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Sediment cadmium contamination poses risks to aquatic ecosystems. Phytoremediation is an environmentally sustainable method to mitigate cadmium contamination. Submerged macrophytes are affected by cadmium stress, but plant growth-promoting rhizobacteria (PGPR) can restore the health status of submerged macrophytes. Herein, we aimed to reduce sediment cadmium concentration and reveal the mechanism by which the combined application of the PGPR Enterobacter ludwigii and the submerged macrophyte Vallisneria natans mitigates cadmium contamination. Sediment cadmium concentration decreased by 21.59% after submerged macrophytes were planted with PGPR, probably because the PGPR colonized the rhizosphere and roots of the macrophytes. The PGPR induced a 5.09-fold increase in submerged macrophyte biomass and enhanced plant antioxidant response to cadmium stress, as demonstrated by decreases in oxidative product levels (reactive oxygen species and malondialdehyde), which corresponded to shift in rhizosphere metabolism, notably in antioxidant defence systems (i.e., the peroxidation of linoleic acid into 9-hydroperoxy-10E,12Z-octadecadienoic acid) and in some amino acid metabolism pathways (i.e., arginine and proline). Additionally, PGPR mineralized carbon in the sediment to promote submerged macrophyte growth. Overall, PGPR mitigated sediment cadmium accumulation via a synergistic plant microbe mechanism. This work revealed the mechanism by which PGPR and submerged macrophytes control cadmium concentration in contaminated sediment. [Display omitted] • The study proposed a strategy for mitigating sedimentary cadmium. • PGPR inoculation maximized the accumulation of cadmium in submerged macrophytes. • PGPR may help submerged macrophytes overcome carbon constraints. [ABSTRACT FROM AUTHOR]

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans , elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems. [Display omitted] • Al stimulated filamentous Cyanobacteriota growth, increasing epiphytic biofilm thickness. • Al enhanced micro-eukaryotic Shannon diversity but inhibited bacteria diversity. • Al had a greater impact on bacterial community assembly than micro-eukaryotic community. • Al stress might disrupt microbial food webs through top-down control. [ABSTRACT FROM AUTHOR]

Microcystin-LR (MCLR) and copper are commonly found in eutrophic water bodies because of eutrophic run-offs, cyanobacterial blooms, and copper algicide applications. However, the ecotoxicological risk of their combination remains unknown. This study investigated the effect of MCLR, Cu, and their mixture on the growth and physiological responses of Vallisneria natans . Results showed that the combined toxicity of them was concentration dependent. Synergistic effects were elicited at low concentrations of MCLR and Cu exposure (≤0.25 + 0.64 mg/L). Additive or antagonistic effects were induced at higher concentrations. Single and combined exposures could induce oxidative stress, such as increased superoxide anion radical levels. To cope with oxidative stress, V. natans could activate their antioxidant defense systems, such as enhanced superoxide dismutase production and changes in peroxidase activities. Exposure to combined MCLR and Cu (even only with 0.005 + 0.041 mg/L) adversely affected their antioxidant defense systems. As a consequence, malondialdehyde levels significantly increased. The interaction of MCLR and Cu could also significantly increase the bioaccumulations of MCLR and Cu. This increase could be accounted for their synergistic toxic effects on V. natans . Our results suggested that the exacerbated ecological hazard of MCLR and Cu with environmental concentrations may harm aquatic ecosystems. [ABSTRACT FROM AUTHOR]

In this study, Vallisneria natans plants were exposed to 5 and 20 nm of titanium dioxide nanoparticles (TiO₂ NPs) anatase and 600–1000 nm of bulk at 5 and 20 mg/L for 30 days. SEM images and EDX spectra revealed that epiphytic biofilms were more prone to TiO₂ NPs adhesion than bare plant leaves. TiO₂ NPs injured plant leaf cells, ruptured epiphytic diatoms membranes and increased the ratio of free-living microbes. The TN, NH 4 ⁺-N and NO 3 ˉ-N concentrations significantly decreased, respectively, by 44.9%, 33.6%, and 23.6% compared to bulk treatments after 30 days due to macrophyte damage and a decline in diversity of epiphytic bacterial community and abundance of nitrogen cycle bacteria. TiO₂ NPs size-dependent decrease in bacterial relative abundance was detected, including phylum Cyanobacteria, Planctomycetes, and Verrucomicrobia. Although TiO₂ NPs increased eukaryotic diversity and abundance, abundances of Bacillariophyceae and Vampyrellidae classes and Gastrotricha and Phragmoplastophyta phylum decreased significantly under TiO₂ NPs exposure compared to bulk and control. TiO₂ NPs reduced intensities of interaction relationships among epiphytic microbial genera. This study shed new light on the potential effects of TiO₂ NPs toxicity toward aquatic plants and epiphytic microbial communities and its impacts on nitrogen species removal in wetlands. [Display omitted] There is credence for the present age to be known as the nanomaterials Age, including titanium dioxide nanoparticles (TiO₂ NPs). Ironically the useful properties of TiO₂ NPs confer them with unexpected hazards. This study is the first of its kind to explore the size and dose role in direct and indirect (water quality) toxicity effects toward plants and microbes in wetlands using Illumina sequencing. The results demonstrated that TiO₂ NPs reduced interaction and disturbed microbial community depending on NPs size more than dose. These were accompanied by a decrease in chlorophyll and damage of v. natans leaves. Thus, helping to control and avoid TiO₂ NPs toxicity effects. • Titanium oxide nanoparticles (TiO₂ NPs) damaged diatoms and plants in aquatic system. • TiO₂ NPs attached to epiphytic biofilms more than aquatic plant leaves. • TiO₂ NPs decreased bacteria abundance and diversity in epiphytic biofilm in wetlands. • TiO₂ NPs decreased nitrogen removal capacity and epiphytic-related bacteria. • TiO₂ NPs impaired interaction relationships among epiphytic microbial genera. [ABSTRACT FROM AUTHOR]

