Effect of luminescent materials on the aquatic macrophyte Vallisneria natans and periphytic biofilm

Luminescent materials can adjust the spectrum of light energy utilization by plants. However, current research on the effects of luminescent materials on aquatic plants and periphytic biofilms is limited. This study investigated the effects of the luminescent materials 4-(di-p-tolylamino) benzaldehyde-A (DTB-A) and 4-(di-p-tolylamino) benzaldehyde-M (DTB-M) on the submerged macrophyte Vallisneria natans (V. natans) and periphytic biofilm. Result demonstrated that low concentrations of DTB (0.1 μM) significantly promoted the growth and photosynthetic rate of V. natans. In terms of enzyme activity, exposure to a higher concentration of DTB (10 μM) increased the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT). A combination of DTB-A and DTB-M treatment significantly changed the V. natans morphology and physiological characteristics, reducing the thickness of the cell wall and subsequently, promoting protein accumulation in leaves. There was no difference in the removal of ammonia or phosphate by V. natans at the 0.1 μM concentration, and the removal of ammonia and phosphate by V. natans decreased significantly as the concentration of luminescent material increased. A total of 3563 OTUs were identified in the biofilm community. The microbial community was dominated by Pseudomonas and Fusobacteria. Furthermore, results showed that an obvious decrease in diversity in the DTB-A and DTB-M mixed treatment group. In addition, the migratory aggregation of DTB molecules in plants was observed by fluorescence imaging. Overall, these findings extend our understanding of the mechanism of effect of luminescent materials on submerged macrophytes and their periphytic microorganisms.

Mitigating sediment cadmium contamination through combining PGPR Enterobacter ludwigii with the submerged macrophyte Vallisneria natans

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 plantmicrobe mechanism. This work revealed the mechanism by which PGPR and submerged macrophytes control cadmium concentration in contaminated sediment.

Underwater light source changes microecosystem constructed by Vallisneria spinulosa Yan for water restoration: Efficiency of water purification, characteristics of growth, and rhizosphere

Submerged macrophytes are effective in ecological restoration of water bodies polluted by nitrogen and phosphorus, and its restoration capacity depends on underwater illumination condition. This study explored the influencing mechanism of illumination on Vallisneria spinulosa Yan (V. spinulosa Yan) for water restoration. Addition of underwater light source increased the total nitrogen, ammonia nitrogen, total phosphorus, and phosphate removal loads of the V. spinulosa Yan growth system by 61.5, 39.2, 8.5, and 5.0 mg m-2 d-1, respectively. Meanwhile, the growth of V. spinulosa Yan was obviously promoted, even with high water turbidity. Although the biological nitrogen removal processes were inhibited by adding underwater light source, the growth of V. spinulosa Yan can be significantly improved, thus enhancing the efficiency of water purification via the absorption of nitrogen and phosphorus by V. spinulosa Yan. This study provides a theoretical foundation and technical support for application of submerged macrophytes in ecological water restoration.

Growth and physiological responses of submerged macrophytes to linear alkylbenzene sulfonate (LAS)

The potential toxic effects of linear alkylbenzene sulfonate (LAS), widely used in commercial detergents and cleaners, on submerged macrophytes remain unclear. We conducted a two-week exposure experiment to investigate LAS toxicity on five submerged macrophytes (four native and one exotic), focusing on their growth and physiological responses. The results showed that lower concentrations of LAS (< 5 mg/L) slightly stimulated the growth of submerged macrophytes, while higher doses inhibited it. Increasing LAS concentration resulted in decreased chlorophyll content, increased MDA content and POD activity, and initially increased SOD and CAT activities before declining. Moreover, Elodea nuttallii required a higher effective concentration for growth compared to native macrophytes. These findings suggest that different species of submerged macrophytes exhibited specific responses to LAS, with high doses (exceeding 5 ∼ 10 mg/L) inhibited plant growth and physiology. However, LAS may promote the dominance of surfactant-tolerant exotic submerged macrophytes in polluted aquatic environments.

The distinctive level of interaction between carbon and nitrogen metabolisms in the leaves of submerged macrophytes plays a key role in ammonium detoxification

Possible ammonium detoxification mechanisms have been proposed recently, on submerged macrophytes, evidently illustrating that glutamate dehydrogenase (GDH) plays a greater role in ammonium detoxification compared to the primary glutamine synthetase/glutamate oxaloacetate transaminase (GS/GOGAT) pathway. In the current investigation, we cultured three submerged macrophytes to extreme concentrations of [NH4+-N] of up to 50 mg/L with the aim of clarifying the interaction between carbon and nitrogen metabolisms. The activities of carboxylation enzymes pyruvate orthophosphate dikinase (PPDK) and phosphoenolpyruvate carboxylase (PEPC), in lieu of Rubisco, increased almost two-fold for ammonium tolerant species P. maackianus and M. spicatum, compared with the sensitive species P. lucens. While these enzymes are well known for their central role in CO2 fixation, their inference in conferring resistance to ammonium stress has not been well elucidated before. In this study, we demonstrate that the overproduction of PEPC and PPDK led to improved photosynthesis, better ammonium assimilation and overall ammonium detoxification in M. spicatum and P. maackianus. These findings propose likelihood for the existence of a complementary ammonium detoxification pathway that targets carbon metabolism, thus, presenting a relatively efficient linkage between nitrogen and carbon metabolisms and identify candidate species for practical restoration of fresh water resources.

