electrochemistry significantly improved SMX removal and plant activity. Dense and uniform iron plaque was found on root surfaces in L-E-Fe which improved the plant adaptability at low temperatures and provided more adsorption sites for bacteria. The microbial community structure was optimized and the key functional bacteria for SMX degradation (e.g., Actinobacteriota, Pseudomonas) were enriched. Electrochemistry improves the relative abundance of enzymes related to energy metabolism, thereby increasing energy responses to SMX and low temperatures. Notably, electrochemistry improved the expression of target genes (sadB and sadC, especially sadC) involved in SMX degradation. Electrochemistry enhances hydrogen bonding and electrostatic interactions between SMX and sadC, thereby enhancing SMX degradation and transformation. This study provides a deeper understanding of the electrochemical stability of antibiotic degradation at low temperatures.

The role of arbuscular mycorrhizal symbiosis in plant abiotic stress

Arbuscular mycorrhizal fungi (AMF) can penetrate plant root cortical cells, establish a symbiosis with most land plant species, and form branched structures (known as arbuscules) for nutrient exchange. Plants have evolved a complete plant-AMF symbiosis system to sustain their growth and development under various types of abiotic stress. Here, we highlight recent studies of AM symbiosis and the regulation of symbiosis process. The roles of mycorrhizal symbiosis and host plant interactions in enhancing drought resistance, increasing mineral nutrient uptake, regulating hormone synthesis, improving salt resistance, and alleviating heavy metal stress were also discussed. Overall, studies of AM symbiosis and a variety of abiotic stresses will aid applications of AMF in sustainable agriculture and can improve plant production and environmental safety.

Arbuscular mycorrhizal fungi alleviate erosional soil nitrogen loss by regulating nitrogen cycling genes and enzymes in experimental agro-ecosystems

Nutrient losses from agricultural ecosystems are increasingly threatening global environmental and human health. Although arbuscular mycorrhizal (AM) fungi have the potential to regulate soil nitrogen (N) loss by enhancing plant uptake and soil particle immobilization, the microbial mechanism behind such mycorrhizal effect is unknown. Herein, by conducting a simulated erosion experiment, we compared the effects of exogenous AM fungal inoculation (Funneliformis mosseae) on the gene abundances and enzyme activities of N-cycling processes, and associated such effect to N uptake and loss. The experiment was composed of combinations of two AM fungal treatments (control vs. AM fungal inoculation), two crops (maize vs. soybean) and two slopes of the plots (6° vs. 20°). The experimental plots subjected to natural rainfalls to simulate the erosion events. We showed that the effects of AM fungi were greater in the maize soils than in the soybean soils. In the maize soils, AM fungi increased the abundances of N-fixing (+81.1 %) and nitrifying genes (+200.7 %) and N cycling enzyme activity (+22.3 %). In the soybean soils, AM fungi increased the N-fixing gene abundance (+36.9 %) but decreased the abundance of nitrifying genes (-18.9 %). The abundance of N-fixing gene was positively correlated with N uptake but negatively correlated with N loss. Additionally, AM fungi enhanced the effects of mycorrhizal colonization and moisture but decreased the effects of nutrients on soil microbial metrics related to N-cycling processes. Therefore, AM fungal inoculation enhanced N uptake and reduced N loss by increasing N-fixing gene abundance, and that AM fungi should be preferably used for the low N environments or for the ecosystems highly limited by or competing for N.

Integrative application of biochar and arbuscular mycorrhizal fungi for enhanced chromium resistance in Medicago sativa

Soil chromium (Cr) contamination has become an environmental problem of global concern. However, the joint effects of combined utilization of biochar and arbuscular mycorrhizal (AM) fungal inoculum, which are considered as two promising remediation strategies of soil heavy metal pollutions, on plant Cr resistance are still poorly understood. In this study, a two-factor pot experiment was conducted to investigate how biochar and AM fungus Rhizophagus irregularis regulate Medicago sativa growth, physiological trait, nutrient and Cr uptake, relevant gene expressions, soil properties, and Cr speciation, independently or synergistically. The results showed that biochar notably decreased AM colonization, while biochar and AM fungus could simultaneously increase plant dry biomass. The greatest growth promotion was observed in mycorrhizal shoots at the highest biochar level (50 g kg-1 soil) by 91 times. Both biochar application and AM fungal inoculation enhanced plant photosynthesis and P nutrition, but the promoting effects of AM fungus on them were significantly greater than that of biochar. In addition, the combined application of biochar and AM fungus dramatically reduced shoot and root Cr concentrations by up to 92 % and 78 %, respectively, compared to the non-amended treatment. Meanwhile, down-regulated expressions were observed for metal chelating-related genes. Furthermore, Cr translocation from roots to shoots was reduced by both two soil amendments. Transcriptional levels of genes involved in reactive oxygen species and proline metabolisms were also regulated by biochar application and AM fungal colonization, leading to alleviation of Cr phytotoxicity. Furthermore, AM fungal inoculation slightly elevated soil pH but decreased plant-available soil P, which was, by contrast, lifted by biochar addition. The combined application reduced soil acid-extractable Cr concentration by 40 %. This study provides new insights into comprehensively understanding of the mechanisms of biochar and AM fungi combination on improving plant Cr tolerance.

Arbuscular Mycorrhizal Fungi Can Inhibit the Allocation of Microplastics from Crop Roots to Aboveground Edible Parts

Microplastics are emerging pollutants that threaten soil health and food safety. Recently, there has been increasing interest in understanding the behavior of these particles in the rhizosphere, specifically regarding the potential uptake of microplastics into crops. Arbuscular mycorrhizal (AM) fungi are widespread soil fungi, forming symbiotic associations with most terrestrial plants. Therefore, it is essential to investigate if AM fungi could protect crops from microplastics in soil. Here, we grew vegetables (Lactuca sativa) inoculated with/without the AM fungus Rhizophagus irregularis at various levels of poly(methyl methacrylate) (PMMA) soil pollution (0, 0.05, 0.1, 0.2, and 0.4%, mass ratio of the pollutant to soil). Our findings revealed that the proportion of transport of PMMA from roots to shoots decreased significantly in mycorrhizal crops. This reduction occurred because some PMMA particles were immobilized by AM vesicles and intraradical fungal hyphae. However, AM symbiosis did not substantially reduce the uptake of microplastics by crops from soil. Mycorrhizal fungi might enhance the resistance of crops to microplastics through transforming the chemical properties of microplastics, reducing their complexation to crop components, and promoting crop phosphorus nutrition at high microplastic addition levels. Our study is the first report to achieve rapid quantification of microplastics in mycorrhizal crops using microscale combustion calorimetry, demonstrating that AM fungi have the ability to immobilize microplastics. The study allows a deeper insight into microplastic behavior in AM-associated crops and supports the potential application of AM fungi in crop cultivation under microplastic contamination.

