Arbuscular mycorrhizal fungi colonization and physiological functions toward wetland plants under different water regimes

Functional insights into microbial community dynamics and resilience in mycorrhizal associated constructed wetlands under pesticide stress

Arbuscular mycorrhizal fungi (AMF) are critical mutualistic symbionts in most terrestrial ecosystems, where they facilitate nutrient acquisition, enhance plant resilience to environmental stressors, and shape the surrounding microbiome. However, its contributions (especially for microorganisms) to constructed wetlands (CWs) under pesticide stress remain poorly understood. This study investigated the effects of AMF on microbial community composition, diversity, metabolic pathways, and functional genes by metagenomics in CWs exposed to pesticides stress. Using comparative analyses of AMF-colonized and non-colonized CWs, we found that AMF enhanced overall microbial diversity, as evidenced by increases of 2.22 % (Chao1) and 2.83 % (observed species). Under fungicide stress, nitrogen-cycling microorganisms (e.g., Nitrososphaerota and Mucoromycota) increased in relative abundance, while carbon cycle-related microorganisms (e.g., Pseudomonadota and Bacteroidota) generally declined. AMF colonization improved microbial resilience, demonstrated by a 312 % rise in Rhizophagus abundance and significant increases in phosphorus-cycling microorganisms (e.g., Bradyrhizobium and Mesorhizobium). Functional gene analysis further revealed that AMF helped mitigate fungicide-induced reductions in genes related to nitrogen and carbon cycling, lowering the average decline rates to 4.02 % and 1.44 %, respectively, compared to higher rates in non-AMF treatments. In summary, these findings highlight the crucial role of AMF in enhancing pesticide stress resilience, maintaining microbial community stability, and improving the bioremediation capacity of CWs.

Different Flooding Conditions Affected Microbial Diversity in Riparian Zone of Huihe Wetland

The soil microbiome plays an important role in wetland ecosystem services and functions. However, the impact of soil hydrological conditions on wetland microorganisms is not well understood. This study investigated the effects of wetted state (WS); wetting-drying state (WDS); and dried state (DS) on the diversity of soil bacteria, fungi, and archaea. The Shannon index of bacterial diversity was not significantly different in various flooding conditions (p > 0.05), however, fungal diversity and archaeal communities were significantly different in different flooding conditions (p < 0.05). Significant differences were found in the beta diversity of bacterial, fungal, and archaeal communities (p < 0.05). Additionally, the composition of bacteria, fungi, and archaea varied. Bacteria were predominantly composed of Proteobacteria and Actinobacteria, fungi mainly consisted of Ascomycota and Mucoromycota, and archaea were primarily represented by Crenarchaeota and Euryarchaeota. Bacteria exhibited correlations with vegetation coverage, fungi with plant diversity, and archaea with aboveground vegetation biomass. The pH influenced bacterial and archaeal communities, while soil bulk density, moisture, soil carbon, soil nitrogen, and plant community diversity impacted fungal communities. This study provides a scientific basis for understanding the effects of different hydrological conditions on microbial communities in the Huihe Nature Reserve; highlighting their relationship with vegetation and soil properties, and offers insights for the ecological protection of the Huihe wetland.

Enhancement of PFAS stress tolerance and wastewater treatment efficiency by arbuscular mycorrhizal fungi in constructed wetlands

This study aims to explore the effects of arbuscular mycorrhizal fungi (AMF) on the growth of Iris pseudacorus L. and treatment efficacy in constructed wetlands (CWs) subjected to stress from per-and poly-fluoroalkyl substances (PFASs). The findings reveal that PFASs exposure induces oxidative damage and inhibits the growth of I. pseudacorus. However, AMF symbiosis enhances plant tolerance to PFAS stress by modulating oxidative responses. AMF treatment not only promoted plant growth but also improved photosynthetic efficiency under PFAS exposure. Compared to non-AMF treatment, those with AMF treatment exhibited significantly increased levels of peroxidases and antioxidant enzymes, including peroxidase and superoxide dismutase, along with a notable reduction in lipid peroxidation. Additionally, AM symbiosis markedly enhanced the efficacy of CWs in the remediation of wastewater under PFASs-induced stress, with removal efficiencies for COD, TP, TN, and NH4+-N increasing by 19-34%, 67-180%, 106-137%, and 25-95%, respectively, compared to the AMF- treatments. In addition, the metabolic pathways of PFASs appeared to be influenced by their carbon chain length, with long-chain PFASs like perfluorooctanoic acid (PFOA) and perfluoro anionic acid (PFNA) exhibiting more complex pathways compared to short-chain PFASs such as perfluoro acetic acid (PFPeA), and perfluoro hexanoic acid (PFHpA). These results suggest that AMF-plant symbiosis can enhance plant resilience against PFAS-induced stress and improve the pollutant removal efficiency of CWs. This study highlights the significant potential of AMF in enhancing environmental remediation strategies, providing new insights for the more effective management of PFAS-contaminated ecosystems.

