Arbuscular Mycorrhizal Fungal Hyphae Alter Soil Bacterial Community and Enhance Polychlorinated Biphenyls Dissipation

A transition from arbuscular to ectomycorrhizal forests halts soil carbon sequestration during subtropical forest rewilding

Ecological succession and restoration rapidly promote multiple dimensions of ecosystem functions and mitigate global climate change. However, the factors governing the limited capacity to sequester soil organic carbon (SOC) in old forests are poorly understood. Ecological theory predicts that plants and microorganisms jointly evolve into a more mutualistic relationship to accelerate detritus decomposition and nutrient regeneration in old than young forests, likely explaining the changes in C sinks across forest succession or rewilding. To test this hypothesis, we conducted a field experiment of root-mycorrhizal exclusion in successional subtropical forests to investigate plant-decomposer interactions and their effects on SOC sequestration. Our results showed that SOC accrual rate at the 0-10 cm soil layer was 1.26 mg g-1 yr-1 in early-successional arbuscular mycorrhizal (AM) forests, which was higher than that in the late-successional ectomycorrhizal (EcM) forests with non-significant change. A transition from early-successional AM to late-successional EcM forests increase fungal diversity, especially EcM fungi. In the late-successional forests, the presence of ectomycorrhizal hyphae promotes SOC decomposition and nutrient cycle by increasing soil nitrogen and phosphorus degrading enzyme activity as well as saprotrophic microbial richness. Across early- to late-successional forests, mycorrhizal priming effects on SOC decomposition explain a slow-down in the capacity of older forests to sequester soil C. Our findings suggest that a transition from AM to EcM forests supporting greater C decomposition can halt the capacity of forests to provide nature-based global climate change solutions.

Sustainable Remediation of Soil and Water Utilizing Arbuscular Mycorrhizal Fungi: A Review

Phytoremediation is recognized as an environmentally friendly technique. However, the low biomass production, high time consumption, and exposure to combined toxic stress from contaminated media weaken the potential of phytoremediation. As a class of plant-beneficial microorganisms, arbuscular mycorrhizal fungi (AMF) can promote plant nutrient uptake, improve plant habitats, and regulate abiotic stresses, and the utilization of AMF to enhance phytoremediation is considered to be an effective way to enhance the remediation efficiency. In this paper, we searched 520 papers published during the period 2000-2023 on the topic of AMF-assisted phytoremediation from the Web of Science core collection database. We analyzed the author co-authorship, country, and keyword co-occurrence clustering by VOSviewer. We summarized the advances in research and proposed prospective studies on AMF-assisted phytoremediation. The bibliometric analyses showed that heavy metal, soil, stress tolerance, and growth promotion were the research hotspots. AMF-plant symbiosis has been used in water and soil in different scenarios for the remediation of heavy metal pollution and organic pollution, among others. The potential mechanisms of pollutant removal in which AMF are directly involved through hyphal exudate binding and stabilization, accumulation in their structures, and nutrient exchange with the host plant are highlighted. In addition, the tolerance strategies of AMF through influencing the subcellular distribution of contaminants as well as chemical form shifts, activation of plant defenses, and induction of differential gene expression in plants are presented. We proposed that future research should screen anaerobic-tolerant AMF strains, examine bacterial interactions with AMF, and utilize AMF for combined pollutant removal to accelerate practical applications.

Combined application of arbuscular mycorrhizal fungi and selenium fertilizer increased wheat biomass under cadmium stress and shapes rhizosphere soil microbial communities

BACKGROUND

Selenium (Se) fertilizer and arbuscular mycorrhizal fungi (AMF) are known to modulate cadmium (Cd) toxicity in plants. However, the effects of their co-application on wheat growth and soil microbial communities in Cd-contaminated soil are unclear.

RESULTS

A pot experiment inoculation with two types of AMF and the application of Se fertilizer under Cd stress in wheat showed that inoculation AMF alone or combined with Se fertilizer significantly increased wheat biomass. Se and AMF alone or in combination significantly reduced available Cd concentration in wheat and soil, especially in the Se combined with Ri treatment. High throughput sequencing of soil samples indicated that Se and AMF application had stronger influence on bacterial community compared to fungal community and the bacterial network seemed to have more complex interconnections than the fungal network, and finally shaped the formation of specific microflora to affect Cd availability.

CONCLUSION

These results indicate that the application of Se and AMF, particularly in combination, could successfully decrease soil Cd availability and relieve the harm of Cd in wheat by modifying rhizosphere soil microbial communities.

