Unraveling the Influence of Arbuscular Mycorrhizal Colonization on Arsenic Tolerance in Medicago: Glomus mosseae is More Effective than G. intraradices, Associated with Lower Expression of Root Epidermal Pi Transporter Genes

Co-application of earthworms and arbuscular mycorrhizal fungi enhances arsenic tolerance of upland rice and improves soil health

Earthworms and arbuscular mycorrhizal fungi (AMF) are essential soil organisms that interactively shape soil-plant dynamics. This study elucidates the mechanistic basis of their co-inoculation in enhancing arsenic (As) tolerance in upland rice (Oryza sativa L.) and improving soil health in a pot experiment with As-contaminated soil (250.18 mg kg-1). This study revealed that the inoculation effects of co-inoculation on rice biomass, N uptake, and P uptake were 86 %, 109 %, and 177 %, respectively, while reducing As concentration in shoot by 38 %. Physiological analyses revealed a 40.17 % reduction in malondialdehyde (MDA) content and a 6 % increase in superoxide dismutase (SOD) activity, indicating enhanced antioxidant capacity. Subcellular As compartmentalization shifted markedly, with organelle-bound As decreasing by 27 % (roots) and 48 % (leaves), while soluble fraction and cell wall sequestration increased. Soil health metrics improved, evidenced by elevated catalase (38 %), urease (15 %), and acid phosphatase (39 %) activities, alongside a 13 % reduction in bioavailable As fractions (As-F1 and As-F2) due to increased As-F4 stabilization. These findings demonstrate that earthworm-AMF synergy mitigates As toxicity by dual strategies: (1) enhancing plant antioxidant defenses and subcellular As compartmentalization, and (2) promoting plant growth via soil enzyme activation and nutrient cycling. This integrated approach offers a scalable, eco-sustainable strategy for safe rice cultivation in As-contaminated agroecosystems.

Impact of two arbuscular mycorrhizal fungi species on arsenic tolerance and accumulation in safflower (Carthamus tinctorius L.)

BACKGROUND

Arbuscular mycorrhizal fungi (AMF) can regulate metal(loid) tolerance in plants and their capacity for phytoremediation. These effects can vary depending on the host plant and the AMF species. The impact of different AMF species on the ability of safflower (Carthamus tinctorius L.) for arsenic (As) phytoremediation is still largely unknown. Therefore, this study aimed to assess the effect of two AMF species, Rhizophagus irregularis, and Funneliformis mosseae, on the tolerance and accumulation of As in safflower in soils spiked with varying arsenate concentrations (0, 25, 50, and 100 mg kg-1).

RESULTS

The results indicated that both AMF species established effective symbiotic relationships with safflower. However, plants inoculated with R. irregularis exhibited higher mycorrhizal dependency and root colonization, especially under 100 mg kg-1 As. Both AMF species significantly improved plant growth parameters, chlorophyll content, and phosphorus (P) nutrition, which resulted in increased P/As ratio and enhanced tolerance index in safflower plants. In addition, AMF inoculation reduced As-induced lipid peroxidation by enhancing catalase and peroxidase activity in leaves and roots. While the mycorrhizal symbiosis didn't affect As availability in soils, it significantly reduced shoot As concentration and the translocation factor under all As levels. Furthermore, mycorrhizal inoculation, especially with R. irregularis, increased As concentration and modified-bioconcentration factor in the roots and enhanced total As uptake per plant.

CONCLUSIONS

Based on the results and multivariate analyses, both AMF species, particularly R. irregularis, enhanced safflower's As tolerance by retaining As in roots, improving phosphorus nutrition, and increasing antioxidant enzyme activity, showcasing their potential to enhance phytostabilization in safflower plants.

Effects of arbuscular mycorrhizal fungi on the reduction of arsenic accumulation in plants: a meta-analysis

