Phenanthrene and pyrene uptake by arbuscular mycorrhizal maize and their dissipation in soil

A new strategy of using periphyton to simultaneously promote remediation of PAHs-contaminated soil and production of safer crops

Contaminated farmland leads to serious problems for human health through biomagnification in the soil-crop-human chain. In this paper, we have established a new soil remediation strategy using periphyton for the production of safer rice. Four representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (Phe), pyrene (Pyr), benzo[b]fluoranthene (BbF), and benzo[a]pyrene (BaP), were chosen to generate artificially contaminated soil. Pot experiments demonstrated that in comparison with rice cultivation in polluted soil with ΣPAHs (50 mg kg-1) but without periphyton, adding periphyton decreased ΣPAHs contents in both rice roots and shoots by 98.98% and 99.76%, respectively, and soil ΣPAHs removal reached 94.19%. Subsequently, risk assessment of ΣPAHs based on toxic equivalent concentration (TEQ), pollution load index (PLI), hazard index (HI), toxic unit for PAHs mixture (TUm), and incremental lifetime cancer risk (ILCR) indicated that periphyton lowered the ecological and carcinogenicity risks of PAHs. Besides, the role of periphyton in enhancing the rice productivity was revealed. The results indicated that periphyton alleviated the oxidative stress of PAHs on rice by reducing malondialdehyde (MDA) content and increasing total antioxidant capacity (T-AOC). Periphyton reduced the toxic stress of PAHs on the soil by promoting soil carbon cycling and metabolic activities as well. Periphyton also improved the soil's physicochemical properties, such as the percentage of soil aggregate, the contents of humic substances (HSs) and nutrients, which increased rice biomass. These findings confirmed that periphyton could improve rice productivity by enhancing soil quality and health. This study provides a new eco-friendly strategy for soil remediation and simultaneously enables the production of safe crops on contaminated land.

The role of microplastics in the process of laccase-assisted phytoremediation of phenanthrene-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic pollutants widely distributed in terrestrial environments and laccase was considered as an effective enzyme in PAHs bioremediation. However, laccase-assisted phytoremediation of PAHs-contaminated soil has not been reported. Moreover, the overuse of plastic films in agriculture greatly increased the risk of co-existence of PAHs and microplastics in soil. Microplastics can adsorb hydrophobic organics, thus altering the bioavailability of PAHs and ultimately affecting the removal of PAHs from soil. Therefore, this study aimed to evaluate the efficiency of laccase-assisted maize (Zea mays L.) in the remediation of phenanthrene (PHE)-contaminated soil and investigate the effect of microplastics on this remediation process. The results showed that the combined application of laccase and maize achieved a removal efficiency of 83.47 % for soil PHE, and laccase significantly reduced the accumulation of PHE in maize. However, microplastics significantly inhibited the removal of soil PHE (10.88 %) and reduced the translocation factor of PHE in maize (87.72 %), in comparison with PHE + L treatment. Moreover, microplastics reduced the laccase activity and the relative abundance of some PAHs-degrading bacteria in soil. This study provided an idea for evaluating the feasibility of the laccase-assisted plants in the remediation of PAHs-contaminated soil, paving the way for reducing the risk of secondary pollution in the process of phytoremediation.

The fate of sulfonamides in microenvironments of rape and hot pepper rhizosphere soil system

Sulfonamides (SAs) in agricultural soils can be degraded in rhizosphere, but can also be taken up by vegetables, which thereby poses human health and ecological risks. A glasshouse experiment was conducted using multi-interlayer rhizoboxes to investigate the fate of three SAs in rape and hot pepper rhizosphere soil systems to examine the relationship between the accumulation and their physicochemical processes. SAs mainly entered pepper shoots in which the accumulation ranged from 0.40 to 30.64 mg kg-1, while SAs were found at high levels in rape roots ranged from 3.01 to 16.62 mg kg-1. The BCFpepper shoot exhibited a strong positive linear relationship with log Dow, while such relationship was not observed between other bioconcentration factors (BCFs) and log Dow. Other than lipophilicity, the dissociation of SAs may also influence the uptake and translocation process. Larger TF and positive correlation with log Dow indicate preferential translocation of pepper SAs. There was a significant (p < 0.05) dissipation gradient of SAs observed away from the vegetable roots. In addition, pepper could uptake more SAs under solo exposure, while rape accumulated more SAs under combined exposure. When SAs applied in mixture, competition between SAs might occur to influence the translocation and dissipation patterns of SAs.