The bioremediation of the typical persistent organic pollutants (POPs) by microalgae-bacteria consortia: A systematic review

With industrialisation and the rapidly growing agricultural demand, many organic compounds have been leaked into the environment, causing serious damage to the biosphere. Persistent organic pollutants (POPs) are a type of toxic chemicals that are resistant to degradation through normal chemical, biological or photolytic approaches. With their stable chemical structures, POPs can be accumulated in the environment, and transported through wind and water, causing global environmental issues. Many researches have been conducted to remediate POPs contamination using various kinds of biological methods, and significant results have been seen. Microalgae-bacteria consortium is a newly developed concept for biological technology in contamination treatment, with the synergetic effects between microalgae and bacteria, their potential for pollutants degradation can be further released. In this review, two types of POPs (polychlorinated biphenyls and polycyclic aromatic hydrocarbons) are selected as the targeted pollutants to give a systematic analysis of the biodegradation through microalgae and bacteria, including the species selection, the identification of dominant enzymes, as well as the real application performance of the consortia. In the end, some outlooks and suggestions are given to further guide the development of applying microalgae-bacteria consortia in remediating POPs contamination. In general, the coculturing of microalgae and bacteria is a novel and efficient way to fulfil the advanced treatment of POPs in soil or liquid phase, and both monooxygenase and dioxygenase belonging to oxygenase play a vital role in the biodegradation of PCBs and PAHs. This review provides a general guide in the future investigation of biological treatment of POPs.

Nutrient-dependent cross-kingdom interactions in the hyphosphere of an arbuscular mycorrhizal fungus

Introduction

The hyphosphere of arbuscular mycorrhizal (AM) fungi is teeming with microbial life. Yet, the influence of nutrient availability or nutrient forms on the hyphosphere microbiomes is still poorly understood.

Methods

Here, we examined how the microbial community (prokaryotic, fungal, protistan) was affected by the presence of the AM fungus Rhizophagus irregularis in the rhizosphere and the root-free zone, and how different nitrogen (N) and phosphorus (P) supplements into the root-free compartment influenced the communities.

Results

The presence of AM fungus greatly affected microbial communities both in the rhizosphere and the root-free zone, with prokaryotic communities being affected the most. Protists were the only group of microbes whose richness and diversity were significantly reduced by the presence of the AM fungus. Our results showed that the type of nutrients AM fungi encounter in localized patches modulate the structure of hyphosphere microbial communities. In contrast we did not observe any effects of the AM fungus on (non-mycorrhizal) fungal community composition. Compared to the non-mycorrhizal control, the root-free zone with the AM fungus (i.e., the AM fungal hyphosphere) was enriched with Alphaproteobacteria, some micropredatory and copiotroph bacterial taxa (e.g., Xanthomonadaceae and Bacteroidota), and the poorly characterized and not yet cultured Acidobacteriota subgroup GP17, especially when phytate was added. Ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira were significantly suppressed in the presence of the AM fungus in the root-free compartment, especially upon addition of inorganic N. Co-occurrence network analyses revealed that microbial communities in the root-free compartment were complex and interconnected with more keystone species when AM fungus was present, especially when the root-free compartment was amended with phytate.

Conclusion

Our study showed that the form of nutrients is an important driver of prokaryotic and eukaryotic community assembly in the AM fungal hyphosphere, despite the assumed presence of a stable and specific AM fungal hyphoplane microbiome. Predictable responses of specific microbial taxa will open the possibility of using them as co-inoculants with AM fungi, e.g., to improve crop performance.

Advanced biotechnology strategies for detoxification of persistent organic pollutants and toxic elements in soil

This paper aims to comprehensively examine and present the current state of persistent organic pollutants (POPs) and toxic elements (TEs) in soil. Additionally, it seeks to assess the viability of employing advanced biotechnology, specifically phytoremediation with potent microbial formulations, as a means of detoxifying POPs and TEs. In the context of the "global treaty," which is known as the Stockholm Convention, we analyzed the 3D chemical structures of POPs and its prospects for living organisms which have not been reviewed up to date. The obstacles associated with the phytoremediation strategy in biotechnology, including issues like slow plant growth and limited efficiency in contaminant uptake, have also been discussed and demonstrated. While biotechnology is recognized as a promising method for detoxifying persistent organic pollutants (POPs) and facilitating the restoration of contaminated and degraded lands, its full potential in the field is constrained by various factors. Recent advances in biotechnology, such as microbial enzymes, designer plants, composting, and nanobiotechnology techniques, have opened up new avenues for mitigating persistent organic pollutants (POPs) and toxic elements (TEs). The insights gained from this review can contribute to the development of innovative, practical, and economically viable approaches for remediating and restoring soils contaminated with persistent organic pollutants (POPs) and toxic elements (TEs). The ultimate aim is to reduce the risks to both human and environmental health.

