Arbuscular mycorrhizal fungi in two vertical-flow wetlands constructed for heavy metal-contaminated wastewater bioremediation

Fungal removal of cyanotoxins in constructed wetlands: The forgotten degraders

Harmful cyanobacterial blooms have increased globally, releasing hazardous cyanotoxins that threaten the safety of water resources. Constructed wetlands (CWs) are a nature-based and low-cost solution to purify and remove cyanotoxins from water. However, bio-mechanistic understanding of the biotransformation processes expected to drive cyanotoxin removal in such systems is poor, and primarily focused on bacteria. Thus, the present study aimed at exploring the fungal contribution to microcystin-LR and cylindrospermopsin biodegradation in CWs. Based on CW mesocosms, two experimental approaches were taken: a) amplicon sequencing studies were conducted to investigate the involvement of the fungal community; and b) CW fungal isolates were tested for their microcystin-LR and cylindrospermopsin degradation capabilities. The data uncovered effects of seasonality (spring or summer), cyanotoxin exposure, vegetation (unplanted, Juncus effusus or Phragmites australis) and substratum (sand or gravel) on the fungal community structure. Additionally, the arbuscular mycorrhizal fungus Rhizophagus and the endophyte Myrmecridium showed positive correlations with cyanotoxin removal. Fungal isolates revealed microcystin-LR-removal potentials of approximately 25 % in in vitro biodegradation experiments, while the extracellular chemical fingerprint of the cultures suggested a potential intracellular metabolization. The results from this study may help us understand the fungal contribution to cyanotoxin removal, as well as their ecology in CWs.

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.

Recent advances in microbial engineering approaches for wastewater treatment: a review

In the present era of global climate change, the scarcity of potable water is increasing both due to natural and anthropogenic causes. Water is the elixir of life, and its usage has risen significantly due to escalating economic activities, widespread urbanization, and industrialization. The increasing water scarcity and rising contamination have compelled, scientists and researchers, to adopt feasible and sustainable wastewater treatment methods in meeting the growing demand for freshwater. Presently, various waste treatment technologies are adopted across the globe, such as physical, chemical, and biological treatment processes. There is a need to replace these technologies with sustainable and green technology that encourages the use of microorganisms since they have proven to be more effective in water treatment processes. The present review article is focused on demonstrating how effectively various microbes can be used in wastewater treatment to achieve environmental sustainability and economic feasibility. The microbial consortium used for water treatment offers many advantages over pure culture. There is an urgent need to develop hybrid treatment technology for the effective remediation of various organic and inorganic pollutants from wastewater.

Plant and microbial communities responded to copper and/or tetracyclines in mycorrhizal enhanced vertical flow constructed wetlands microcosms with Canna indica L

Arbuscular mycorrhizal fungi (AMF) play a significant role in pollutants removal in constructed wetlands (CWs). However, the purification effects of AMF on combined copper (Cu) and tetracycline (TC) pollution in CWs remains unknown. This study investigated the growth, physiological characteristics and AMF colonization of Canna indica L. living in vertical flow CWs (VFCWs) treated for Cu and/or TC pollution, the purification effects of AMF enhanced VFCWs on Cu and TC, and the microbial community structures. The results showed that (1) Cu and TC inhibited plant growth and decreased AMF colonization; (2) the removal rates of TC and Cu by VFCWs were 99.13-99.80% and 93.17-99.64%, respectively; (3) the growth, Cu and TC uptakes of C. indica and Cu removal rates were enhanced by AMF inoculation; (4) TC and Cu stresses reduced and AMF inoculation increased bacterial operational taxonomic units (OTUs) in the VFCWs, Proteobacteria, Bacteroidetes, Firmicutes and Acidobacteria were the dominant bacteria, and AMF inoculation decreased the relative abundance of Novosphingobium and Cupriavidus. Therefore, AMF could enhance the pollutants purification in VFCWs by promoting plant growth and altering the microbial community structures.