Rhizodegradation using submersed macrophytes Vallisneria natans (V. natans) is a promising biotechnology with the potential to restore polycyclic aromatic hydrocarbon (PAH)-contaminated sediments. However, how different sediment types influence the rhizoremediation outcome and the characterization of microbial community along the sediment- V. natans continuum is poorly understood. Here, we collect V. natans , sediments and overlying water from two types of vegetation zones with different levels of PAHs pollutions and set up sediment microcosms for phytoremediation tests. V. natans presence was particularly useful for PAHs remediation in the highly contaminated sites and had a significant effect on PAHs rhizodegradation and microbial communities, especially rhizosphere sediments. The structural composition of microbial communities along the sediment-plant continuum was shaped predominantly by compartment niche of V. natans. Moreover, selective enrichment of specific microbial taxa like Herbaspirillum (relative abundance = 94.80%) in endosphere of V. natans was observed. Herbaspirillum could use PAH as carbon source and promote the growth of plants. In the highly contaminated sediment, V. natans could recruit these bacteria for toxicant degradation into the root interior. Thus, understanding the complex V. natans -microbe interactions could help set up novel decontamination strategies based on the rhizosphere and root interior interactions between plants and their microbial associates. [Display omitted] • V.natans was particularly useful for rhizoremediation of PAH-contaminated sediment. • V.natans had a significant effect on rhizosphere sediment microbial communities. • Specific microbial taxa like Herbaspirillum was enriched in endosphere of V.natans. • Microbiome along sediment-plant continuum was shaped by compartment niche of V.natans. [ABSTRACT FROM AUTHOR]

Abstract: The overarching goal of this in situ study was to investigate the integrated impact(s) that metal/metalloid contamination might have on the overall health and performance of the ecologically important aquatic macrophyte, Vallisneria neotropicalis. Morphological (i.e., shoot growth-based endpoints) and photo-physiological (i.e., photosynthetic activity measured as chlorophyll a fluorescence and oxygen exchange) variables, along with aboveground tissue metal/metalloid concentrations, were measured in natural populations of V. neotropicalis that differed with respect to their anthropogenic pressure. With the exception of an overall negative effect on growth, our results suggest that there were no detrimental effects of low/moderate contamination of V. neotropicalis by trace elements (i.e., arsenic As and mercury Hg; 1.04–2.77μgg−1 drywt. and 3.76–15.18ngg−1 drywt., respectively) on the photosynthetic physiological performance of this species. V. neotropicalis appears to tolerate low/moderate levels of trace element contamination with little impact on plant health and performance. [Copyright &y& Elsevier]

Abstract: Microcystins produced by cyanobacteria in the aquatic environment are a potential risk to aquatic plants. In the present study, the uptake of microcystin-LR (MC-LR) and related physiological and biochemical effects on Vallisneria natans (Lour.) Hara were investigated at concentrations of 0.1–25.0μgL−1. Results showed that O2 − intensity was significantly induced at 1.0μgL−1 and reached a maximum level at 5.0μgL−1. Superoxide dismutase (SOD) and peroxidase (POD) were induced with increasing MC-LR concentrations as an antioxidant response. Catalase (CAT) was significantly induced while GSH/GSSG (reduced/oxidized glutathione) ratio was significantly reduced at 0.1μgL−1. The induction of glutathione S-transferase (GST) and inhibition of GSH revealed that GSH was involved in the detoxification of MC-LR in plants. Oxidative damage was evidenced by the significant increase of malondialdehyde content at 1.0μgL−1. A pigment pattern change and a series of significant ultrastructural alterations were also observed due to MC-LR exposure. The lowest non-effect concentration of MC-LR for V. natans at the subcellular and molecular level is around 0.5μgL−1. These results imply that even at relatively low MC-LR concentrations the aquatic plants may still suffer a negative ecological impact. [Copyright &y& Elsevier]