Dual effects of nZVI on maize growth and water use are positively mediated by arbuscular mycorrhizal fungi via rhizosphere interactions

Nanoscale zero-valent iron (nZVI) might generate positive and negative effects on plant growth, since it acts as either hazardous or growth-promotion role. It is still unclear whether such dual roles can be mediated by arbuscular mycorrhizal fungi (AMF) in plant-AMF symbiosis. We first identified that in 1.5 g kg^-1 nZVI (≤1.5 g kg^-1 positively), maize biomass was increased by 15.83%; yet in 2.0 g kg^-1 nZVI, it turned to be declined by 6.83%, relative to non-nZVI condition (CK, p < 0.05), showing a negative effect. Interestingly, the inoculation of AMF massively improved biomass by 45.18% in 1.5 g kg^-1 nZVI, and relieved the growth inhibition by 2.0 g kg^-1 nZVI. The event of water use efficiency followed similar trend as that of biomass. We found that proper concentration of nZVI can positively interact with rhizosphere AMF carrier, enabling more plant photosynthetic carbon to be remobilized to mycorrhiza. The scanning of transmission electron microscopy showed that excessive nZVI can infiltrate into root cortical cells and disrupt cellular homeostasis mechanism, significantly increasing iron content in roots by 76.01% (p < 0.05). Simultaneously, the images of scanning electron microscopy showed that nZVI were attached on root surface to form an insoluble iron ion (Fe³⁺) layer, hindering water absorption. However, they were efficiently immobilized and in situ intercepted by extraradical hyphae in mycorrhizal-nZVI symbiosis, lowering iron translocation efficiency by 6.07% (p < 0.05). Herein, the optimized structure remarkably diminished aperture blockage at root surface and improved root activities by 30.06% (p < 0.05). Particularly, next-generation sequencing demonstrated that appropriate amount of nZVI promoted the colonization and development of Funneliformis mosseae as dominant species in rhizosphere, confirming the positive interaction between AMF and nZVI, and its regulatory mechanism. Therefore, dual effects of nZVI can be actively mediated by AMF via rhizosphere interactions. The findings provided new insights into the safe and efficient application of nanomaterials in agriculture.

Interactions between pyrene and heavy metals and their fates in a soil-maize (Zea mays L.) system: Perspectives from the root physiological functions and rhizosphere microbial community

The co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in agricultural soils has become a worldwide food crop security concern. Pot experiments, rhizosphere microbial metagenomic sequencing, and root metatranscriptomic sequencing were performed to investigate the interactions among pyrene, Cu, and Cd in a soil-maize (Zea mays L.) system. This study provided direct evidence that the co-presence of PAHs and heavy metals changed the root physiological functions and the rhizosphere microbial community, which subsequently influenced the fate of the contaminants. Co-contamination at low levels tended to enhance the uptake potential and biodegradation performance of the plant, whereas increased contaminant concentrations produced opposite effects. The co-presence of 1000 mg/kg Cu decreased the abundance of Mycobacterium in the rhizosphere and reduced pyrene degradation by 12%-16%. The presence of 400-750 mg/kg pyrene altered the metabolic processes, molecular binding functions, and catalytic activity of enzymes in the maize roots, thus impeding the phytoextraction of Cu and Cd. Competitive absorption between Cu and Cd was observed for the 800-1000 mg/kg Cu and 50-100 mg/kg Cd co-treatment, in which Cu showed a competitive advantage, enhancing its root-to-shoot translocation. These findings provide important information for the production of safe crops and for the development of phytoremediation technologies.