The function and community structure of arbuscular mycorrhizal fungi in ecological floating beds used for remediation of Pb contaminated wastewater

Arbuscular mycorrhizal fungi (AMF) have been demonstrated to be ubiquitous in aquatic ecosystems. However, their distributions and ecological functions are rarely studied. To date, a few studies have combined sewage treatment facilities with AMF to improve removal efficiency, but appropriate and highly tolerant AMF strains have not been explored, and the purification mechanisms remain unclear. In this study, three ecological floating-bed (EFB) installations inoculated with different AMF inocula (mine AMF inoculum, commercial AMF inoculum and non-AMF inoculated) were constructed to investigate their removal efficiency for Pb-contaminated wastewater. The AMF community structure shifts in the roots of Canna indica inhabiting EFBs during the three phases (pot culture phase, hydroponic phase and hydroponic phase with Pb stress) were tracked utilizing quantitative real-time polymerase chain reaction and Illumina sequencing techniques. Furthermore, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to detect the Pb location in mycorrhizal structures. The results showed that AMF could promote host plant growth and enhance the Pb removal efficiency of the EFBs. The higher the AMF abundance, the better the effect of the AMF on Pb purification by EFBs. Both flooding and Pb stress decreased the AMF diversity but did not significantly inhibit the abundance. The three inoculation treatments showed different community compositions with different dominant AMF taxa in different phases, and an uncultured Paraglomus species (Paraglomus sp. LC516188.1) was found to be the most dominant (99.65 %) AMF in the hydroponic phase with Pb stress. The TEM and EDS analysis results showed that the Paraglomus sp. could accumulate Pb in plant roots through their fungal structures (intercellular mycelium, intracellular mycelium, etc.), which alleviated the toxic effect of Pb on plant cells and limited Pb translocation. The new findings provide a theoretical basis for the application of AMF in plant-based bioremediation of wastewater and polluted waterbodies.

Uptake of different pharmaceuticals in soil and mycorrhizal artichokes from wastewater

The irrigation with treated wastewater is among the main anthropogenic sources for the release of pharmaceuticals (PhACs) into the soils and their translocation into crops, with possible toxic and adverse effects on humans. The arbuscular mycorrhizal fungi (AMF) can be employed for the reduction of organic soil pollutants, even if their efficiency depends on the mycorrhizal fungi, the plant colonized, and the type and concentration of the contaminant. This study aimed to evaluate the uptake of PhACs from wastewaters of different qualities used for the irrigation of mycorrhizal artichoke plants, the presence in their edible parts and the role of the arbuscular mycorrhizal fungi. The research was carried out on artichoke plants not inoculated and inoculated with two different AMF and irrigated with treated wastewater (TW), groundwater (GW) or GW spiked with different and selected PhACs (SGW). The inocula were a crude inoculum of Septoglomus viscosum (MSE) and a commercial inoculum of Glomus intraradices and Glomus mosseae (MSY). The results of the present study showed that carbamazepine and fluconazole were found in the artichoke only with SGW irrigation. The mycorrhizal plants showed a reduction of the pharmaceutical's uptake, and within the AMF, MSE was more effective in preventing their absorption and translocation.

Transcriptome analysis reveals the molecular mechanisms of Phragmites australis tolerance to CuO-nanoparticles and/or flood stress induced by arbuscular mycorrhizal fungi

The molecular mechanism of arbuscular mycorrhizal fungi (AMF) in vertical flow constructed wetlands (VFCWs) for the purification of copper oxide nanoparticles (CuO-NPs) contaminated wastewater remains unclear. In this study, transcriptome analysis was used to explore the effect of AMF inoculation on the gene expression profile of Phragmites australis roots under different concentrations of CuO-NPs and/or flood stress. 551, 429 and 2281 differentially expressed genes (DEGs) were specially regulated by AMF under combined stresses of CuO-NPs and flood, single CuO-NPs stress and single flood stress, respectively. Based on the results of DEG function annotation and enrichment analyses, AMF inoculation under CuO-NPs and/or flood stress up-regulated the expression of a number of genes involved in antioxidant defense systems, cell wall biosynthesis and transporter protein, which may contribute to plant tolerance. The expression of 30 transcription factors (TFs) was up-regulated by AMF inoculation under combined stresses of CuO-NPs and flood, and 44 and 44 TFs were up-regulated under single CuO-NPs or flood condition, respectively, which may contribute to the alleviating effect of symbiosis on CuO-NPs and/or flood stress. These results provided a theoretical basis for enhancing the ecological restoration function of wetland plants for metallic nanoparticles (MNPs) by mycorrhizal technology in the future.