Myco- and phyco-remediation of polychlorinated biphenyls in the environment: a review

Polychlorinated biphenyls (PCBs) are toxic organic compounds and pose serious threats to environment and public health. PCBs still exist in different environments such as air, water, soil, and sediments even on ban. This review summarizes the phyco- and myco-remediation technologies developed to detoxify the PCB-polluted sites. It was found that algae mostly use bioaccumulation to biodegradation strategies to reclaim the environment. As bio-accumulator, Ulva rigida C. Agardh has been best at 25 ng/g dry wt to remove PCBs. Evidently, Anabaena PD-1 is the only known PCB degrading alga and efficiently degrade Aroclor 1254 and dioxin-like PCBs up to 84.4% and 37.4% to 68.4%, respectively. The review suggested that factors such as choice of algal strains, response of microalgae, biomass, the rate of growth, and cost-effective cultivation conditions significantly influence the remediation of PCBs. Furthermore, the Anabaena sp. linA gene of Pseudomonas paucimobilis Holmes UT26 showed enhanced efficiency. Pleurotus ostreatus (Jacq.) P. Kumm is the most efficient PCB degrading fungus, degrading up to 98.4% and 99.6% of PCB in complex and mineral media, respectively. Combine metabolic activities of bacteria and yeast led to the higher detoxification of PCBs. Fungi-algae consortia would be a promising approach in remediation of PCBs. A critical analysis on potentials and limits of PCB treatment through fungal and algal biosystems have been reviewed, and thus, new insights have emerged for possible bioremediation, bioaccumulation, and biodegradation of PCBs.

Effects of ecohydrological interfaces on migrations and transformations of pollutants: A critical review

With the rapid development of society, the soil and water environments in many countries are suffering from severe pollution. Pollutants in different phases will eventually gather into the soil and water environments, and a series of migrations and transformations will take place at ecohydrological interfaces with water flow. However, it is still not clear how ecohydrological interfaces affect the migration and the transformation of pollutants. Therefore, this paper summarizes the physical, ecological, and biogeochemical characteristics of ecohydrological interfaces on the basis of introducing the development history of ecohydrology and the concept of ecohydrological interfaces. The effects of ecohydrological interfaces on the migration and transformation of heavy metals, organic pollutants, and carbon‑nitrogen‑phosphorus (C-N-P) pollutants are emphasized. Lastly, the prospects of applying ecohydrological interfaces for the removal of pollutants from the soil and water environment are put forward, including strengthening the ability to monitor and simulate ecohydrological systems at micro and macro scales, enhancing interdisciplinary research, and identifying main influencing factors that can provide theoretical basis and technical support.

Recent advances in PCB removal from historically contaminated environmental matrices

Despite being drastically restricted in the 1970s, polychlorinated biphenyls (PCBs) still belong among the most hazardous contaminants. The chemical stability and dielectric properties of PCBs made them suitable for a number of applications, which then lead to their ubiquitous presence in the environment. PCBs are highly bioaccumulative and persistent, and their teratogenic, carcinogenic, and endocrine-disrupting features have been widely reported in the literature. This review discusses recent advances in different techniques and approaches to remediate historically contaminated matrices, which are one of the most problematic in regard to decontamination feasibility and efficiency. The current knowledge published in the literature shows that PCBs are not sufficiently removed from the environment by natural processes, and thus, the suitability of some approaches (e.g., natural attenuation) is limited. Physicochemical processes are still the most effective; however, their extensive use is constrained by their high cost and often their destructiveness toward the matrices. Despite their limited reliability, biological methods and their application in combinations with other techniques could be promising. The literature reviewed in this paper documents that a combination of techniques differing in their principles should be a future research direction. Other aspects discussed in this work include the incompleteness of some studies. More attention should be given to the evaluation of toxicity during these processes, particularly in terms of monitoring different modes of toxic action. In addition, decomposition mechanisms and products need to be sufficiently clarified before combined, tailor-made approaches can be employed.

Changes in Bacterial Diversity and Composition in Response to Co-inoculation of Arbuscular Mycorrhizae and Zinc-Solubilizing Bacteria in Turmeric Rhizosphere

In the present study, the impact of co-inoculation of arbuscular mycorrhizal fungi (AM Rhizophagus sp., NCBI-MN710507) and Zinc solubilizing bacteria (ZSB2- Bacillus megaterium, NCBI-KY687496) on plant growth, soil dehydrogenase activity, soil respiration and the changes in bacterial diversity in rhizosphere of turmeric (Curcuma longa) were examined. Our results showed that higher plant height and dry biomass were observed in treatments co-inoculated with AM and ZSB2. Likewise, dehydrogenase activity and soil respiration were more significant in the co-inoculation treatment, indicating abundance of introduced as well as inherent microflora. Bacterial community analysis using 16S rRNA revealed changes in the structure and diversity of various taxa due to co-inoculation of AM and ZSB2. Alpha diversity indexes (Shannon and Chao1) and beta diversity indexes obtained through unweighted unifrac approach also showed variation among the treated samples. Chloroflexi was the dominant phylum followed by Proteobacteria, Actinobacteria and Acidobacteria which accounted for 80% of all treated samples. The composition of bacterial communities at genus level revealed that co-inoculation caused distinct bacterial profiles. The Linear discriminant analysis effect size revealed the dominance of ecologically significant genera such as Bradyrhizobium, Candidatus, Pedomicrbium, Thermoporothrix, Acinetobacter and Nitrospira in treatments co-inoculated with AM and ZSB2. On the whole, co-inoculated treatments revealed enhanced microbial activities and caused significant positive shifts in the bacterial diversity and abundance compared to treatments with sole application of ZSB2 or AM.