Responses of submerged macrophytes to different particle size microplastics and tetracycline co-pollutants at the community and population level

Microplastics (MPs) and antibiotics are ubiquitous in aquatic ecosystems, and their accumulation and combined effects are considered emerging threats that may affect biodiversity and ecosystem function. The particle size of microplastics plays an important role in their combined effects with antibiotics. Submerged macrophytes are crucial in maintaining the health and stability of freshwater ecosystems. However, little is known about the combined effects of different particle size of MPs and antibiotics on freshwater plants, particularly their effects on submerged macrophyte communities. Thus, there is an urgent need to study their effects on the macrophyte communities to provide essential information for freshwater ecosystem management. In the present study, a mesocosm experiment was conducted to explore the effects of three particle sizes (5 µm, 50 µm, and 500 µm) of polystyrene-microplastics (PSMPs) (75 mg/L), tetracycline (TC) (50 mg/L), and their co-pollutants on interactions between Hydrilla verticillata and Elodea nuttallii. Our results showed that the effects of MPs are size-dependent on macrophytes at the community level rather than at the population level, and that small and medium sized MPs can promote the growth of the two test macrophytes at the community level. In addition, macrophytes at the community level have a stronger resistance to pollutant stress than those at the population level. Combined exposure to MPs and TC co-pollutants induces species-specific responses and antagonistic toxic effects on the physio-biochemical traits of submerged macrophytes. Our study provides evidence that MPs and co-pollutants not only affect the morphology and physiology at the population level but also the interactions between macrophytes. Thus, there are promising indications on the potential consequences of MPs and co-pollutants on macrophyte community structure, which suggests that future studies should focus on the effects of microplastics and their co-pollutants on aquatic macrophytes at the community level rather than only at the population level. This will improve our understanding of the profound effects of co-pollutants in aquatic environments on the structure and behavior of aquatic communities and ecosystems.

Epiphytic microorganisms of submerged macrophytes effectively contribute to nitrogen removal

Submerged macrophytes play important roles in nutrient cycling and are widely used in ecological restoration to alleviate eutrophication and improve water quality in lakes. Epiphytic microbial communities on leaves of submerged macrophytes might promote nitrogen cycling, but the mechanisms and quantification of their contributions remain unclear. Here, four types of field zones with different nutrient levels and submerged macrophytes, eutrophic + Vallisneria natans (EV), eutrophic + V. natans + Hydrilla verticillata, mesotrophic + V. natans + H. verticillata, and eutrophic without macrophytes were selected to investigate the microbial communities that involved in nitrification and denitrification. The alpha diversity of bacterial community was higher in the phyllosphere than in the water, and that of H. verticillata was higher compared to V. natans. Bacterial community structures differed significantly between the four zones. The highest relative abundance of dominant bacterioplankton genera involved in nitrification and denitrification was observed in the EV zone. Similarly, the alpha diversity of the epiphytic ammonia-oxidizing archaea and nosZI-type denitrifiers were highest in the EV zone. Consist with the diversity patterns, the potential denitrification rates were higher in the phyllosphere than those in the water. Higher potential denitrification rates in the phyllosphere were also found in H. verticillata than those in V. natans. Anammox was not detected in all samples. Nutrient loads, especially nitrogen concentrations were important factors influencing potential nitrification, denitrification rates, and bacterial communities, especially for the epiphytic nosZI-type taxa. Overall, we observed that the phyllosphere harbors more microbes and promotes higher denitrification rates compared to water, and epiphytic bacterial communities are shaped by nitrogen nutrients and macrophyte species, indicating that epiphytic microorganisms of submerged macrophytes can effectively contribute to the N removal in shallow lakes.

Analysis of diversity and function of epiphytic bacterial communities associated with macrophytes using a metagenomic approach

Epiphytic bacteria constitute a vital component of aquatic ecosystems, pivotal in regulating elemental cycling. Despite their significance, the diversity and functions of epiphytic bacterial communities adhering to various submerged macrophytes remain largely unexplored. In this study, we employed a metagenomic approach to investigate the diversity and function of epiphytic bacterial communities associated with six submerged macrophytes: Ceratophyllum demersum, Hydrilla verticillata, Myriophyllum verticillatum, Potamogeton lucens, Stuckenia pectinata, and Najas marina. The results revealed that the predominant epiphytic bacterial species for each plant type included Pseudomonas spp., Microbacterium spp., and Stenotrophomonas rhizophila. Multiple comparisons and linear discriminant analysis effect size indicated a significant divergence in the community composition of epiphytic bacteria among the six submerged macrophytes, with 0.3-1% of species uniquely identified. Epiphytic bacterial richness associated with S. pectinata significantly differed from that of both C. demersum and H. verticillata, although no significant differences were observed in diversity and evenness. Functionally, notable variations were observed in the relative abundances of genes associated with carbon, nitrogen, and phosphorus cycling within epiphytic bacterial communities on the submerged macrophyte hosts. Among these communities, H. verticillata exhibited enrichment in genes related to the 3-hydroxypropionate bicycle and nitrogen assimilation, translocation, and denitrification. Conversely, M. verticillatum showcased enrichment in genes linked to the reductive citric acid cycle (Arnon-Buchanan cycle), reductive pentose phosphate cycle (Calvin cycle), polyphosphate degradation, and organic nitrogen metabolism. In summary, our findings offer valuable insights into the diversity and function of epiphytic bacteria on submerged macrophyte leaves, shedding light on their roles in lake ecosystems.

