Restoring the plant productivity of heavy metal-contaminated soil using phosphate sludge, marble waste, and beneficial microorganisms

Trace element pollution tracking in the complex multi-aquifer groundwater system of Al-Hassa oasis (Saudi Arabia) using spatial, chemometric and index-based techniques

In a global context, trace element pollution assessment in complex multi-aquifer groundwater systems is important, considering the growing concerns about water resource quality and sustainability worldwide. This research addresses multiple objectives by integrating spatial, chemometric, and indexical study approaches, for assessing trace element pollution in the multi-aquifer groundwater system of the Al-Hassa Oasis, Saudi Arabia. Groundwater sampling and analysis followed standard methods. For this purpose, the research employed internationally recognized protocols for groundwater sampling and analysis, including standardized techniques outlined by regulatory bodies such as the United States Environmental Protection Agency (USEPA) and the World Health Organization (WHO). Average values revealed that Cr (0.041) and Fe (2.312) concentrations surpassed the recommended limits for drinking water quality, posing serious threats to groundwater usability by humans. The trace elemental concentrations were ranked as: Li < Mn < Co < As < Mo < Zn < Al < Ba < Se < V < Ni < Cr < Cu < B < Fe < Sr. Various metal(loid) pollution indices, including degree of contamination, heavy metal evaluation index, heavy metal pollution index, and modified heavy metal index, indicated low levels of groundwater pollution. Similarly, low values of water pollution index and weighted arithmetic water quality index were observed for all groundwater points, signifying excellent groundwater quality for drinking and domestic purposes. Spatial distribution analysis showed diverse groundwater quality across the study area, with the eastern and western parts displaying a less desirable quality, while the northern has the best, making water users in the former more vulnerable to potential pollution effects. Thus, the zonation maps hinted the necessity for groundwater quality enhancement from the western to the northern parts. Chemometric analysis identified both human activities and geogenic factors as contributors to groundwater pollution, with human activities found to have more significant impacts. This research provides the scientific basis and insights for protecting the groundwater system and ensuring efficient water management.

Revitalizing contaminated lands: A state-of-the-art review on the remediation of mine-tailings using phytoremediation and genomic approaches

The mining industry has historically served as a critical reservoir of essential raw materials driving global economic progress. Nevertheless, the consequential by-product known as mine tailings has consistently produced a substantial footprint of environmental contamination. With annual discharges of mine tailings surpassing 10 billion tons globally, the need for effective remediation strategies is more pressing than ever as traditional physical and chemical remediation techniques are hindered by their high costs and limited efficacy. Phytoremediation utilizing plants for remediation of polluted soil has developed as a promising and eco-friendly approach to addressing mine tailings contamination. Furthermore, sequencing of genomic DNA and transcribed RNA extracted from mine tailings presents a pivotal opportunity to provide critical supporting insights for activities directed towards the reconstruction of ecosystem functions on contaminated lands. This review explores the growing prominence of phytoremediation and metagenomics as an ecologically sustainable techniques for rehabilitating mine-tailings. The present study envisages that plant species such as Solidago chilensis, Festuca arundinacea, Lolium perenne, Polygonum capitatum, Pennisetum purpureum, Maireana brevifolia, Prosopis tamarugo etc. could be utilized for the remediation of mine-tailings. Furthermore, a critical evaluation of the organic and inorganic ammendments that optimize conditions for the remediation of mine tailings is also provided. The focus of this review extends to the exploration of environmental genomics to characterize microbial communities in mining sites. By delving into the multifaceted dimensions of phytoremediation and genomics for mine tailings, this study contributes to the ongoing efforts to revitalize contaminated lands for a sustainable and environmentally friendly future.

Nutrients in overlying water affect the environmental behavior of heavy metals in coastal sediments

Excessive nutrients in aquatic ecosystems are the main driving factors for eutrophication and water quality deterioration. However, the influence of nutrients in overlying water on sediment heavy metals is not well understood. In this study, the effects of nitrate nitrogen (NO3-N) addition and phosphate addition in the overlying water on the environmental behaviors of chromium (Cr), copper (Cu), and cadmium (Cd) in coastal river sediments were investigated. Fresh estuary sediments and synthetic saltwater were used in microcosm studies conducted for 13 d. To determine the biological effect, unsterilized and sterilized treatments were considered. The results showed that the diffusion of Cr and Cu was inhibited in the unsterilized treatments with increased NO3-N. However, under the NO3-N sterilized treatments, Cr and Cu concentrations in the overlying water increased. This was mostly related to changes in the microbial regulation of dissolved organic carbon and pH in the unsterilized treatments. Further, in the unsterilized treatments, NO3-N addition considerably increased the concentrations of the acid-soluble (Cr, Cu, and Cd increased by 5%-8%, 29%-41%, and 31%-42%, respectively) and oxidizable (Cr, Cu, and Cd increased by 10%, 5%, and 14%, respectively) fractions. Additionally, compared with that in the unsterilized treatments, Cu and Cd concentrations in P-3 treatments decreased by 7% and 63%, respectively. By producing stable metal ions, microorganisms reduced the amount of unstable heavy metals in the sediment and heavy metal concentration in the overlying water, by considerably enhancing the binding ability of phosphate and heavy metal ions. This study provides a theoretical basis for investigating the coupling mechanisms between heavy metals and nutrients.

Mechanisms of combined bioremediation by phosphate-solubilizing fungus and plants and its effects on cadmium contamination in phosphate-mining wastelands

Owing to uncontrolled mining activities and lack of ecological protection measures, phosphate-mining wastelands are contaminated with the heavy metal Cd. In this study, Penicillium oxalicum strain ZP6, a Cd-resistant phosphate-solubilizing fungus, was used in combination with the fast-growing, high-biomass plant Brassica juncea L. to enhance Cd remediation in phosphate-mining wastelands. Further, the bioremediation mechanisms were explored and elucidated. In pot experiments, strain ZP6 and Brassica juncea L. alone were significantly effective in removing Cd from phosphate-mining wastelands; however, their combination was more effective, exhibiting a high removal rate of 88.75%. The presence of phosphorite powder increases soil-enzyme activity, promotes plant growth, and reduces the bioaccumulation and translocation factors. However, Cd-inhibited plant growth and chlorophyll content increased malondialdehyde accumulation, which was alleviated by inoculation with strain ZP6. The results from the study indicate that bioremediation using a combination of strain ZP6 and plants is a restoration strategy with appreciable potential to resolve Cd contamination in phosphate-mining wastelands.