Dynamic distribution and accumulation of PAHs in winter wheat during whole plant growth: Field investigation

A field investigation was conducted to study the dynamic distribution and accumulation of polycyclic aromatic hydrocarbons (PAHs) in winter wheat in the surrounds of a coal-fired power plant. During March to June 2019, various tissues of winter wheat and the corresponding rhizosphere soil were collected for determination of PAHs. A clear spatial downward trend was found in concentration of Σ₁₅PAHs in rhizosphere soil and wheat grain (194-237 μg kg^-1 DM) with the increasing distance from the coal-fired power plant. Moreover, Σ₁₅PAHs concentration in rhizosphere soil (1081 μg kg^-1 DM), root (464 μg kg^-1 DM) and stem (365 μg kg^-1 DM) of winter wheat at regreening stage and leaf (323 μg kg^-1 DM) at anthesis stage were significantly (p < 0.001) higher than that (895, 432, 287 and 265 μg kg^-1 DM) at maturity stage, respectively. From regreening to maturity stage, root concentration factors (RCF) of 3- and 4-ring PAHs exhibited an increasing trend but the 5-ring PAHs showed an apparently downward trend. However, stem concentration factors (SCF) of 3- and 4-ring PAHs showed a decrease trend while the 5- and 6-ring showed first down and then stable trend. There were positive linear relationship between logKow and logSCF at anthesis (r = 0.681, p < 0.05) and maturity stage (r = 0.751, p < 0.05). Based on linear regression analysis, PAHs in grain mainly came from the transfer of vegetative tissues, and the contribution of PAHs from stem and leaf to grain was higher than that from root. In addition, the present study also found that the physicochemical properties of PAHs play a crucial role in transfer of PAHs from root to vegetative tissues and then to grain. The present research provided more comprehensive information on the fate of PAHs in winter wheat and the safety of the agricultural products.

Dioxins/furans disturb the life cycle of the arbuscular mycorrhizal fungus, Rhizophagus irregularis and chicory root elongation grown under axenic conditions

Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is a promising technology for sustainable removal of hazardous pollutants like dioxins/furans (PCDD/F) from the soil. However, little is known on AMF development in the presence of the persistent organic pollutants, PCDD/F. Thus, the present work aims at investigating the impact of increasing PCDD/F concentrations on the development of both partners of the symbiosis: the AMF, Rhizophagus irregularis and the chicory roots, Cichorium intybus L. grown under axenic conditions. Our results show that even R. irregularis spore germination is not affected by PCDD/F, it occurred mainly in linear way. However, root colonization, extra-radical hyphal elongation and sporulation are reduced by 40, 30, and 75%, respectively, at the highest PCDD/F concentration. In addition, while non-mycorrhizal root growth (length and dry weight) decreased at the highest PCDD/F concentration, no negative effect was observed on the dry weight of mycorrhizal roots. In conclusion, our findings show that although high PCDD/F concentrations disturb the main stages of R. irregularis development, the AMF remains able to fulfill its life cycle in the presence of PCDD/F. Moreover, the mycorrhizal inoculation protects the host plant against PCDD/F phytotoxicity. AMF could thus represent an interesting amendment option to assist phytoremediation of PCDD/F contaminated soils.

AM fungi increase uptake of Cd and BDE-209 and activities of dismutase and catalase in amaranth (Amaranthus hypochondriacus L.) in two contaminants spiked soil

Soil co-contaminated with cadmium (Cd) and decabromodiphenyl ether (BDE-209) is a widespread environmental problem, especially in electronic waste contaminated surroundings. Accumulation of Cd and BDE-209 in crops has possibly harmful effects on local human health. In order to assess the potential of arbuscular mycorrhizal (AM) fungi and amaranth (Amaranthus hypochondriacus L.) in remediation of soil co-contaminated with Cd and BDE-209, pot trials were performed to investigate interactive effects of AM fungi, Cd and BDE-209 on growth of amaranth, uptake of Cd and BDE-209, distribution of chemical forms of Cd and activities of antioxidant enzymes in shoots and dissipation of BDE-209 in soil. The present results showed that shoot biomass of non-mycorrhizal plants was significantly inhibited by increasing of Cd addition (5-15 mg kg^-1), but were only slightly declined with BDE-209 addition (5 mg kg^-1). The interaction of Cd and BDE-209 reduced the proportions of ethanol- and d-H₂O-extractable Cd in shoots, consequently alleviated Cd toxicity to plants and enhanced root uptake of Cd and BDE-209. Inoculation of AM fungi resulted in significantly greater shoot biomass as well as higher concentrations of Cd and BDE-209 compared with non-mycorrhizal treatment. Moreover, AM fungi played a beneficial role in relieving oxidative stress on amaranth by increasing the activities of dismutase (SOD) and catalase (CAT) in shoots and significantly improved the dissipation of BDE-209 in soil. The present study suggested that combination of AM fungi and amaranth may be a potential option for remediation of Cd and BDE-209 co-contaminated soils.

