Vallisneria Natans Research Articles

Purification Efficiency of Eutrophic Water by Three Submerged Plants

The increase of nitrogen and phosphorus causes eutrophication in water bodies. Using submerged plants to decrease the pollution from water bodies is an effective way. In this research, three common submerged plants (Vallisneria natans, Hydrilla verticillata, and Ceratophyllum demersum) and their combinations were used to purify eutrophic water. The control treatment did not contain any plants. The removal effects and dynamic regulations of the three plants with their combinations of nutrients (such as nitrogen and phosphorus) in water were analyzed. All three species and their combinations above could grow in the eutrophic water and efficiently remove aquatic nutrients. All the treatment groups had a higher pollutant removal rate for total nitrogen (TN) and total phosphorus (TP) than that of the blank control. In these treatment groups, treatment F (50 g Vallisneria natans plus 50 g Ceratophyllum demersum) had the highest removal rate of TP at 57.53%; treatment B (100 g Vallisneria natans) had the best removal rate of TN at 92.04 %. Among these plants and their combinations, Vallisneria natans and Ceratophyllum demersum showed better purification ability; the combination of these two submerged plants and the combination of three submerged plants were more applicable for the restoration of eutrophic water.

Plant Compartments Shape the Assembly and Network of Vallisneria natans-Associated Microorganisms

The submerged plant Vallisneria natans can provide an attachment matrix and habitat for diverse microorganisms and plays an important role in maintaining the structure and function of the shallow lake ecosystem. However, little is known about how V. natans-related microorganism components, especially bacteria, adapt to specific plant compartments. In this study, we investigated the assembly and network of bacterial communities living in different plant compartments (sediment, rhizosphere, rhizoplane, root endosphere, and leaf endosphere) associated with V. natans by 16S rRNA gene sequencing. The results showed that the diversity and network complexity of the bacterial community in the sediment was significantly higher than that in other plant compartments. The bacterial community composition showed that the dominant phyla were Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, Desulfobacterota, and Chloroflexi, among which Proteobacteria were extremely abundant in all samples, and there were notable differences in bacterial community composition related to plant compartments. Different networks based on sediment and plant compartments showed distinct co-occurrence patterns and exhibited distinct topological features. Additionally, functional predictions from FAPROTAX indicate that the predominant biogeochemical cycle function of the V. natans-related bacterial community is to participate in the carbon and nitrogen cycle. These results strongly suggested how the microbial community adapted to different plant compartments and provided theoretical and technical data for isolating beneficial bacteria from macrophytes in the future.

Effects of benthic fish and light regimes on water quality and the growth of Vallisneria natans with two sediment types.

In shal low eutrophic lakes, submersed macrophytes are essential for maintaining a clear water state and they are significantly affected by benthic fish disturbance, light availability, and sediment types. We conducted a mesocosm experiment with benthic fish (Misgurnus anguillicaudatus), two light regimes, and submerged macrophyte (Vallisneria natans) growing in two sediment types to investigate the ecological effects of benthic fish and light regimes on water quality and the growth of submersed macrophyte. Our findings indicated that the benthic fish increased the concentrations of total nitrogen, total phosphorus, and total dissolved phosphorus in the overlying water. The effects of benthic fish on ammonia-nitrogen (NH4+-N) and chlorophyll a (Chl-a) contents were related to light regimes. Fish disturbance indirectly promoted the growth of macrophytes growing in sand by increasing NH4+-N content in overlying water. However, the increasing Chl-a content stimulated by fish disturbance and high light regime reduced the growth of submersed macrophytes growing in clay due to shading. Macrophytes with different sediments had different strategies coping with light. Plants growing in sand responded to low light mainly by adjusting the leaf and root biomass allocation, whereas plants growing in clay responded to low light by physiologically adjusting the soluble carbohydrate content. The findings of this study might help restore lake vegetation to some degree, and using nutrient-poor sediment might be an appropriate method to avoid the detrimental effects of fish-mediated disturbances on the growth of submerged macrophytes.