Perfluoroalkyl acids (PFAAs) have emerged as a global concern in aquatic environment remediation due to their abundance, persistence, bioaccumulation, and toxicity. To comprehensively understand the removal potential of multiple PFAAs by submerged macrophytes in aquatic environments, systematic investigations into the tolerance of the typical submerged macrophyte Vallisneria natans to 12 typical PFAAs and the removal capacity to PFAAs in V. natans -microbiota systems were carried out. Results showed that although PFAAs could induce the accumulation of hydrogen peroxide and malondialdehyde, V. natans was overall resistant to multiple PFAAs with natural concentrations. Catalase is one of the main strategies of V. natans to alleviate PFAA stress. Microbiota can remove 18.10–30.84% of the PFAAs from the water column. 24.35–73.45% of PFAAs were removed from water in V. natans -microbiota systems. The uptake of plant tissues and the bioaccumulation of microbiota were proposed as the main removal processes. The removal rates were significantly correlated with the perfluorinated carbon atoms numbers (p < 0.05). PFAAs and V. natans increased the relative abundance of Betaproteobacteria , Nostocales , Microscillaceae , Sphingobacteriales , SBR1031 , Chlamydiales , Phycisphaerae , Caldilineales , Rhodobacterales , and Verrucomicrobiales. The present study suggested that V. natans can be a potential species to remove multiple PFAAs in aquatic environments, and further providing insights into the PFAAs' remediation. [Display omitted] • V. natans can relatively tolerate multiple PFAAs via the regulation of catalase. • The presence of V. natans significantly enhanced the PFAAs removal from water. • 24.35–73.45% of PFAAs were removed via plant uptake and microbial absorption. • Dominant microbiota and biomarkers in water and biofilms were identified. • V. natans was suggested as a potential species to remove multiple PFAAs in water. [ABSTRACT FROM AUTHOR]

• Increasing Al amount in aquatic systems greatly stressed submerged plants restoration. • Al aquatic-phytotoxicity on entire individuals of V. natans , with root as target. • Al and V. natans growth have synergistic effect on rhizospheric N and P component. • Sediment microbia community construction varied by Al and V. natans synergistically. Increasing aluminum (Al) use and its effects on aquatic systems have been a global issue, however the Al impacts on submerged plants and their ecological functions were poorly understood. Aquatic simulation experiments were performed to study Al-toxicity on the germination and seedling morphological and physiological characteristics of Vallisneria natans , and investigate their synergistic effect on nitrogen (N), phosphorus (P) change and microbial community in sediment. The seeds germination characteristics, growth and physiological parameters of seedlings, including root activity, were significantly affected by alum treatments and the inhibition levels increased with Al3+ concentration. The Al accumulation in roots and leaves were significantly different. Al3+ concentration above 0.3 mg/L showed toxic to V. natans. TN, TP, IP, Fe/Al-P contents in sediments varied markedly under co-existence of Al and V. natans. Additionally, the relative abundance of sediment microbial community related to N, P cycle was effected. Results concluded that the increasing aquatic Al-concentration inhibits growth and propagation of submerged plants and the ecological restoration effect, and exerts synergistic effect with submerged plants on N, P components in sediments. Such findings were helpful for Al ecological evaluation, and were instructive for the submerged plants restoration in shallow eutrophic lakes with Al input. [ABSTRACT FROM AUTHOR]

• Detoxification of arsenic by thiol, carboxylic and hydroxyl group in plant cell. • Compartmentalization of arsenic in vacuole of plant cell. • Cell loss, MDA production and EL induced in plants by arsenic stress. • Enhanced plant growth and arsenic uptake by indigenous strain. • V.denseserrulata as a hyper-accumulator of arsenic. The symbiosis between Vallisneria denseserrulata and indigenous Bacillus sp. XZM was investigated for arsenic removal for the first time. It was found that the native bacterium was able to reduce arsenic toxicity to the plant by producing higher amount of extra cellular polymeric substances (EPS), indole-3-acetic acid (IAA) and siderosphore. Interestingly, V. denseserrulata-Bacillus sp. XZM partnership showed significantly higher arsenic uptake and removal efficiency. The shift in FT-IR spectra indicated the involvement of amide, carboxyl, hydroxyl and thiol groups in detoxification of arsenic, and the existence of an arsenic metabolizing process in V. denseserrulata leaves. The scanning electron microscopy (SEM) images further confirmed that the bacterium colonized on plant roots and facilitated arsenic uptake by plant under inoculation condition. In plant, most of the arsenic existed as As(III) (85%) and was massively (>77%) found in vacuole of particularly leaves cells. Thus, these findings are highly suggested for arsenic remediation in the constructed wetlands. [ABSTRACT FROM AUTHOR]