Aided Phytoremediation to Clean Up Dioxins/Furans-Aged Contaminated Soil: correlation between microbial communities and pollutant dissipation

To restore and clean up polluted soils, aided phytoremediation was found to be an effective, eco-friendly, and feasible approach in the case of many organic pollutants. However, little is known about its potential efficiency regarding polychlorinated dibenzo-p-dioxins and furans-contaminated soils. Thus, phytoremediation of aged dioxins/furans-contaminated soil was carried out through microcosm experiments vegetated with alfalfa combined with different amendments: an arbuscular mycorrhizal fungal inoculum (Funneliformis mosseae), a biosurfactant (rhamnolipids), a dioxins/furans degrading-bacterium (Sphingomonas wittichii RW1), and native microbiota. The total dioxins/furans dissipation was estimated to 23%, which corresponds to 48 ng.kg-1 of soil, after six months of culture in the vegetated soil combined with the four amendments compared to the non-vegetated soil. Our findings showed that the dioxins/furans dissipation resulted from the stimulation of soil microbial enzyme activities (fluorescein diacetate hydrolase and dehydrogenase) and the increase of bacterial abundance, richness, and diversity, as well as fungal diversity. Amplicon sequencing using Illumina MiSeq analysis led to identification of several bacterial (Bacillaceae, Sphingomonadaceae) and fungal (Chaetomium) groups known to be involved in dioxins/furans degradation. Furthermore, concomitant cytotoxicity and dioxins/furans concentration decreases were pointed out in the phytoremediated soil. The current study demonstrated the usefulness of combining different types of amendments to improve phytoremediation efficacy of aged dioxins/furans-contaminated soils.

Community composition of arbuscular mycorrhizal fungi associated with native plants growing in a petroleum-polluted soil of the Amazon region of Ecuador

Arbuscular mycorrhizal fungi (AMF) are worldwide distributed plant symbionts. However, their occurrence in hydrocarbon-polluted environments is less investigated, although specific communities may be present with possible interest for remediation strategies. Here, we investigated the AMF community composition associated with the roots of diverse plant species naturally recolonizing a weathered crude oil pond in the Amazon region of Ecuador. Next generation 454 GS-Junior sequencing of an 800 bp LSU rRNA gene PCR amplicon was used. PCR amplicons were affiliated to a maximum-likelihood phylogenetic tree computed from 1.5 kb AMF reference sequences. A high throughput phylogenetic annotation approach, using an evolutionary placement algorithm (EPA) allowed the characterization of sequences to the species level. Fifteen species were detected. Acaulospora species were identified as dominant colonizers, with 73% of relative read abundance, Archaeospora (19.6%) and several genera from the Glomeraceae (Rhizophagus, Glomus macrocarpum-like, Sclerocystis, Dominikia and Kamienskia) were also detected. Although, a diverse community belonging to Glomeraceae was revealed, they represented <10% of the relative abundance in the Pond. Seventy five % of the species could not be identified, suggesting possible new species associated with roots of plants under highly hydrocarbon-polluted conditions.