Transformation and degradation of tebuconazole and its metabolites in constructed wetlands with arbuscular mycorrhizal fungi colonization

Arbuscular mycorrhizal fungi (AMF) colonization has been used in constructed wetlands (CWs) to enhance treatment performance. However, its role in azole (fungicide) degradation and microbial community changes is not well understood. This study aims to explore the impact of AMF on the degradation of tebuconazole and its metabolites in CWs. Total organic carbon levels were consistently higher with the colonization of AMF (AMF+; 9.63- 16.37 mg/L) compared to without the colonization of AMF (AMF-; 8.79-14.48 mg/L) in CWs. Notably, tebuconazole removal was swift, occurring within one day in both treatments (p = 0.885), with removal efficiencies ranging from 94.10 % to 97.83 %. That's primarily due to rapid substrate absorption at the beginning, while degradation follows with a longer time. Four metabolites were reported in CWs first time: tebuconazole hydroxy, tebuconazole lactone, tebuconazole carboxy acid, and tebuconazole dechloro. AMF decreased the abundance of tebuconazole dechloro in the liquid phase, suggesting an inhibitory effect of AMF on dechlorination processes. Furthermore, tebuconazole carboxy acid and hydroxy were predominantly found in plant roots, with a higher abundance observed in AMF+ treatments. Metagenomic analysis highlighted an increasing abundance in bacterial community structure in favor of beneficial microorganisms (xanthomonadales, xanthomonadaceae, and lysobacter), along with a notable presence of functional genes like codA, NAD, and deaD in AMF+ treatments. These findings highlight the positive influence of AMF on tebuconazole stress resilience, microbial community modification, and the enhancement of bioremediation capabilities in CWs.

The role of arbuscular mycorrhizal fungi in micronutrient homeostasis and cadmium uptake and transfer in rice under different flooding intensities

Flooding intensity significantly alters the availability of iron (Fe), zinc (Zn), and cadmium (Cd) in paddy soil. However, the influence of arbuscular mycorrhizal fungi (AMF) on the uptake and transfer of Cd and micronutrients (Fe and Zn) under Cd stress in varying flooding conditions is not well understood. A pot experiment was conducted to investigate the micronutrient homeostasis and Cd uptake and transfer in rice cultivated in Cd-contaminated soil with AMF inoculation under continuous and intermittent flooding conditions. Compared to non-inoculation controls, mycorrhizal inoculation decreased Cd concentration in rice plants under continuous and intermittent flooding, and improved grain yield by 39.2 % for early season rice and 21.1 % for late season rice under continuous flooding. Mycorrhizal inoculation balanced the availability of Zn and Fe and decreased the availability of Cd in soil, lowering the ratios of soil-available Cd to both soil-available Zn and soil Fe2+. These changes led to a redistribution of Zn and Fe concentrations in rice, thereby reducing Cd acquisition in a soil-rice system. Structural equation model (SEM) analysis revealed that mycorrhizal inoculation had a strong direct negative effect on the expression of Zn and Fe-related genes OsNRAMP1, OsIRT1, and OsIRT2 in the roots of rice, which in turn directly affected root Cd concentration. Furthermore, mycorrhizal colonization decreased Cd transfer coefficients from leaves to grains under continuous flooding and from nodes and leaves to grains under intermittent flooding. In the nodes, the Fe concentration and the expression of genes OsIRT1 and OsHMA2 were associated with Cd transfer from the nodes to grains. Similarly, in the leaves, the expression of genes OsZIP1 and OsMTP1 corresponded with Cd transfer from leaves to grains. This study provides insights into the role of AMF in affecting micronutrient concentrations and Cd uptake in rice under varying flooding conditions.