Evaluation of organic matter and nitrogen removals, electricity generation and bacterial community responses in sediment microbial fuel cell coupled with Vallisneria natans

With the development of industrial civilization, a large amount of carbon and nitrogen compounds from industrial, agricultural, and human activities are discharged into the environment, which has seriously affected the quality of the surface water. The current remediation methods, such as aeration or chemical addition, not only exhibit high energy consumption but may also lead to secondary pollution. This study constructed a sediment microbial fuel cell system coupled Vallisneria natans (P-SMFC) to remove surface water and sediment pollutants, generate electricity, and reduce the demand for additional oxygen supply. P-SMFC demonstrated excellent pollutant removal and power generation performance under three different pollution loads. P-SMFC exhibited a COD removal efficiency of 80.48% at organic loading rate of 10.64 g/(m3d), which was 10.01%, 26.01%, and 41.77% higher than that of normal SMFC system without plants (SMFC), open-circuit control system with plants (C-P), and open-circuit control system without plants (C-S), respectively. P-SMFC exhibited a TN removal efficiency of 92.61% at nitrogen loading rate of 1.06 g/(m3d), which was 17.31%, 9.92%, and 40.58% higher than that of SMFC, C-P, and C-S, respectively. The maximum power density of the P-SMFC was 45.36 mW·m−3, which was 18.57 mW·m-3 higher than that of the SMFC. The oxygen release and root secretion of organic substances by Vallisneria natans promoted the enrichment of microorganisms with power generation and nitrogen removal functions, such as Geobacter, Acidovorax, Nitrosomonas, Pseudomonas, and Delftia. This study developed a novel, sustainable, and low-cost technology for the in-situ remediation of contaminated surface water.

Water exchange unevenness alters the species dominance and community composition of submerged macrophytes in Erhai Lake and the potential mechanisms revealed by laboratory experiment

Water exchange unevenness (WEU) is defined as the coefficient of variation in water exchange intensity over time. Although its influence on aquatic plant characteristics has been recently investigated, there is limited understanding regarding the effects of this hydrodynamic change on submerged vegetation. This study investigated the impacts of WEU on the species dominance and community composition of submerged macrophytes in three bays with different WEU conditions in Erhai Lake, China. Subsequently, a laboratory experiment was conducted to elucidate the mechanisms underlying these effects. The field investigation showed that the dominance values of submerged macrophytes were influenced by WEU. As WEU decreased, the average dominance value decreased for Vallisneria natans (by 34.54 %), Myriophyllum spicatum (16.82 %), and Hydrilla verticillata (12.84 %); showed no significant change for Potamogeton lucens; and increased for Potamogeton maackianus (14.22 %) and Ceratophyllum demersum (17.52 %). The laboratory experiment showed that lower WEU markedly inhibited the growth of V. natans, slightly inhibited that of M. spicatum, and stimulated that of P. maackianus, consistent with the field observations. The inhibitory effect was attributed to a reduced concentration of carbon dioxide in the water; adaptive strategies, i.e., plant height, biomass allocation, and root traits, were more effective for M. spicatum than for V. natans. The stimulated growth of P. maackianus was attributed to increased dissolved oxygen concentration, which promoted root growth and nutrient uptake. Our results indicate that WEU has significant effects on the growth and community characteristics of submerged macrophytes.

Effect of environmental factors on phosphorus transformation during the growth of submerged macrophytes

Three submerged macrophytes, Hydrilla verticillata, Vallisneria natans, and Potamogeton crispus, were planted in winter and spring to investigate the environmental mechanism of phosphorus transformation during submerged macrophyte growth periods. The experimental buckets each contained 4,832.80 g of dry sediment (depth: 10 cm) and 100 L water. The phosphorus (P) fractions in the water and sediment were investigated along with the environmental factors, including pH, dissolved oxygen (DO), and redox potential (ORP). The concentrations of the different forms of P in the water and sediment were lower in the submerged macrophyte groups. Submerged macrophyte uptake was the primary reason for the decrease in P in the water and sediment. At the end of the experiment, the total amounts of phosphorus accumulated by H. verticillata, V. natans, and P. crispus were 156.05 g, 282.24 g, and 115.84 g, respectively, and the three submerged macrophytes enriched P by 4.18%, 7.56%, and 3.10%. The levels of the environmental factors pH, DO, and ORP were higher in the submerged macrophyte groups than the control groups. The environmental factors had different effects on the different forms of P during growth of the submerged macrophytes. H. verticillata primarily acted on the soluble reactive phosphorus (SRP) through environmental factors, while P. crispus acted on the dissolved total phosphorous, SRP, dissolved organic phosphorus, and particulate phosphorous through these factors. V. natans had a weak impact on P content in the water through the environmental factors. Hence, the transformation of P between the sediment and water was affected by environmental factors. Overall, the results of this study reveal the effects of environmental factors under submerged macrophyte growth on water purification as well as the migration and transformation of P in the sediment and on the surface and provide a theoretical basis for the ecological restoration of eutrophicated shallow lakes.