Silver nanoparticles strengthen Zea mays against toxic metal-related phytotoxicity via enhanced metal phytostabilization and improved antioxidant responses

This study investigated the phytostabilization and plant-promoting abilities of silver nanoparticles (AgNPs). Twelve Zea mays seeds were planted in water and AgNPs (10, 15 and 20 mg mL-1) irrigated soil for 21 days on soil containing 0.32 ± 0.01, 3.77 ± 0.03, 3.64 ± 0.02, 69.91 ± 9.44 and 13.17 ± 0.11 mg kg-1 of As, Cr, Pb, Mn and Cu, respectively. In soil treated with AgNPs, the metal contents were reduced by 75%, 69%, 62%, 86%, and 76%. The different AgNPs concentrations significantly reduced accumulation of As, Cr, Pb, Mn, and Cu in Z. mays roots by 80%, 40%, 79%, 57%, and 70%, respectively. There were also reductions in shoots by 100%, 76%, 85%, 64%, and 80%. Translocation factor, bio-extraction factor and bioconcentration factor demonstrated a phytoremediation mechanism based on phytostabilization. Shoots, roots, and vigor index improved by 4%, 16%, and 9%, respectively in Z. mays grown with AgNPs. Also, AgNPs increased antioxidant activity, carotenoids, chlorophyll a and chlorophyll b by 9%, 56%, 64%, and 63%, respectively, while decreasing malondialdehyde contents in Z. mays by 35.67%. This study discovered that AgNPs improved the phytostabilization of toxic metals while also contributing to Z. mays' health-promoting properties.

Biomining Sesuvium portulacastrum for halotolerant PGPR and endophytes for promotion of salt tolerance in Vigna mungo L

Halophytic plants can tolerate a high level of salinity through several morphological and physiological adaptations along with the presence of salt tolerant rhizo-microbiome. These microbes release phytohormones which aid in alleviating salinity stress and improve nutrient availability. The isolation and identification of such halophilic PGPRs can be useful in developing bio-inoculants for improving the salt tolerance and productivity of non-halophytic plants under saline conditions. In this study, salt-tolerant bacteria with multiple plant growth promoting characteristics were isolated from the rhizosphere of a predominant halophyte, Sesuvium portulacastrum grown in the coastal and paper mill effluent irrigated soils. Among the isolates, nine halotolerant rhizobacterial strains that were able to grow profusely at a salinity level of 5% NaCl were screened. These isolates were found to have multiple plant growth promoting (PGP) traits, especially 1-aminocyclopropane-1-carboxylic acid deaminase activity (0.32-1.18  μM of α-ketobutyrate released mg^-1 of protein h^-1) and indole acetic acid (9.4-22.8  μg mL^-1). The halotolerant PGPR inoculation had the potential to improve salt tolerance in Vigna mungo L. which was reflected in significantly (p < 0.05) higher germination percentage (89%) compared to un-inoculated seeds (65%) under 2% NaCl. Similarly, shoot length (8.9-14.6 cm) and vigor index (792-1785) were also higher in inoculated seeds. The strains compatible with each other were used for the preparation of two bioformulations and these microbial consortia were tested for their efficacy in salt stress alleviation of Vigna mungo L. under pot study. The inoculation improved the photosynthetic rate (12%), chlorophyll content (22%), shoot length (5.7%) and grain yield (33%) in Vigna mungo L. The enzymatic activity of catalase and superoxide dismutase were found to be lower (7.0 and 1.5%, respectively) in inoculated plants. These results revealed that halotolerant PGPR isolated from S. portulacastrum can be a cost-effective and ecologically sustainable method to improve crop productivity under high saline conditions.

Coriander (Coriandrum sativum) Cultivation Combined with Arbuscular Mycorrhizal Fungi Inoculation and Steel Slag Application Influences Trace Elements-Polluted Soil Bacterial Functioning

The cultivation of aromatic plants for the extraction of essential oils has been presented as an innovative and economically viable alternative for the remediation of areas polluted with trace elements (TE). Therefore, this study focuses on the contribution of the cultivation of coriander and the use of arbuscular mycorrhizal fungi (AMF) in combination with mineral amendments (steel slag) on the bacterial function of the rhizosphere, an aspect that is currently poorly understood and studied. The introduction of soil amendments, such as steel slag or mycorrhizal inoculum, had no significant effect on coriander growth. However, steel slag changed the structure of the bacterial community in the rhizosphere without affecting microbial function. In fact, Actinobacteria were significantly less abundant under slag-amended conditions, while the relative proportion of Gemmatimonadota increased. On the other hand, the planting of coriander affects the bacterial community structure and significantly increased the bacterial functional richness of the amended soil. Overall, these results show that planting coriander most affected the structure and functioning of bacterial communities in the TE-polluted soils and reversed the effects of mineral amendments on rhizosphere bacterial communities and their activities. This study highlights the potential of coriander, especially in combination with steel slag, for phytomanagement of TE-polluted soils, by improving soil quality and health.