Arbuscular mycorrhizal fungi communities and promoting the growth of alfalfa in saline ecosystems of northern China

Arbuscular mycorrhizal fungi (AMF) are universally distributed in soils, including saline soils, and can form mycorrhizal symbiosis with the vast majority of higher plants. This symbiosis can reduce soil salinity and influence plant growth and development by improving nutrient uptake, increasing plant antioxidant enzyme activity, and regulating hormone levels. In this study, rhizosphere soil from eight plants in the Songnen saline-alkaline grassland was used to isolate, characterize, and screen the indigenous advantageous AMF. The promoting effect of AMF on alfalfa (Medicago sativa L.) under salt treatment was also investigated. The findings showed that 40 species of AMF in six genera were identified by high-throughput sequencing. Glomus mosseae (G.m) and Glomus etunicatum (G.e) are the dominant species in saline ecosystems of northern China. Alfalfa inoculated with Glomus mosseae and Glomus etunicatum under different salt concentrations could be infested and form a symbiotic system. The mycorrhizal colonization rate and mycorrhizal dependence of G.m inoculation were significantly higher than those of G.e inoculation. With increasing salt concentration, inoculation increased alfalfa plant height, fresh weight, chlorophyll content, proline (Pro), soluble sugar (SS), soluble protein (SP), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activity while decreasing the malondialdehyde (MDA) content and superoxide anion production rate. The results highlight that inoculation with G.m and G.e effectively alleviated salinity stress, with G.m inoculation having a significant influence on salt resistance in alfalfa. AMF might play a key role in alfalfa growth and survival under harsh salt conditions.

Arbuscular Mycorrhizal Fungi Mediate the Acclimation of Rice to Submergence

Flooding is a critical factor that limits the establishment of a symbiosis between rice and arbuscular mycorrhizal fungi (AMF) in wetland ecosystems. The distribution of carbon resources in roots and the acclimation strategies of rice to flooding stress in the presence of AMF are poorly understood. We conducted a root box experiment, employing nylon sheets or nylon meshes to create separate fungal chambers that either prevented or allowed the roots and any molecules to pass through. We found that the mycorrhizal colonization rate and the expression of genes OsD14L and OsCERK1, which are involved in fungal perception during symbiosis, both increased in mycorrhizal rice roots following intermittent flooding compared to continuous flooding. Furthermore, AMF inoculation affected root morphological traits, facilitating both shallower and deeper soil exploration. Increased submergence intensity led to carbohydrate deprivation in roots, while high mycorrhizal colonization increased soil oxygen consumption and decreased the neutral lipid concentration in roots. However, mycorrhizal inoculation increased the rice photosynthesis rate and facilitated acclimation to submergence by mediating the expression of the genes OsCIPK15 and OsSUB1A to enhance rice shoot elongation and the sugar concentration in roots as a result of reduced competition for carbon between rice and AMF under different flooding conditions.

Investigating the simultaneous effect of chitosan and arbuscular mycorrhizal fungi on growth, phenolic compounds, PAL enzyme activity and lipid peroxidation in Salvia nemorosa L

Considering the importance of Salvia nemorosa L. in the pharmaceutical and food industries, and also beneficial approaches of arbuscular mycorrhizal fungi (AMF) symbiosis and the use of bioelicitors such as chitosan to improve secondary metabolites, the aim of this study was to evaluate the performance of chitosan on the symbiosis of AMF and the effect of both on the biochemical and phytochemical performance of this plant and finally introduced the best treatment. Two factors were considered for the factorial experiment: AMF with four levels (non-inoculated plants, Funneliformis mosseae, Rhizophagus intraradices and the combination of both), and chitosan with six levels (0, 50, 100, 200, 400 mg L-1 and 1% acetic acid). Four months after treatments, the aerial part and root length, the levels of lipid peroxidation, H2O2, phenylalanine ammonia lyase (PAL) activity, total phenol and flavonoid contents and the main secondary metabolites (rosmarinic acid and quercetin) in the leaves and roots were determined. The flowering stage was observed in R. intraradices treatments and the highest percentage of colonization (78.87%) was observed in the treatment of F. mosseae × 400 mg L-1 chitosan. Furthermore, simultaneous application of chitosan and AMF were more effective than their separate application to induce phenolic compounds accumulation, PAL activity and reduce oxidative compounds. The cluster and principal component analysis based on the measured variables indicated that the treatments could be classified into three clusters. It seems that different treatments in different tissues have different effects. However, in an overview, it can be concluded that 400 mg L-1 chitosan and F. mosseae × R. intraradices showed better results in single and simultaneous applications. The results of this research can be considered in the optimization of this medicinal plant under normal conditions and experiments related to abiotic stresses in the future.