Sediment remediation using submerged plants mitigated the bioaccumulation of organic contaminants in benthic organisms in simulated freshwater aquaculture ponds

Few studies have investigated whether growing submerged plants can provide significant mitigation of both polycyclic aromatic hydrocarbons (PAHs) and antibiotics (ATBs) in sediments and cultured aquaculture products. In this study, Corbicula fluminea was selected as the indicator organism in the laboratory simulation experiment, and four remediation systems using Vallisneria natans L. (VN), Hydrilla verticillate L. (HV), Elodea nuttallii P. (EL) and Control Check (CK) were constructed individually. The accumulated concentrations (Cb) and changes in both bioavailability (Cfree) and bulk burden (Cs) of 16 PAHs and four ATBs were analyzed before, during, and after the experiment. Compared with the CK group, the introduction of VN, HV, and EL reduced: Cb of ΣPAHs by 43%, 32%, and 27%, respectively; ΣATBs by 68%, 49%, and 39%, respectively, in Corbicula fluminea; the corresponding cancer risk of ΣPAHs by 19%, 8.9%, and 13%, respectively; and the target hazard quotients of ΣATBs by 73%, 48%, and 41%, respectively. The freely dissolved concentrations of ΣPAHs and ΣATBs (Cfree) in the experimental groups decreased by 38%− 58% and 37%− 70%, respectively. More ATBs than PAHs were reduced in biota, with VN showing the highest efficiency. Reduction in Cfree was more related to reduction in Cb than reduction in Cs. In terms of Cb reduction, Cfree was more indicative for ATBs than PAHs. Analyses of the bacterial community revealed that the introduction of submerged plants significantly increased the abundance of Sphingomonas and Mycobacterium, with specific degradation effects observed for high molecular weight PAHs in the sediment.

Vallisneria natans decreased CH4 fluxes in wetlands: Interactions among plant physiological status, nutrients and epiphytic bacterial community

Submerged macrophytes provide niches for epiphytic microbes (including aerobic methanotrophs) growth. However, little is known about the impacts of submerged macrophytes growth status and nutrients loadings on methanotroph community and methane release in wetlands. In the present study, methane fluxes, bacterial and methanotroph community in epiphytic biofilm, and environmental parameters were investigated during Vallisneria natans senescence in wetlands under low (VnL) and high (VnH) nutrients for seven weeks. Relative conductivity and concentration of H2O2, total chlorophyll and malondialdehyde were higher in leaves of V. natans in VnH than VnL at the same sampling time. Nutrients loading increased methane fluxes in treatments with or without (Control) macrophytes, while healthy V. natans plants reduced the methane flux and nutrients concentration in water columns. CH4 fluxes were positively correlated to temperature and COD (p < 0.05). Methane oxidation rates were 3.04–31.68 μmol methane mg−1 fresh weight of V. natans leaves - epiphytic biofilm within 1 h. Proteobacteria, Cyanobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Actinobacteria and Acidobacteria were dominant phylum in all epiphytic biofilms. The mean abundances of pmoA/16S rRNA were higher in VnL than VnH. According to Illumina sequencing results of pmoA gene, γ-proteobacteria and α-proteobacteria were the dominant methanotroph class in epiphytic biofilm from VnH and VnL, respectively. Among seven detected methanotrophic genera, Methylomonas was significantly higher in VnH than VnL. Network analysis revealed that there were much closer relationships between the environmental parameters and epiphytic bacterial community in VnH than in VnL. COD and MDA were negatively correlated with Methyloglobulus, Methylosarcina, Methylobacter and Methylocystis, but positively correlated with Methylomonas and Methylosinus. This study highlights that methanotrophs in epiphytic biofilm play important roles in methane-oxidizing, which can be affected by plant physiological status and environmental parameters.