Facilitating New Chromium Reducing Microbes to Enhance Hexavalent Chromium Reduction by In Situ Sonoporation-Mediated Gene Transfer in Soils

Chromium (Cr) is a heavy metal with a high toxicity and pathogenicity. Microbial reduction is an effective strategy to remove Cr(VI) at contaminated sites but suffers from the low populations and activities of Cr-reducing microorganisms in soils. This study proposed an in situ sonoporation-mediated gene transfer approach, which improved soil Cr(VI) reduction performance by delivering exogenous Cr-transporter chrA genes and Cr-reducing yieF genes into soil microorganisms with the aid of ultrasound. Besides the increasing populations of Cr-resistant bacteria and elevated copy numbers of chrA and yieF genes after sonoporation-mediated gene transfer, three new Cr-reducing strains were isolated, among which Comamonas aquatica was confirmed to obtain Cr-resistant capability. In addition, sonoporation-mediated gene transfer was the main driving force significantly shaping soil microbial communities owing to the predominance of Cr-resistant microbes. This study pioneered and evidenced that in situ soil sonoporation-mediated gene transfer could effectively deliver functional genes into soil indigenous microbes to facilitate microbial functions for enhanced bioremediation, e.g., Cr-reduction in this study, showing its feasibility as a chemically green and sustainable remediation strategy for heavy metal contaminated sites.

The Role of Lignin in the Compartmentalization of Cadmium in Maize Roots Is Enhanced by Mycorrhiza

In nature, arbuscular mycorrhizal fungi (AMF) play a crucial role in the root systems of plants. They can help enhance the resistance of host plants by improving the compartmentalization of toxic metal contaminants in the cell walls (CWs). However, the functions and responses of various CW subfractions to mycorrhizal colonization under Cd exposure remain unknown. Here we conducted a study to investigate how Cd is stored in the cell walls of maize roots colonized by Funneliformis mosseae. Our findings indicate that inoculating the roots with AMF significantly lowers the amount of Cd in the maize shoots (63.6 ± 6.54 mg kg-1 vs. 45.3 ± 2.19 mg kg-1, p < 0.05) by retaining more Cd in the mycorrhized roots (224.0 ± 17.13 mg kg-1 vs. 289.5 ± 8.75 mg kg-1, p < 0.01). This reduces the adverse effects of excessive Cd on the maize plant. Additional research on the subcellular distribution of Cd showed that AMF colonization significantly improves the compartmentalization of 88.2% of Cd in the cell walls of maize roots, compared to the 80.8% of Cd associated with cell walls in the non-mycorrhizal controls. We observed that the presence of AMF did not increase the amount of Cd in pectin, a primary binding site for cell walls; however, it significantly enhanced the content of lignin and the proportion of Cd in the total root cell walls. This finding is consistent with the increased activity of lignin-related enzymes, such as PAL, 4CL, and laccase, which were also positively impacted by mycorrhizal colonization. Fourier transform infrared spectroscopy (FTIR) results revealed that AMF increased the number and types of functional groups, including -OH/-NH and carboxylate, which chelate Cd in the lignin. Our research shows that AMF can improve the ability of maize plants to tolerate Cd by reducing the amount of Cd transferred from the roots to the shoots. This is achieved by increasing the amount of lignin in the cell walls, which binds with Cd and prevents it from moving through the plant. This is accomplished by activating enzymes related to lignin synthesis and increasing the exposure of Cd-binding functional groups of lignin. However, more direct evidence on the immobilization of Cd in the mycorrhiza-altered cell wall subfractions is needed.

Cr(VI) Reduction and Fe(II) Regeneration by Penicillium oxalicum SL2-Enhanced Nanoscale Zero-Valent Iron

Nanoscale zero-valent iron (nZVI) faces significant challenges in Cr(VI) remediation through aggregation and passivation. This study identified a Cr(VI)-resistant filamentous fungus (Penicillium oxalicum SL2) for nZVI activation and elucidated the synergistic mechanism in chromium remediation. P. oxalicum SL2 and nZVI synergistically and effectively removed Cr(VI), mainly by extracellular nonenzymatic reduction (89.1%). P. oxalicum SL2 exhibited marked iron precipitate solubilization and Fe(II) regeneration capabilities. The existence of the Fe(II)-Cr(V)-oxalate complex (HCrFeC₄O₉) indicated that in addition to directly reducing Cr(VI), iron ions generated by nZVI stimulated Cr(VI) reduction by organic acids secreted by P. oxalicum SL2. RNA sequencing and bioinformatics analysis revealed that P. oxalicum SL2 inhibited phosphate transport channels to suppress Cr(VI) transport, facilitated iron and siderophore transport to store Fe, activated the glyoxylate cycle to survive harsh environments, and enhanced organic acid and riboflavin secretion to reduce Cr(VI). Cr(VI) exposure also stimulated the antioxidative system, promoting catalase activity and maintaining the intracellular thiol/disulfide balance. Cr(VI)/Fe(III) reductases played crucial roles in the intracellular reduction of chromium and iron, while nZVI decreased cellular oxidative stress and alleviated Cr(VI) toxicity to P. oxalicum SL2. Overall, the P. oxalicum SL2-nZVI synergistic system is a promising approach for regenerating Fe(II) while reducing Cr(VI).

Arbuscular mycorrhizal fungi-induced tolerance to chromium stress in plants

Chromium (Cr) is one of the toxic elements that harms all forms of life, including plants. Industrial discharges and mining largely contribute to Cr release into the soil environment. Excessive Cr pollution in arable land significantly reduces the yield and quality of important agricultural crops. Therefore, remediation of polluted soil is imperative not only for agricultural sustainability but also for food safety. Arbuscular mycorrhizal fungi (AMF) are widespread soil-borne endophytic fungi that form mutualistic relationships with the vast majority of land plants. In mycorrhizal symbiosis, AMF are largely dependent on the host plant-supplied carbohydrates and lipids, in return, AMF aid the host plants in acquiring water and mineral nutrients, especially phosphorus, nitrogen and sulfur from distant soils, and this distinguishing feature of the two-way exchange of resources is a functional requirement for such mutualism and ecosystem services. In addition to supplying nutrients and water to plants, the AMF symbiosis enhances plant resilience to biotic and abiotic stresses including Cr stress. Studies have revealed vital physiological and molecular mechanisms by which AMF alleviate Cr phytotoxicity and aid plants in nutrient acquisition under Cr stress. Notably, plant Cr tolerance is enhanced by both the direct effects of AMF on Cr stabilization and transformation, and the indirect effects of AMF symbiosis on plant nutrient uptake and physiological regulation. In this article, we summarized the research progress on AMF and associated mechanisms of Cr tolerance in plants. In addition, we reviewed the present understanding of AMF-assisted Cr remediation. Since AMF symbiosis can enhance plant resilience to Cr pollution, AMF may have promising prospects in agricultural production, bioremediation, and ecological restoration in Cr-polluted soils.

The function and community structure of arbuscular mycorrhizal fungi in ecological floating beds used for remediation of Pb contaminated wastewater

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to be ubiquitous in aquatic ecosystems. However, their distributions and ecological functions are rarely studied. To date, a few studies have combined sewage treatment facilities with AMF to improve removal efficiency, but appropriate and highly tolerant AMF strains have not been explored, and the purification mechanisms remain unclear. In this study, three ecological floating-bed (EFB) installations inoculated with different AMF inocula (mine AMF inoculum, commercial AMF inoculum and non-AMF inoculated) were constructed to investigate their removal efficiency for Pb-contaminated wastewater. The AMF community structure shifts in the roots of Canna indica inhabiting EFBs during the three phases (pot culture phase, hydroponic phase and hydroponic phase with Pb stress) were tracked utilizing quantitative real-time polymerase chain reaction and Illumina sequencing techniques. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to detect the Pb location in mycorrhizal structures. The results showed that AMF could promote host plant growth and enhance the Pb removal efficiency of the EFBs. The higher the AMF abundance, the better the effect of the AMF on Pb purification by EFBs. Both flooding and Pb stress decreased the AMF diversity but did not significantly inhibit the abundance. The three inoculation treatments showed different community compositions with different dominant AMF taxa in different phases, and an uncultured Paraglomus species (Paraglomus sp. LC516188.1) was found to be the most dominant (99.65 %) AMF in the hydroponic phase with Pb stress. The TEM and EDS analysis results showed that the Paraglomus sp. could accumulate Pb in plant roots through their fungal structures (intercellular mycelium, intracellular mycelium, etc.), which alleviated the toxic effect of Pb on plant cells and limited Pb translocation. The new findings provide a theoretical basis for the application of AMF in plant-based bioremediation of wastewater and polluted waterbodies.