Improving vanadium removal from contaminated river water in constructed wetlands: The role of arbuscular mycorrhizal fungi

Industrial activities pose a significant ecological risk to water resources as they pollute surrounding waters with vanadium (V). Although the contribution of plants and substrates to V removal in constructed wetlands (CWs) has been reported, the role of arbuscular mycorrhizal fungi (AMF) is unclear. The aim of the present study was to investigate the role of AMF in V removal in CWs and to elucidate the underlying mechanisms. Reed plants (Phragmites australis) were inoculated with an AMF strain (Rhizophagus irregularis) in CW columns, creating AMF-inoculated (+AMF) and non-inoculated (-AMF) treatments. Three levels of influent V concentrations (low: 0.50 mg L-1, medium: 1.14 mg L-1 and high: 1.52 mg L-1) were examined. The + AMF treatment showed higher V removal (60%-98%) than the control (40%-82%) in all three conditions, although the difference was not significant in some cases. The mean mycorrhizal effects were 75%, 19%, and 28% for low, moderate, and high influent V concentrations, respectively. The +AMF treatment showed a higher GRSP-bonded V concentration (5.5 mg g-1) than the -AMF treatment (4.0 mg g-1). Furthermore, +AMF treatment showed larger plants with higher V concentrations in their tissues, accompanied by increased biological concentration factors and biological accumulation factors. Given the remarkable positive effect of AMF on V removal, our study suggests that treating AMF in CWs is a worthwhile approach.

Community responses of arbuscular mycorrhiza fungi to hydrological gradients in a riparian Phragmites australis wetland

The hydrological regime is considered to be the major factor that affects the distribution of arbuscular mycorrhiza (AM) fungi in wetlands. We aimed to investigate the responses of AM fungal community to different hydrological gradients. Illumina Miseq sequencing technology was used to study the AM fungal community structure in roots and rhizosphere soils of Phragmites australis in different moisture areas (dry area, alternating wet and dry area, and flooded area) in Mengjin Yellow River wetland. The rhizosphere soils and roots hosted different AM fungal communities. In roots, the AM fungal colonization and Chao1 richness in dry area were significantly higher than that in alternating wet and dry area and flooded area, but the community composition did not vary clearly under different water conditions. In rhizosphere soils, the Chao1 richness of AM fungi in flooded area was significantly higher than that in alternating wet and dry area and dry area, and the AM fungal community structure obviously differed across different areas. The redundancy analyses indicated that changes in the AM fungal community in soils were associated with altered soil properties, and the abundance of the dominant genus Glomus was mostly positively correlated with alkali-hydrolyzable nitrogen in soils. This study helps us to understand the responses of AM fungal community to hydrological gradients in wetlands.

Potential synergy of microplastics and nitrogen enrichment on plant holobionts in wetland ecosystems

Wetland ecosystems are global hotspots for environmental contaminants, including microplastics (MPs) and nutrients such as nitrogen (N) and phosphorus (P). While MP and nutrient effects on host plants and their associated microbial communities at the individual level have been studied, their synergistic effects on a plant holobiont (i.e., a plant host plus its microbiota, such as bacteria and fungi) in wetland ecosystems are nearly unknown. As an ecological entity, plant holobionts play pivotal roles in biological nitrogen fixation, promote plant resilience and defense chemistry against pathogens, and enhance biogeochemical processes. We summarize evidence based on recent literature to elaborate on the potential synergy of MPs and nutrient enrichment on plant holobionts in wetland ecosystems. We provide a conceptual framework to explain the interplay of MPs, nutrients, and plant holobionts and discuss major pathways of MPs and nutrients into the wetland milieu. Moreover, we highlight the ecological consequences of loss of plant holobionts in wetland ecosystems and conclude with recommendations for pending questions that warrant urgent research. We found that nutrient enrichment promotes the recruitment of MPs-degraded microorganisms and accelerates microbially mediated degradation of MPs, modifying their distribution and toxicity impacts on plant holobionts in wetland ecosystems. Moreover, a loss of wetland plant holobionts via long-term MP-nutrient interactions may likely exacerbate the disruption of wetland ecosystems' capacity to offer nature-based solutions for climate change mitigation through soil organic C sequestration. In conclusion, MP and nutrient enrichment interactions represent a severe ecological risk that can disorganize plant holobionts and their taxonomic roles, leading to dysbiosis (i.e., the disintegration of a stable plant microbiome) and diminishing wetland ecosystems' integrity and multifunctionality.

Mycorrhizal colonization had little effect on growth of Carex thunbergii but inhibited its nitrogen uptake under deficit water supply

BACKGROUND AND AIMS

Plant nitrogen (N) acquisition via arbuscular mycorrhizal fungi (AMF) serves as a dominant pathway in the N nutrition of many plants, but the functional impact of AMF in acquisition of N by wetland plants has not been well quantified. Subtropical lake-wetland ecosystems are characterized by seasonal changes in the water table and low N availability in soil. Yet, it is unclear whether and how AMF alters the N acquisition pattern of plants for various forms of N and how this process is influenced by soil water conditions.

METHODS

We performed a pot study with Carex thunbergii that were either colonized by AMF or not colonized and also subjected to different water conditions. We used 15N labelling to track plant N uptake.