Diversity and interaction of bacterial and microeukaryotic communities in sediments planted with different submerged macrophytes: Responses to decabromodiphenyl ether

Although various persistent organic pollutants (POPs) can affect microbial communities and functions in aquatic ecosystems, little is known about how bacteria and microeukaryotes respond to the POPs in sediments planted with different submerged macrophytes. Here, a 60-day microcosm experiment was carried out to investigate the changes in the diversity and interaction of bacterial and microeukaryotic communities in sediments collected from Taihu lake, either with decabromodiphenyl ether (BDE-209) own or combined with two common submerged macrophyte species (Vallisneria natans and Hydrilla verticillate). The results showed that BDE-209 significantly decreased the bacterial α-diversity but increased the microeukaryotic one. In sediments planted with submerged macrophytes, the negative effect of BDE-209 on bacterial diversity was weakened, and its positive effect on microeukaryotic one was strengthened. Co-occurrence network analysis revealed that the negative relationship was dominant in bacterial and microeukaryotic communities, while the cooperative relationship between microbial species was increased in planted sediments. Among nine keystone species, one belonging to bacterial family Thermoanaerobaculaceae was enriched by BDE-209, and others were inhibited. Notably, such inhibition was weakened, and the stimulation was enhanced in planted sediments. Together, these observations indicate that the responses of bacteria and microeukaryotes to BDE-209 are different, and their communities under BDE-209 contamination are more stable in sediments planted with submerged macrophytes. Moreover, the effects of plant species on the microbial responses to BDE-209 need to be explored by more specific field studies in the future.

Phytoremediation Competence of Composite Heavy-Metal-Contaminated Sediments by Intercropping Myriophyllum spicatum L. with Two Species of Plants.

A variety of remediation approaches have been applied to reduce the harm and diffusion of heavy metals in aquatic sediments; however, phytoremediation in co-contaminated soils is still not clear. In order to explore the phytoremediation of sediments contaminated by Cu and Pb, two submerged plants with different characteristics, Vallisneria natans and Hydrilla verticillata, were interplanted with Myriophyllum spicatum. By simulating a submerged plant ecological environment, medium-scale-simulated ecological remediation experiments were carried out. The results showed that the two planting patterns were effective in repairing the sediments in the Cu and Pb contaminated sediments. The intercropping of Myriophyllum spicatum and Vallisneria natans can be used as the plant stabilizer of Cu because of the TF > 1 and BCF < 1, and the intercropping with Hydrilla verticillata can regulate the enrichment efficiency of Myriophyllum spicatum. The removal rates of Cu and Pb in sediments reached 26.1% and 68.4%, respectively, under the two planting patterns. The risk grade of the restored sediments was RI < 150, indicating a low risk.

Submerged macrophytes mediated remediation of molybdenum-contaminated sediments.

Molybdenum (Mo) sourced mainly from artificial activities is an emerging environmental concern whose remediation is seldom reported. This study screened the Mo-enriched macrophyte Vallisneria natans (Lour.) Hara due to its high enrichment factor (10.25). Phytoremediation (V. natans) and microorganism-assisted phytoremediation (V. natans-Serratia marcescens A2) efficiency were compared. S. marcescens A2 improved phytoremediation in the early stage, however, it reduced the total Mo removal rate by 8.42%. Further experiments were conducted to investigate the environmental factors (light intensity and overlying water flow rate) on the phytoremediation by V. natans. The optimal phytoremediation performance was achieved under a high overlying water flow rate (0.022cm·s-1) with intense light (60μmol·m-2·s-1) conditions. In addition, increasing the light intensity or flow rate increased the microbial communities' diversity in the sediment. Notably, the abundance of norank_f__Bacteroidetes_vadinHA17, related to Mo release in sediments, increased by 147.96% at optimal conditions. This study illustrated that the phytoremediation of Mo-contaminated sediments by V. natans is of practical potential.