Influence of arbuscular mycorrhizal fungi on mercury accumulation in rice (Oryza sativa L.): From enriched isotope tracing perspective

The microorganisms that co-exist between soil and rice systems in heavy metal-contaminated soil environments play important roles in the heavy metal pollution states of rice, as well as in the growth of the rice itself. In this study, in order to further examine the effects of soil microorganisms on the mercury (Hg) uptake of rice plants and determine potential soil phytoremediation agents, an enriched ¹⁹⁹Hg isotope was spiked in a series of pot experiments to trace the absorption and migration of Hg and rice growth in the presence of arbuscular mycorrhizal fungi (AMF). It was observed that the AMF inoculations significantly reduced the Hg concentration in the rice. The Hg concentration in rice in the AMF inoculation group was between 52.82% and 96.42% lower than that in the AMF non-inoculation group. It was also interesting to note that the presence of AMF tended to cause Hg (especially methyl-Hg (Me¹⁹⁹Hg)) to migrate and accumulate in the non-edible parts of the rice, such as the stems and leaves. Under the experimental conditions selected in this study, the proportion of Me¹⁹⁹Hg in rice grains decreased from 9.91% to 27.88%. For example, when the exogenous Hg concentration was 0.1 mg/kg, the accumulated methyl-Hg content in the grains of the rice in the AMF inoculation group accounted for only 20.19% of the Me¹⁹⁹Hg content in the rice plants, which was significantly lower than that observed in the AMF non-inoculated group (48.07%). AMF also inhibited the absorption of Hg by rice plants, and the decrease in the Hg concentration levels in rice resulted in significant improvements in growth indices, including biomass and micro-indexes, such as antioxidant enzyme activities. The improvements occurred mainly because the AMF formed symbiotic structures with the roots of rice plants, which fixed Hg in the soil. AMF also reduce the bioavailability of Hg by secreting a series of substances and changing the physicochemical properties of the rhizosphere soil. These findings suggest the possibility of using typical co-existing microorganisms for the remediation of soil heavy metal contamination and provide valuable insights into reducing human Hg exposure through rice consumption.

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.

Influence of arbuscular mycorrhizal fungi on bioaccumulation and bioavailability of As and Cd: A meta-analysis

Increasing industrial activity has led to a growing risk of arsenic (As) and cadmium (Cd) accumulations and biomagnifications in plants and humans. Arbuscular mycorrhizal fungi (AMF) have been extensively studied as a soil amendment owing to their capability to reduce the accumulation of As and Cd in plant tissues. However, a quantitative and data-based consensus has yet to be reached on the effect of AMF on As and Cd bioaccumulation and bioavailability. Here, a meta-analysis was conducted to quantitatively evaluate the impact of AMF using 1430 individual observations from 194 articles. The results showed that AMF inoculation caused a decrease in shoot and root As and Cd accumulation compared to control, and the reduction rates were affected by experimental duration, P fertilizer, AMF species, plant family, plant lifecycle, and soil properties. Intermediate experimental duration (lasting 56-112 days) and no P fertilizer favored AMF to reduce the shoot As and root Cd accumulation. Compared to other plant families, the reduction in As and Cd accumulation in legumes was the greatest, following AMF inoculation. The soils with alkaline, high organic carbon (OC), and low available phosphorus (AP) appeared to be more favorable for AMF to reduce As accumulation in plant tissues, while soils with low AP were more conducive to reducing the Cd accumulation in plant tissues. In addition, AMF inoculation increased pH (1.92%), OC (6.27%), easily-extractable glomalin-related soil protein (EE-GRSP) (29.36%), and total glomalin-related soil protein (T-GRSP) (29.99%), and reduced bioavailable As (0.52%) and Cd (2.35%) in soils compared to control. Overall, the meta-analysis provides valuable guidelines for the optimal use of AMF in different plant-soil systems.

Physio-Biochemical and Transcriptomic Features of Arbuscular Mycorrhizal Fungi Relieving Cadmium Stress in Wheat

Arbuscular mycorrhizal fungi (AMF) can improve plant cadmium (Cd) tolerance, but the tolerance mechanism in wheat is not fully understood. This study aimed to examine the physiological properties and transcriptome changes in wheat inoculated with or without Glomus mosseae (GM) under Cd stress (0, 5, and 10 mg·kg^-1 CdCl₂) to understand its role in wheat Cd tolerance. The results showed that the Cd content in shoots decreased while the Cd accumulation in roots increased under AMF symbiosis compared to the non-inoculation group and that AMF significantly promoted the growth of wheat seedlings and reduced Cd-induced oxidative damage. This alleviative effect of AMF on wheat under Cd stress was mainly attributed to the fact that AMF accelerated the ascorbate-glutathione (AsA-GSH) cycle, promoted the production of GSH and metallothionein (MTs), improved the degradation of methylglyoxal (MG), and induced GRSP (glomalin-related soil protein) secretion. Furthermore, a comparative analysis of the transcriptomes of the symbiotic group and the non-symbiotic group revealed multiple differentially expressed genes (DEGs) in the 'metal ion transport', 'glutathione metabolism', 'cysteine and methionine metabolism', and 'plant hormone signal transduction' terms. The expression changes of these DEGs were basically consistent with the changes in physio-biochemical characteristics. Overall, AMF alleviated Cd stress in wheat mainly by promoting immobilization and sequestration of Cd, reducing ROS production and accelerating their scavenging, in which the rapid metabolism of GSH may play an important role.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Current status of pesticide effects on environment, human health and it's eco-friendly management as bioremediation: A comprehensive review

Pesticides are either natural or chemically synthesized compounds that are used to control a variety of pests. These chemical compounds are used in a variety of sectors like food, forestry, agriculture and aquaculture. Pesticides shows their toxicity into the living systems. The World Health Organization (WHO) categorizes them based on their detrimental effects, emphasizing the relevance of public health. The usage can be minimized to a least level by using them sparingly with a complete grasp of their categorization, which is beneficial to both human health and the environment. In this review, we have discussed pesticides with respect to their global scenarios, such as worldwide distribution and environmental impacts. Major literature focused on potential uses of pesticides, classification according to their properties and toxicity and their adverse effect on natural system (soil and aquatic), water, plants (growth, metabolism, genotypic and phenotypic changes and impact on plants defense system), human health (genetic alteration, cancer, allergies, and asthma), and preserve food products. We have also described eco-friendly management strategies for pesticides as a green solution, including bacterial degradation, myco-remediation, phytoremediation, and microalgae-based bioremediation. The microbes, using catabolic enzymes for degradation of pesticides and clean-up from the environment. This review shows the importance of finding potent microbes, novel genes, and biotechnological applications for pesticide waste management to create a sustainable environment.