Richness of Arbuscular Mycorrhizal Fungi in a Brazilian Tropical Shallow Lake: Assessing an Unexpected Assembly in the Aquatic-Terrestrial Gradient

Aquatic ecosystems are historically overlooked regarding the occurrence of Arbuscular Mycorrhizal Fungi (AMF). Tropical lakes in the southern hemisphere are generally impacted by human actions, such as those in Brazil, although they still preserve a great diversity of macrophyte species that can support AMF communities. Thus, the study aimed to test (i) whether AMF community structure (composition, richness, diversity, dominance, and evenness) differs between aquatic and terrestrial conditions, and (ii) between seasons—rainy and dry. A total of 60 AMF species, distributed in 10 families and 17 genera, were found, with a difference in AMF composition between conditions (terrestrial and aquatic) and seasons (dry and rainy). The absolute species richness differed between conditions, seasons, and interactions. The aquatic/rainy season, which retrieved the most significant number of species, had the highest absolute richness and number of glomerospores and differed significantly from the terrestrial/rainy season. The results suggest that a shallow oligotrophic lake harbors a high AMF richness. In addition, this environment has a distinct AMF community from the adjacent coastal sand plain vegetation and is affected by seasonality.

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.

Effects of Arbuscular Mycorrhizal Fungi on Rice Growth Under Different Flooding and Shading Regimes

Arbuscular mycorrhizal fungi (AMF) are present in paddy fields, where they suffer from periodic soil flooding and sometimes shading stress, but their interaction with rice plants in these environments is not yet fully explained. Based on two greenhouse experiments, we examined rice-growth response to AMF under different flooding and/or shading regimes to survey the regulatory effects of flooding on the mycorrhizal responses of rice plants under different light conditions. AMF had positive or neutral effects on the growth and yields of both tested rice varieties under non-flooding conditions but suppressed them under all flooding and/or shading regimes, emphasizing the high importance of flooding and shading conditions in determining the mycorrhizal effects. Further analyses indicated that flooding and shading both reduced the AMF colonization and extraradical hyphal density (EHD), implying a possible reduction of carbon investment from rice to AMF. The expression profiles of mycorrhizal P pathway marker genes (GintPT and OsPT11) suggested the P delivery from AMF to rice roots under all flooding and shading conditions. Nevertheless, flooding and shading both decreased the mycorrhizal P benefit of rice plants, as indicated by the significant decrease of mycorrhizal P responses (MPRs), contributing to the negative mycorrhizal effects on rice production. The expression profiles of rice defense marker genes OsPR1 and OsPBZ1 suggested that regardless of mycorrhizal growth responses (MGRs), AMF colonization triggered the basal defense response, especially under shading conditions, implying the multifaceted functions of AMF symbiosis and their effects on rice performance. In conclusion, this study found that flooding and shading both modulated the outcome of AMF symbiosis for rice plants, partially by influencing the mycorrhizal P benefit. This finding has important implications for AMF application in rice production.

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).

The positive effects of inoculation using arbuscular mycorrhizal fungi and/or dark septate endophytes on the purification efficiency of CuO-nanoparticles-polluted wastewater in constructed wetland