Arsenic (As) accumulation in plants is a global concern. Although the application of arbuscular mycorrhizal fungi (AMF) has been suggested as a potential solution to decrease As concentration in plants, there is currently a gap in a comprehensive, quantitative assessment of the abiotic and biotic factors influencing As accumulation. A meta-analysis was performed to quantitatively investigate the findings of 76 publications on the impacts of AMF, plant properties, and soil on As accumulation in plants. Results showed a significant dose-dependent As reduction with higher mycorrhizal infection rates, leading to a 19.3% decrease in As concentration. AMF reduced As(V) by 19.4% but increased dimethylarsenic acid (DMA) by 50.8%. AMF significantly decreased grain As concentration by 34.1%. AMF also improved plant P concentration and dry biomass by 33.0% and 62.0%, respectively. The most significant reducing effects of As on AMF properties were seen in single inoculation and experiments with intermediate durations. Additionally, the benefits of AMF were significantly enhanced when soil texture, soil organic carbon (SOC), pH level, Olsen-P, and DTPA-As were sandy soil, 0.8%-1.5%, ≥7.5, ≥9.1 mg/kg, and 30-60 mg/kg, respectively. AMF increased easily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) by 23.0% and 28.0%, respectively. Overall, the investigated factors had significant implications in developing AMF-based methods for alleviating the negative effects of As stress on plants.

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.

Metalloid hazards: From plant molecular evolution to mitigation strategies

Metalloids such as boron and silicon are key elements for plant growth and crop productivity. However, toxic metalloids such as arsenic are increasing in the environment due to inputs from natural sources and human activities. These hazardous metalloids can cause serious health risks to humans and animals if they enter the food chain. Plants have developed highly regulated mechanisms to alleviate the toxicity of metalloids during their 500 million years of evolution. A better understanding the molecular mechanisms underlying the transport and detoxification of toxic metalloids in plants will shed light on developing mitigation strategies. Key transporters and regulatory proteins responsive to toxic metalloids have been identified through evolutionary and molecular analyses. Moreover, knowledge of the regulatory proteins and their pathways can be used in the breeding of crops with lower accumulation of metalloids. These findings can also assist phytoremediation by the exploration of plants such as fern species that hyperaccumulate metalloids from soils and water, and can be used to engineer plants with elevated uptake and storage capacity of toxic metalloids. In summary, there are solutions to remediate contamination due to toxic metalloids by combining the research advances and industrial technologies with agricultural and environmental practices.

Arbuscular mycorrhizal fungi alleviate Cd phytotoxicity by altering Cd subcellular distribution and chemical forms in Zea mays

Arbuscular mycorrhizal fungus (AMF) can relieve Cd phytotoxicity and improve plant growth, but the mechanisms involved in this process have still been not completely known. In the present work, a pot experiment was conducted to examine productions of glutathione (GSH) and phytochelatins (PCs), and absorption, chemical forms and subcellular distribution of Cd in maize (Zea mays) inoculated with or without AMF (Rhizophagus intraradices (Ri) and Glomus versiforme (Gv)) in Cd-amended soils (0, 1 and 5 mg Cd kg^-1 soil). In general, both Ri and Gv inoculation dramatically enhanced biomass production and reduced Cd concentrations in shoots and roots of maize when compared to the non-mycorrhizal treatment. Moreover, both Ri and Gv symbiosis obviously increased contents of GSH and PCs, both in shoots and roots. Subcellular distribution of Cd in maize indicated that most of Cd (more than 90%) was accumulated in cell wall and soluble fraction. In addition, Cd proportions in soluble fractions in shoots of maize inoculated with Gv or Ri were considerably increased, but reduced in cell wall fractions compared to non-mycorrhizal maize, indicating that mycorrhizal symbiosis promoted Cd transfer to vacuoles. Furthermore, proportions of Cd in inorganic and water-soluble forms were declined, but elevated in pectates and proteins-integrated forms in mycorrhizal maize, which suggested that Gv and Ri could convert Cd into inactive forms. These observations could provide a further understanding of potential Cd detoxification mechanism in maize inoculated with AMF.

Comparison of arbuscular mycorrhizal fungal effects on the heavy metal uptake of a host and a non-host plant species in contact with extraradical mycelial network

The effects of inoculation with an arbuscular mycorrhizal (AM) fungus on Cd and Ni tolerance and uptake in Medicago sativa, an AM host, and Sesuvium portulacastrum, a non-host plant, were investigated in a greenhouse experiment. The plants were cultivated in sterilized sand in a two-compartmented system, which prevented root competition but enabled colonization of the whole substrate by AM fungal extraradical mycelium. M. sativa was either left non-inoculated or inoculated with the AM fungus Rhizophagus irregularis, and both plants were either cultivated without heavy metal (HM) addition or supplied with cadmium (Cd) or nickel (Ni), each in two doses. Additional pots with singly cultivated plants were established to control for the effect of the co-cultivation. AM significantly enhanced the growth of M. sativa and substantially increased its uptake of both HMs. The roots of S. portulacastrum became colonized by AM fungal hyphae and vesicles. The presence of the AM fungus in the cultivation system tended to increase the HM uptake of S. portulacastrum, but the effect was less consistent and pronounced than that in M. sativa. We conclude that AM fungal mycelium radiating from M. sativa did not negatively affect the growth and HM uptake of S. portulacastrum. On the contrary, we hypothesize that it stimulated the absorption and translocation of Cd and Ni in the non-host species. Thus, our results suggest that AM fungal mycelium radiating from mycorrhizal plants does not decrease the HM uptake of non-host plants, many of which are considered promising candidate plants for phytoremediation.