Arbuscular Mycorrhizal Fungi Symbiosis to Enhance Plant–Soil Interaction

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with plants; a symbiotic relationship is one in which both partners benefit from each other. Fungi benefit plants by improving uptake of water and nutrients, especially phosphorous, while plants provide 10–20% of their photosynthates to fungus. AMF tend to make associations with 85% of plant families and play a significant role in the sustainability of an ecosystem. Plants’ growth and productivity are negatively affected by various biotic and abiotic stresses. AMF proved to enhance plants’ tolerance against various stresses, such as drought, salinity, high temperature, and heavy metals. There are some obstacles impeding the beneficial formation of AMF communities, such as heavy tillage practices, high fertilizer rates, unchecked pesticide application, and monocultures. Keeping in view the stress-extenuation potential of AMF, the present review sheds light on their role in reducing erosion, nutrient leaching, and tolerance to abiotic stresses. In addition, recent advances in commercial production of AMF are discussed.

Salicylic Acid, a Multifaceted Hormone, Combats Abiotic Stresses in Plants

In recent decades, many new and exciting findings have paved the way to the better understanding of plant responses in various environmental changes. Some major areas are focused on role of phytohormone during abiotic stresses. Salicylic acid (SA) is one such plant hormone that has been implicated in processes not limited to plant growth, development, and responses to environmental stress. This review summarizes the various roles and functions of SA in mitigating abiotic stresses to plants, including heating, chilling, salinity, metal toxicity, drought, ultraviolet radiation, etc. Consistent with its critical roles in plant abiotic tolerance, this review identifies the gaps in the literature with regard to the complex signalling network between SA and reactive oxygen species, ABA, Ca²⁺, and nitric oxide. Furthermore, the molecular mechanisms underlying signalling networks that control development and stress responses in plants and underscore prospects for future research on SA concerning abiotic-stressed plants are also discussed.

Plant-Mycorrhizal Fungi Interactions in Phytoremediation of Geogenic Contaminated Soils

Soil contamination by geogenic contaminants (GCs) represents an imperative environmental problem. Various soil remediation methods have been successfully employed to ameliorate the health risks associated with GCs. Phytoremediation is considered as an eco-friendly and economical approach to revegetate GC-contaminated soils. However, it is a very slow process, as plants take a considerable amount of time to gain biomass. Also, the process is limited only to the depth and surface area of the root. Inoculation of arbuscular mycorrhizal fungi (AMF) with remediating plants has been found to accelerate the phytoremediation process by enhancing plant biomass and their metal accumulation potential while improving the soil physicochemical and biological characteristics. Progress in the field application is hindered by a lack of understanding of complex interactions between host plant and AMF that contribute to metal detoxification/(im)mobilization/accumulation/translocation. Thus, this review is an attempt to reveal the underlying mechanisms of plant-AMF interactions in phytoremediation.

Arbuscular Mycorrhizal Fungi Are an Influential Factor in Improving the Phytoremediation of Arsenic, Cadmium, Lead, and Chromium

The increasing expansion of mines, factories, and agricultural lands has caused many changes and pollution in soils and water of several parts of the world. In recent years, metal(loid)s are one of the most dangerous environmental pollutants, which directly and indirectly enters the food cycle of humans and animals, resulting in irreparable damage to their health and even causing their death. One of the most important missions of ecologists and environmental scientists is to find suitable solutions to reduce metal(loid)s pollution and prevent their spread and penetration in soil and groundwater. In recent years, phytoremediation was considered a cheap and effective solution to reducing metal(loid)s pollution in soil and water. Additionally, the effect of soil microorganisms on increasing phytoremediation was given special attention; therefore, this study attempted to investigate the role of arbuscular mycorrhizal fungus in the phytoremediation system and in reducing contamination by some metal(loid)s in order to put a straightforward path in front of other researchers.

Structure and diversity of fungal communities in long-term copper-contaminated agricultural soil

Copper (Cu) contamination threatens the stability of soil ecosystems. As important moderators of biochemical processes and soil remediation, the fungal community in contaminated soils has attracted much research interest. In this study, soil fungal diversity and community composition under long-term Cu contamination were investigated based on high-throughput sequencing. The co-occurrence networks were also constructed to display the co-occurrence patterns of the soil fungal community. The results showed that the richness and Chao1 index both significantly increased at 50 mg kg^-1 Cu and then significantly decreased at 1600 and 3200 mg kg^-1 Cu. Soil fungal diversity was significantly and positively correlated with plant dry weight. Specific tolerant taxa under different Cu contamination gradients were illustrated by linear discriminant analysis effect size (LEfSe). Soil Cu concentration and shoot dry weight were the strongest driving factors influencing fungal composition. The relative abundance of arbuscular mycorrhizal fungi increased first and then declined along with elevating Cu concentrations via FUNGuild analysis. The interactions among fungi were enhanced under light and moderate Cu contamination but weakened under heavy Cu contamination by random matrix theory (RMT)-based molecular ecological network analysis. Penicillium, identified as a keystone taxon in Cu-contaminated soils, had the function of removing heavy metals and detoxification, which might be vital to trigger the resistance of the fungal community to Cu contamination. The results may facilitate the identification of Cu pollution indicators and the development of in situ bioremediation technology for contaminated cultivated fields.

Potential use of arbuscular mycorrhizal fungi for simultaneous mitigation of arsenic and cadmium accumulation in rice

Rice polluted by metal(loid)s, especially arsenic (As) and cadmium (Cd), imposes serious health risks. Numerous studies have demonstrated that the obligate plant symbionts arbuscular mycorrhizal fungi (AMF) can reduce As and Cd concentrations in rice. The behaviours of metal(loid)s in the soil-rice-AMF system are of significant interest for scientists in the fields of plant biology, microbiology, agriculture, and environmental science. We review the mechanisms of As and Cd accumulation in rice with and without the involvement of AMF. In the context of the soil-rice-AMF system, we assess and discuss the role of AMF in affecting soil ion mobility, chemical forms, transport pathways (including the symplast and apoplast), and genotype variation. A potential strategy for AMF application in rice fields is considered, followed by future research directions to improve theoretical understanding and encourage field application.

Assessment of hexavalent chromium (VI) biosorption competence of indigenous Aspergillus tubingensis AF3 isolated from bauxite mine tailing

The intention of this research was to find the most eminent metal tolerant and absorbing autochthonous fungal species from the waste dump of a bauxite mine. Out of the 4 (BI-1, BI-II, BI-III, and BI-IV) predominant isolates, BI-II had an excellent metal tolerance potential against most of the metals in the subsequent order: Cr(VI) (1500), Cu(II) (600), Pb(II) (500), and Zn(II) (500-1500 μg mL^-1). BI-II had shown tolerance to Cr(VI) up to 1500 mg L^-1. The excellent metal tolerant isolate was characterized and identified as Aspergillus tubingensis AF3 through 18S rRNA sequencing method and submitted to GenBank and received an accession number (MN901243). A. tubingensis AF3 had the efficiency to absorb Cr(VI) and Cu(II) at <70 & 46.3% respectively under the standard growth conditions. Under the optimized conditions (25 °C, pH 7.0, 0.5% of dextrose, and 12 days of incubation), A. tubingensis AF3 absorbed 74.48% of Cr(VI) in 12 days (reduction occurred as 822.3, 719.13, 296.66, and 255.2 mg L^-1 of Cr(VI) on the 3^rd, the 6^th, the 9^th and the 12^th day, respectively). The adsorbed metal was sequestered in the mycelia of the fungus in a precipitated form; it was confirmed by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray analysis (EDX) analyses. The possible biosorption mechanisms were analyzed by Fourier-Transform Infrared Spectroscopy (FTIR) analysis, the results showed the presence of N-H primary amines (1649.98 cm^-1) and Alkanes (914.30 cm^-1) in the cell wall of the fungus, while being treated with Cr(VI) they supported and enhanced the Cr(VI) absorption. The entire results concluded that the biomass of A. tubingensis AF3 had the potential to absorb a high concentration of Cr(VI).

