Microbial assemblages such as biofilms around aquatic plants play a major role in arsenic (As) cycling, which has often been overlooked in previous studies. In this study, arsenite (As(III))-oxidizing, arsenate (As(V))-reducing and As(III)-methylating bacteria were found to coexist in the phyllosphere of Hydrilla verticillata, and their relative activities were shown to determine As speciation, accumulation and efflux. When exposed to As(III), As(III) oxidation was not observed in treatment H(III)-B, whereas treatment H(III)+B showed a significant As(III) oxidation ability, thereby indicating that epiphytic bacteria displayed a substantial As(III) oxidation ability. When exposed to As(V), the medium only contained 5.89% As(III) after 48 h of treatment H(V)-B, while an As(III) content of 86.72% was observed after treatment H(V)+B, thereby indicating that the elevated As(III) in the medium probably originated from As(V) reduction by epiphytic bacteria. Our data also indicated that oxidizing bacteria decreased the As accumulation (by approximately 64.44% compared with that of treatment H(III)-B) in plants, while reducing bacteria played a critical role in increasing As accumulation (by approximately 3.31-fold compared with that of treatment H(V)-B) in plants. Regardless of whether As(III) or As(V) was supplied, As(III) was dominant in the plant tissue (over 75%). Furthermore, the presence of epiphytic bacteria enhanced As efflux by approximately 9-fold. Metagenomic analysis revealed highly diverse As metabolism genes in epiphytic bacterial community, particularly those related to energetic metabolism (aioAB), and As resistance (arsABCR, acr3, arsM). Phylogenetic analysis of As metabolism genes revealed evidence of both vertical inheritance and horizontal gene transfer, which might have contributed to the evolution of the As metabolism genes. Taken together, our research suggested that the diversity of As metabolism genes in epiphytic bacterial community is associated with aquatic submerged macrophytes which may play an important role in As biogeochemistry in aquatic environments.

The bacterial communities and ecological contribution of biofilm-leaves of the Vallisneria natans (VN), Hydrilla verticillata (HV) and artificial plant (AP) settled in sediments with different polluted levels of phenanthrene were investigated by high-throughput sequencing in different growth periods. There was no significant difference among the detected Alpha diversity indices based on three classification, attached surface, spiking concentration and incubation time. While Beta diversity analysis assessed by PCoA on operational taxonomic units (OTU) indicated that bacterial community structures were significantly influenced in order of attached surface > incubation time > spiking concentration of phenanthrene in sediment. Moreover, the results of hierarchical dendrograms and heat maps at genus level were consistent with PCoA analysis. We speculated that the weak influence of phenanthrene spiking concentration in sediment might be related to lower concentration and smaller concentration gradient of phenanthrene in leaves. Meanwhile, difference analysis suggested that attached surface was inclined to influence the rare genera up to significant level than incubation time. In general, the results proved that phenanthrene concentrations, submerged macrophytes categories and incubation time did influence the bacterial community of biofilm-leaves. In turn, results also showed a non-negligible ecological contribution of biofilm-leaves in dissipating the phenanthrene in sediments (>13.2%–17.1%) in contrast with rhizosphere remediation (2.5%–3.2% for HV and 9.9%–10.6% for VN).

The effects of maifanite on the physiological and phytochemical process of submerged macrophytes Hydrilla verticillate (H.verticillata) were investigated for the first time in the study. The growth index: plant biomass, root length, plant height and leaf spacing, and physiological and phytochemical indexes: chlorophyll, soluble protein, malondialdehyde (MDA), peroxidase (POD), superoxide dismutase (SOD) content and vitality of the roots of H.verticillata were tested. The results found that maifanite can significantly promote the growth of H.verticillata. The modified maifanite were more conducive to plant growth compared with the raw maifanite, and the MM1 group had the best growth promoting effect. The physiological and phytochemical indexes showed that maifanite can delay the aging process of H.verticillata (P < 0.05). The possible reasons for promoting H.verticillata growth were that maifanite can provide excellent propagation conditions for plant rhizosphere microorganisms, contains abundant major and microelements, and improve the sediment microenvironment. This study may provide a technique for the further application of maifanite in the field of ecological restoration.

Silver nanoparticles (AgNPs) inevitably discharge into aquatic environments due to their abundant use in antibacterial products. It was reported that in laboratory conditions, AgNPs display dose-dependent toxicity to aquatic organisms, such as bacteria, algae, macrophytes, snails and fishes. However, AgNPs could behave differently in natural complex environments. In the present study, a series of microcosms were established to investigate the distribution and toxicity of AgNPs at approximately 500 μg L−1 in aquatic systems. As a comparison, the distribution and toxicity of the same concentration of AgNO3 were also determined. The results showed that the surface layer of sediment was the main sink of Ag element for both AgNPs and AgNO3. Both aquatic plant (Hydrilla verticillata) and animals (Gambusia affinis and Radix spp) significantly accumulated Ag. With short-term treatment, phytoplankton biomass was affected by AgNO3 but not by AgNPs. Chlorophyll content of H. verticillata increased with both AgNPs and AgNO3 short-term exposure. However, the biomass of phytoplankton, aquatic plant and animals was not significantly different between control and samples treated with AgNPs or AgNO3 for 90 d. The communities, diversity and richness of microbes were not significantly affected by AgNPs and AgNO3; in contrast, the nitrification rate and its related microbe (Nitrospira) abundance significantly decreased. AgNPs and AgNO3 may affect the nitrogen cycle and affect the environment and, since they might be also transferred to food web, they represent a risk for health.