The Secchi disk depth to water depth ratio affects morphological traits of submerged macrophytes: Development patterns and ecological implications

Water clarity, represented by Secchi disk depth (SD), and water depth (WD) alter bottom light availability, and SD/WD is critical for morphological trait development of submerged macrophytes in freshwater ecosystems. However, the underlying mechanism and trait development patterns of submerged macrophytes to a decreasing SD/WD gradient remains largely unknown. Here, we performed a 42-day mesocosm experiment with the erect type submerged macrophyte, Hydrilla verticillata, along a decreasing SD/WD gradient to study the relationship of morphological trait development with light availability, to determine the critical SD/WD at which changes in the development of morphological traits occur, and to gain insights into the potential mechanism involved. The results indicate that most of the morphological traits, including biomass, relative growth rate, number of clonal propagules, and the root/shoot ratio decreased with a decrease in the SD/WD ratio. Conversely, plant height and shoot increment rate increased with a decrease in the SD/WD ratio. Principal component analysis indicated that the SD/WD ratio is critical in determining the growth, stability, and reproduction of H. verticillata, and that only SD/WD ratios ≥ 0.45 and ≥0.55 ensured growth ability and stability, respectively. Possible development patterns of functional traits in relation to SD/WD reduction were investigated, and patterns of key traits of H. verticillata were distinct from those of Vallisneria natans, indicating different strategies for the adaptation to conditions of decreasing light availability. These results highlight the role of adaptive changes in morphology, resource allocation and life strategies for the maintenance of growth, stability and resilience of submerged macrophytes in low light conditions. Our present study provides a basis from which we could enhance our understanding of the critical transition mechanisms involved in morphological trait development in response to bottom light availability.

Coupling of submerged macrophytes and epiphytic biofilms reduced methane emissions from wetlands: Evidenced by an antibiotic inhibition experiment

Wetlands are the largest natural methane source, but how submerged macrophytes affect methane emission remains controversial. In this study, the impacts of submerged macrophytes on methane fluxes, water purification, and epiphytic microbial community dynamics were investigated in simulated wetlands (with and without Hydrilla verticillata) treated with norfloxacin (NOR) for 24 days. Mean methane fluxes were significantly lower in treatments with Hydrilla verticillata (56.84-90.94 mg/m2/h) than bulks (65.96-113.21 mg/m2/h) (p < 0.05) during the experiment regardless of NOR. The relative conductivity (REC) values, H2O2, and malondialdehyde (MDA) contents increased in plant leaves, while water nutrients removal rates decreased with increasing NOR concentration at the same sampling time. The partial least squares path model analysis revealed that plant physiological indices and water nutrients positively affected methane fluxes (0.72 and 0.49, p < 0.001). According to illumina sequencing results of 16S rRNA and pmoA genes, α-proteobacteria (type II) and γ-proteobacteria (type I) were the dominant methanotroph classes in all epiphytic biofilms. The ratio of type I/type II methanotrophs and pmoA gene abundance in epiphytic biofilm was considerably lower in treatment with 16 mg/L NOR than without it (p < 0.05). pmoA gene abundance was negatively correlated with methane fluxes (p < 0.05). Additionally, the assembly of epiphytic bacterial community was mainly governed by deterministic processes, while stochastic dispersal limitation was the primary assembly process in the epiphytic methanotrophic community under NOR stress. The deterministic process gained more importance with time both in bacterial and methanotrophic community assembly. Network analysis revealed that relationships among bacteria in epiphytic biofilms weakened with time but associations among methanotrophic members were enhanced under NOR stress over time. It could be concluded that submerged macrophytes-epiphytic biofilms symbiotic system exhibited potential prospects to reduce methane emissions from wetlands under reasonable management.

Regime shifts in shallow lakes explained by critical turbidity

Worldwide, water quality managers target a clear, macrophyte-dominated state over a turbid, phytoplankton-dominated state in shallow lakes. The competition mechanisms underlying these ecological states were explored in the 1990s, but the concept of critical turbidity seems neglected in contemporary water quality models. In particular, a simple mechanistic model of alternative stable states in shallow lakes accounting for resource competition mechanisms and critical turbidity is lacking. To this end, we combined Scheffer's theory on critical turbidity with insights from nutrient and light competition theory founded by Tilman, Huisman and Weissing. This resulted in a novel graphical and mathematical model, GPLake-M, that is relatively simple and mechanistically understandable and yet captures the essential mechanisms leading to alternative stable states in shallow lakes. The process-based PCLake model was used to parameterize the model parameters and to test GPLake-M using a pattern-oriented strategy. GPLake-M's application range and position in the model spectrum are discussed. We believe that our results support the fundamental understanding of regime shifts in shallow lakes and provide a starting point for further mechanistic and management-focused explorations and model development. Furthermore, the concept of critical turbidity and the relation between light-limited submerged macrophytes and nutrient-limited phytoplankton might provide a new focus for empirical aquatic ecological research and water quality monitoring programs.

Response of dissolved organic matter (DOM) and microbial community to submerged macrophytes restoration in lakes: A review

Microorganisms play a crucial role in the biogeochemical processes of Dissolved Organic Matter (DOM), and the properties of DOM also significantly influence changes in microbial community characteristics. This interdependent relationship is vital for the flow of matter and energy within aquatic ecosystems. The presence, growth state, and community characteristics of submerged macrophytes determine the susceptibility of lakes to eutrophication, and restoring a healthy submerged macrophyte community is an effective way to address this issue. However, the transition from eutrophic lakes dominated by planktic algae to medium or low trophic lakes dominated by submerged macrophytes involves significant changes. Changes in aquatic vegetation have greatly affected the source, composition, and bioavailability of DOM. The adsorption and fixation functions of submerged macrophytes determine the migration and storage of DOM and other substances from water to sediment. Submerged macrophytes regulate the characteristics and distribution of microbial communities by controlling the distribution of carbon sources and nutrients in the lake. They further affect the characteristics of the microbial community in the lake environment through their unique epiphytic microorganisms. The unique process of submerged macrophyte recession or restoration can alter the DOM-microbial interaction pattern in lakes through its dual effects on DOM and microbial commu-----nities, ultimately changing the stability of carbon and mineralization pathways in lakes, such as the release of methane and other greenhouse gases. This review provides a fresh perspective on the dynamic changes of DOM and the role of the microbiome in the future of lake ecosystems.