Mycoremediation of heavy metals: processes, mechanisms, and affecting factors

Industrial processes and mining of coal and metal ores are generating a number of threats by polluting natural water bodies. Contamination of heavy metals (HMs) in water and soil is the most serious problem caused by industrial and mining processes and other anthropogenic activities. The available literature suggests that existing conventional technologies are costly and generated hazardous waste that necessitates disposal. So, there is a need for cheap and green approaches for the treatment of such contaminated wastewater. Bioremediation is considered a sustainable way where fungi seem to be good bioremediation agents to treat HM-polluted wastewater. Fungi have high adsorption and accumulation capacity of HMs and can be potentially utilized. The most important biomechanisms which are involved in HM tolerance and removal by fungi are bioaccumulation, bioadsorption, biosynthesis, biomineralisation, bioreduction, bio-oxidation, extracellular precipitation, intracellular precipitation, surface sorption, etc. which vary from species to species. However, the time, pH, temperature, concentration of HMs, the dose of fungal biomass, and shaking rate are the most influencing factors that affect the bioremediation of HMs and vary with characteristics of the fungi and nature of the HMs. In this review, we have discussed the application of fungi, involved tolerance and removal strategies in fungi, and factors affecting the removal of HMs.

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.

Response of Cyperus involucratus to sulfamethoxazole and ofloxacin-contaminated environments: Growth physiology, transportation, and microbial community

Plant-microbe is a complementary coupling system for antibiotics removing in constructed wetlands (CWs), but how plant and rhizosphere microbiomes respond to antibiotics exposure and the occurrence of ARGs in this microenvironment have seldom been researched. Thus, the response of the plant-microbe coupling system to different levels of antibiotics (sulfamethoxazole (SMZ) and ofloxacin (OFL)) was investigated. The results showed that two antibiotic stressors have hormetic effects on plant growth, physiology, and microbial community evolution, and the antibiotic toxic effects presented as SMZ + OFL > SMZ > OFL. Antibiotic accumulation in the plants was in the order of roots > stems > leaves. Notably, the root attachments affected antibiotic transportation. The accumulation of antibiotics in the under-ground parts affected the rhizosphere microbial community structure, and the microorganisms were more sensitive to SMZ + OFL than the plants, with inflection points of 0.5 mg L^-1 and 1 mg L^-1, respectively. Pseudomonas was highly resistant to antibiotics, while Acidovorax and Devosia may play a role in antibiotic degradation. Correlation analysis and network analysis showed that antibiotic enrichment and the bacterial community contributed significantly to the abundance of antibiotic-resistant genes (ARGs), further revealing the co-occurrence of int1, ARGs, and the potential bacterial hosts.

Interaction of ZnO nanoparticle and AM fungi mitigates Pb toxicity in wheat by upregulating antioxidants and restricted uptake of Pb

The study aims at investigating the efficacy of individual as well as combined application of AM fungi (Glomus macrocarpum) and ZnO nanoparticles on the uptake of lead and its toxicity in wheat (Triticum aestivum L.). The plants were grown in pots with different treatments of AM Fungi, ZnO NP, and Pb. The individual applications of AM fungi (Glomus macrocarpum) and ZnO NPs increased the growth and biochemical attributes of wheat and decreased the Pb uptake under Pb stress. The combined application of AM fungi (Glomus macrocarpum) and ZnO nanoparticles synergistically enhanced the overall growth performance of the plant and significantly reduced the uptake of Pb in wheat grown in Pb spiked soils. The combined application was effective, with 30.66 % increase in plant height, 30.62 % increase in plant fresh weight, 54.26 % increase in plant dry weight, 45.45 % increase in total chlorophyll content, 19.59 % increase in proline content, 26.65 % higher activity of SOD, 15.12 % higher activity of catalase (CAT), 17.69 % increase in H₂O₂ content, 17.69 % increase in lipid peroxidation content, 52.09 % and 58.19 % decrease in Pb concentration in root and shoot of wheat, respectively, grown in Pb spiked soil (100 mg kg^-1 soil). The results indicate that combined application of AM fungi and ZnO nanoparticles can be a promising technique for the utilization of Pb-contaminated soils.

Arbuscular mycorrhiza and Aspergillus terreus inoculation along with compost amendment enhance the phytoremediation of Cr-rich technosol by Solanum lycopersicum under field conditions

Chromium (Cr) contamination is a potential threat to the agricultural soil. Arbuscular mycorrhizal (AM) fungi have potential to remediate the heavy metal polluted soils. It was hypothesized that Cr phytoremediation potentiality of AM fungi could be enhanced in combination with saprophytic filamentous fungi and soil amendment. Tomato plants were raised in Cr polluted technosol amended with compost, inoculated with mixed-culture of AM fungi and Aspergillus terreus. It was found that, triple treatment (soil amendment with compost along with AM fungi and A. terreus inoculation) enhanced biomass production (up to 315%), fruit setting (up to 49%), photosynthetic pigments (up to 214%) and carbohydrate content (up to 400%) whereas reduced the proline (up to 76.5%), catalase (up to 34.2%), peroxidase (up to 58.9%) and root membrane permeability (up to 74.2%). The effect of AM fungi with compost amendment was additive, while it was synergistic with A. terreus. AM fungi enhanced the extraction of Cr from the substrate, but retained in the mycorrhizal root, thereby reduced the translocation into shoot and in fruit, Cr translocation was undetectable. At the end of experiment Cr content in the substrate was significantly decreased (up to 37.9%). Soil amendment with compost along with AM fungi and A. terreus inoculation can be used for reclamation of Cr polluted soils at field scale.

Uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid and perfluorooctane sulfonic acid by wetland plant Alisma orientale

Perfluoroalkyl substances (PFASs) are of particular environmental concern due to their environmental persistence and potential toxicity. Phytoremediation may be used to remove PFASs from wastewater. Here we investigated the uptake mechanism, subcellular distribution, and uptake process of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS) in the wetland plant Alisma orientale by using a series of hydroponic experiments. Active uptake facilitated by water transporters and anion channels was involved in the uptake of PFASs by plant roots. PFOA and PFOS were mainly distributed in the water-soluble fraction (46.2-70.8%) and in cell walls (45.6-58.4%), respectively. The uptake process was proposed as follows: PFOS and PFOA were first distributed in the soluble fraction; a proportion of PFOS and PFOA were adsorbed gradually by the cell wall, and a proportion of PFOS and PFOA in the cell wall passed through the cell wall and plasmalemma and bind with organelles. PFOS and PFOA were transported from the external solution to the vascular bundle of the plant root through both symplastic and apoplastic routes.