Glomalin-related soil protein influences the accumulation of polycyclic aromatic hydrocarbons by plant roots

Studies have demonstrated that the inoculation of soil with arbuscular mycorrhizal fungi (AMF) enhances the content of glomalin-related soil protein (GRSP), which in turn elevates the availability of polycyclic aromatic hydrocarbons (PAHs) in soil. However, few studies have examined the influence of GRSP on PAH accumulation by plants and their tissues. Understanding of this issue would provide new perspectives on the role of GRSP in PAH uptake by plants at contaminated sites. This investigation was the first observational study of the GRSP-influenced PAH accumulation in roots of ryegrass (Lolium multiflorum Lam.). GRSP (0-120 mg/L) enhanced the root PAH accumulation in a GRSP-concentration-dependent manner, based on the observed root concentrations and root concentration factors (RCFs). The greatest enhancement of ΣPAH accumulation appeared at 40 mg/L of the total GRSP (T-GRSP) and 80 mg/L of the easily extracted GRSP (EE-GRSP), respectively. The weakly and strongly adsorbed fractions accounted for 88.8-94.4%, while the absorbed fraction contributed no >11.2% of total PAH accumulation in roots. The capacity of PAH adsorption on roots was enlarged in the presence of GRSP (0-120 mg/L). As the adsorbed fraction dominated the total PAH contents in roots overwhelmingly, the GRSP-induced changes in root PAH accumulation were ascribed to GRSP-affected PAH sorption by roots.

The arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 41833 increases the phosphorus uptake and biomass of Medicago truncatula, a benzo[a]pyrene-tolerant plant species

The accumulation of phosphorus (P) in plants increases their biomass and resistance/tolerance to organic pollutants. Both characteristics are mandatory for the utilization of plants in phytoremediation. Arbuscular mycorrhizal (AM) fungi improve plant P nutrition, and thus growth. However, only a few studies have focused on the dynamics of inorganic P (Pi) uptake in AM fungal-colonized plants in the presence of organic pollutants. Indeed, most of the results so far were obtained after harvesting the plants, thus by evaluating P concentration and content at a single time point. Here, we investigated the effects of the AM fungus Rhizophagus irregularis MUCL 41833 on the short-term Pi uptake dynamics of Medicago truncatula plants grown in the presence of benzo[a]pyrene (B[a]P), a polyaromatic hydrocarbon (PAH) frequently found in polluted soils. The study was conducted using a non-destructive circulatory semi-hydroponic cultivation system to investigate the short-term Pi depletion from a nutrient solution and as a corollary, the Pi uptake by the AM fungal-colonized and non-colonized plants. The growth, P concentration, and content of plants were also evaluated at harvest. The presence of B[a]P neither impacted the development of the AM fungus in the roots nor the plant growth and Pi uptake, suggesting a marked tolerance of both organisms to B[a]P pollution. A generally higher Pi uptake coupled with a higher accumulation of P in shoots and roots was noticed in AM fungal-colonized plants as compared to the non-colonized controls, irrespective of the presence or absence of B[a]P. Therefore, fungal-colonized plants showed the best growth. Furthermore, the beneficial effect provided by the presence of the AM fungus in roots was similar in presence or absence of B[a]P, thus opening the door for potential utilization in phytomanagement of PAH-polluted soils.

Effect of single and mixed polycyclic aromatic hydrocarbon contamination on plant biomass yield and PAH dissipation during phytoremediation

Polycyclic aromatic hydrocarbon (PAH)-contaminated sites have a mixture of PAH of varying concentration which may affect PAH dissipation differently to contamination with a single PAH. In this study, pot experiments investigated the impact of PAH contamination on Medicago sativa, Lolium perenne, and Festuca arundinacea biomass and PAH dissipation from soils spiked with phenanthrene (Phe), fluoranthene (Flu), and benzo[a]pyrene (B[a]P) in single and mixed treatments. Stimulatory or inhibitory effects of PAH contamination on plant biomass yields were not different for the single and mixed PAH treatments. Results showed significant effect of PAH treatments on plant growth with an increased root biomass yield for F. arundinacea in the Phe (175%) and Flu (86%) treatments and a root biomass decrease in the mixed treatment (4%). The mean residual PAHs in the planted treatments and unplanted control for the single treatments were not significantly different. B[a]P dissipation was enhanced for single and mixed treatments (71-72%) with F. arundinacea compared to the unplanted control (24-50%). On the other hand, B[a]P dissipation was inhibited with L. perenne (6%) in the single treatment and M. sativa (11%) and L. perenne (29%) in the mixed treatment. Abiotic processes had greater contribution to PAH dissipation compared to rhizodegradation in both treatments. In most cases, a stimulatory effect of PAH contamination on plant biomass yield without an enhancement of PAH dissipation was observed. Plant species among other factors affect the relative contribution of PAH dissipation mechanisms during phytoremediation. These factors determine the effectiveness and suitability of phytoremediation as a remedial strategy for PAH-contaminated sites. Further studies on impact of PAH contamination, plant selection, and rhizosphere activities on soil microbial community structure and remediation outcome are required.