Accumulation and Transfer of Cadmium Isotope (112Cd) by Sonchus asper Intercropped with Vicia faba and Implications for Phytoremediation

Accumulation and transfer of Cd by Sonchus asper intercropped with a legume crop, Vicia faba were determined via ¹¹²Cd as a tracer to assess the potential of Sonchus asper as a hyperaccumulator. In this study, Sonchus asper and Vicia faba were planted side by side in soils amended with arbuscular mycorrhizae, and ¹¹²Cd was applied to either Sonchus asper or Vicia faba planted soils while the neighboring plant received ¹¹²Cd across a nylon net impermeable to the roots. Mean concentration of ¹¹²Cd in the shoot of Sonchus asper was 7.0 times higher than Vicia faba. The translocation factor of ¹¹²Cd in Sonchus asper were 39 and 400 times higher than in Vicia faba under the ¹¹²Cd direct and indirect treatments, respectively. The results suggested that the intercropping of Sonchus asper as a hyperaccumulator with Vicia faba, might be a feasible approach for phytoremediation of Cd contaminated soil.

Arbuscular mycorrhizal fungus facilitates ryegrass (Lolium perenne L.) growth and polychlorinated biphenyls degradation in a soil applied with nanoscale zero-valent iron

Nanoscale zero-valent iron (nZVI) shows an excellent degradation effect on chlorinated contaminants in soil, but poses a threat to plants in combination with phytoremediation. Arbuscular mycorrhizal (AM) fungus can reduce the phyototoxicity of nZVI, but their combined impacts on polychlorinated biphenyls (PCBs) degradation and plant growth remain unclear. Here, a greenhouse pot experiment was conducted to investigate the influences of nZVI and/or Funneliformis caledonium on soil PCB degradation and ryegrass (Lolium perenne L.) antioxidative responses. The amendment of nZVI significantly reduced not only the total and homolog concentrations of PCBs in the soil, but also the ryegrass biomass as well as soil available P and root P concentrations. Moreover, nZVI significantly decreased leaf superoxide disutase (SOD) activity, while tended to decrease the protein content. In contrast, the additional inoculation of F. caledonium significantly increased leaf SOD activity and protein content, while tended to increase the catalase activity and tended to decrease the malondialdehyde content. The additional inoculation of F. caledonium also significantly increased soil alkaline phosphatase activity, and tended to increase root P concentration, but had no significantly effects on soil available P concentration, the biomass and P acquisition of ryegrass, which could be attributed to the fixation of soil available nutrients by nZVI. Additionally, F. caledonium facilitated PCB degradation in the nZVI-applied soil. Thus, AM fungus can alleviate the nZVI-induced phytotoxicity, showing great application potentials in accompany with nZVI for soil remediation.

Metabolite profiling of the hyphal exudates of Rhizophagus clarus and Rhizophagus irregularis under phosphorus deficiency

Arbuscular mycorrhizal (AM) fungal extraradical hyphae exude their metabolites into the soil. Root exudate metabolites are affected by plant species and P status. However, the effect of P status on AM hyphal exudate metabolites has been unknown. This study aimed to examine hyphal exudate metabolite composition of two AM fungal species and their response to P deficiency through metabolite profiling. Rhizophagus clarus and R. irregularis were grown in a two-compartment in vitro culture system of Linum usitatissimum roots on solid modified Strullu-Romand medium in combination with two P levels (3 µM (P3) and 30 µM (P30)). Hyphal exudates were collected from the hyphal compartment at 118 days after inoculation (DAI). The metabolite composition of the hyphal exudates was determined by capillary electrophoresis/time-of-flight mass spectrometry, resulting in the identification of a total of 141 metabolites at 118 DAI. In the hyphal exudates of R. clarus, the concentrations of 18 metabolites, including sugars, amino acids, and organic acids, were significantly higher (p < 0.05) under P3 than under P30 conditions. In contrast, the concentrations of 10 metabolites, including sugar and amino acids, in the hyphal exudates of R. irregularis were significantly lower (p < 0.05) under P3 than under P30 conditions. These findings suggest that the extraradical hyphae of AM fungi exude diverse metabolites of which concentrations are affected by P conditions and differ between AM fungal species.

The Aromatic Plant Clary Sage Shaped Bacterial Communities in the Roots and in the Trace Element-Contaminated Soil More Than Mycorrhizal Inoculation - A Two-Year Monitoring Field Trial