Cr(VI) removal by Penicillium oxalicum SL2: Reduction with acidic metabolites and form transformation in the mycelium

Bioremediation of Cr(VI) contamination using microorganisms is a promising method for reducing its environmental risks. The objective of this study was to clarify Cr(VI) removal by Penicillium oxalicum SL2 in terms of indirect Cr(VI) reduction by metabolites, interaction sites, and form transformation of chromium. Strain SL2 could sequentially remove Cr(VI) in the bioreactor. Oxalic acid produced by the fungus contributed to Cr(VI) reduction. Scanning transmissiony X-ray microscop (STXM) analysis suggested strain SL2 could partly reduce Cr(VI) to Cr(III) in the cell. Amine, carboxyl, and phosphate groups were related to Cr(VI) removal. Chromium K-edge X-ray absorption near edge structure (XANES) analysis implied Cr(III)-Cys potentially acted as an intermediate for the formation of chromium oxalate complexes during the process of treatment. This study would support the application of strain SL2 in Cr(VI) bioremediation and expand knowledge on the interaction of chromium with fungus.

Mutual effects of selenium and chromium on their removal by Chlorella vulgaris and associated toxicity

The release of selenium (Se) and chromium (Cr) into the environment from anthropogenic activities has posed a hazard to aquatic ecosystems. In this study, we used Chlorella vulgaris for Se/Cr bioremediation and evaluated their mutual effects on the removal efficiency. Our results found C. vulgaris highly effective in removing selenite-Se(IV) (49.5 ± 1.9%), selenate-Se(VI) (93.0 ± 0.5%), chromic nitrate-Cr(III) (89.0 ± 3.2%) and dichromate-Cr(VI) (88.1 ± 1.3%) over a 72 h period. Cr(VI) significantly impeded Se removal, particularly for selenate, due to competition between both for algal uptake, whereas Cr(III) obviously enhanced Se removal, increasing Se volatilization by ~29%. Similarly, Se significantly increase Cr removal rates, with a maximum of 94.6 ± 0.2% for the algal co-exposed to Se(IV) and Cr(III). To reduce residual pollutants in the alga, we applied combustion as a post-treatment to burn off >99% of the biomass Se for all Se treatments, whereas most of the biomass Cr (54.7-81.6%) remained in the ash at significantly higher levels (~7430 μg Cr/g DW). For toxicity, our speciation analysis found organo-Se (SeCys and SeMet) dominant in the alga exposed to Se, particularly selenite. No Cr(VI) but Cr(III) forms were detected in all Cr-exposed alga. Elemental Se disappeared from all Se-exposed alga in the presence of Cr(VI), while Se resulted in the emergence of Cr-acetate in all Cr(III)-treated alga. After combustion, mineral Se, particularly elemental Se dominated most of the ash; likewise, elemental Cr, along with Cr₂O₃, was found in all the ash. Overall, our research would contribute to developing a low ecotoxic algal treatment system for Se/Cr contaminated water.

Uptake and Translocation of Perfluorooctanoic Acid (PFOA) and Perfluorooctanesulfonic Acid (PFOS) by Wetland Plants: Tissue- and Cell-Level Distribution Visualization with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) and Transmission Electron Microscopy Equipped with Energy-Dispersive Spectroscopy (TEM-EDS)

Perfluoroalkyl substances (PFASs) are persistent chemicals in the environment. So far, little is known about their uptake potential in wetland plants. Here, we investigated the uptake and translocation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in eight common wetland plants, namely, Canna indica (Ci), Thalia dealbata (Td), Cyperus alternifolius (Ca), Phragmites australis (Pa), Arundo donax (Ad), Pontederia cordata (Pc), Cyperus papyrus (Cp), and Alisma orientale (Ao) by hydroponic experiments and visualized their tissue- and cell-level distribution with desorption electrospray ionization mass spectrometry (DESI-MS) and transmission electron microscopy equipped with energy-dispersive spectroscopy (TEM-EDS). The results showed that the PFASs accumulated in plants accounted for 1.67-16.7% of the total mass spiked into the hydroponic systems, and PFOS accumulated largely in roots (48.8-95.8%), while PFOA was stored mostly in the aboveground part (29.3-77.4%). DESI-MS and TEM-EDS analysis showed that PFASs in Ci, Td, Pa, and Ca were transported from the hydroponic solution to the root cortex via both apoplastic (e.g., across cell walls and/or intercellular spaces) and symplastic routes (e.g., across plasma membranes or via plasmodesmata) and further to the vascular bundle via symplastic route in Td and Pa and via both routes in Ci and Ca. These two chemicals were transported from roots to stems mainly through the cortex in Td and through both the cortex and vascular bundles in Ci and Ca.

Integration of earthworms and arbuscular mycorrhizal fungi into phytoremediation of cadmium-contaminated soil by Solanum nigrum L

Arbuscular mycorrhizal fungi (AMF) and earthworms independently enhance plant growth, heavy metal (HM) tolerance, and HM uptake, thus they are potential key factors in phytoremediation. However, few studies have investigated their interactions in HM phytoextraction by hyperaccumulators. This study highlights the independent and interactive effects of earthworms and AMF on Solanum nigrum. Plants inoculated with either AMF or earthworms exhibited ameliorated growth via enhancement of productivity, metal tolerance, and phosphorus (P) acquisition. Co-inoculation with both had more pronounced effects on plant biomass and P acquisition in shoots, but not in roots, and in Cd-polluted soils it significantly promoted (P < 0.05) shoot biomass (20.7-134.6 %) and P content (20.4-112.0 %). AMF and earthworms increased Cd accumulation in plant tissues, but only AMF affected Cd partitioning between shoots and roots. Although AMF decreased root-to-shoot translocation of Cd at high Cd levels, this was counterbalanced by earthworms. Both AMF and its combination with earthworms enhanced Cd phytoavailability by altering Cd chemical fractions and decreasing pH. Co-inoculation increased Cd removal amounts up to 149.3 % in 120 mg kg^-1 Cd-spiked soils. Interactions between the two organisms were synergistic in Cd phytoextraction. Thus, earthworm-AMF-plant symbiosis potentially plays an essential role in phytoremediation of HM-polluted soils.

Hexavalent chromium reduction ability and bioremediation potential of Aspergillus flavus CR500 isolated from electroplating wastewater

Hexavalent chromium reduction by microbes can mitigate the chromium toxicity to the environment. In the present study Cr_[VI] tolerant fungal isolate (CR500) was isolated from electroplating wastewater, was able to tolerate 800 mg/L of Cr_[VI. Based on the ITS region sequencing, the isolate was identified as Aspergillus flavus CR500, showed multifarious biochemical (reactive oxygen species, antioxidants response and non-protein thiol) and morphological (protrusion less, constriction and swelling/outwards growth in mycelia) response under Cr_[VI] stress. Batch experiment was conducted at different Cr_[VI] concentration (0-200 mg/L) to optimize the Cr_[VI] reduction and removal ability of isolate CR500; results showed 89.1% reduction of Cr_[VI] to Cr_[III] within 24 h and 4.9 ± 0.12 mg of Cr per gram of dried biomass accumulation within 144 h at the concentration of 50 mg/L of Cr_[VI]. However, a maximum of 79.4% removal of Cr was recorded at 5 mg/L within 144 h. Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy and X-ray diffraction analysis revealed that chromium removal also happened via adsorption/precipitation on the mycelia surface. Fungus treated and without treated 100 mg/L of Cr_[VI] solution was subjected to phytotoxicity test using Vigna radiata seeds and result revealed that A. flavus CR500 successfully detoxified the Cr_[VI] via reduction and removal mechanisms. Isolate CR500 also exhibited efficient bioreduction potential at different temperature (20-40 °C), pH (5.0-9.0), heavy metals (As, Cd, Cu, Mn, Ni and Pb), metabolic inhibitors (phenol and EDTA) and in sterilized tannery effluent that make it a potential candidate for Cr_[VI] bioremediation.