Effect of Glomus mosseae, cadmium, and elevated air temperature on main flavonoids and phenolic acids contents in alfalfa

Global warming and heavy metal-contaminated soils co-occur in natural ecosystems. Flavonoids and phenolic acids in plants have significant antioxidant activity and free radical scavenging ability, which can quickly increase under adverse environments. Arbuscular mycorrhizal fungi (AMF) colonization can affect the synthesis of flavonoids and phenolic acids in host plants. This study focused on the main effect of Glomus mosseae, cadmium (Cd, 8 mg kg^-1 dry soils), and elevated temperature (ET, + 3 °C) on main flavonoids and phenolic acids in 120-d Medicago sativa L. (alfalfa). Elevated temperature decreased G. mosseae colonization ratio by 49.5% under Cd exposure. Except for p-hydroxybenzoic acid, flavonoids and phenolic acids content in shoots increased (p < 0.05) under G. mosseae + Cd relative to Cd only. G. mosseae and Cd showed significant effects on rutin, quercetin, apigenin, liquiritigenin, gallic acid, p-hydroxybenzoic acid, p-coumaric acid, and ferulic acid, and G. mosseae colonization led to increases in these compounds by 41.7%, 35.4%, 32.2%, 267.8%, 84.7%, 33.5%, 102.8%, and 89.4%, respectively, under ET + Cd. Carbon, N, and Cd in alfalfa and G. mosseae colonization rate were significant factors on flavonoids and phenolic acids accumulation. Additionally, P content in shoots significantly influenced flavonoids content. G. mosseae inoculation significantly stimulated the synthesis of main flavonoids and phenolic acids in alfalfa shoots under ET + Cd, which was helpful to understand the regulation of AMF on non-enzyme antioxidant system of plants grown in heavy metal-contaminated soils under global change scenarios.

Relationships between soil properties and species establishment in the restoration of mined soils in the Cerrado biome

Restoring the ecosystems of the Cerrado biome is challenging considering the diversity of phytophysiognomies present in the biome, some of which are composed of species from different strata (herbaceous, shrubby, and arboreal), which increases the complexity of restructuring the floristic composition. Other factors was involved, such as soil quality, which directly influences the success of restoration, water storage, and nutrients, the financial costs, and a slow ecological process, due to the adverse circumstances found in the area. be restored. The strong anthropogenic interventions by mining processes reduce dramatically the physical and nutritional composition of the soil. We studied two restoration areas in Paracatu, Brazil, to examine their edaphic conditions six years after mining activities ceased and relate them to the status of the restoration process. In 2009, a Cerrado restoration were established in an area previously explored for gravel extraction. Plants were sampled and identified in 11 transects along the planting lines. The diameter base (DB) and total height (HT) were measured. The physical/chemical quality of the soil substrate was determined using a collection of samples in open trenches at four types of points: Cerrado (TC); dead plant pits (TM); seedling pits having living individuals of the most abundant species (TT); and those of the second-most abundant species (TE). Cecropia pachystachya Trécul and Tapirira guianensis Aubl. were most abundant and demonstrated the potential to thrive in areas degraded by mining having low mortality rates and growth at relatively DB and HT. The physical quality indicators in the gravel pits were not limiting, indicating that substrate preparation was efficient in this regard. The organic matter content in TM, TT, and TE was low in comparison to that of TC, and the chemical conditions in the TE pit substrates were similar to those in TM pits, suggesting C. pachystachya is a species with good plasticity, whereas T. guianensis is present in pits with higher levels of phosphorus.

Estimation of heavy metal concentrations (Cd and Pb) in plant leaves using optimal spectral indicators and artificial neural networks

The necessity of continuously monitoring the agricultural products in terms of their health has enforced the development of rapid, low-cost, and non-destructive monitoring solutions. Heavy metal contamination of the plants is known as a source of health threats that are made by their proximities with pollutant soil, water, and air. In this paper, a method was proposed to measure lead (Pb) and cadmium (Cd) contamination of plant leaves through field spectrometry as a low-cost solution for continuous monitoring. The study area was Mahneshan county of Zanjan province in Iran with rich heavy metal mines that have more potential for plant contamination. At first, we collected different plant samples throughout the study area and measured the Pb and Cd concentrations using ICP-AES, in which we observed that the concentrations of Pb and Cd are in the range of 1.4 ~ 282.6 and 0.3 ~ 66.7 μgg-1, respectively, and then we tried to find the optimum estimator model through a multi-objective version of genetic algorithm (GA) optimization that finds simultaneously the structure of an artificial neural network and its input features. The features extracted from the raw spectrums have been collimated to be compatible with the Sentinel-2 multispectral bands for the possibility of further developments. The results demonstrate the efficiency of the optimum estimator model in estimation of the leaves' Pb and Cd contamination, irrespective of the plant type, which has reached the R2 of 0.99 and 0.85 for Pb and Cd, respectively. Additionally, the results suggested that the 783-, 842-, and 865-nm spectral bands, which are similar to the 7, 8, and 8a sentinel-2 spectral bands, are more efficient for this purpose.

The Anatomical Basis of Heavy Metal Responses in Legumes and Their Impact on Plant-Rhizosphere Interactions

Rapid industrialization, urbanization, and mine tailings runoff are the main sources of heavy metal contamination of agricultural land, which has become one of the major constraints to crop growth and productivity. Finding appropriate solutions to protect plants and agricultural land from heavy metal pollution/harmful effects is important for sustainable development. Phytoremediation and plant growth-promoting rhizobacteria (PGPR) are promising methods for this purpose, which both heavily rely on an appropriate understanding of the anatomical structure of plants. Specialized anatomical features, such as those of epidermis and endodermis and changes in the root vascular tissue, are often associated with heavy metal tolerance in legumes. This review emphasizes the uptake and transport of heavy metals by legume plants that can be used to enhance soil detoxification by phytoremediation processes. Moreover, the review also focuses on the role of rhizospheric organisms in the facilitation of heavy metal uptake, the various mechanisms of enhancing the availability of heavy metals in the rhizosphere, the genetic diversity, and the microbial genera involved in these processes. The information presented here can be exploited for improving the growth and productivity of legume plants in metal-prone soils.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.