The extent to which, and mechanisms by which, arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) purify wetlands polluted by metallic nanoparticles (metallic NPs) are not well understood. In this study, micro-vertical flow constructed wetlands (MVFCWs) with the Phragmites australis (reeds)-AMF/DSE symbiont were used to treat CuO nanoparticles (CuO-NPs)-polluted wastewater. The results showed that (1) the removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and CuO-NPs in three inoculated groups significantly exceeded those in the control check (CK) groups by 28.94-98.72%, 16.63-47.66%, and 0.53-19.12%, respectively; (2) inoculation with AMF and/or DSE significantly promoted the growth, nutrient content, and photosynthesis of reeds, increased the osmoregulation substance content and antioxidant enzyme activities, and decreased the malondialdehyde and reactive oxygen species contents of reeds under CuO-NPs stress; (3) higher Cu accumulation and smaller transport coefficients were found in the inoculated groups than in the CK group; (4) inoculation with AMF and/or DSE changed the subcellular structure distribution and chemical form of Cu in reeds. We therefore conclude that inoculation with AMF and/or DSE in MVFCWs improves the purification of CuO-NPs-polluted wastewater, and the MVFCW-reeds-AMF/DSE associations exhibit great potential for application in remediation of metallic-NPs-polluted wastewater.

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.

Effects of Aeration on the Formation of Arbuscular Mycorrhiza under a Flooded State and Copper Oxide Nanoparticle Removal in Vertical Flow Constructed Wetlands

In this study, six vertical flow constructed wetlands (VFCWs) planted with Phragmites australis were operated at different aeration times (4 h day^-1 and 8 h day^-1), aeration modes (continuous and intermittent), and arbuscular mycorrhizal fungi (AMF) inoculation treatments (inoculation with Rhizophagus intraradices and no inoculation) to explore the effects of different aeration strategies on the formation of arbuscular mycorrhiza under a flooded state in VFCWs. In addition, these VFCWs were further used to treat copper oxide nanoparticle (CuO-NP) wastewater to evaluate the correlations among aeration, colonization, growth, and CuO-NP removal. The highest AMF 28S copy number (1.99×10⁵) and colonization in reed roots, with values of 67%, 21%, and 1% for frequency (F%), intensity (M%), and arbuscule abundance (A%), were observed in the treatment with intermittent aeration for 4 h day^-1. Aeration significantly increased the dissolved oxygen (DO) concentration and AMF colonization in VFCWs, thereby promoting plant growth and the purification of the CuO-NPs. However, excessive and continuous aeration had little positive effect on AMF colonization. This study provides a theoretical basis for the application of AMF for improving pollutant removal performance in constructed wetlands.

Genetic Engineering-Facilitated Coassembly of Synthetic Bacterial Cells and Magnetic Nanoparticles for Efficient Heavy Metal Removal

Heavy-metal pollution is becoming a worldwide problem severely threatening our health and ecosystem. In this study, we constructed a genetic-engineering-driven coassembly of synthetic bacterial cells and magnetic nanoparticles (MNPs) for capturing heavy metals. The Escherichia coli cells were genetically engineered by introducing a de novo synthetic heavy-metal-capturing gene (encoding a protein SynHMB containing a six-histidine tag, two cystine-rich peptides, and a metallothionein sequence) and a synthetic type VI secretory system (T6SS) cluster of Pseudomonas putida, endowing the synthetic cells (SynEc2) with high ability of displaying the heavy-metal-capturing SynHMB on cell surface. MNPs were synthesized by a coprecipitation method and further modified by polyethylenimine (PEI) and diethylenetriaminepentaacetic acid (DTPA). Owing to the surface exposure of six-histidine tag on the synthetic bacteria and carboxyl groups on the modified MNPs (MNP@SiO₂-PEI-DTPA), the synthetic bacterial cells and MNPs coassembled to form biotic/abiotic complex exhibiting a self-developing characteristic. In the culture medium containing both Cd²⁺ and Pb²⁺, the coassemblies captured these heavy metals with high removal efficiency (>90% even at 50 mg/L of Cd²⁺ and 50 mg/L of Pb²⁺) and were conveniently recycled by artificial magnetic fields. Moreover, the coassemblies realized coremoval of organic carbon pollutants with the removal efficiency of >80%. This study builds a novel biotic/abiotic coassembling platform facilitated by genetic engineering and sheds light on development of artificial magnetic biological systems for efficient treatment of environmental pollution.