Dynamic Characteristics of Periphytic Algae Communities on Different Substrates and the Host Response in Subtropical-Urban-Landscape Lakes

Outbreaks of periphytic algae, including filamentous algae, have been observed after submerged macrophyte restoration and are common in early stages. Dynamic changes in the periphytic algae community on Vallisneria natans and artificial V. natans were investigated in situ, and their characteristics were compared on the two substrates. The results showed that more periphytic algae species occurred on V. natans (77 taxa) than on artificial V. natans (66 taxa) (F = 2.089, p = 0.047). The cell density and chlorophyll a (Chl. a) content of periphytic algae were 3.42–202.62-fold and 2.07–15.50-fold higher on the artificial substrate than on V. natans, respectively. Except for Lyngbya perelagans (i.e., the only common dominant periphytic algae species on the two substrates), the dominant species on V. natans were Cocconeis placentula and Ulothrix tenerrima, while those on the artificial substrate were Stigeoclonium aestrivale, Oscillatoria tenuis and Achnanthes minutissima. The cell density of periphytic algae was significantly affected by the total phosphorus (TP) and NO3−-N and electric conductivity on V. natans, and by TP and NH4+-N on artificial V. natans. The malondialdehyde content of V. natans was significantly correlated with the periphytic algae biomass. V. natans was more affected by periphytic algae during its slow-growing period, and the contribution order of stress to V. natans was diatoms &gt; cyanobacteria &gt; green algae. Our findings might contribute to the understanding the effect of substrate specificity on periphytic algae communities, and have important implications for the restoration of submerged plants in eutrophic lakes.

PGPR Promotes the Recovery of Submerged Macrophytes via Indigenous Microbiome Modulations under Combined Abiotic Stress

The restoration of submerged macrophytes is commonly limited by abiotic stress. Here, we isolated PGPR strains from the rhizosphere of submerged macrophytes using ACC deaminase selective medium, and evaluated their growth promoting effects on Vallisneria natans (V. natans) under low light intensity and (or) high sediment organic matter load, and also explored the indigenous microbiome response of V. natans seedlings to PGPR inoculants. Ten isolates were chosen from the 252 isolated strains based on the ACC deaminase activity and the production of IAA and siderophore. M1 (Pseudomonas vancouverensis) and E15 (Enterobacter ludwigii) had the best growth promoting effects under low light stress and under double stress of low light and high sediment organic matter load, and the shoot height increased by 36% and 46%, respectively. The results of indigenous microbiome analysis showed that PGPR inoculants could regulate the relative abundance of unclassified_f_Enterobacteriaceae and improve the α-diversity of the rhizosphere bacterial community. Under high sediment organic matter load, inoculation of PGPR obviously shifted the β-diversity of rhizosphere bacterial communities to promote the early growth of V. natans. This study expands the application of plant–microbe interaction in the field of freshwater ecological restoration.

Ecotoxic side-effects of allelochemicals on submerged plant and its associated microfloras effectively relieved by sustained-release microspheres

Harmful algae bloom caused by water eutrophication is a burning question worldwide. Allelochemicals sustained-release microspheres (ACs-SMs) exhibited remarkable inhibition effect on algae, however, few studies have focused on the ecotoxic side-effects of ACs-SMs on submerged plant and its associated microfloras. Herein the effects of different exposure situations including single high-concentration ACs (15 mg/L, SH-ACs), repeated low-concentration ACs (3 × 5 mg/L, RL-ACs) and ACs-SMs containing 15 mg/L ACs on morphological indexes, chlorophyll content, lipid peroxidation, enzymatic activity, and chlorophyll fluorescence indexes of submerged plant Vallisneria natans and the richness and diversity of its associated microfloras (epibiotic microbes and sediment microbes) were studied. The results showed that pure ACs (RL-ACs and SH-ACs groups) had negative effects on plant height, mean leaf number and area of V. natans, but promoted the increase of mean leaf length. In addition, pure ACs caused lipid peroxidation, activated the antioxidant defense system, decreased chlorophyll content, and damaged photosynthetic system in leaves. Interestingly, ACs-SMs not only had barely negative effects on above indexes of V. natans, but had certain positive effects at the later experiment stage (days 50–60). Pure ACs and ACs-SMs all reduced the richness and diversity of microfloras in each group, and promoted the increase of relative abundance of dominant bacteria Pseudomonas, leading to a simpler community structure. Significantly, V. natans leaves diminished the effects of pure ACs and ACs-SMs on epibiotic microbes, and the plant rhizosphere was beneficial to the increase of dominant bacteria that promoted plant growth. Thus, sustained-release microspherification technology can effectively relieve the ecotoxic side-effects of pure ACs on submerged plant and its associated microfloras. This study fills the gap on the ecological safety knowledge of ACs-SMs and provides primary data for evaluating the feasibility and commercialization prospects of ACs-SMs as algae inhibitor in aquatic ecosystem.