Effects of Different Native Plants on Soil Remediation and Microbial Diversity in Jiulong Iron Tailings Area, Jiangxi

Phytoremediation is an important solution to heavy metal pollution in soil. However, the impact of plants on microbial communities in contaminated soil also requires attention. Community-level physiological profiling (CLPP) based on the Biolog™ EcoPlate and high-throughput sequencing were used to study the soil microbial community in this article. The rhizosphere and bulk soil samples of six native species were collected from the iron mine tailings on Jiulong Mountain, Jiangxi Province. According to the average well color development (AWCD), all plants improved the activity and diversity of the contaminated soil microbial community to varying degrees. Cunninghamia lanceolate is considered to have good effects and led to the appearance of Cunninghamia lanceolata > Zelkova schneideriana > Toona ciliata > Alnus cremastogyne > Cyclobalanopsis myrsinifolia > Pinus elliottii. The Shannon–Wiener diversity index and principal component analysis (PCA) show that the evenness and dominance of soil microbial communities of several plants are structurally similar to those of uncontaminated soil (UNS). The results of high-throughput sequencing indicated that the bacterial community diversity of C. lanceolata, A. cremastogyne, and P. elliottii is similar to UNS, while fungal community diversity is different from UNS. C. lanceolata has a better effect on soil nutrients, C. myrsinifolia and P. elliottii may have a better effect on decreasing the Cu content. The objective of this study was to assess the influence of native plants on microbial communities in soils and the soil remediation capacity. Mortierellomycota was the key species for native plants to regulate Cu and microbial community functions. Native plants have decisive influence on microbial community diversity.

New mechanism of FA in composted sludge inducing Cu fixation on Albite in open-pit mine soil

Fulvic acid (FA), typical organic matter derived from humification process in composted sludge, possesses the potential to remediate mine soils contaminated by heavy metals. To understand the cooper (Cu) immobilizing process in open-pit mine soil induced by FA, changes of Cu speciation in mixture of open-pit mine soil and composted sludge was tracked over 180 days. It was observed that the organic-bound and residual fraction of Cu increased dramatically with the corresponding decrease of Fe/Mn oxide-bound Cu in the first 60 days, then the organic-bound fraction decreased to about its initial proportion during 60-120 days, while residual fraction still increased, and the proportion of residual Cu accounted for over 85% and became stable after 120 days. To reveal the mechanism of FA inducing Cu fixation on Albite which is the main phase of soil primary ore, two groups of Cu adsorption experiments with and without FA were designed. With the addition of FA, the adsorption capacity of Cu by Albite increased by 1.55 times and the content of residual Cu in Albite increased by 7.7 times. It was found that the Cu absorbed in smaller Albite particle induced by FA formed a secondary mineral--Chrysocolla, causing increase of residual fraction of Cu. These results revealed the mechanism: FA was absorbed on the surface of Albite after complexing with Cu ions in the solution, and then it induced Cu into the interlayer and pore channels of Albite. The Cu in the Albite was immobilized by forming Chrysocolla finally.

Combined application of marble waste and beneficial microorganisms: toward a cost-effective approach for restoration of heavy metals contaminated sites

Heavy metal (HM) pollution and the need to preserve the environment have gathered increasing scientific attention. The immobilization of HMs into less-soluble, less mobile, and less toxic forms in addition to the improvement of Medicago sativa L. growth and HMs accumulation were evaluated after the application of marble waste (MW) and/or beneficial PGP rhizobacteria and mycorrhizae to the mining soil compost. A greenhouse assay was conducted to elucidate the influence of both amendment and beneficial microorganisms. The application of marble waste to the soil-compost resulted in decreasing the bioavailability of metals (Cu, Zn, Pb, and Cd), thus ameliorating the installation of the vegetal cover for 6 months of culture. Cultivation of M. sativa under 5% MW-amended soil for 6 months increased the shoot dry weight by almost twofold, while the inoculation with rhizobacteria-mycorrhizae combined with the application of 15% MW resulted in an improvement of 3.5-fold in case of shoot dry weight. In addition, the application of marble waste amendment or their combination with metallo-resistant bacteria resulted in decreasing HM accumulation leading to HM content below the threshold recommended for animal grazing. Thus, the application of amendments and beneficial microorganisms appeared to guarantee the safe cultivation of alfalfa for 6 months of culture. The dual combination amendments and beneficial microorganisms showed the good potential to restore HM polluted soils and could stand as a novel approach for restoration of HM-contaminated soils.

Assessment of the antioxidative response and culturable micro-organisms of Lygeum spartum Loefl. ex L. for prospective phytoremediation applications

Abundant plant species in arid industrial areas are mining phyto-resources for sustainable phyto-management. However, the association with their rhizosphere is still poorly known for phytoremediation purposes. This study aims to assess the heavy metals (HMs) and metalloids uptake of Lygeum spartum Loefl. ex L. growing in cement plant vicinity and screen associated culturome for potential phytoremediation use. Bioaccumulation factor (BAF), the translocation factor (TF), and the mobility ratio (MR) were studied along with four sites. Lipid peroxidation (MDA), free proline (Pro), Non-protein thiols (NPTs), and reduced glutathione (GSH) were tested for evaluating the plant antioxidative response. Bacteria and fungi associated with L. spartum Loefl. ex L. were identified by 16S rRNA and fungal internal transcribed spacer (ITS1-ITS2) gene sequencing. Our results showed an efficient uptake of As, Pb, and Zn and enhanced GSH (0.34 ± 0.03) and NPTs (528.7 ± 14.4 nmol g^-1 FW) concentrations in the highly polluted site. No significant variation of Arbuscular Mycorrhizal Fungi (AMF) was found. Among 29 bacterial isolates, potential bioremediation were Bacillus simplex and Bacillus atrophaeus. Thus, L. spartum Loefl. ex L. and its associated microbiota have the potential for phytoremediation applications. Novelty statement: This work has been set in line with the investigation of the integrative biology of Lygeum spartum Loefl ex L. and the screening of its associated microbiome for potential phytoremediation applications. This work is the first work conducted in a cement plant vicinity investigating the associated fungi and bacteria of L. spartum Loefl. ex L. and been part of a sectorial research project since 2011, for assessing the impact of industrial pollution and recognizing the accumulation potential of plant species for further phyto-management applications.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Biomolecules from Plant Wastes Potentially Relevant in the Management of Irritable Bowel Syndrome and Co-Occurring Symptomatology