To cope with soil contamination by trace elements (TE), phytomanagement has attracted much attention as being an eco-friendly and cost-effective green approach. In this context, aromatic plants could represent a good option not only to immobilize TE, but also to use their biomass to extract essential oils, resulting in high added-value products suitable for non-food valorization. However, the influence of aromatic plants cultivation on the bacterial community structure and functioning in the rhizosphere microbiota remains unknown. Thus, the present study aims at determining in TE-aged contaminated soil (Pb - 394 ppm, Zn - 443 ppm, and Cd - 7ppm, respectively, 11, 6, and 17 times higher than the ordinary amounts in regional agricultural soils) the effects of perennial clary sage (Salvia sclarea L.) cultivation, during two successive years of growth and inoculated with arbuscular mycorrhizal fungi, on rhizosphere bacterial diversity and community structure. Illumina MiSeq amplicon sequencing targeting bacterial 16S rRNA gene was used to assess bacterial diversity and community structure changes. Bioinformatic analysis of sequencing datasets resulted in 4691 and 2728 bacterial Amplicon Sequence Variants (ASVs) in soil and root biotopes, respectively. Our findings have shown that the cultivation of clary sage displayed a significant year-to-year effect, on both bacterial richness and community structures. We found that the abundance of plant-growth promoting rhizobacteria significantly increased in roots during the second growing season. However, we didn't observe any significant effect of mycorrhizal inoculation neither on bacterial diversity nor on community structure. Our study brings new evidence in TE-contaminated areas of the effect of a vegetation cover with clary sage cultivation on the microbial soil functioning.

The synergy effect of arbuscular mycorrhizal fungi symbiosis and exogenous calcium on bacterial community composition and growth performance of peanut (Arachis hypogaea L.) in saline alkali soil

Peanut (Arachis hypogaea. L) is an important oil seed crop. Both arbuscular mycorrhizal fungi (AMF) symbiosis and calcium (Ca²⁺) application can ameliorate the impact of saline soil on peanut production, and the rhizosphere bacterial communities are also closely correlated with peanut salt tolerance; however, whether AMF and Ca²⁺ can withstand high-salinity through or partially through modulating rhizosphere bacterial communities is unclear. Here, we used the rhizosphere bacterial DNA from saline alkali soil treated with AMF and Ca²⁺ alone or together to perform high-throughput sequencing of 16S rRNA genes. Taxonomic analysis revealed that AMF and Ca²⁺ treatment increased the abundance of Proteobacteria and Firmicutes at the phylum level. The nitrogen-fixing bacterium Sphingomonas was the dominant genus in these soils at the genus level, and the soil invertase and urease activities were also increased after AMF and Ca²⁺ treatment, implying that AMF and Ca²⁺ effectively improved the living environment of plants under salt stress. Moreover, AMF combined with Ca²⁺ was better than AMF or Ca²⁺ alone at altering the bacterial structure and improving peanut growth in saline alkali soil. Together, AMF and Ca²⁺ applications are conducive to peanut salt adaption by regulating the bacterial community in saline alkali soil.

Transportation and degradation of decabrominated diphenyl ether in sequential anoxic and oxic crop rotation

This work evaluated the debromination and uptake of ¹⁴C-labeled BDE-209 in rice cultivars grown in anoxic soil for 120 days (d) followed by cultivation of vegetables (peanut, eggplant and pepper) in oxic soil (120 d). Degradation of BDE-209 to lower polybrominated diphenyl ethers (PBDEs) occurred in cultivated soils, and more metabolites were released in oxic soil than in anoxic soil. The crop rotation from anoxic to oxic greatly enhanced the dissipation of BDE-209 in the soil (P < 0.05), in which the dissipation in anoxic soil planted with Huanghuazhan (HHZ, indica) and Yudao 1 (YD1, indica) were 6.8% and 2.4%, respectively, while in oxic soil with peanut and pepper were increased to 25.8% and 21.7%, respectively. The crop rotation also enhanced the degradation of BDE-209 in the soil, the recovered BDE-209 in soil after 120 d anoxic incubation with YD1 was 81.1%, but it decreased to 47.8% and 45.8% after another 120 d oxic incubation. Bioconcentration factors were between 0.23 and 0.36 for rice, eggplant and pepper but reached to 0.5 in peanut, which contains more lipids in the edible portion than the other test crops. The estimated daily intake for vegetables was 0.01-0.07 μg BDE-209-equivalent kg^-1 bw day^-1, which is at least two orders of magnitude below the maximum acceptable oral dose (7 μg kg^-1 bw day^-1). Our work confirms that crop rotation from rice to vegetable enhanced the dissipation and debromination of BDE-209 in the soil, and indicate that sequential anoxic-oxic rotation practice is considered to be effective in remediation of environmental pollutants.

Changes in rhizobacterial community mediating atrazine dissipation by arbuscular mycorrhiza