Degradation of sulfonamide antibiotics in the rhizosphere of two dominant plants in Huixian karst wetland, Guangxi, China

Abstract In this work, Phragmites australis and Vallisneria natans were selected as the research objects and were cultured for 10 d under 0.10 μg L−1 sulfadiazine (SD) stress in a simulated surface flow wetland reactor. SD degradation was conducted at pH = 7 and 25 °C for 96 h. Each plant group conformed to the first-order kinetic model of degradation, and the degradation rate increased with time, reaching the maximum at 96 h. At 96 h, the degradation rate of P. australis communities was higher than that of V. natans. SD metabolites showed that the degradation pathways in the plant rhizosphere were mainly hydroxylation, aminolation, and S–N bond cleavage. In the analysis of rhizosphere bacterial community structure, the bacterial phyla that could degrade antibiotics accounted for a large proportion. Compared with before degradation, the dominant phylum and genus did not change after degradation (96 h), but their abundance changed to varying degrees, and new genera appeared in the P. australis group. This research provides a reference for the degradation of antibiotics in karst areas and new information on the mechanism of SA degradation in the plant rhizosphere.

Interactive Effects of Rising Temperature, Elevated CO2 and Herbivory on the Growth and Stoichiometry of a Submerged Macrophyte Vallisneria natans

Global climate changes are affecting organisms and their interactions in terrestrial and aquatic ecosystems, such as the increase in temperature and CO2 concentration. Herbivory interaction is a very important part of nutrient cycle and energy flow in freshwater ecosystem, and climate changes may directly or indirectly affect aquatic plants, aquatic herbivores and their interactions. In this study, we explored the effects of the rising temperature, elevated CO2 concentrations and herbivory by an herbivorous snail (Radix auricularia L.) on a submerged plant (Vallisneria natans L.). Our results showed that herbivory, temperature, and CO2 had specific effects on snail and plant growth, statistically there was only one interaction-a reduction in leaf number. Under different experimental conditions, snail herbivory always has negative effects on biomass accumulation and growth of V. natans. Moreover, the increases in temperature also inhibited its growth. Snail herbivory reduced the content of total carbon and total nitrogen of V. natans in all treatments, while the total phenols content increased. Our findings indicate that the rising temperature, elevated CO2 concentrations and herbivory have interactive effects on the growth and stoichiometry of submerged macrophytes, but further research is needed between aquatic plants and aquatic herbivores to aid prediction the impact of climate change on freshwater ecosystems.

Impact of submerged macrophytes on growth and 2-MIB release risk of Pseudanabaena sp.: From field monitoringa to cultural experiments.

The off-flavor compound 2-methylisoborneol (2-MIB) is generally associated with the proliferation and metabolism of filamentous cyanobacteria in shallow freshwater ecosystems. Here field monitoring in East Taihu Lake from July to October 2021, along with cultural experiments, was conducted to determine the impact of submerged macrophytes on the growth and 2-MIB production of filamentous cyanobacteria. Pseudanabaena sp. was identified as the 2-MIB producer with the highest detection rate (100%) and correlation coefficient (R=0.68, p<0.001). The 2-MIB concentration and algal growth in the macrophyte-dominated zones were markedly decreased compared with those in the phytoplankton-dominated zone. Five submerged macrophytes classified into flat-leaf type (Vallisneria natans and Potamogeton crispus) and thin-leaf type (Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum) exhibited strong inhibition effects against Pseudanabaena sp.: Overall inhibition efficiencies (IEs) of 92.7%±6.8% and 92.7%±8.4% for cell growth and 2-MIB production were achieved, respectively. Moreover, the thin-leaf macrophytes exhibited significant higher IEs for cell growth (94.0% vs. 84.7%) and 2-MIB production (99.4% vs. 82.6%) than the flat-leaf macrophytes and can be selected as pioneer species in controlling odor problems. Nutrient uptake, increasing water clarity, shading effects, and allelopathic effects of the submerged macrophytes were found to be the dominant inhibition mechanisms.