During and following the processing of a plant’s raw material, considerable amounts are wasted, composted, or redistributed in non-alimentary sectors for further use (for example, some forms of plant waste contribute to biofuel, bioethanol, or biomass production). However, many of these forms of waste still consist of critical bioactive compounds used in the food industry or medicine. Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders. The primary treatment is based on symptomatology alleviation and controlled dietary management. Thus, this review aimed to describe the possible relevance of molecules residing in plant waste that can be used to manage IBS and co-occurring symptoms. Significant evidence was found that many forms of fruit, vegetable, and medicinal plant waste could be the source of some molecules that could be used to treat or prevent stool consistency and frequency impairments and abdominal pain, these being the main IBS symptoms. While many of these molecules could be recovered from plant waste during or following primary processing, the studies suggested that enriched food could offer efficient valorization and prevent further changes in properties or stability. In this way, root, stem, straw, leaf, fruit, and vegetable pomaces were found to consist of biomolecules that could modulate intestinal permeability, pain perception, and overall gastrointestinal digestive processes.

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Phytoremediation of potentially toxic elements (PTEs) contaminated soils using alfalfa (Medicago sativa L.): A comprehensive review

Soil contamination with potentially toxic elements (PTEs) is an increasing environmental problem, posing serious threats to the living organisms. Phytoremediation is a sustainable and highly accepted technology for remediation of PTE-contaminated soils. Alfalfa has been widely adopted for the phytoremediation of PTE-contaminated soils due to its large biomass productivity, high PTE tolerance, and strong capacity to take up PTEs. However, there are still no literature reviews systematically summarized the potential of alfalfa in the phytoremediation. Therefore, we review the available literatures that present its PTE uptake, phytotoxicity, tolerance mechanisms, and aided techniques improving the phytoremediation efficiency. In this review, alfalfa shows high amounts of PTEs accumulation, especially in their root tissue. Meanwhile, the inner mechanisms of PTE tolerance and accumulation in alfalfa are discussed including: (i) the activation of antioxidant enzyme system, (ii) subcellular localization, (iii) production of glutathione, phytochelatins, and proline, and (iv) regulation of gene expression. Indeed, excessive PTE can overcome the defense system, which causes oxidative damage in alfalfa plants, thereby inhibiting growth and physiological processes and weakening the ability of PTE uptake. Till now, several approaches have been developed to improve the tolerance and/or accumulation of PTE in alfalfa plants as follows: (i) selection of PTE tolerant cultivars, (ii) applying plant growth regulators, (iii) addition of chelating agents, fertilizer, and biochar materials, and (iv) inoculation of soil microbes. Finally, we indicate that the selection of PTE-tolerant cultivars along with inoculation of soil microbes may be an efficient and eco-friendly strategy of the soil PTE phytoremediation.

The effects of different electrode materials on seed germination of Solanum nigrum L. and its Cd accumulation in soil

The effects of different electrode on Solanum nigrum L. seed germination were determined. The result showed that germination percentage (GP) of seeds in treatment T2 (titanium electrode) was 26.6% higher than in control (CK, without electric field). High potassium and calcium concentrations were beneficial for seed enzymatic activity in treatment T2, which could partly explain the increase in GP. Cd accumulation (μg/pot) in S. nigrum treated with any electric field was significantly higher (p<0.05) than in CK without electric field. Specifically, Cd accumulation under the treatment T3 (stainless steel electrode) was the highest both in roots and shoots; this accumulation in shoots and roots were 74.7 % and 67.4 % higher for stainless steel than in CK. This increase must have been associated with a higher Cd concentration in plants and did not exert a significant effect on the biomass. In particular, Cd concentrations in roots and shoots under stainless steel treatment were both significantly higher than in CK (p<0.05), which had to be related to the higher available Cd concentration in the soil in the middle region. Furthermore, it could be attributed to altered soil pH and other soil properties. Moreover, none of the biomasses were significantly affected (p<0.05) by different electrode materials compared to CK.

Novel scheme for synergistic purification of copper mine tailings and orthophosphate

Copper tailings (CTs) and orthophosphate are major environmental pollutants. CTs cause severe heavy metal pollution, and orthophosphate is one of the primary causes of water body eutrophication. This study aimed to alleviate heavy metal pollution by CTs and the eutrophication of water caused by orthophosphate. To this end, a 50 mg/L orthophosphate was used as a chemically active leaching solution and passed through a CT soil column. The tail water was then collected. Laboratory leaching tests showed that the thermally modified CTs effectively trapped orthophosphate, and the orthophosphate content in the leachate was 0.15 mg/L. After chemical washing, Cu²⁺, Cd²⁺, and Zn²⁺ were tested in the tail water, and the heavy metal ions in the tail water were removed using an advanced treatment technology. After treatment with 20.0 g/L water hyacinth biochar (WHBC), the removal rates (R%) of Cu²⁺, Cd²⁺, and Zn²⁺ were 99.48, 94.94, and 94.84%, respectively. These results demonstrated that this novel scheme for the synergistic purification of CTs and orthophosphate was feasible in the laboratory. This study provides new theoretical guidance and technical support for CT soil heavy metal remediation and water eutrophication treatment.