Ability of natural attenuation and phytoremediation using maize (Zea mays L.) to decrease soil contents of polycyclic aromatic hydrocarbons (PAHs) derived from biomass fly ash in comparison with PAHs-spiked soil

A 120-day pot experiment was conducted to compare the ability of natural attenuation and phytoremediation approaches to remove polycyclic aromatic hydrocarbons (PAHs) from soil amended with PAHs-contaminated biomass fly ash. The PAH removal from ash-treated soil was compared with PAHs-spiked soil. The removal of 16 individual PAHs from soil ranged between 4.8% and 87.8% within the experiment. The natural attenuation approach led to a negligible total PAH removal. The phytoremediation was the most efficient approach for PAH removal, while the highest removal was observed in the case of ash-treated soil. The content of low molecular weight (LMW) PAHs and the total PAHs in this treatment significantly decreased (P <.05) over the whole experiment by 47.6% and 29.4%, respectively. The tested level of PAH soil contamination (~1600 µg PAH/kg soil dry weight) had no adverse effects on maize growth as well on the biomass yield. In addition, the PAHs were detected only in maize roots and their bioaccumulation factors were significantly lower than 1 suggesting negligible PAH uptake from soil by maize roots. The results showed that PAHs of ash origin were similarly susceptible to removal as spiked PAHs. The presence of maize significantly boosted the PAH removal from soil and its aboveground biomass did not represent any environmental risk.

Fate and adverse effects of hexabromocyclododecane diastereoisomers (HBCDDs) in a soil-ryegrass pot system

This study explored the fate and adverse effects of 3 main hexabromocyclododecane diastereoisomers (α-, β-, and γ-HBCDDs) in a soil pot system planted with ryegrass (Lolium perenne L.) using a short-term (8 weeks) experiment. At the end of the experiment, soil urease activity in planted spiked soil increased and catalase activity decreased; while there was no obvious change in sucrase and peroxidase activities. HBCDDs mainly accumulated in the root of ryegrass, with root concentration factors (RCF) in the range of 1.46-4.43 and only a small part was transferred to the stem (SCF: 0.198-0.305) and leaf (LCF: 0.042-0.062). The concentration factors varied for different HBCDD diastereoisomers, being in the order of α- > β- > γ-HBCDD for all tissues, indicating preferential accumulation of α-HBCDD in ryegrass tissues. Moreover, the enantiomeric analysis revealed an enrichment of (+)-α-, (-)-β- and (+)-γ-HBCDD enantiomers in ryegrass tissues. β- and γ-HBCDDs (up to 1.90% and 4.11%, respectively) were transformed to aα-HBCDD in ryegrass, while no isomerization product from α-HBCDD was found. Hydroxylated HBCDDs metabolites, such as monoOHHBCDDs and diOHHBCDDs were found in ryegrass tissues for the first time.

Prospects for arbuscular mycorrhizal fungi (AMF) to assist in phytoremediation of soil hydrocarbon contaminants

Arbuscular mycorrhizal fungi (AMF) form mutualistic associations with the roots of 80-90% of vascular plant species and may constitute up to 50% of the total soil microbial biomass. AMF have been considered to be a tool to enhance phytoremediation, as their mycelium create a widespread underground network that acts as a bridge between plant roots, soil and rhizosphere microorganisms. Abundant extramatrical hyphae extend the rhizosphere thus creating the hyphosphere, which significantly increases the area of a plant's access to nutrients and contaminants. The paper presents and evaluates the role and significance of AMF in phytoremediation of hydrocarbon contaminated sites. We focused on (1) an impact of hydrocarbons on arbuscular mycorrhizal symbiosis, (2) a potential of AMF to enhance phytoremediation, (3) determinants that influence effectiveness of hydrocarbon removal from contaminated soils. This knowledge may be useful for selection of proper plant and fungal symbionts and crucial to optimize environmental conditions for effective AMF-mediated phytoremediation. It has been concluded that three-component phytoremediation systems based on synergistic interactions between plant roots, AMF and hydrocarbon-degrading microorganisms demonstrated high effectiveness in dissipation of organic pollutants in soil.