Aluminum phytotoxicity induced structural and ultrastructural changes in submerged plant Vallisneria natans

Aluminum (Al) is a concentration-dependent toxic metal found in the crust of earth that has no recognized biological use. Nonetheless, the mechanism of Al toxicity to submerged plants remains obscure, especially from a cell/subcellular structure and functional group perspective. Therefore, multiple dosages of Al3+ (0, 0.3, 0.6, 1.2, and 1.5 mg/L) were applied hydroponically to the submerged plant Vallisneria natans in order to determine the accumulation potential of Al at the subcellular level and their ultrastructural toxicity. More severe structural and ultrastructural damage was determined when V. natans exposed to ≥ 0.6 mg/L Al3+. In 1.2 and 1.5 mg/L Al3+ treatment groups, the total chlorophyll content of leaves significantly reduced 3.342, 3.838 mg/g FW, some leaves even exhibited chlorosis and fragility. Under 0.3 mg/L Al3+ exposure, the middle-age and young leaves were potent phytoexcluders, whereas at 1.5 mg/L Al3+, a large amount of Al could be transferred from the roots to other parts, among which the aged leaves were the most receptive tissues (7.306 mg/g). Scanning/Transmission electron microscopy analysis displayed the Al-mediated disruption of vascular bundle structure in leaf cells, intercellular space and several vegetative tissues, and demonstrated that Al in vacuole and chloroplast subcellular segregation into electron dense deposition. Al and P accumulation in the roots, stolons and leaves varied significantly among treatments and different tissues (P < 0.05). Fourier transform infrared spectroscopy of plant biomass also indicated possible metabolites (amine, unsaturated hydrocarbon, etc.) of V. natans that may bind Al3+. Conclusively, results revealed that Al3+ disrupts the cellular structure of leaves and roots or binds to functional groups of biological tissues, thereby affecting plant nutrient uptake and photosynthesis. Findings might have scientific and practical significance for the restoration of submerged vegetation in Al-contaminated lakes.

Nitrogen removal efficiency in sustainable eco-ditches with floating ryegrass mats: The effect of loading (hydraulic and nitrogen) and water level on N removal

Drainage ditches are used for surface water management as well as for the interception of pollutants from farmlands. In this study, ditches with floating ryegrass mat (FRM), Vallisneria natans (VN) and the combination of the two (FRMVN) (including an unamended control ditch) were trialed to evaluate the N interception rates of simulated, low-concentrated run offs at low temperature. The nitrogen removal efficiency of FRMs under low and high-water level (25 cm and 50 cm, respectively) was also investigated during a warmer period. The results showed that the NH4+ removal efficiency was fairly stable for the ditches with FRMs and the interception rates were 30.5% ∼ 46.0% for the low and high influent N concentration (5 mg L−1 and 15 mg L−1) respectively. These NH4+ interception rates were higher than those from the control, especially in the phases of high influent N. The NO3− and TN removal efficiency was kept low for all treatments especially during the cold period likely due to lack of readily available carbon source. Water level had no significant influence to the FRM-based TN, NH4+, and NO3− removal - interception rates though were higher compared to those from the Control ditches during the low N period. In terms of nitrogen budget, the N reduction from FRMs treatments was 8.4% ∼ 16.9% higher than those of the controls due to plant uptake, adsorption, and other pathways. Further improvement in denitrification can be achieved by supplementing cellulosic carbon.

Potential mechanism of humic acid attenuating toxicity of Pb2+ and Cd2+ in Vallisneria natans

Humic substances are widely present in aquatic environments. Due to the high affinity of humic substances for metals, the interactions have been particularly studied. To assess the effect of humic acid (HA) on submerged macrophytes and biofilms exposed to heavy metal stress, Vallisneria natans was exposed to solutions containing different concentrations of HA (0.5–2.0 mg·L−1), Pb2+ (1 mg·L−1) and Cd2+ (1 mg·L−1). Results suggested that HA positively affected the plant growth and alleviated toxicity by complexing with metals. HA increased the accumulation of metals in plant tissues and effectively induced antioxidant responses and protein synthesis. It was also noted that the exposure of HA and metals promoted the abundance and altered the structure of microbial communities in biofilms. Moreover, the positive effects of HA were considered to be related to the expression of related genes resulting from altered DNA methylation levels, which were mainly reflected in the altered type of demethylation. These results demonstrate that HA has a protective effect against heavy metal stress in Vallisneria natans by inducing effective defense mechanisms, altering biofilms and DNA methylation patterns in aquatic ecosystems.