The objectives of this study were to (i) assess trace metal concentrations in Hydrilla verticillata and sediment from an estuarine creek in Alabama (USA), where high metal levels in biota were previously reported, and (ii) investigate the relationship between metal concentrations in H. verticillata and the sediment compartment. Our results indicate that sediment and H. verticillata exhibit moderate metal concentrations in the study area. We found that levels in plant tissues can be up to five times higher than in the sediment (e.g., Cd), suggesting that H. verticillata can take up and store several trace metals (Cd, Hg, Ni, and Zn) from this compartment. Together with studies focused on the uptake and accumulation of trace metals from the surrounding water, laboratory- and field-based studies are needed to better evaluate this plant’s ability to acquire metals from the sediment that constitutes a contaminant sink in human-impacted coastal regions.

Arsenic (As) contamination of the environment has emerged as a concerning issue recently for which phytoremediation has been suggested as a viable solution. Hydrilla verticillata (L.f.) Royle is a widely distributed rapidly growing aquatic weed possessing significant potential to accumulate As and is thus a potential candidate for the purpose of As phytoremediation. In the present study, an investigation of thiol metabolism was conducted in H. verticillata, which revealed differential effects upon exposure to arsenite [As(III)] and arsenate [As(V)]. The accumulation of arsenic was found to be higher upon exposure to As(III) than to As(V). Besides, As(III) was found to induce the activities of enzymes, such as cysteine synthase and γ-glutamylcysteine synthetase and the amounts of cysteine and glutathione (GSH) to higher levels than that observed with As(V). The activity of glutathione-S-transferase was, however, stimulated to a higher level upon exposure to As(V) than As(III). The activity of arsenate reductase was found to increase upon As(V) exposure at all concentrations and durations. In addition, a significant stimulation in the activity of phytochelatin synthase was noticed in vitro with an increase in As/GSH concentration and time of incubation. Arsenic detoxification in H. verticillata thus appeared to involve an induction of thiol synthesis and consumption in a coordinated manner, though differentially upon exposure to As(III) and As(V). The information gained through this study would help in better designing of the pilot experiment at the field level depending on the chemical composition of the contaminated water.

The mechanism of morphological and physiological regulation of submerged aquatic plants (Hydrilla verticillata) is influenced by spatial and environmental changes related to water depth gradients. In the present study, changes in the aquatic microcosm were explored at the depth gradients of 0.3 m, 0.6 m, 0.9 m, 1.2 m, and 1.5 m, and the depth was recognized as a critical factor for improving water quality, especially for the removal of total phosphorus (TP) and recalcitrant protein-like molecules. At 0.9 m, the removal rates of TP and protein-like substances reached 78% and 18.67%, respectively, 1.76 times and 1.28 times the rates at 0.3 m. The maximum shoot/root growth and chlorophyll (a + b) suggest photosynthesis inhibition is minimal at 1.2 m. Fluctuations in enzyme activities imply an antioxidant response to lipid peroxidation damage under different oxidative stress. The adjusted activities of glutamine synthetase (GS) and alkaline phosphatase (APA) were an adaptive nutrient utilization strategy to different water depths. Microbiological diversity analysis of biofilms indicates that community structure changes in response to water depth. Considering the growth status and nutrient removal effects, the results indicate that the optimal planting depth for H. verticillata is 0.9–1.2 m. These findings contribute to understanding water purification mechanisms in depth gradients, and support the effective rebuilding and management of submerged macrophyte communities in natural shallow lakes.

In the present study, the performance of three selected aquatic plants [Hydrilla verticillata (H), Ceratophyllum demersum (C), and Lemna minor (L)] was evaluated for As removal from water when used in a successive application approach. The plants were subjected to 4 L of As-containing Hoagland medium (500 and 2500 μg L⁻¹ as low and high exposure, respectively) for a period of 21 days in slots of 7 days each. The results showed that total As removal in 21 days varied in different combinations. The best combination was HCL showing 27 and 18% As removal in low and high As treatments, respectively, followed by HLC (21 and 16%), and LCH (15% and 12%). The lowest As removal was achieved by LHC and CLH combination in low As treatment (11%) and by CLH in high As treatment (6%). Individual plant exhibited different removal potential from combination to combination and from application at various stages. The contribution of Hydrilla varied from 8 to 52%, Ceratophyllum from 18 to 64% and Lemna from 18 to 66%. The study advocates the combination of Hydrilla-Ceratophyllum-Lemna for achieving the maximum As removal in the same period.

Contamination of metal ions in soil and water represents more pressing threats to resources as well as human health. The present research was carried out to screen the phytosequester plants growing in industrial waste- and wastewater-affected industrial areas of Okhla, New Delhi, India. Accumulation trend of metal Fe, Zn, Cu, Cr, Pb, Cd, Hg, and As from soil and wastewater by plants were collected for study. Among aquatic plants Hydrilla verticillata, Marsilea quadrifolia, and Ipomea aquatica were found to be highest metals accumulator, Eclipta alba and Sesbania cannabina among terrestrial plant were highest accumulator of metals. Among the algal spp. Spirulina platensis and Phormidium papyraceum were the most efficient in accumulating Cd and Hg. The maximum bioconcentration factor (BCF) was recorded in Hygroryza aristata for the metals (Hg, Cd) in M. quadrifolia (Cd, Cr), in E. alba (Cr, Cu), and in S. platensis (Hg, Pb). However, the translocation factor (TF) of metals was found more in M. quadrifolia followed by I. aquatica than other plants. Among all the plants, H. verticillata showed high TF and low BCF values for toxic metals (Pb, Cr) and was suitable for phytostabilization of these metals. Our study showed that native plant species growing on contaminated sites may have a potential of phytosequestration of these metals.