Positive Effects on Alfalfa Productivity and Soil Nutrient Status in Coastal Wetlands Driven by Biochar and Microorganisms Mixtures

Biochar application in reclaiming degraded soils and improving plant productivity has been recognized as a promising technology. Yet, the impacts of biochar and mixtures with compound effective microorganisms (CEM) on alfalfa growth and soil quality in coastal wetlands are poorly understood. A greenhouse experiment was set to systematically reveal the impacts of biochar and biochar combined with CEM on alfalfa growth traits, nutrient uptake, biomass, soil quality, and enzyme activities. Eight treatments were included: (1) control (CK−CEM), (2) 10-g/kg biochar (B10−CEM); (3) 20-g/kg biochar (B20−CEM); (4) 30-g/kg biochar (B30−CEM), (5) CEM without biochar (CK + CEM); (6) 10-g/kg biochar with CEM (B10 + CEM), (7) 20-g/kg biochar with CEM (B20 + CEM), (8) 30-g/kg biochar with CEM (B30 + CEM). The utilization of biochar promoted seed germination, height, and tissue nutrient contents of alfalfa, and the combined biochar with CEM showed greater effects. Alfalfa biomass showed the maximum value in the B20 + CEM treatment, and the biomass of root, shoot, leaf in the B20 + CEM treatment increased by 200, 117.3, 144.6%, respectively, relative to the CK−CEM treatment. Alfalfa yield in the CK + CEM, B10 + CEM, B20 + CEM, B30 + CEM treatments was 71.91, 84.11, 138.5, and 120.5% higher than those in the CK−CEM treatment. The use of biochar and CEM decreased soil salinity and elevated soil nutrient content effectively. Biochar elevated soil organic carbon (SOC) and microbial biomass carbon (MBC), NH4+, NO3–, and enzymatic activities, and the positive impacts of biochar combined with CEM were additive. The combined addition of 20-g/kg biochar with CEM showed the pronounced improvement effects on improving soil fertility and nutrient availability as well as soil enzyme activities. Path analysis indicated that the application of biochar mixture with CEM promoted alfalfa biomass by regulating plant nutrient uptake, soil quality (soil nitrogen, SOC, MBC, NH4+, NO3–), and soil enzymatic activities (sucrase, urease, and alkaline phosphatases). Thus, incorporation of suitable biochar and CEM can serve as an effective measure to promote alfalfa productivity and restore coastal wetlands soils.

Characterization of an exopolysaccharide produced by Enterobacter sp. YU16-RN5 and its potential to alleviate cadmium induced cytotoxicity in vitro

Natural biopolymers have gained remarkable attention for bioremediation particularly in heavy metal removal and oil degradation due to their non-toxic nature and lack of secondary pollution. The exopolysaccharides (EPS) produced by the bacteria have become an important class of biopolymers that are employed in bioremediation. The bacteria isolated from the rhizospheric soil have higher metal tolerance and their EPS are effective in biosorption of heavy metals. Here, we report the characterization of an EPS (EPS-RN5) isolated from the root nodule-associated bacteria, Enterobacter cancerogenus strain YU16-RN5 and its heavy metal biosorption abilities. The bacteria isolated from the West coast of India was cultured in yeast extract mannitol (YEM) medium for EPS extraction and to study the production kinetics on a temporal scale. The biochemical composition, rheological properties and thermostability of EPS-RN5 was characterized by standard methods. The biosorption potential of EPS-RN5 against the selected heavy metals was analyzed by employing the inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique. Further, cell culture experiments were used to test the role of EPS-RN5 in reducing the cytotoxicity exerted by the heavy metals in vitro using a human embryonic kidney cell line (HEK 293T). The bacteria showed good growth in YEM media and the maximum EPS yield was 1800 mg/L at 96 h. The molecular weight of EPS-RN5 was 0.7 × 106 Da and it contained 61.5% total sugars and 14.5% proteins. The monosaccharide composition of the EPS included glucose, sorbose and galactose in the ratio 0.25:0.07:1.0. The EPS-RN5 showed high thermal stability with a degradation temperature of 273 °C. Rheological analysis revealed the non-Newtonian behavior, with pseudoplastic characteristics. The EPS-RN5 efficiently absorbed cadmium and other heavy metals such as mercury, strontium, copper, arsenic, and uranium. In vitro studies revealed significant protective effect against the cadmium-induced cytotoxicity in HEK 293T cells. These results indicate the potential applications of EPS-RN5.

Marble Waste Sludges as Effective Nanomaterials for Cu (II) Adsorption in Aqueous Media

This study evaluated the waste generated by a Spanish marble-producing company as adsorbent for the removal of copper (Cu [II]) from aqueous media. Six marble waste sludge samples were studied, and the following operational parameters were analyzed in discontinuous regime, including pollutant concentration, pH, temperature, nature of aqueous medium, and ionic strength. The applicability of the adsorbent material was assessed with experiments in both continuous and discontinuous regimes under close-to-real-life conditions. A pseudo-second order model yielded a better fit to the kinetic data. Application of the intraparticle diffusion model revealed two well-differentiated adsorption stages, in which the external material transfer is negligible and intraparticle diffusion is the controlling stage. The equilibrium study was better fitted to a Freundlich-type isotherm, predicting elevated maximum adsorption values (22.7 mg g⁻¹) at a relatively low initial Cu (II) concentration (25 ppm), yielding a highly favorable chemisorption process (n >> 1). X-ray fluorescence study identified calcite (CaCO₃) as the main component of marble waste sludges. According to X-ray diffraction analysis, Cu (II) ion adsorption occurred by intercalation of the metallic cation between CaCO₃ layers and by the formation of surface complexes such as CaCO₃ and Cu₂(CO₃)(OH)₂. Cu (II) was more effectively removed at medium pH, lower temperature, and lower ionic strength of the aqueous medium. The salinity and dissolved organic matter in surface, ground-, and waste-waters negatively affected the Cu (II) removal process in both continuous and discontinuous regimes by competing for active adsorption sites. These findings demonstrate the applicability and effectiveness of marble-derived waste sludges as low-cost and readily available adsorbents for the treatment of waters polluted by Cu (II) under close-to-real-life conditions.

Measurement and ecological risk assessment of heavy metals accumulated in sediment and water collected from Gomishan international wetland, Iran

This study aimed to measure and ecologically assess heavy metals, including As, Cr, Pb, Cd, and Ni in water and sediment samples taken from Gomishan, an international wetland located in Golestan, Iran. Four sampling stations were selected to cover all parts of the wetland. The analyses of the heavy metals were performed by ICP-MS. Based on the content of the heavy metals in the sediments, the values of risks for individual heavy metals, as Er, and for total heavy metals, as IR, were estimated. Igeo and EF also presented the soil quality in terms of accumulated contamination. The average content of the heavy metals in water was 23.12, 4.14, 10.04, 6.71, and 94.48 μg/L for As, Cd, Cr, Ni, and Pb, respectively. The heavy metal concentrations in sediments were decreased in the following order: Pb (2130 ppb) > As (655 ppb) > Cr (295 ppb) > Ni (148.8 ppb) > Cd (148.8 ppb). The potential risk values for individual heavy metals were in the low range, Er < 40, except for Cd, which mostly posed a moderate ecological risk. The values of EF and Igeo showed that the sediments sampled from the Gomishan wetland were minimally enriched and contaminated. As the Gomishan wetland has a moderate risk of heavy metal contamination, conservative and monitoring activities should be performed.