Cellular distribution of cadmium in two amaranth (Amaranthus mangostanus L.) cultivars differing in cadmium accumulation

Differences in cellular cadmium (Cd) distribution between Cd-tolerant and Cd-sensitive lines of amaranth (Amaranthus mangostanus L.) may reveal mechanisms involved in Cd tolerance and hyperaccumulation. We compared the cellular distribution and accumulation of Cd in roots, stems, and leaves between a low-Cd accumulating cultivar (Zibeixian, L-Cd) and a high-Cd accumulating cultivar (Tianxingmi, H-Cd) in a hydroponic experimental system. In all treatments, H-Cd grew better than L-Cd and accumulated more Cd. As the Cd concentration increased, the H-Cd plants grew normally and their biomass increased, except in the 60 μM Cd treatment. The biomass of L-Cd decreased with increasing Cd concentrations. The highest Cd concentration in the roots, stems, and leaves of H-Cd was 950 mg/kg, 305 mg/kg, and 205 mg/kg, respectively, compared with 269 mg/kg, 62.9 mg/kg, and 74.8 mg/kg, respectively, in L-Cd. The Cd distribution differed between the two cultivars. Scanning and transmission electron microscopy and energy-dispersive spectrometry analyses showed that Cd was distributed across the entire cross section of H-Cd roots but largely restricted to the epidermal cells and the exodermis of L-Cd roots. The main Cd storage sites were the root apoplast, cell walls, and intercellular spaces in H-Cd and the root epidermal cells and the exodermis in L-Cd. In H-Cd leaves, Cd accumulated mainly in vacuoles of epidermal cells and, at high external Cd concentrations, in the vacuoles of mesophyll cells.

Are Fungal Endophytes Merely Mycorrhizal Copycats? The Role of Fungal Endophytes in the Adaptation of Plants to Metal Toxicity

The contamination of soil with toxic metals is a worldwide problem, resulting in the disruption of plant vegetation and subsequent crop production. Thus, remediation techniques for contaminated soil and water remain a constant interest of researchers. Phytoremediation, which utilizes plants to remove or stabilize contaminants, is perceived to be a promising strategy. However, phytoremediation's use to date is limited because of constraints associated with such factors as slow plant growth rates or metal toxicity. Microbial-assisted phytoremediation serves as an alternative solution, since the impact of the microbial symbionts on plant growth and stress tolerance has frequently been described. Endophytic fungi occur in almost every plant in the natural environment and contribute to plant growth and tolerance to environmental stress conditions. Although this group of symbiotic fungi was found to form association with a wide range of hosts, including the non-mycorrhizal Brassicaceae metallophytes, their role in the response of plants to metal toxicity has not been thoroughly elucidated to date. This review summarizes the current knowledge regarding the role of endophytic fungi in the tolerance of plants to toxic metals and highlights the similarities and differences between this group of symbiotic fungi and mycorrhizal associations in terms of the survival of the plant during heavy metal stress.

Effects of arbuscular mycorrhizal fungi, biochar and cadmium on the yield and element uptake of Medicago sativa

The synergistic effects of arbuscular mycorrhizal fungi (AMF) inoculation and biochar application on plant growth and heavy metal uptake remain unclear. A pot experiment was carried out to investigate the influence of AMF inoculation, biochar and cadmium (Cd) addition on the growth, nutrient and cadmium uptake of Medicago sativa, as well as soil biological and chemical characteristics. In comparison to the non-Cd pollution treatment, Cd addition significantly decreased mycorrhizal colonization, biomass, and N, P, Ca and Mg contents of shoots and roots in the absence of biochar. Biochar amendment did not increase mycorrhizal colonization at either Cd levels. Regardless of the biochar amendment, AMF inoculation significantly promoted contents of N and P in plant shoots grown in the Cd-contaminated soils. Nevertheless, in the presence of Cd pollution, biochar dramatically elevated the biomass and N, P, K and Ca contents of plant tissues in both AMF inoculation treatments. Biochar addition significantly reduced soil DTPA-extracted Cd. The treatments with AMF inoculation and biochar amendment showed the lowest shoot Cd concentrations and contents, highest plant tissue N and P contents in the Cd addition group. These results suggested that combined use of AMF inoculation and biochar amendment had significant synergistic effects not only on nutrient uptake but also on the reduction in cadmium uptake of alfalfa grown in Cd-polluted soil.

Effects of arbuscular mycorrhizal fungi on the growth and heavy metal accumulation of bermudagrass [Cynodon dactylon (L.) Pers.] grown in a lead-zinc mine wasteland

A pot experiment was conducted to investigate the potential influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Diversispora spurcum, on the growth and nutrient (P and S) and heavy metal (HMs) (Pb, Zn, and Cd) content of bermudagrass [Cynodon dactylon (L.) Pers.] in a lead-zinc mine wasteland. The D. spurcum inoculation significantly increased the bermudagrass growth, whereas the F. mosseae inoculation did not. The AMF inoculation significantly increased the soil pH and uptake of P, S, and HMs by bermudagrass, decreased the contents of available Pb and Zn in soils and Pb in shoots, reduced the translocation factor (TF) and translocation capacity factor (TF') of Pb and Cd in bermudagrass and increased the TF and TF' of Zn in bermudagrass. A significant negative correlation was found between pH and available HMs in soil, whereas a significant positive correlation was noted between the HMs content and nutrient content in bermudagrass shoots. Experiment results provide evidence of the potential role of AMF in improving bermudagrass performance for the vegetation restoration of metalliferous mine wastelands.

Accumulation of 152+154Eu(III) by Aspergillus sydowii and Trichoderma harzianum

Radionuclides-resistant filamentous fungi were isolated from radionuclides' contaminated soils. Effects of contact time, mycelia dosage, pH, ionic strength and thiol compounds on ^152+154Eu(III) accumulation on two kinds of filamentous fungi (Aspergillus sydowii and Trichoderma harzianum, denoted as A. sydowii and T. harzianum, respectively) were investigated by batch techniques. The maximum tolerance to Eu(III) concentration of A. sydowii and T. harzianum reached 3000 mg/L and 3500 mg/L, and the Eu(III) accumulation on A. sydowii and T. harzianum can be fitted better with the pseudo-second-order kinetic model, respectively. Filamentous fungi were characterized by FT-IR and acid base titrations, and morphological structures of mycelia changed obviously under Eu(III) stress by SEM and TEM analysis. The results suggested that filamentous fungi could play an important role in the migration and transformation of radionuclides in the environment.