Although it was well known that arbuscular mycorrhizal fungus (AMF) inoculation significantly increased atrazine dissipation in the soil, the effect of AMF on bacterial community, especially potential atrazine-degrading bacteria mediating atrazine dissipation has been overlooked. In the present study, there were four different treatments: Funnelliformis mosseae inoculation with or without atrazine; and non-AMF inoculation with or without atrazine. F. mosseae significantly increased atrazine dissipation rate from 28.7% to 53.3%. Then 16S rRNA gene sequencing results indicated that bacteria community differed significantly by F. mosseae inoculation and atrazine addition. The Shannon index decreased significantly with AMF and atrazine at phylum and family level, and significant inhibition of atrazine on evenness was also observed. LEFSe analysis revealed that Terrimonas and Arthrobacter were significantly associated with F. mosseae, as well as unidentified_Nitrospiraceae associated with atrazine addition. There are several bacterial taxa associated with both F. mosseae inoculation and atrazine addition. Totally, twelve atrazine-degrading bacterial genera (>0.10%) were identified. When atrazine was added, the abundance of Arthrobacter, Burkholderia, Mycobacterium and Streptomyces increased in F. mosseae inoculation treatment, but Nocardioides, Pseudomonas, Bradyrhizobium, Rhizobium, Rhodobacter, Methylobacterium, Bosea and Shinella decreased. In the presence of atrazine, activities of dehydrogenase, urease, acid and alkaline phosphatase in F. mosseae inoculation treatment were significantly higher than those in non-inoculation. However, there was no significant relationship between bacterial community and any soil enzyme activity in four treatments. Our findings reveal the potential relationship between soil bacterial community and AMF inoculation during atrazine dissipation.

Initial microbial status modulates mycorrhizal inoculation effect on rhizosphere microbial communities

Arbuscular mycorrhizal fungi (AMF) play a central role in rhizosphere functioning as they interact with both plants and soil microbial communities. The conditions in which AMF modify plant physiology and microbial communities in the rhizosphere are still poorly understood. In the present study, four different plant species, (clover, alfalfa, ryegrass, tall fescue) were cultivated in either sterilized (γ ray) or non-sterilized soil and either inoculated with a commercial AMF (Glomus LPA Val 1.) or not. After 20 weeks of cultivation, the mycorrhizal rate and shoot and root biomasses were measured. The abundance and composition of bacteria, archaea, and fungi were analyzed, respectively, by quantitative PCR (qPCR) and fingerprinting techniques. Whilst sterilization did not change the AMF capacity to modify plant biomass, significant changes in microbial communities were observed, depending on the taxon and the associated plant. AMF inoculation decreases both bacterial and archaeal abundance and diversity, with a greatest extent in sterilized samples. These results also show that AMF exert different selections on soil microbial communities according to the plant species they are associated with. This study suggests that the initial abundance and diversity of rhizosphere microbial communities should be considered when introducing AMF to cultures.

Effects of β-cyclodextrin on phytoremediation of soil co-contaminated with Cd and BDE-209 by arbuscular mycorrhizal amaranth

Pot experiments were conducted to investigate the effects of a series of β-cyclodextrin (β-CD) on phytoremediation of soil co-contaminated with Cd and BDE-209 by amaranth (Amaranthus hypochondriacus L.) inoculated with arbuscular mycorrhizal fungus (AMF) - Rhizophagus intraradices. Results showed that the combination of mycorrhizal amaranth and 0.4% β-CD (RI+β_0.4) significantly enhanced Cd concentrations and contents in shoots, total PBDEs concentration in roots, and BDE-209 dissipation in soil. Moreover, the RI+β_0.4 treatment exerted the highest removal efficiency of both Cd and BDE-209. On the contrary, the xylem area, shoot Cd and BDE-209 concentrations and contents, and removal efficiency of Cd were markedly reduced in mycorrhizal amaranth with 0.8% or 1.2% β-CD treatments (RI+β_0.8, RI+β_1.2), compared with single inoculation treatment. The well-organized chloroplast and well-defined root anatomical structure were also observed in the treatment of RI+β_0.4. Positive correlation was found between shoot biomass and chlorophyll concentrations. Shoot Cd or BDE-209 concentrations were positively correlated with xylem areas. In conclusion, mycorrhizal amaranth added with 0.4% β-CD could be used for the decontamination of soil polluted with mixture of Cd and BDE-209 due to the higher chlorophyll concentration and the larger xylem area.

Contrasting dynamics of polychlorinated biphenyl dissipation and fungal community composition in low and high organic carbon soils with biochar amendment

Biochar amendment has been advocated as an effective method to remediate organic pollutant-contaminated soils through adsorption and stimulating microbial degradation. However, such effects can vary depending on soil properties and biochar physiochemical characteristics. The objective of this study was to compare the dynamic variations of polychlorinated biphenyls (PCBs) in low and high soil organic carbon (SOC) soils both amended with biochar and to investigate its linkage with fungal community composition. Two soils having the same texture and soil type but varying in SOC contents were contaminated with PCBs to a final concentration of 60 mg kg^-1 and amended with 2% bamboo biochar. Temporal changes of PCB remaining in soils and adsorbed on biochar particles were determined during a 2-month incubation. Diversity and composition of fungal communities in both low and high SOC soils were investigated with Illumina MiSeq sequencing. The results showed that the PCB concentrations in low SOC soil were significantly lower than those in high SOC soil during the incubation. In the low SOC soil, the biochar particle adsorbed higher amounts of PCB, tetra-, and penta-chlorobiphenyls (CBs) than those in high SOC soil, and stimulated the dissipation of di- and tri-CBs. The nonmetric multidimensional scaling profile showed significant (p < 0.05) differences in the fungal community composition between the low and high SOC soils. The relative abundances of Eurotiomycetes were gradually increased, whereas those of Sordariomycetes and Dothideomycetes were decreased with increasing incubation time in the low SOC soils. In contrast, the fungal communities in high SOC soils were relatively stable. The relative abundances of Eurotiomycetes and Sordariomycetes were positively correlated with PCB dissipation in low and high SOC content soils, respectively. Our results suggest that SOC content affects PCB dissipation and fungal community composition in biochar-amended soils, and biochars have a high remediation potential of PCB in soils with low SOC contents.