Responses of sediment nitrogen forms and bacterial communities to different aquatic nitrogen conditions in three submerged macrophyte-type ecological treatment systems

Ecological treatment system (ETS) is a promising technology for mitigating agricultural non-point pollution. However, the responses of sediment nitrogen (N) forms and bacterial communities to different aquatic N conditions during the treatment procedure are currently unknown. Therefore, a four-month microcosm experiment was conducted to investigate the effects of three aquatic N conditions (2 mg/L NH₄⁺-N, 2 mg/L NO₃^--N and 1 mg/L NH₄⁺-N + 1 mg/L NO₃^--N) on sediment N forms and bacterial communities in three ETSs vegetated by Potamogeton malaianus, Vallisneria natans and artificial aquatic plant, respectively. Four transferable N fractions were monitored, and the valence state of N in ion-exchange and weak acid extractable fractions were mainly determined by aquatic N conditions, while significant N accumulation was observed only in strong oxidant extractable and strong alkali extractable fractions. Sediment N profiles were primarily influenced by time and plant type, with N condition having secondary effect. Moreover, sediment bacterial community structures experienced a significant shift over time and were slightly influenced by plant type. Functional genes related to N fixation, nitrification, assimilable nitrate reduction, dissimilatory nitrite reduction (DNRA) and denitrification were substantially enriched in month 4. Additionally, the sediment bacterial co-occurrence network exhibited less complexity but more stability under NO₃^- condition compared to others. Furthermore, certain sediment N fractions were found to have strong relationships with specific sediment bacteria, such as nitrifiers, denitrifiers and DNRA bacteria. Our findings highlight the significant influence of aquatic N condition in submerged macrophyte-type ETSs on sediment N forms and bacterial communities.

Potamogeton crispus restoration increased the epiphytic microbial diversity and improved water quality in a micro-polluted urban river

Special characterization and assembly of epiphytic microbial communities remain unclear in micro-polluted water column during submersed macrophytes restoration. In this study, an in-situ enclosure area sowing with turions of Potamogeton crispus (P. crispus) was conducted in a micro-polluted urban river to investigate the characterization of P. crispus and epiphytic microbial communities and their response to water environment under different water depths. Turions completely germinated in water column with <90 cm water depth and the germination speed decreased with increasing water depth within 18 days. There were obvious differences in morphological characteristics of P. crispus between deep and shallow water layers. P. crispus restoration decreased by 12-32%, 13-36%, 9-43% and 5-36% of COD, NH₄⁺-N, TN and TP concentration, respectively, in enclosed overlying water compared to the river (P < 0.05) during 5 months of experiment. Illumina sequencing was employed to explore the epiphytic bacterial and microeukayotic communities at water depth 25-35 cm (shallow area) and 80-90 cm (deep area). A total of 9 bacterial and 12 microeukayotic dominant phyla were obtained in eight samples. It should be noted that the algae abundances were higher in shallow area than deep area but a reverse trend was observed for methanotrophs. Null model analysis revealed that dispersal limitation and undominated process was the most important assembly process, whereas stochastic processes gained more importance in shallow area than deep one. According to cooccurrence analysis (|r| > 0.6, P < 0.05), there were more strongly correlated edges in shallow area (456 edges) than deep area (340 edges). These results highlight that submerged macrophytes restoration can increase microbial diversity and improve water quality, and provide a "summer disease cured in winter" way by using could-resistant P. crispus for water purification in micro-polluted rivers in low-temperature season.

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.

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.

Bacterial community are more susceptible to nanoplastics than algae community in aquatic ecosystems dominated by submerged macrophytes

As a ubiquitous emerging pollutant, microplastics can interact with algal and bacterial communities in aquatic ecosystems. Currently, knowledge on how microplastics influence algae/bacteria is mostly limited to toxicity tests using either monocultures of algae/bacteria or specific algal-bacterial consortium. However, information on the effect of microplastics on algal and bacterial communities in natural habitats is not easily available. Here, we conducted a mesocosm experiment to test the effect of nanoplastics on algal and bacterial communities in aquatic ecosystems dominated by different submerged macrophytes. The community structure of algae and bacteria suspended in the water column (planktonic) and attached to the surface of submerged macrophytes (phyllospheric) were identified, respectively. Results showed that both planktonic and phyllospheric bacteria were more susceptible to nanoplastics, and these variations driven by decreased bacterial diversity and increased abundance of microplastic-degrading taxa, especially in aquatic systems dominated by V. natans. The community composition of both algae and bacteria were influenced to varying degrees by nanoplastics and/or plant types, but RDA results showed that only bacterial community composition was strongly correlated with environmental variables. Correlation network analysis showed that nanoplastics not only reduced the intensity of associations between planktonic algae and bacteria (average degree reduced from 4.88 to 3.24), but also reduced proportion of positive correlations (from 64% to 36%). Besides, nanoplastics also decreased the algal/bacterial connections between planktonic and phyllospheric habitats. Our study elucidates the potential interactions between nanoplastics and algal-bacterial community in natural aquatic ecosystems. These findings suggest that in aquatic ecosystems, bacterial community are more vulnerable to nanoplastics and may serve as a protective barrier for algae community. Further research is needed to reveal the protective mechanism of bacteria against algae at the community level.

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.