KEY RESULTS

Colonization by AMF had little effect on the biomass components of C. thunbergii but did significantly affect the plant functional traits and N acquisition in ways that were dependent on the soil water conditions. The N uptake rate of AMF-colonized plants was significantly lower than that of the non-colonized plants in conditions of low soil water. A decreased NO3- uptake rate in AMF-colonized plants reduced the N:P ratio of the plants. Although C. thunbergii predominantly took up N in the form of NO3-, higher water availability increased the proportion of N taken up as NH4+, irrespective of the inoculation status.

CONCLUSIONS

These results emphasize the importance of AMF colonization in controlling the N uptake strategies of plants and can improve predictions of N budget under the changing water table conditions in this subtropical wetland ecosystem.

Arbuscular Mycorrhizal Fungi Alter Arsenic Translocation Characteristics of Iris tectorum Maxim

Arsenic (As) pollution in wetlands, mainly as As(III) and As(V), has threatened wetland plant growth. It has been well documented that arbuscular mycorrhizal (AM) fungi can alleviate As stress in terrestrial plants. However, whether AM fungi can protect natural wetland plants from As stress remains largely unknown. Therefore, three hydroponic experiments were conducted in which Iris tectorum Maxim. (I. tectorum) plants were exposed to As(III) or As(V) stresses, to investigate the effects of mycorrhizal inoculation on As uptake, efflux, and accumulation. The results suggested that short-term kinetics of As influx in I. tectorum followed the Michaelis-Menten function. Mycorrhizal inoculation decreased the maximum uptake rate (Vmax) and Michaelis constant (Km) of plants for As(III) influx, while yielding no significant difference in As(V) influx. Generally, mycorrhizal plants released more As into environments after 72 h efflux, especially under As(V) exposure. Moreover, mycorrhizal plants exhibited potential higher As accumulation capacity, probably due to more active As reduction, which was one of the mechanisms through which AM fungi mitigate As phytotoxicity. Our study has revealed the role of aerobic microorganism AM fungi in regulating As translocation in wetland plants and supports the involvement of AM fungi in alleviating plant As stress in anaerobic wetlands.

Plant growth-promoting microbes improve stormwater retention of a newly-built vertical greenery system

On-site decentralized urban stormwater management has gained significant momentum in urban planning. Recently, vegetated roofs have been recommended as a viable decentralized stormwater management system and nature-based solution to meet the challenge of urban floods. However, as another type of unconventional green infrastructure, vertical greenery systems (VGS), also known as vegetated facades, have received much less research attention. Even though some researchers suggest that stormwater management by VGS is comparable to that of vegetated roofs, empirical evidence to substantiate this claim is limited. In this study, we conducted rain simulations on newly-built vegetation containers with water storage compartments. These vegetation containers were designed to be incorporated into a VGS specifically for stormwater management. We tested variables that could influence water retention efficiency and evapotranspiration of the containers under field conditions, i.e., inoculation of plant growth-promoting microbes (PGPMs) (Rhizophagus irregularis and Bacillus amyloliquefaciens), different substrate types (sandy loam and reed-based substrate), simulated rain quantity, natural precipitation, substrate moisture, and air temperature. The inoculation of PGPMs significantly reduced runoff quantity from the vegetation containers. Meanwhile, the well-ventilated sandy-loam substrate significantly reduced the remaining water in the water storage compartments over 1-week periods between rain simulation events, achieving high water-use efficiency. The selected microbes were established successfully in the containers and promoted the growth of 2 out of 5 plant species. R. irregularis colonization responded to substrate type and host plant species, while B. amyloliquefaciens population density in the substrate did not respond to these factors. Environmental conditions, such as antecedent substrate moisture, air temperature, and natural precipitation also influenced the efficiency of stormwater retention and/or evapotranspiration. In conclusion, this study provides instructive and practical insights to reduce urban flood risk by using VGS.