Arbuscular mycorrhizal wheat inoculation promotes alkane and polycyclic aromatic hydrocarbon biodegradation: Microcosm experiment on aged-contaminated soil

Very few studies reported the potential of arbuscular mycorrhizal symbiosis to dissipate hydrocarbons in aged polluted soils. The present work aims to study the efficiency of arbuscular mycorrhizal colonized wheat plants in the dissipation of alkanes and polycyclic aromatic hydrocarbons (PAHs). Our results demonstrated that the inoculation of wheat with Rhizophagus irregularis allowed a better dissipation of PAHs and alkanes after 16 weeks of culture by comparison to non-inoculated condition. These dissipations observed in the inoculated soil resulted from several processes: (i) a light adsorption on roots (0.5% for PAHs), (ii) a bioaccumulation in roots (5.7% for PAHs and 6.6% for alkanes), (iii) a transfer in shoots (0.4 for PAHs and 0.5% for alkanes) and mainly a biodegradation. Whereas PAHs and alkanes degradation rates were respectively estimated to 12 and 47% with non-inoculated wheat, their degradation rates reached 18 and 48% with inoculated wheat. The mycorrhizal inoculation induced an increase of Gram-positive and Gram-negative bacteria by 56 and 37% compared to the non-inoculated wheat. Moreover, an increase of peroxidase activity was assessed in mycorrhizal roots. Taken together, our findings suggested that mycorrhization led to a better hydrocarbon biodegradation in the aged-contaminated soil thanks to a stimulation of telluric bacteria and hydrocarbon metabolization in mycorrhizal roots.

The effect of Funnelliformis mosseae inoculation on the phytoremediation of atrazine by the aquatic plant Canna indica L. var. flava Roxb

Funnelliformis mosseaeinoculation exhibited a beneficial effect on the phytoremediation of atrazine in water by the aquatic plantCanna indicaL.

Influence of rice growth on the fate of polycyclic aromatic hydrocarbons in a subtropical paddy field: a life cycle study

We measured the concentrations and profiles of polycyclic aromatic hydrocarbons (PAHs) in the soil, water, and rice tissues from a typical subtropical paddy system at various stages of rice growth over two growing seasons. Rice growth had a significant impact on the distribution and dissipation of PAHs in the paddy field. While rice was growing, the concentrations of PAHs in the soils decreased at an average decline rate of 5.3±2.9 ng PAHs g(-1) soild(-1), whereas, the concentrations of PAHs in rice tissues increased with growth time. However, the concentrations of PAHs in the rice leaves decreased during the heading stage of both two growing seasons. PAH profiles in soil, water, and different rice tissues also showed different patterns with the growing time of rice. Irrigation water was a significant source of PAHs to the paddy field. Rice growth enhanced the dissipation and transport of PAHs in the paddy system, while the sewage irrigation and straw burning after harvest added or returned PAHs to the system. For food safety precaution, sewage irrigation and straw burning should be well monitored and controlled.

Polyaromatic hydrocarbons impair phosphorus transport by the arbuscular mycorrhizal fungus Rhizophagus irregularis