Temporal Succession of Bacterial Community Structure, Co-occurrence Patterns, and Community Assembly Process in Epiphytic Biofilms of Submerged Plants in a Plateau Lake

In shallow macrophytic lakes, epiphytic biofilms are formed on the surface of submerged plant stems and leaves because of algae and bacterial accumulation. Epiphytic biofilms significantly impact the health of the host vegetation and the biogeochemical cycling of lake elements. However, community diversity, species interactions, and community assembly mechanisms in epiphytic bacterial communities (EBCs) of plants during different growth periods are not well understood. We investigated the successional dynamics, co-occurrence patterns, and community assembly processes of epiphytic biofilm bacterial communities of submerged plants, Najas marina and Potamogeton lucens, from July to November 2020. The results showed a significant seasonal variation in EBC diversity and richness. Community diversity and richness increased from July to November, and the temperature was the most important driving factor for predicting seasonal changes in EBC community structure. Co-occurrence network analysis revealed that the average degree and graph density of the network increased from July to November, indicating that the complexity of the EBC network increased. The bacterial community co-occurrence network was limited by temperature, pH, and transparency. The phylogeny-based null model analysis showed that deterministic processes dominated the microbial community assembly in different periods, increasing their contribution. In addition, we found that as the dominance of deterministic processes increased, the microbial co-occurrence links increased, and the potential interrelationships between species became stronger. Thus, the findings provide insights into the seasonal variability of EBC assemblage and co-occurrence patterns in lacustrine ecosystems.

Water quality profits by the submerged macrophyte community consisting of multi-functional species-rich groups

The re-establishment of submerged macrophytes facilitates the formation of a clear-water state in shallow eutrophic lakes. But most restorations of submerged macrophytes are often unstable and cannot maintain a stable clear-water state, probably because the species and functional diversity have not been fully taken into account. In this study, we try to explore submerged macrophyte communities and water quality changes under different submerged macrophyte combinations through mesocosm experiments. We hypothesized that communities with high species and functional diversity would be more conducive to improving water quality. The results showed that the mean community biomass of single-species and 8-species were higher than 5-species. And the stability and mean relative growth rate of the 8-species community were higher than the 5-species community. With the same configuration of three functional groups, the 8-species community was more stable and had better water quality than the 5-species community. The path analysis revealed that different functional groups of submerged macrophytes play different roles. The erect and canopy-producing submerged macrophytes were conducive to reducing total suspended solids (TSS) concentrations in the water column during community construction. In contrast, bottom-dwelling submerged macrophytes were conducive to reducing total nitrogen, total phosphorus, and TSS concentrations during the stage of disturbances. Our results also suggested that canopy-producing groups may have a competitive advantage for light over bottom-dwelling species. Based on the above results and biodiversity insurance hypothesis, we conclude that the community consisting of multi-functional species-rich groups is conducive to building stable submerged macrophyte communities and obtaining a stable clear-water state. Our findings will improve water quality management and pollution control for eutrophic shallow lakes.

Combined toxic effects of enrofloxacin and microplastics on submerged plants and epiphytic biofilms in high nitrogen and phosphorus waters

With the wide application of plastic products, microplastic pollution has become a major environmental issue of global concern. Microplastics in aquatic environments can interact with organic pollutants, causing a combined effect on submerged macrophytes. This study investigated the response mechanisms of the submerged plant Myriophyllum verticillatum and epiphytic biofilm to the antibiotic enrofloxacin, microplastics, and their combined exposure in a high nitrogen and phosphorus environment. The results indicated that Myriophyllum verticillatum was not sensitive to enrofloxacin of 1 mg L^-1, while 10 and 50 mg L^-1 enrofloxacin inhibited the uptake of nitrogen and phosphorus by the plants, as well as triggered oxidative stress in the plant leaves, causing irreversible damage to the plant cells. In addition, enrofloxacin altered the structure of the leaf epiphytic biofilm community. Interestingly, 1, 5, and 20 mg L^-1 microplastics had no significant effect on the plant, while they facilitated the aggregation of microorganisms, increasing the abundance of the leaf epiphyte biofilm. The combination of enrofloxacin and microplastics induced a synergistic effect on Myriophyllum verticillatum. Specifically, the rate of nitrogen and phosphorus uptake by the plant was reduced, the content of photosynthetic pigments decreased, and antioxidant enzyme activity was further increased. In addition, the diversity of the leaf epiphytic biofilm community was similar to the single enrofloxacin exposure. These results demonstrated the differences between single and combined exposures and provided a new theoretical basis to evaluate the harmful effects of enrofloxacin and microplastics on submerged macrophytes.

Unraveling the ecological mechanisms of bacterial succession in epiphytic biofilms on Vallisneria natans and Hydrilla verticillata during bioremediation of phenanthrene and pyrene polluted wetland

In wetland ecosystem, the microbial succession in epiphytic biofilms of submerged macrophytes remains to be fully elucidated, especially submerged macrophytes used to remediate organic pollutants contaminated sediment. Herein, 16 S rRNA gene sequencing was used to investigate the bacterial dynamics and ecological processes in the biofilms of two typical submerged macrophytes (Vallisneria natans and Hydrilla verticillata) settled in sediment polluted by polycyclic aromatic hydrocarbons (PAHs) at two growth periods. The results presented that the variations of bacterial community in the biofilms were influenced by attached surfaces (explanation ratio: 17.30%), incubation time (32.30%) and environmental factors (39.10%). Bacterial community assembly was mainly driven by dispersal limitation which triggered more positive co-occurrence associations in microbial networks, maintaining ecological stability in the process of bioremediation of PAHs. Additionally, the functional redundancy strength of bacterial community was more affected by attached surface than incubation time. The structural equation model illustrated that community assembly drove β-diversity and explained a part of ecological functions. Environmental factors, community assembly, and β-diversity jointly affected microbial networks. Overall, our study offers new insights into the microbial ecology in biofilms attached on the submerged macrophytes settled in PAH-polluted sediment, providing important information for deeply understanding submerged macrophyte-biofilm complex and promoting sustainable phytoremediation in shallow lacustrine and marshy ecosystems.