Immobilization of chromium enhanced by arbuscular mycorrhizal fungi in semi-aquatic habitats with biochar addition

Arbuscular mycorrhizal fungi (AMF) exhibit great potential in heavy-metal immobilization in semi-aquatic habitats. Under high heavy-metal stress, however, the role of AMF is limited, and the detoxification mechanism of AMF in heavy metals' stabilization remains unclear. This study investigated the effects of AMF on a wetland plant (Iris pseudacorus) and chromium (Cr) immobilization at different water depths in semi-aquatic habitats with biochar addition. Results showed that AMF increased the physiological and photosynthetic functions in I. pseudacorus under Cr exposures. Besides, AMF alleviated the accumulation of reactive oxygen species and lipid peroxidation by enhancing the antioxidant enzyme activities. AMF and biochar significantly decreased Cr concentrations in outlet water and increased Cr accumulation in I. pseudacorus. Besides, biochar also vastly improved Cr accumulation in the substrate under the fluctuating water depth. AMF reduced Cr bioavailability in the substrate, with Cr (Ⅵ) concentrations and acid-soluble forms of Cr decreased by 0.3-64.5% and 19.0-40.8%, respectively. Micro-proton-induced X-ray emission was used to determine element localization and revealed that AMF improved the nutrients uptake by wetland plants and inhibited Cr translocation from roots to shoots. Overall, this study demonstrated that the interaction between AMF and biochar could significantly enhance the immobilization of high Cr concentrations in semi-aquatic habitats.

The positive effects of arbuscular mycorrhizal fungi inoculation and/or additional aeration on the purification efficiency of combined heavy metals in vertical flow constructed wetlands

Inoculation with arbuscular mycorrhizal fungi (AMF) and additional aeration (AA), as two approaches to improve the functioning of treatment wetlands, can further promote the capacity of wetlands to purify pollutants. The extent to which, and mechanisms by which, AMF and AA purify wetlands polluted by combined heavy metals (HMs) are not well understood. In this study, the effects and mechanisms of AMF and/or AA on combined HMs removal in vertical flow constructed wetlands (VFCWs) with the Phragmites australis (reeds) were investigated at different HMs concentrations. The results showed that (1) AA improved the AMF colonization in VFCWs and AMF accumulated the combined HMs in their structures; (2) AMF inoculation and/or AA significantly promoted the reeds growth and antioxidant enzymes activities, thereby alleviating oxidative stress; (3) AMF inoculation and AA significantly enhanced the removal rates of Pb, Zn, Cu, and Cd under the stress of high combined HMs concentrations comparing to the control check (CK) treatment (autoclaved AMF inoculation and no aeration), which increased by 22.72%, 30.31%, 12.64%, and 50.22%, respectively; (4) AMF inoculation and/or AA significantly promoted the combined HMs accumulation in plant roots and substrates and altered the distribution of HMs at the subcellular level. We therefore conclude that AMF inoculation and/or AA in VFCWs improves the purification of combined HM-polluted water, and the VFCWs-reeds-AMF/AA associations exhibit great potential for application in remediation of combined HM-polluted wastewater.

Taxonomic Diversity of Fungi and Bacteria in Azoé-NP® Vertical Flow Constructed Wetlands

Plants, fungi, bacteria and protozoa are highly interconnected in constructed wetlands. These heterogeneous groups of organisms constitute a single system with complex internal trophic interactions. Thus, the joint activity of micro- and macroorganisms in constructed wetlands provides highly efficient wastewater treatment: both nutrients and complex organic substances can be effectively removed in branched trophic chains. The bacterial community of constructed wetlands has recently received much attention, while the fungal component remains less studied, particularly saprotrophic fungi. This paper reveals a taxonomic analysis of the cultivated saprotrophic fungi combined with the bacterial community in vertical flow constructed wetlands (VSCWs) operated by the Azoé-NP® process. These systems have unique features to affect the microbial community, which results in a high treatment efficiency and nitrogen removal. There are very few studies of saprotrophic fungi in VFCWs, while this work shows their abundance and diversity in VFCWs. We found 62 species of cultivated microscopic fungi and described the taxonomic composition of bacterial and fungal community at all wastewater treatment stages. In the studied VFCWs, we identified the species of micromycetes, which proved effective in the removal of contaminants. The data obtained can provide a deeper insight into the characteristics of Azoé-NP® systems and the treatment processes occurring in constructed wetlands.

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

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

Nitrogen absorption efficiency and mechanism in Arbuscular mycorrhizal fungi - Canna indica symbiosis

Arbuscular mycorrhizal fungi (AMF) and its symbiosis with Canna indica on nitrogen (N) absorption was investigated for the remediation of contaminated soil. Canna indica plants with rhizome and leaf integrity intact were collected in spring and autumn seasons. To maintain the ideal nutrient composition, Hoagland concentrated nutrient solution was diluted with deionized water and additional nutrient solution was added periodically. Treated root samples were observed with an optical microscope and the number of hyphae and intersections as well as inoculation status were examined. High-throughput sequencing experiment was conducted to quantify AMF inoculation. Alpha diversity study was used to characterize abundance and diversity of the symbiosis. Hydroponic experiments were conducted to explore the absorption effectiveness of AMF-Canna symbiosis under different NH₄⁺-N and NO₃^--N combinations. Hyphal colonization rate was only about 5.66 ± 1.08% in seedling stage in spring, but enhanced in the adult stage in autumn (53.89 ± 1.43%). Results revealed that AMF had no significant impact on NO₃^--N absorption by Canna roots, however, absorption of NH₄⁺-N was improved by 63% under low concentration. Results revealed that when NH₄⁺-N and NO₃^--N were applied combinedly in a 1:1 ratio, their respective absorption rates were enhanced to 99.63% and 99.50%. Compared with the case of NH₄⁺-N as N source alone, synergistic effect of NH₄⁺-N and NO₃^--N significantly changed the absorption of NH₄⁺-N by C. indica, but its correlation with AMF inoculation was still not significant. Current findings could enhance understanding for effective N uptake and resource recovery.