The heavy metal paradox in arbuscular mycorrhizas: from mechanisms to biotechnological applications

Arbuscular mycorrhizal symbioses that involve most plants and Glomeromycota fungi are integral and functional parts of plant roots. In these associations, the fungi not only colonize the root cortex but also maintain an extensive network of hyphae that extend out of the root into the surrounding environment. These external hyphae contribute to plant uptake of low mobility nutrients, such as P, Zn, and Cu. Besides improving plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal (HM) toxicity to their host plants. HMs, such as Cu, Zn, Fe, and Mn, play essential roles in many biological processes but are toxic when present in excess. This makes their transport and homeostatic control of particular importance to all living organisms. AMF play an important role in modulating plant HM acquisition in a wide range of soil metal concentrations and have been considered to be a key element in the improvement of micronutrient concentrations in crops and in the phytoremediation of polluted soils. In the present review, we provide an overview of the contribution of AMF to plant HM acquisition and performance under deficient and toxic HM conditions, and summarize current knowledge of metal homeostasis mechanisms in arbuscular mycorrhizas.

Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas

Capturing the full growth potential in crops under future elevated CO2 (eCO2) concentrations would be facilitated by improved understanding of eCO2 effects on uptake and use of mineral nutrients. This study investigates interactions of eCO2, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO2 effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO2 were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon Growth of M. truncatula was increased by AM at low P conditions at both CO2 levels and eCO2×AM interactions were sparse. Elevated CO2 had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO2, but effects were inconsistent across genes and species. The ability of eCO2 to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO2-rich climates.

Sex-specific responses of Populus deltoides to Glomus intraradices colonization and Cd pollution

The positive effects of arbuscular mycorrhizal fungi (AM) on the survival, growth and physiology of plants under various stress conditions have been widely recognized. However, whether sex-dependent susceptibility to AM colonization exists, which can induce a differential tolerance between the sexes to stress conditions, is still unclear. In this study, we investigated the effects of Glomus intraradices on Cd-stressed males and females of Populus deltoides (spiked with 10 mg Cd per kg dry substrate) in terms of morphology, physiology, biochemistry, ultrastructure, and toxin storage and translocation. Exposure to Cd promoted the colonization by G. intraradices in males, but not in females. Generally, females suffered more impairments than males in response to Cd stress, reflected by leaf symptoms, the extent of lipid peroxidation, and integrity of the cellular ultrastructure, whether they were inoculated or not. Inoculation with G. intraradices alleviated the phytotoxic effects of Cd in females by stimulating antioxidant enzymes, decreasing levels of reactive oxygen species (ROS) and restricting Cd transfer to the shoots. In contrast, these beneficial effects induced by AM were not detected in mycorrhizal males compared to non-mycorrhizal males, based on thiobarbituric acid-reactive substances (TBARS) and cellular ultrastructure. Inoculation with AM promoted Cd accumulation in males but not in females, and caused the sequestration of more toxic Cd in the root systems in both sexes. Therefore, our results suggest that inoculated males of P. deltoides are suitable candidates for phytostabilization in Cd-polluted soils, due to their higher accumulation ability and greater tolerance relative to inoculated females.

Water management, rice varieties and mycorrhizal inoculation influence arsenic concentration and speciation in rice grains

A pot experiment was carried out to investigate the effects of water management and mycorrhizal inoculation on arsenic (As) uptake by two rice varieties, the As-resistant BRRI dhan 47 (B47) and As-sensitive BRRI dhan 29 (B29). Grain As concentration of B47 plants was significantly lower than that of B29, and grain As concentration of B47 was higher under flooding conditions than that under aerobic conditions. In general, mycorrhizal inoculation (Rhizophagus irregularis) had no significant effect on grain As concentrations, but decreased the proportion of inorganic arsenic (iAs) in grains of B47. The proportion of dimethylarsinic acid (DMA) in the total grain As was dramatically higher under flooding conditions. Results demonstrate that rice variety selection and appropriate water management along with mycorrhizal inoculation could be practical countermeasures to As accumulation and toxicity in rice grains, thus reducing health risks of As exposure in rice diets.