Arbuscular mycorrhizal fungal community in the topsoil of a subtropical landfill restored after 18 years

Restoration of disturbed habitats (e.g., landfills and mine tailings) is important to recover ecosystem services. Arbuscular mycorrhizal (AM) fungal community is an important indicator of ecological performance of ecosystems. Rhizospheric soils were collected in two sites (A1 and A2) within the restored area of a landfill (18 yrs after restoration), and two sites (B and C, serving as control) in the adjacent natural area. Soil properties were analysed. AM fungal communities in soils were analysed by sequencing 18S small subunit rRNA gene. Results showed that genera Glomus (the most abundant, relative abundance: 10-24%), Paraglomus and Rhizophagus were commonly found at all sites. Acaulospora and Redeckera were found exclusively at natural sites, while Scutellospora only at the restored site. On average, AM fungal species richness was lower (87 operational taxonomy units, OTUs), while diversity was higher (Shannon index 3.2) in restored site, compared with control (107 OTUs, Shannon index 2.8). The structure of the AM fungal communities was influenced by soil nitrogen and cation exchange capacity. The restored sites possessed a more phylogenetically heterogeneous fungal community than that in natural sites. AM fungal community at restored sites clearly deviated from that at natural sites, indicating that current restoration practice is certainly inadequate. The trend of ecological succession could be significantly influenced by rehabilitation methods, such as adjustment of initial soil properties and selection of plant species. This study highlights the necessity of assessing AM fungal community during ecological restoration for sustainable ecosystem, in addition to plant and bacteria.

Dynamic changes of polychlorinated biphenyls (PCBs) degradation and adsorption to biochar as affected by soil organic carbon content

Biochar amendment constitutes an effective soil remediation strategy for organic contaminants, but how the soil organic carbon (SOC) content affects polychlorinated biphenyls (PCBs) degradation and adsorption to biochar remains unclear. A 120-day biochar amendment experiment was conducted to investigate the dynamic effects of SOC on PCBs degradation in soil and adsorption to biochar. Biochar in low-SOC (LSOC) soils adsorbed a significantly higher amount of PCBs than did that in high-SOC (HSOC) soils. PCBs degradation was also greatly enhanced in LSOC soils when compared with that in HSOC soils after 30 days of biochar amendment. Degradation of di- and tri-chlorobiphenyls (CBs) were significantly enhanced in the LSOC soils than in the HSOC soils, while the biochar in the LSOC soil tended to adsorb significantly higher amount of tetra- and penta-CBs. Compared to biochar adsorption, microbial degradation contributed significantly to soil PCBs removal. Soil bacterial 16S rDNA abundance increased concomitantly with soil PCBs degradation. Regardless of SOC, soil bacterial communities and PCB congener compositions changed significantly after 30 days of biochar amendment. The abundance of Actinobacteria and Firmicutes were negatively correlated with the soil PCBs removal, while Gemmatimonadetes and Proteobacteria were positively correlated. The results of this study revealed that, compared with that to HSOC soils, biochar amendment to LSOC soils may have a greater positive effect on both soil PCB degradation and biochar adsorption. Therefore, the application of bamboo biochar to LSOC soils could be more effective than that to HSOC soils with respect to the remediation of PCBs contamination.

Arbuscular mycorrhizal inoculum sources influence bacterial, archaeal, and fungal communities' structures of historically dioxin/furan-contaminated soil but not the pollutant dissipation rate

Little is known about the influence of arbuscular mycorrhizal fungi (AMF) inoculum sources on phytoremediation efficiency. Therefore, the aim of this study was to compare the effects of two mycorrhizal inocula (indigenous and commercial inocula) in association with alfalfa and tall fescue on the plant growth, the bacterial, fungal, and archaeal communities, and on the removal of dioxin/furan (PCDD/F) from a historically polluted soil after 24 weeks of culture in microcosms. Our results showed that both mycorrhizal indigenous and commercial inocula were able to colonize plant roots, and the growth response depends on the AMF inoculum. Nevertheless, the improvement of root dry weight in inoculated alfalfa with indigenous inoculum and in inoculated tall fescue with commercial inoculum was clearly correlated with the highest mycorrhizal colonization of the roots in both plant species. The highest shoot dry weight was obtained in inoculated alfalfa and tall fescue with the commercial inoculum. AMF inoculation differently affected the number of bacterial and archaeal OTUs and bacterial diversity, with elevated bacterial and archaeal OTUs and bacterial diversity observed with indigenous inoculum. Mycorrhizal inoculation increases the abundance of bacterial OTUs (in particular with indigenous inoculum) and microbial richness but it does not improve PCDD/F dissipation. Vegetation had no effect on the abundance of microbial OTUs nor on richness but stimulated specific communities (Planctomycetia and Gammaproteobacteria) likely to be involved in the dissipation of PCDD/F. The reduction of toxic equivalency PCDD/F concentration also could be explained by the stimulation of soil microbial activities estimated with dehydrogenase and fluorescein diacetate hydrolase.