Responses of submerged macrophyte Ceratophyllum demersum to the gradient concentrations of microcystin-LR (MC-LR)

The responses of Ceratophyllum demersum to gradient concentrations (0, 0.8, 3.2, and 10 µg/L) of microcystin-LR (MC-LR) were comprehensively investigated by laboratory simulation experiments. The high reduction and accumulation efficiency of MC-LR by C. demersum were verified in this study. Results showed that the reduction ratio of MC-LR in the cultivation medium was up to 99% after 14 days of exposure, and the accumulation of MC-LR in C. demersum was highest at an exposure concentration of 10 μg/L, the value of which was 0.9 ng/g fresh weight (FW). Meanwhile, a series of negative effects on C. demersum was detectable, accompanied by a significant biomass reduction of the plant and changes in microbial community composition. In particular, this study indicated that the amount of Flavobacteria was elevated under the stress of MC-LR, provoking great threats to aquatic ecosystems. Moreover, oxidative damage was evidenced by the changes in total antioxidant capacity, superoxide dismutase, and glutathione. The results also demonstrated significant increases in sugar (0.025 mg/g FW), protein (0.3 mg/g FW), and carotenoids (0.6 mg/g FW) in C. demersum stressed by 10 μg/L of MC-LR, compared with the control without microcystins, which were among the defense strategies for dealing with adverse conditions. These results verified the good potential of submerged macrophytes as an eco-friendly strategy for controlling cyanobacterial blooms. However, the negative effects of MC-LR on the macrophytes themselves were also demonstrated, which would be considered in future practice and management.

Interactions between suspended sediments and submerged macrophytes-epiphytic biofilms under water flow in shallow lakes

Suspended sediments (SS) pollution is one of the factors affecting the transfer from turbid water state to clear water state in shallow lakes. However, the interactions between suspended sediments and submerged plants are far from clear. In this study, we investigated the settlement laws of SS in overlying water and its impact on the epiphytic biofilm of Myriophyllum verticillatum and Vallisneria natans under water flow. At least 90% of turbidity can be removed from overlying water, and the decreasing trend of water turbidity fitted the logarithmic decay model in all treatments. The size distribution of SS fit the log-normal distribution model in the first 240 min after SS addition. It should be noted that the main peak particle sizes were lower in treatments with submerged macrophytes (8.71-13.18 μm) than without plants (15.14-19.95 μm). Water flow and SS addition significantly increased the thickness of biofilms attached to M. verticillatum (p < 0.05), but they together significantly reduced the biofilm thickness on V. natans (p < 0.05). SS increased the bacterial α-diversity but decreased eukaryotic one in epiphytic biofilms. However, water flow had a more significant impact on microbial communities (especially eukaryotes) than SS and plant species. The relative abundances of dominant phylum Proteobacteria, class Alphaproteobacteria and Betaproteobacteria, and class Verrucomicrobiae increased in epiphytic biofilms after SS addition. Co-occurrence networks reveal that photosynthetic microbes in epiphytic biofilms played an important role in microbial communities under water flow and SS, and many hub microbes were increased by SS addition but reduced by water flow. These data highlight that SS decline can be predicted by the logarithmic decay model and, SS and water flow can affect the epiphytic-biofilm on submerged macrophytes.

Responses of macrozoobenthos communities to changes in submerged macrophyte biomass in 19 temperate lakes in China

Macrozoobenthos and submerged macrophytes interact closely. However, studies in China have focused on the middle and lower reaches of the Yangtze River, where shallow lakes are concentrated, rather than on temperate lakes. To clarify the responses of taxonomic and functional groups of macrozoobenthos in temperate lakes to changes in submerged macrophyte biomass (B_Mac) on a large scale, 19 temperate lakes within Baiyangdian Lake were investigated in this study. The B_Mac differed greatly across the 19 lakes, and Potamogeton crispus was the dominant species. According to the B_Mac, the 19 lakes were divided into 4 groups. One-way analysis of variance and Pearson correlation analysis showed that the water environmental parameters were different among the 4 groups, and the B_Mac was significant correlated with all the physical and chemical parameters of water bodies (except for water depth). Forty-one taxa of macrozoobenthos were identified in the 19 lakes, with oligochaetes, Hirudinea, gastropods, crustaceans, chironomid larvae, and aquatic insects (excluding chironomid larvae) represented by 9, 1, 4, 2, 19, and 6 species, respectively. Chironomid larvae and oligochaetes dominated by density, and gastropods and chironomid larvae dominated by biomass. Canonical correspondence analysis showed that the B_Mac was the most important factor affecting the macrozoobenthos community structure in group 1 to group 4. Macrozoobenthos with low pollution tolerance values were mainly found in areas with high B_Mac, while species with high pollution tolerance values were mainly distributed in areas with low B_Mac and high nutrient contents. Different taxonomic and functional groups of macrozoobenthos responded differently to changes in B_Mac. As B_Mac increased, density and biomass of oligochaetes and chironomid larvae tended to decrease, while those of gastropods and aquatic insects tended to first decrease and then increase. Collectors had more species than any other functional group in group 1 to group 4. As B_Mac increased, density and biomass of collectors gradually decreased, while density of predators, shredders, and scrapers tended to first decrease and then increase.

Antidote or Trojan horse for submerged macrophytes: Role of microplastics in copper toxicity in aquatic environments

Due to their unique surface structures and physicochemical properties, microplastics (MPs) can adsorb other contaminants, thus impacting their toxicity and fate in aquatic ecosystems. In the present study, the adsorption and transportation of copper ions (Cu²⁺) in polyethylene (PE, 5 and 150 μm) and their combined effects on four submerged macrophyte species were assessed. Results demonstrated that the addition of PE reduced the Cu²⁺ concentration in copper sulfate (CuSO₄) solution and the adsorption of Cu²⁺ in PE (10 mg/L) increased with CuSO₄ concentration (100-600 μmol/L). PE alone exhibited no inhibitory effects on macrophytes, while Cu²⁺ showed fatal toxicity toward the macrophytes. However, the combination of PE and Cu²⁺ showed lower inhibitory effects on macrophytes and the toxicity attenuation varied among species. Additionally, PE may act as a carrier (like a Trojan horse) for the environmental transfer of Cu²⁺, thereby hosting Cu²⁺ toxicity against macrophytes in the imported environment. Our findings indicate that PE acts as both an antidote to and carrier of Cu²⁺ toxicity in macrophytes. This study should help in clarifying the combined effects and risk assessments of MPs and heavy metals in future studies.