Arbuscular mycorrhizal fungi play a role in protecting roots of Sophora viciifolia Hance. from Pb damage associated with increased phytochelatin synthase gene expression

Understanding the influence of arbuscular mycorrhizal (AM) fungi on the expressions of the dominant plant-related genes under heavy metal (HM) stress is important for developing strategies to reclaim polluted sites. In this study, we cloned full-length cDNAs of phytochelatin synthase gene (PCS1) and Actin of Sophora viciifolia Hance., a predominant plant in Qiandongshan lead and zinc mine, by rapid amplification of cDNA ends. Consequently, we studied the response of SvPCS1 to Funneliformis mosseae inoculation under lead stress (0, 50, and 200 μM Pb(NO3)2) at different durations (1, 3, and 7 days) using quantitative reverse-transcription polymerase chain-reaction (qRT-PCR) technique. The Pb concentrations and chlorophyll fluorescence parameters were also measured to assay Pb toxicity to Sophora viciifolia. We found that Pb concentrations in roots increased with increasing Pb application and the durations; the F v /F m , F v /F o , qP, and Y(II) decreased; NPQ rose with increasing Pb concentrations; mycorrhizal symbiosis alleviated the Pb toxicity to plants; and SvPCS1 was constitutively expressed in the roots. It was also found that F. mosseae inoculation could promote the expression of SvPCS1 with the concentration ≤ 200 μM at the exposure time shorter than 7 days.

Opening the black box: outcomes of interactions between arbuscular mycorrhizal (AM) and non-host genotypes of Medicago depend on fungal identity, interplay between P uptake pathways and external P supply

We investigated the physiology that underlies the influence of arbuscular mycorrhizal (AM) colonization on outcomes of interactions between plants. We grew Medicago truncatula A17 and its AM-defective mutant dmi1 in intragenotypic (two plants per pot of the same genotype, x2) or intergenotypic (one plant of each genotype, 1 + 1) combinations, inoculated or not with Rhizophagus irregularis (formerly Glomus intraradices) or Gigaspora margarita. We measured plant growth, colonization, contributions of AM and direct P uptake pathways using (32)P, and expression of plant Pi transporter genes at two levels of P supply. A17 (x2) responded positively to inoculation only at low P. The response was enhanced with 1 + 1 even at high P where colonization in A17 was reduced. With R. irregularis P uptake by the AM pathway was unaffected by P supply, whereas with G. margarita, the AM pathway was lower at high P, and direct uptake higher. Gene expression varied and was unrelated to P uptake through the two pathways. There was no evidence of plant control of P uptake via R. irregularis at high P but there was via G. margarita. Importantly, growth responses of plant genotypes grown alone did not predict outcomes of intergenotypic interactions.

Epigenetic control of heavy metal stress response in mycorrhizal versus non-mycorrhizal poplar plants

It was previously shown that arbuscular mycorrhizal fungi (AMF) exert a significant improvement of growth in a tolerant white poplar (Populus alba L.) clone (AL35) grown on Cu- and Zn-polluted soil via foliar alterations in the levels of defence/stress-related transcripts and molecules. However, nothing is known about the epigenetic changes which occur during tolerance acquisition in response to heavy metals (HMs) in the same mycorrhizal vs. non-mycorrhizal poplar plants. In order to analyse the epigenome in leaves of AL35 plants inoculated or not with AMF and grown in a greenhouse on multimetal polluted or unpolluted soil, the Methylation Sensitive Amplification Polymorphism (MSAP) approach was adopted to detect cytosine DNA methylation. Modest changes in cytosine methylation patterns were detected at first sampling (4 months from planting), whereas extensive alterations (hypomethylation) occurred at second sampling (after 6 months) in mycorrhizal plants grown in the presence of HMs. The sequencing of MSAP fragments led to the identification of genes belonging to several Gene Ontology categories. Seven MSAP fragments, selected on the basis of DNA methylation status in treated vs control AL35 leaves at the end of the experiment, were analysed for their transcript levels by means of qRT-PCR. Gene expression varied in treated samples relative to controls in response to HMs and/or AMF inoculation; in particular, transcripts of genes involved in RNA processing, cell wall and amino acid metabolism were upregulated in the presence of AMF with or without HMs.