Arbuscular mycorrhizal symbiosis in constructed wetlands with different substrates: Effects on the phytoremediation of ibuprofen and diclofenac

This study investigated the role of arbuscular mycorrhizal fungal (AMF) for the removal of ibuprofen (IBU) and diclofenac (DCF) in constructed wetlands (CWs) with four different substrates. Results showed that AMF colonization in adsorptive substrate (perlite, vermiculite, and biochar) systems was higher than that in sand systems. AMF enhanced the tolerance of Glyceria maxima to the stress of IBU and DCF by promoting the activities of antioxidant enzymes (peroxidase and superoxide dismutase) and the contents of soluble protein, while decreasing the contents of malondialdehyde and O₂^•-. The removal efficiencies of IBU and DCF were increased by 15%-18% and 25%-38% in adsorptive substrate systems compare to sand systems. Adsorptive substrates enhanced the accumulation of IBU and DCF in the rhizosphere and promoted the uptake of IBU and DCF by plant roots. AMF promoted the removal of IBU and DCF in sand systems but limited their reduction in adsorptive substrate systems. In all scenarios, the presence of AMF decreased the contents of CECs metabolites (2-OH IBU, CA IBU, and 4'-OH IBU) in the effluents and promoted the uptake of IBU by plant roots. Therefore, these results indicated that the addition of adsorptive substrates could enhance the removal of IBU and DCF in CWs. The role of AMF on the removal of IBU and DCF was influenced by CW substrate. These may provide useful information for the application of AMF in CWs to remove contaminants of emerging concern.

Diverse and abundant arbuscular mycorrhizal fungi in ecological floating beds used to treat eutrophic water

An increasing number of investigations have shown the universal existence of arbuscular mycorrhizal fungi (AMF) in aquatic ecosystems. However, little is known about the accurate distribution and function of AMF inhabiting aquatic ecosystems, especially ecological floating beds (EFBs), which are constructed for the remediation of polluted water bodies. In this study, we collected root samples of Canna generalis, Cyperus alternifolius, and Eichhornia crassipes from three EFBs on two eutrophic lakes in Wuhan, China. We aimed to investigate the resources and distribution of AMF in EFBs using Illumina Mi-seq technology. A total of 229 operational taxonomic units (OTUs) and 21 taxa from 348,799 Glomeromycota sequences were detected. Glomus and Acaulospora were the most dominant and second most dominant genera of AMF in the three EFBs, respectively. Different aquatic plant species showed varying degrees of AMF colonization (3.83-71%), diversity (6-103 OTUs, 3-15 virtual taxa), and abundance (14-57,551 sequences). Low AMF abundance, but relatively high AMF diversity, was found in C. alternifolius, which is usually considered non-mycorrhizal. This finding indicated the high accuracy of Illumina sequencing. Our results also revealed a lognormal species abundance distribution that was observed across AMF taxa in the three plant species. The AMF community composition was closely related to nitrogen and phosphorus contents. Overall, our data show that EFBs harbor diverse and abundant AMF communities. Additionally, the AMF community composition is closely related to the water quality of eutrophic lakes treated by the EFBs, indicating the potential application of AMF in plant-based bioremediation of wastewater. KEYPOINTS: • Aquatic plants in EFBs harbor diverse (229 OTUs) and abundant (348,799 sequences) AMF. • Different plant species host different taxa of AMF. Cyperaceae, originally considered non-mycorrhizal, may in fact be a variable mycorrhizal plant family. • The AMF community composition in EFBs is closely related to nutrient concentrations (nitrogen and phosphorus).