Do mycorrhizae increase plant growth and pollutant removal in stormwater biofilters?

Mycorrhizae can improve plant growth and drought tolerance by enhancing plant uptake of nutrients and water, which are important targets for biofilters, a common stormwater treatment system. This study evaluated the role of mycorrhizal inoculation on plant growth, photosynthetic efficiency and pollutant removal in two Australian plant species grown in stormwater biofilters. During the establishment period and column study, Ficinia nodosa showed over 80% mycorrhizal colonization, leading to a doubling of shoot and root biomass compared to the control, while Carex appressa showed less than 26% mycorrhizal colonization and no effect on shoot and root biomass. Columns planted with mycorrhizal-inoculated F. nodosa had 5% higher removal of total phosphorus and 10% higher removal of total nitrogen (Figure 5), phosphate (Figure 6), and cadmium (Table 3). Mycorrhizal colonization did not appear to affect plant stress during drought as indicated by similar photosynthetic efficiencies within species. Our results indicate that mycorrhizal inoculation can be highly successful in biofilters while increasing plant growth and nutrient removal, opening opportunities to further study the role of mycorrhizae in enhancing plant drought tolerance and pollutant removal in existing biofiltration systems.

Foliar application of silver nanoparticles differentially intervenes remediation statuses and oxidative stress indicators in Abelmoschus esculentus planted on gold-mined soil

The study assessed the intervention of foliar application of silver nanoparticles (AgNPs) on heavy metal toxicity and phytoremediation status of Abelmoschus esculentus planted in gold-mined soil. The green synthesized AgNPs absorbed maximally at 425 nm, had an average particle size of 55 ± 2.3 nm and peaks at 3,443 and 1,636 cm^-1. A. esculentus seeds were grown in gold-mined soil and its seedlings were wetted with water and different concentrations of AgNPs (0.75, 0.50 and 0.25 mg/mL). Foliar applications of AgNPs significantly improved percentage heavy metal remediation and reduced contamination intensity by 60% and 44%, respectively in A. esculentus. Heavy metals induced oxidative stress in A. esculentus wetted with water which manifested in the reduction of growth performance and photosynthetic pigments by 43% and 15% in that order. Significant overexpression of superoxide dismutase activity and malondialdehyde by 70% and 86%, respectively together with a significant reduction in carotenoid contents and antioxidant activity by 92% and 15%, respectively were obtained for A. esculentus in control. The intervention of foliar application considerably protected A. esculentus with improved physiology, enzymic and non-enzymic antioxidant activities. These results conclude that foliar application AgNPs beneficially mediated toxicities of heavy metals in plants. Novelty statementGold mining is an economic venture but contamination of ecological matrixes by heavy metals usually accompanies it. Farming on either an active or abandoned gold site can predispose residents to the toxicity of heavy metals. Therefore, remediation before or during cultivation is key to ensuring safety. Silver nanoparticles have proved effective in remediating heavy metals and improving biochemical activities in plants due to their intrinsic properties and adsorptive potentials.

Characteristics and Influencing Factors of Microbial Community in Heavy Metal Contaminated Soil under Silicon Fertilizer and Biochar Remediation

Silicon fertilizer and biochar have been widely used to remediate soil contaminated by heavy metals. The effects and mechanism of silicon fertilizer and biochar addition on the heavy metal availability, soil biological properties, and microbial community characteristics need further study in soils contaminated by heavy metals. Therefore, this research determined how silicon fertilizer, biochar, and their combined using affected microbial communities related with nitrogen and phosphorus cycling. The abundance and composition of the microbial community were evaluated by quantitative PCR and phospholipid fatty acid analysis, respectively. Results showed that silicon fertilizer and biochar addition significantly changed soil properties, including pH, total organic carbon, ammonium, nitrate. The Cd and Zn speciation were significantly reduced by silicon fertilizer, biochar, and their integrated application. Microbial community abundance and structure were also significantly changed. Principal component analysis shows that the difference in soil microbial community structure is the most obvious under the combined addition of biochar, silicon fertilizer and biochar. In addition, the results of fluorescence quantitative PCR showed that with biological addition, the number of soil bacteria was significantly reduced. This study reveals the influence of silicon fertilizer and biochar on bacterial and fungal communities in heavy metal soils and the effect of soil heavy metal availability.

Responses of ammonia-oxidizing microorganisms to biochar and compost amendments of heavy metals-polluted soil

Heavy metal pollution affects soil ecological function. Biochar and compost can effectively remediate heavy metals and increase soil nutrients. The effects and mechanisms of biochar and compost amendments on soil nitrogen cycle function in heavy-metal contaminated soils are not fully understood. This study examined how biochar, compost, and their integrated use affected ammonia-oxidizing microorganisms in heavy metal polluted soil. Quantitative PCR was used to determine the abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB). Ammonia monooxygenase (AMO) activity was evaluated by the enzyme-linked immunosorbent assay. Results showed that compost rather than biochar improved nitrogen conversion in soil. Biochar, compost, or their integrated application significantly reduced the effective Zn and Cd speciation. Adding compost obviously increased As and Cu effective speciation, bacterial 16S rRNA abundance, and AMO activity. AOB, stimulated by compost addition, was significantly more abundant than AOA throughout remediation. Correlation analysis showed that AOB abundance positively correlated with NO₃^--N (r = 0.830, P < 0.01), and that AMO activity had significant correlation with EC (r = -0.908, P < 0.01) and water-soluble carbon (r = -0.868, P < 0.01). Those seem to be the most vital factors affecting AOB community and their function in heavy metal-polluted soil remediated by biochar and compost.