Suppression of the activity of arbuscular mycorrhizal fungi by the soil microbiota

Arbuscular mycorrhizal fungi (AMF) colonise roots of most plants; their extra-radical mycelium (ERM) extends into the soil and acquires nutrients for the plant. The ERM coexists with soil microbial communities and it is unresolved whether these communities stimulate or suppress the ERM activity. This work studied the prevalence of suppressed ERM activity and identified main components behind the suppression. ERM activity was determined by quantifying ERM-mediated P uptake from radioisotope-labelled unsterile soil into plants, and compared to soil physicochemical characteristics and soil microbiome composition. ERM activity varied considerably and was greatly suppressed in 4 of 21 soils. Suppression was mitigated by soil pasteurisation and had a dominating biotic component. AMF-suppressive soils had high abundances of Acidobacteria, and other bacterial taxa being putative fungal antagonists. Suppression was also associated with low soil pH, but this effect was likely indirect, as the relative abundance of, e.g., Acidobacteria decreased after liming. Suppression could not be transferred by adding small amounts of suppressive soil to conducive soil, and thus appeared to involve the common action of several taxa. The presence of AMF antagonists resembles the phenomenon of disease-suppressive soils and implies that ecosystem services of AMF will depend strongly on the specific soil microbiome.

Hyphospheric impacts of earthworms and arbuscular mycorrhizal fungus on soil bacterial community to promote oxytetracycline degradation

A two-compartment microcosm was used to investigate the role of arbuscular mycorrhizal fungus (AMF) hyphae and earthworm in altering soil microbial community and OTC degradation. Treatments comprised OTC-contaminated hyphal compartments with or without AMF hyphae and with or without earthworms. Results indicated both AMF hyphae and earthworms accelerated OTC degradation; two degradation products were identified as 4-epi-oxytetracycline (EOTC) and 2-acetyl-2-decarboxamido-oxytetracycline (ADOTC). Q-PCR results indicated that both earthworms and AMF hyphae increased 16s rDNA gene, enhancing OTC degradation consequently. Illumina sequencing of the 16S rRNA genes showed that AMF hyphae and earthworm altered bacterial community. Earthworms stimulated the growth of class Anaerolineae, family Flavobacteriaceae, Genus Pseudomonas, reducing OTC residues. AMF hyphae significantly increased the abundance of family Pirellulaceae, genus Glycomyces, and Nonomuraea which had a negative correlation with EOTC, accelerating OTC degradation. When used together, AMF hyphae and earthworms enhanced OTC degradation by stimulating class Anaerolineae and family Flavobacteriaceae.

Biotechnological Advances for Restoring Degraded Land for Sustainable Development

Global land resources are under severe threat due to pollution and unsustainable land use practices. Restoring degraded land is imperative for regaining ecosystem services, such as biodiversity maintenance and nutrient and water cycling, and to meet the food, feed, fuel, and fibre requirements of present and future generations. While bioremediation is acknowledged as a promising technology for restoring polluted and degraded lands, its field potential is limited for various reasons. However, recent biotechnological advancements, including producing efficient microbial consortia, applying enzymes with higher degrees of specificity, and designing plants with specific microbial partners, are opening new prospects in remediation technology. This review provides insights into such promising ways to harness biotechnology as ecofriendly methods for remediation and restoration.

Arbuscular mycorrhizal fungi inoculation mediated changes in rhizosphere bacterial community structure while promoting revegetation in a semiarid ecosystem

The main goal of this study was to assess the effect of the inoculation of four autochthonous shrub species with the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices on the rhizosphere bacterial community and to ascertain whether such an effect is dependent on the host plant species. Additionally, analysis of rhizosphere soil chemical and biochemical properties was performed to find relationships between them and the rhizosphere bacterial communities. Non-metric multidimensional scaling analysis and subsequent permutational multivariate analysis of variance revealed differences in bacterial community composition and structure between non-inoculated and inoculated rhizospheres. Moreover, an influence of the plant species was observed. Different bacterial groups were found to be indicator taxonomic groups of non-inoculated and inoculated rhizospheres, Gemmatimonadetes and Anaerolineaceae, respectively, being the most notable indicators. As shown by distance based redundancy analysis, the shifts in bacterial community composition and structure mediated by the inoculation with the AM fungus were mainly related to changes in plant nutrients and growth parameters, such as the shoot phosphorus content. Our findings suggest that the AM fungal inoculum was able to modify the rhizosphere bacterial community assemblage while improving the host plant performance.