Diverse Arbuscular Mycorrhizal Fungi (AMF) Communities Colonize Plants Inhabiting a Constructed Wetland for Wastewater Treatment

Constructed wetlands (CWs) are biological wastewater treatment systems that comprise several components where plants and associated organisms play an important role in water depuration. Microbial studies emphasize bacterial dynamics, whereas studies of arbuscular mycorrhizal fungi (AMF) are scarce and the functional role of AMF in aquatic and wetland plants is poorly understood. The aim of this study was to analyze the AMF communities colonizing the roots of Canna indica, Canna flaccida, and Watsonia borbonica inhabiting a CW treating wastewater of a tourism unit. The dynamics of the AMF communities were evaluated by Denaturing Gradient Gel Electrophoresis (DGGE) of 18S rRNA gene amplification products along cold (C) and hot (H) seasons for three consecutive years. DGGE profiles allowed the estimation of AMF species richness (S), and Shannon-Wienner (H) and Pielou (J) indexes, for the different plant species, showing differences between species and along the years. Excised bands from DGGE were analyzed and identified through sequencing for arbuscular mycorrhiza, revealing the presence of AMF strains closely related to Glomus sp., Rhizophagus sp. and Acaulospora sp. genera. Concomitant water quality analyses showed that the system was effective in organic and nutrient removal during the sampling period. Findings from this study suggest that AMF diversity found in the CW is influenced by the water constituents, season, and plant species.

Positive effects of Funneliformis mosseae inoculation on reed seedlings under water and TiO2 nanoparticles stresses

TiO₂ nanoparticles (TiO₂NPs) is one of the most widely used nanomaterials. Arbuscular mycorrhizal fungi (AMF) are an important and widely distributed group of soil microorganisms, which promote the absorption of nutrients by host plants and increase their tolerance to contaminants. However, the effects and mechanisms of AMF on plant TiO₂NPs tolerance in wetland habitats are not clear. In this experiment, under the conditions of three soil moisture contents (drought 50%, normal 70% and flooding 100%) and four TiO₂NPs concentrations (0, 100, 200 and 500 mg kg^-1), the effects of Funneliformis mosseae on the growth, antioxidant enzyme activities, osmotic substances and the absorption and accumulation of Ti in the Phragmites australis (reed) seedlings were studied. The results showed that the inoculation of F. mosseae under three moisture content conditions significantly increased the plant nutrition and root activities of reeds. Compared with the non-inoculated control, inoculation with F. mosseae increased the activities of antioxidant enzymes, the contents of chlorophyll, proline, soluble protein, and free amino acids, and significantly reduced the contents of malondialdehyde (MDA) and reactive oxygen species (ROS) of leaves. The accumulating ability of inoculated reeds to Ti was significantly higher than that of non-inoculated controls (P < 0.05), and inoculation of F. mosseae changed the distribution of Ti in reeds, increased the accumulation of Ti in roots. It's confirmed that inoculation of F. mosseae under three water conditions could improve the plant growth and nutrition, the activities of antioxidant enzymes, and enhance the reeds tolerance to TiO₂NPs in this study.

Addition of iron materials for improving the removal efficiencies of multiple contaminants from wastewater with a low C/N ratio in constructed wetlands at low temperatures

Constructed wetlands (CWs) are widely used in wastewater treatment. Wastewater generally contains multiple contaminants. In this study, CWs were applied to treat wastewater with a low COD/TN ratio and containing heavy metals. Iron-based material was added in CWs to enhance the treatment efficiency. The contaminant removal efficiency was positively correlated with the dosage of iron-based material. Considering the operation cost, we added 1 g of iron-based material in CW and realized the multi-contaminant removal efficiency after 4-day treatment at low temperature: 99.51% of Cu(II), 87.22% of Cr(VI), 65.62% of TN, and 60.23% of COD. Microbial community analysis and kinetic analysis predicted that the removal mechanism involved ion exchange and microbial denitrification. Specific bacteria were found in CWs with iron-based material, such as Thiobacillus spp. and Thauera spp., indicating that the nitrate removal in the denitrification process was triggered by carbon sources and that Fe²⁺ worked as both the electron donor and the adjuster of the abundances of specific bacteria. The addition of iron-based material into CWs was a green option to improve the pollutant removal performance.