The spatiotemporal characteristics of water quality and phytoplankton community in a shallow eutrophic lake: Implications for submerged vegetation restoration

One of the most serious consequences of eutrophication in shallow lakes is deterioration of water quality, proliferation of phytoplankton and disappearance of submerged macrophytes. After removing herbivorous and plankti-benthivorous fish, submerged macrophyte restoration was utilized at the entire lake (82.7 km²) to combat eutrophication and improve water quality in the shallow subtropical aquaculture of Lake Datong. We conducted two years of monitoring, from March 2018 to February 2020. During the first year of restoration, 80% of the area of Lake Datong (approximately 60 km²) was successfully recovered by submerged vegetation, and the water quality was improved. For example, the phosphorous (P) content (including total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP)) and turbidity decreased, and the Secchi depth (SD) increased. However, the submerged vegetation disappeared from autumn 2019 in the intermittent recovery area (MN), while the continuous recovery area (DX) continued to recover with an abundance of submerged vegetation. During the second year, the water quality continued to improve significantly in the DX area, with high biomass and coverage of submerged vegetation. In the MN area, although turbidity and ammonia nitrogen (NH₄⁺-N) increased significantly and SD decreased significantly, the P content (TP, TDP, and DRP) still continued to decrease. The restoration of submerged macrophytes could significantly decrease the density of phytoplankton. Over time, there was a regime shift in Lake Datong. The structural equation model (SEM) results illustrated that the water level and submerged plant coverage were the primary drivers that triggered changes in the state of the lake ecosystem. Our results highlight the potential of restoring submerged vegetation to control water eutrophication at the whole-lake scale. However, the water level in spring was the primary driver that triggered changes in the state of the lake ecosystem. Water level management should be emphasized during the early stages of recovery of submerged plants.

Combined toxicity of microplastic and lead on submerged macrophytes

Microplastic pollution has become ubiquitous due to industrialization and wide use of plastic products. The continuous discharge of microplastics into aquatic ecosystems, combined with different toxic chemicals can create serious environmental pollution. Lead is an extremely toxic metal which can strongly adsorb to microplastics, however, little is known about their combined toxicity on submerged macrophytes. To test our hypothesis that microplastic can aggravate lead toxicity on submerged macrophytes, we designed a five-day hydroponic experiment to explore the toxic effects of microplastic and lead alone, and in combination, on Potamogeton crispus and Vallisneria denseserrulata. Photosynthetic pigment, chlorophyll fluorescence (Fv/Fm and ETRmax), soluble sugar, protein and malondialdehyde (MDA) declined with increasing lead concentration alone and in the combined treatment. In both submerged macrophytes, the level of superoxide dismutase (SOD) and lead bioaccumulation increased with increasing lead concentration. However, microplastic aggravated lead toxicity on chlorophyll a and SOD activity in P. crispus only under the highest lead concentration. In conclusion, lead alone and combined exposure caused a series of toxic effects on physio-biochemical traits of submerged macrophytes that appeared to be synergistic and species-specific. Our comprehensive results have important implications for appropriate management of microplastics and lead alone, or in combination, for submerged macrophytes.

Submerged macrophytes regulate diurnal nitrous oxide emissions from a shallow eutrophic lake: A case study of Lake Wuliangsuhai in the temperate arid region of China

Submerged macrophytes can increase oxygen concentrations of water and promote diel oxygen fluctuations, and this phenomenon is hypothesized to play a vital role in regulating nitrous oxide (N₂O) emissions from eutrophic lakes. However, the effects of submerged macrophytes on N₂O emissions in shallow eutrophic lakes remain poorly investigated. In this study, Lake Wuliangsuhai, a typical shallow eutrophic lake, was investigated to study the role of submerged macrophytes in regulating N₂O emissions. We measured the N₂O fluxes and related parameters through continual 72-h in situ diel monitoring in two sampling sections that covered dense submerged macrophyte areas and open water. In this study, the dissolved oxygen (DO) concentration of the water in the submerged macrophyte area exhibited significant diurnal variations, with significantly higher water oxygen concentrations than the open water area during the daytime. The N₂O fluxes of Lake Wuliangsuhai ranged from 0.01 to 0.24 μmol m^-2 h^-1, with an average value of 0.11 μmol m^-2 h^-1. Moreover, significant diel variations in the N₂O flux and net N₂O production were observed in the submerged macrophyte areas, where the maximum N₂O flux occurred at midday. The molar ratios of NH₄⁺-N to oxygen (N/O ratio) of the water were responsible for the diel variations in the N₂O production in the lake. However, the high oxygen concentration of the water was the major regulator of the N₂O flux of Lake Wuliangsuhai. Therefore, submerged macrophyte restoration is significant not only for water quality improvement in shallow eutrophic lakes but also for N₂O emission mitigation by increasing the DO concentration of the water.