A methyltransferase gene from arbuscular mycorrhizal fungi involved in arsenic methylation and volatilization

Arbuscular mycorrhizal fungi (AMF), ubiquitous symbiotic fungi associated with the majority of terrestrial plants, were demonstrated to play important roles in arsenic (As) translocation and transformation in the plant-soil continuum, and substantially influence plant As tolerance. However, the direct involvement of AMF in As methylation and volatilization and their molecular mechanisms remain unsolved. Here, an arsenite methyltransferase gene RiMT-11 was identified and characterized from AM fungus Rhizophagus irregularis. Heterologous expression of RiMT-11 enhanced arsenite resistance of E. coli (Δars) through methylating As into monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and ultimately volatile trimethyl arsine (TMAs). In a two-compartment in vitro monoxenic cultivation system, methylated and volatile As were also detected from AM symbioses with arsenate addition, accompanied by strong up-regulation of RiMT-11 expression in extraradical hyphae. The present study provided direct evidence and illustrated an underlying mechanism of As methylation and volatilization by AMF, leading to a deeper insight into the role of AMF in As biogeochemical cycling.

Investigation of lead bioimmobilization and transformation by Penicillium oxalicum SL2

Fungi Penicillium oxalicum SL2 was applied for Pb²⁺ bioremediation in aqueous solution in this study. After 7 days of incubation at different initial concentrations of Pb²⁺ (0, 100, 500 and 2500 mg L^-1), most of Pb²⁺ were removed (90, 98.3, and 86.2%), the maximum Pb content in mycelium reached about 155.6 mg g^-1 dw. Meanwhile, the formation of extracellular secondary minerals and intracellular Pb-complex were observed and identified, the speciation of Pb in mycelium was also detected by X-ray absorption near-edge structure (XANES) spectroscopy, i.e., Pb-oxalate, Pb-citrate, Pb-hydrogen phosphate and Pb-glutathione analogues. In addition, content of glutathione and oxidized glutathione was increased under the exposure of Pb²⁺, which implied that glutathione might play a key role in Pb immobilization and detoxification in P. oxalicum SL2. This study elucidated partial mechanisms of Pb immobilization and speciation transformation of this strain, providing an alternative biomaterial in the bioremediation of Pb-contaminated wastewater.

Arbuscular mycorrhizal fungi enhance antioxidant defense in the leaves and the retention of heavy metals in the roots of maize

In this study, we investigated the effects of the arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae and Diversispora spurcum on the growth, antioxidant physiology, and uptake of phosphorus (P), sulfur (S), lead (Pb), zinc (Zn), cadmium (Cd), and arsenic (As) by maize (Zea mays L.) grown in heavy metal-polluted soils though a potted plant experiment. F. mosseae significantly increased the plant chlorophyll a content, height, and biomass; decreased the H₂O₂ and malondialdehyde (MDA) contents; and enhanced the superoxide dismutase (SOD) and catalase (CAT) activities and the total antioxidant capacity (T-AOC) in maize leaves; this effect was not observed with D. spurcum. Both F. mosseae and D. spurcum promoted the retention of heavy metals in roots and increased the uptake of Pb, Zn, Cd, and As, and both fungi restricted heavy metal transfer, resulting in decreased Pb, Zn, and Cd contents in shoots. Therefore, the fungi reduced the translocation factors for heavy metal content (TF) and uptake (TF') in maize. Additionally, F. mosseae promoted P and S uptake by shoots, and D. spurcum increased P and S uptake by roots. Moreover, highly significant negative correlations were found between antioxidant capacity and the H₂O₂, MDA, and heavy metal contents, and there was a positive correlation with the biomass of maize leaves. These results suggested that AMF alleviated plant toxicity and that this effect was closely related to antioxidant activation in the maize leaves and increased retention of heavy metals in the roots.

Nano Zero-Valent Iron Mediated Metal(loid) Uptake and Translocation by Arbuscular Mycorrhizal Symbioses

Nano zero-valent iron (nZVI) has great potential in the remediation of metal(loid)-contaminated soils, but its efficiency in metal(loid) stabilization in the plant-microbe continuum is unclear. This study investigated nZVI-mediated metal(loid) behavior in the arbuscular mycorrhizal (AM) fungal-maize ( Zea mays L.) plant association. Plants with AM fungal inoculation were grown in metal(loid)- (mainly Zn and Pb) contaminated soils (Litavka River, Czech Republic) amended with/without 0.5% (w/w) nZVI. The results showed that nZVI decreased plant metal(loid) uptake but inhibited AM development and its function in metal(loid) stabilization in the rhizosphere. AM fungal inoculation alleviated the physiological stresses caused by nZVI and restrained nZVI efficiency in reducing plant metal(loid) uptake. Micro proton-induced X-ray emission (μ-PIXE) analysis revealed the sequestration of Zn (possibly through binding to thiols) by fungal structures in the roots and the precipitation of Pb and Cu in the mycorrhizal root rhizodermis (possibly by Fe compounds originated from nZVI). XRD analyses further indicated that Pb/Fe mineral transformations in the rhizosphere were influenced by AM and nZVI treatments. The study revealed the counteractive effects of AM and nZVI on plant metal(loid) uptake and uncovered details of metal(loid) behavior in the AM fungal-root-nZVI system, calling into question about nZVI implementation in mycorrhizospheric systems.

The enhancement by arbuscular mycorrhizal fungi of the Cd remediation ability and bioenergy quality-related factors of five switchgrass cultivars in Cd-contaminated soil

A greenhouse experiment was carried out to investigate the effects of arbuscular mycorrhizal fungi (AMF) on the growth, P and Cd concentrations and bioenergy quality-related factors of five cultivars of switchgrass, including three lowland cultivars (Alamo (Ala), Kanlow (Kan), Performer (Per)) and two highland cultivars (Blackwell (Bw), Summer (Sum)), with 0, 1 and 10 mg/kg Cd addition levels. The results showed that AMF inoculation notably increased the biomass and P concentrations of all the cultivars. The Cd concentrations in the roots were higher than those in the shoots of all cultivars irrespective of inoculation, but the AMF had different effects on Cd accumulation in highland and lowland cultivars. AMF inoculation decreased the shoot and root concentrations in Ala and Kan, increased the shoot and root concentrations of Cd in Bw and Sum, and increased shoot Cd concentrations and decreased root Cd concentrations in Per. The highest Cd concentrations were detected in the roots of Bw and in the shoots of Sum with AMF symbiosis. Bw contained the highest total extracted Cd which was primarily in the roots. Ala had the second highest extracted Cd in the shoots, reaching 32% with 1 mg/kg of added Cd, whereas Sum had the lowest extracted Cd. AMF symbiosis had varied effects on bioenergy quality-related factors: for example, AMF decreased the ash lignin content in Ala and the C/N in Sum, increased the nitrogen, gross calorie values, and maintained the hemicellulose and cellulose contents in all cultivars with all tested concentrations of Cd. A principal component analysis (PCA) showed that AMF inoculation could enhance, weaken or transform (positive-negative, PC1-PC2) the correlations of these factors with the principle components under Cd stress. Therefore, AMF symbiosis enhanced the growth of different cultivars of switchgrass, increased/decreased Cd accumulation, promoted Cd extraction, and regulated the bioenergy quality-related factors in Cd-polluted areas. Bw is a suitable cultivar for phytostabilization due to high root Cd stabilization, whereas Ala is an appropriate cultivar for phytoremediation of less polluted areas because of its high Cd extraction and excellent bioenergy quality.