Effects of Mineral-Solubilizing Microorganisms on Root Growth, Soil Nutrient Content, and Enzyme Activities in the Rhizosphere Soil of Robinia pseudoacacia

Background: Abandoned mining sites are becoming increasingly common due to anthropogenic activities. Consequently, external-soil spray seeding technology has attracted increasing attention as a strategy to remediate them. However, significant challenges remain that greatly inhibit the efficacy of such technologies, such as insufficient nutrients available for plants. Methods: For this study, we designed an experiment, which involved the addition of mineral-solubilizing microorganisms and R. pseudoacacia seedlings to the external-soil spray seeding (ESSS) substrate, and measured the soil nutrients, enzyme activities, and root growth of R. pseudoacacia. Results: First, the combination of certain mineral-solubilizing microorganisms with ESSS advanced its efficiency by increasing the availability of soil nutrients and soil enzymatic activities in association with R. pseudoacacia. Furthermore, the improvement of root growth of R. pseudoacacia was intimately related to soil nutrients, particularly for soil total nitrogen (TN) and total sulfur (TS). In general, the effects of the J2 (combined Bacillus thuringiensis and Gongronella butleri) treatment for soil nutrients, enzyme activities, and plant growth were the strongest. Conclusion: In summary, the results of our experiment revealed that these mineral-solubilizing microorganisms conveyed a promotional effect on R. pseudoacacia seedlings by increasing the soil nutrient content. These results provide basic data and microbial resources for the development and applications of mineral-solubilizing microorganisms for abandoned mine remediation.

Physiological and Biochemical Behaviors of Date Palm Vitroplants Treated with Microbial Consortia and Compost in Response to Salt Stress

The main challenge of the agricultural sector is to develop new ecological technologies that increase the yields and the tolerance of crops to abiotic constraints, especially in arid areas. The objective of this study was to test the potential roles of biofertilizers, namely, arbuscular mycorrhizal fungi (AMF), a native AMF consortium (AMF1) and an exotic AMF strain (AMF2); plant growth-promoting rhizobacteria (PGPR); and compost (comp), applied separately or in combination, in improving the tolerance of date palm vitroplants to salt stress. Plants were grown under non-stressed (0 mM NaCl) or stressed conditions (120 and 240 mM NaCl). Salt stress negatively affected growth and physiological parameters. However, biofertilizers used alone or in combination increased these traits in either the presence or absence of salinity. The two tripartite combinations PGPR+AMF1+Comp and PGPR+AMF2+Comp efficiently increased plant height compared to the controls, with respective enhancements of 47% and 48% under non-stressed conditions (0 mM), 44% and 43% under 120 mM NaCl and 42% and 41% under 240 mM NaCl. Moreover, under 240 mM NaCl level, the PGPR, AMF1+Comp and PGPR+AMF1+Comp treatments improved the shoot dry weight by 128%, 122% and 113% respectively compared to the stressed control plants submitted to 240 mM NaCl. The tripartite combinations PGPR+AMF1/AMF2+Comp improved salt stress tolerance of plants by increasing plant growth, accumulation of osmotic adjustment compounds and antioxidant enzyme activity compared to control plants and the other treatments.

Potential of Native Arbuscular Mycorrhizal Fungi, Rhizobia, and/or Green Compost as Alfalfa (Medicago sativa) Enhancers under Salinity

Salinity is one of the devastating abiotic stresses that cause reductions in agricultural production. The increased salinization affects alfalfa growth, metabolism, and rhizobium capacity for symbiotic N2 fixation negatively. This study was undertaken to investigate the efficiency of green compost (C; made from green waste), arbuscular mycorrhizal fungi (M; field-sourced native consortium), and/or rhizobium (R; a salt-tolerant rhizobium strain) individually or in combination as an effective strategy to improve alfalfa productivity under non-saline and high-saline (120 mM NaCl) conditions. In addition, we aimed to understand the agro-physiological and metabolic basis as well as glomalin content in the soil of biofertilizers-induced salt tolerance in alfalfa. Here, we show that mycorrhizal infection was enhanced after MR inoculation, while C application decreased it significantly. Salinity reduced growth, physiological functioning, and protein concentration, but the antioxidant system has been activated. Application of the selected biofertilizers, especially C alone or combined with M and/or R improved alfalfa tolerance. The tri-combination CMR mitigated the negative effects of high salinity by stimulating plant growth, roots and nodules dry matters, mineral uptake (P, N, and K), antioxidant system, synthesis of compatible solutes, and soil glomalin content, sustaining photosynthesis-related performance and decreasing Na+ and Cl- accumulation, lipid peroxidation, H2O2 content, and electrolyte leakage.

Compost and mycorrhizae application as a technique to alleviate Cd and Zn stress in Medicago sativa

Soil pollution by heavy metals, in the last decades, has become a worldwide major concern for which finding a solution is becoming more important to conserve soil for future generations. This study used an ecotoxicology approach to evaluate the effectiveness of compost and arbuscular mycorrhizal fungus (AMF) and their combination on Medicago sativa performance grown under Zn and Cd stress. At 600 mg/kg of Cd and Zn, a reduction of mycorrhization frequency by 3.6- and 2-fold, respectively, was observed without applying compost. The effect of AMF-Compost combination on alfalfa biomass production was enhanced in the absence and the presence of heavy metals. An improvement of relative water content by 1.7- and 1.5-fold was recorded in case AMF-Compost plant treatments grown under 600 mg/kg of Cd and Zn, respectively. The application of AMF-compost enhanced the stomatal conductance and total chlorophyll in alfalfa plants. Sugar contents were significantly increased in mycorrhized and treated plants with compost compared to the control, regardless of the applied Cd or Zn dose. Phenol content was significantly increased in plants amended with compost alone and treated by Cd. Regarding Cd and Zn accumulation, AMF-compost combination reduced the content of heavy metals accumulated in M. sativa.