Bioaugmentation of treatment wetlands - A review

Bioaugmentation in the form of artificial mycorrhization of plant roots and bacterial inoculation has been successfully implemented in several fields including soil remediation or activated sludge treatment. Likewise, bioaugmentation seems a promising approach to improve the functioning of treatment wetlands, considering that natural mycorrhization has been detected in treatment wetlands and that bacteria are the main driver of contaminant degradation processes. However, to date, full scale implementation seems to be rare. This review synthesizes the effects of bioaugmentation on different types of treatment wetlands, to a large extent performed on a microcosm (<0.5 m²) or mesocosm scale (0.51 to 5 m²). While inoculation with arbuscular mycorrhizal fungi tended to show a positive effect on the growth of some wetland plants (e.g. Phragmites australis), the mechanisms underlying such positive effects are not well understood and the effects of upscaling to full scale treatment wetlands remain unknown. Bacterial inoculation tended to promote plant growth and pollutant degradation, but longer term data is required.

Employ of arbuscular mycorrhizal fungi for pharmaceuticals ibuprofen and diclofenac removal in mesocosm-scale constructed wetlands

This study investigated the effects of arbuscular mycorrhizal fungi (AMF) colonization on the growth of wetland plants (Glyceria maxima), and treatment performance in constructed wetlands (CWs) under the stress of pharmaceuticals ibuprofen (IBU) and diclofenac (DCF). Results showed that the growth of G. maxima was significantly increased by AMF colonization. AMF significantly increased the activities of antioxidant enzymes (peroxidase and superoxide dismutase) and soluble protein content in wetland plants, but the contents of malondialdehyde and O₂^•- were reduced. The removal efficiencies of TOC, PO₄^3--P, NH₄⁺-N, and TN were increased in AMF+ treatments by 6%, 11%, 15% and 11%, respectively. AMF increased the removal efficiencies of IBU and DCF by 6-14% and 2-21%, respectively, and reduced the content of their metabolites (2-OH IBU, CA IBU and 4'-OH DCF) in the effluent. Besides, the presence of AMF increased the contents of IBU and DCF in plant roots, while decreased their transportation to shoots. AMF symbiosis decreased the contents of IBU metabolites (2-OH IBU and CA IBU) but increased the contents of DCF metabolite (4'-OH DCF) in the roots of the host plant. In conclusion, these results indicated that AMF plays a promising role in CWs for emerging pollutants removal.

Antioxidant response in arbuscular mycorrhizal fungi inoculated wetland plant under Cr stress

Arbuscular mycorrhizal fungi (AMF) provide a positive effect on antioxidant mechanisms in terrestrial plants under heavy metal stress. This study investigated the effects of AMF on wetland plant (Iris wilsonii) growth and antioxidant response under Cr stress at different water depths. Results showed that AMF inoculated I. wilsonii had higher antioxidant response than non-inoculated controls, with shoot superoxide dismutase (SOD), root SOD, shoot peroxidase (POD), and root POD contents increased by 4.7-39.6%, 7.5-29.5%, 11.2-68.6%, 16.8-50.3%, respectively. Meanwhile, shoot (root) proline, malondialdehyde (MDA) and superoxide anion (O₂^.-) contents in the AMF inoculated I. wilsonii were 10.2-44.3% (2.8-37.2%), 11.5-35.4% (16.9-28.2), and 14.9-30.5% (-0.9-26.3%) lower than those in the non-inoculated controls, respectively. Besides, AMF improved the growth of I. wilsonii with biomass, height, chlorophyll, K, and P contents in the shoots increased by 10.5-32.5%, 17.4-44.9%, 4.7-37.7%, 12.0-30.7%, 13.5-20.6%, respectively. Moreover, the I. wilsonii tolerance to Cr stress was also enhanced under the water depth of 6-3 cm. Therefore, AMF play an important role in wetland plant growth and antioxidant response under Cr stress, and it can improve wetland plants' tolerance to Cr stress at fluctuating water depth.

Combined process of bio-contact oxidation-constructed wetland for blackwater treatment

In this study, a combined process of bio-contact oxidation and constructed wetland for blackwater treatment was assessed. The effects of hydraulic retention time and particle size on treatment performance were systematically studied. Additionally, microbial communities in the combined process were characterized. The results show that the removal efficiency of COD, TN, NH₄⁺-N, and TP under optimum conditions in this study were 81.6%, 56.1%, 42.2%, and 73.7%, respectively. The maximum nitrogen removal rate reached 16.5 g m^-2 d^-1 (3 d). N and P removed via direct plant absorption accounted for only 19.7% and 16.1% of the total system, respectively. Plants play a crucial role in the microbial community of constructed wetlands and influence the overall performance of the system. The biofilm on roots favored aerobic and heterotrophic bacteria such as the aerobic denitrification microorganisms of Pelagibacterium, Halomonas, and Zoogloea. Overall, the combined process is a suitable technique for the treatment of blackwater.