Phosphate uptake by plant roots is mainly mediated by arbuscular mycorrhizal fungi (AMF). However, the impact on phosphorus (P) transport of polycyclic aromatic hydrocarbons (PAH), persistent organic pollutants widely found in altered soils, is not known up today. Here, we monitored the Rhizophagus irregularis fungal growth and the fungal P transport ability from the extraradical mycelium to the host transformed chicory roots in the presence of anthracene and benzo[a]pyrene (B[a]P) and the combination of both PAH, under in vitro conditions. Firstly, our findings showed that PAH have detrimental effect on the fungal growth. The combination of both PAH was more toxic than each of the PAH individually due to synergistic effects. Secondly, PAH affected the P transport by the fungus from the medium to the roots. This was evidenced by either the decrease in (33)P quantity transported in the roots as well as the decrease in acid phosphatase activity in the mycorrhizal roots. Moreover, the fungal alkaline phosphatase activities remained constant in the extraradical mycelium as well as in the roots in the absence and in the presence of PAH. The GintPT and GiALP (encoding a P transporter and an alkaline phosphatase respectively) gene expressions were also found to be similar in the extraradical mycelium treated with PAH or not (control). These findings suggested that the P uptake by R. irregularis was not affected by PAH but probably the transport from the extraradical mycelium to the intraradical mycelium.

Effects of inoculation of PAH-degrading bacteria and arbuscular mycorrhizal fungi on responses of ryegrass to phenanthrene and pyrene

In order to investigate the effects of soil microorganisms on biochemical and physiological response of plants to PAHs, PAH-degrading bacteria (Acinetobacter sp.) and/or arbuscular mycorrhizal fungus (Glomus mosseae) were inoculated with ryegrass (Lolium multiflorum) under four different concentrations of phenanthrene and pyrene (0, 50 + 50, 100 + 100, 200 + 200 mg kg(-1)) in soils. Acinetobacter sp. played limited roles on the growth of ryegrass, chlorophyll content, water soluble carbohydrate content, malondialdehyde (MDA) content, activities of superoxide dismutase (SOD) and peroxidase (POD) in shoot. By contrast, G. mosseae significantly (P < 0.01) increased ryegrass growth, partially by improving the photosynthetic activity through increasing the chlorophyll content in shoot. G. mosseae also significantly decreased MDA content in shoot. However, G. mosseae significantly increased SOD activity in shoot, which seemed to be resulted from significantly higher pyrene concentrations in shoot. The present study suggested that AM fungi could reduce the damage of cell membranes caused by free radicals, which may be one of the mechanisms involved in mycorrhizal alleviation of plant stress under PAHs. The present study indicated that the dual inoculation was superior to single inoculation in remediating PAHs contaminated soils.

Role of arbuscular mycorrhizal fungus Rhizophagus custos in the dissipation of PAHs under root-organ culture conditions

Polycyclic aromatic hydrocarbons (PAHs) are one of the most common contaminants in soil. Arbuscular mycorrhizal (AM) fungi make host plants resistant to pollutants. This study aims to evaluate the impact of anthracene, phenanthrene and dibenzothiophene on the AM fungus Rhizophagus custos, isolated from soil contaminated by heavy metals and PAHs, under monoxenic conditions. We found a high level of tolerance in R. custos to the presence of PAHs, especially in the case of anthracene, in which no negative effect on AM-colonized root dry weight (root yield) was observed, and also a decrease in the formation of anthraquinone was detected. Increased PAH dissipation in the mycorrhizal root culture medium was observed; however, dissipation was affected by the level of concentration and the specific PAH, which lead us to a better understanding of the possible contribution of AM fungi, and in particular R. custos, to pollutant removal.

Enhancing Aquatic Plant Uptake of PAHs Using Environment-Friendly Surfactant Alkyl Polyglucoside(APG)

Aquatic plant, Scirpus triqueter, uptake of PAHs was investigated with test time for periods of 336h. The effect of APG, an environment-friendly surfactant, on the plant uptake and distribution characteristics of PAHs in root and shoot of the plant were detected. Concentrations of phenanthrene and pyrene in the Scirpus triqueter root increased sharply at the early stage and reached the peak at 16 h, but in shoots elevated significantly and reached the peak at 48h. APG did not show any apparent phytotoxity toward the growth of Scirpus triqueter in the test concentration range. APG(≤30 mg L-1) can enhance the root uptake and root concentration factors (RCF) of phenanthrene in plant, whereas APG(>30 mg L-1) may inhibit the PAHs uptake by the plant. Results indicate that the APG would be a preferred selection for the application of surfactant-enhanced phytoremediation and optimal concentration should be determined before the application of APG.