Substrate type and plant phenolics influence epiphytic bacterial assembly during short-term succession

In natural ecosystems, large amounts of epiphytic bacteria live on the surfaces of submerged plants or non-biological substrates. Although it contributes greatly to host plant health or ecological functions in waters, little is known about the temporal dynamics and assembly mechanisms of epiphytic bacteria. To test whether host plant chemistry leads to divergent community dynamics, we investigated the fine scale temporal community successions of both epiphytic bacteria and the bacterioplankton of the surrounding water in two submerged plants and one non-biological artificial substance. We first observed differentiated epiphytic or surrounding water bacterial communities for different substrates in small spaces (approximately 1 m × 1 m). Selection played dominant roles in affecting the assembly of epiphytic bacteria in the high-phenolic plant Hydrilla verticillata, while for the artificial substance and the low-phenolic plant Vallisneria natans, drift and dispersal drove the assembly of both epiphytic bacteria and bacterioplankton. The higher selection may also contribute to higher turnover rates in both bacterioplankton and epiphytic communities of H. verticillata, with the latter changing drastically in approximately one week. Epiphytic bacteria in H. verticillata developed more complex networks with a higher proportion of positive links, suggesting that more intense interactions such as mutualism or facilitation may exist within epiphytic bacterial communities of the high-phenolic plant. Our results also implied that for the submerged macrophytes used in biological purification, the dynamics of epiphytic biofilm in the purification-related functional capacities might also be considered.

Growth inhibition and oxidative damage of Microcystis aeruginosa induced by aqueous extract of different submerged macrophytes

With the increasing eutrophication of the aquatic environments, cyanobacteria blooms caused certain damage to the animals and plants in the aquatic environments. In this experiment, two species were selected from six species of submerged macrophytes, the experimental conditions were changed to achieve the best inhibitory effect on Microcystis aeruginosa, and oxidative damage analysis was carried out. The experiment results demonstrated that the inhibition rate of Vallisneria natans and Ceratophyllum demersum was nearly 100% at the concentration of 3 g/L after 15 days of anaerobic soaking extract. In addition, the longer the soaking time of the two submerged macrophytes, the weaker the photosynthesis effect, and the lower the chlorophyll fluorescence parameters, the more obvious the inhibition effect on M. aeruginosa. Lipid peroxidation injury of M. aeruginosa could be reflected by malondialdehyde (MDA) concentration. The MDA concentration in the experimental group was significantly higher than the control group. Results showed that V. natans and C. demersum could induce oxidative damage in M. aeruginosa. It was also observed that the secondary metabolites produced by V. natans were mainly fatty acids (e.g., the oxidative acid was 6.92 w/%, and the successful acid was 9.85 w/%) which inhibited M. aeruginosa in gas chromatography-mass spectrometry (GC-MS). The main secondary metabolites in C. demersum were hydroxyl acids (e.g., the 4-hydroxy-3-methoxyphenylacetic acid was 24.33 w/%), which could inhibit the algae through allelopathy. This study provided reference for submerged macrophytes to inhibit M. aeruginosa under different conditions.

Exploring the ammonium detoxification mechanism of young and mature leaves of the macrophyte Potamogeton lucens

Toxicity in aquatic plants, caused by excess ammonium in the environment, is an important ecological problem and active research topic. Recent studies showed the importance of the enzyme Glutamate Dehydrogenase (GDH) in detoxifying ammonium. However, these results mainly derived from species comparisons, hence some mechanisms may have been obscured due to species differences. Our recent finding that young leaves of Potamogeton lucens were less sensitive to ammonium enrichment, than mature leaves allowed us to study ammonium detoxification within a species. We found that, unlike mature leaves, ammonium-tolerant young leaves of P. lucens could assimilate ammonium mainly through GDH. There was a 38% increase of NADH-dependent GDH in 50 mg/L ammonium concentration compared with 0.1 mg/L. Therefore, this study confirms the hypothesis that the GDH pathway plays a major role in the detoxification of ammonium in freshwater macrophytes.

Removal of perfluoroalkyl acids (PFAAs) in constructed wetlands: Considerable contributions of submerged macrophytes and the microbial community

The broad application of perfluoroalkyl acids (PFAAs) has attracted global concern regarding their adverse environmental effects. The possible removal processes of PFAAs in constructed wetlands were excavated and quantified using two typical submerged macrophytes (rooted Potamogeton wrightii and rootless Ceratophyllum demersum). Our results showed that 33.59-88.99% of PFAAs could be removed via not only sediment sorption or phytoextraction but also by the bioaccumulation of microbiota. The sediment acts as a vital sink for PFAAs, preloading 23.51-50.09% and 16.65-52.18% of PFAAs in treatments with P. wrightii (Pw1) and C. demersum (Cd1), respectively. C. demersum showed a better capacity to accumulate PFAAs (0.91-32.03%) than P. wrightii (<10%). Considerable PFAAs were observed to be distributed in microbes, underlining the non-negligible role of microbiota in bioaccumulating PFAAs. The contributions of planktonic microbes, biofilm microbes, and extracellular polymeric substances in biofilms were 0.39-20.96%, 0.03-7.95%, and 0.39-14.15% in Pw1 and 0.23-15.68%, 0.01-15.68%, and 0.53-26.77% in Cd1, respectively. The adsorption/uptake was significantly correlated with the perfluoroalkyl chain length (p<0.05), except for the uptake of biofilms in C. demersum. Furthermore, PFAAs and submerged macrophytes could decrease the richness of microbiota but increase the relative abundance of some strains in Betaproteobacteriales, Sphingomonadales, and Cytophagales. Our results were helpful for understanding the removal processes of PFAAs in constructed wetlands and their linkages with PFAA properties, thus further providing insight into the management and removal of emerging organic contaminants.

Mutual promotion of submerged macrophytes and biofilms on artificial macrophytes for nitrogen and COD removal improvement in eutrophic water

Both submerged macrophytes (SMs) and artificial macrophytes (AMs) have been widely used to improve water quality in eutrophic water. However, in heavily eutrophic aquatic ecosystems, the purification function of SMs is often restricted by the poor growth state due to competition from algae, while the purification function of AMs is often restricted by the limited carbon source supply for biofilm microbes attached to the AM surface. The objective of this study was to develop a new strategy to increase pollutant removal efficiency (RE) by combining the use of SMs and AMs. Pilot-scale microcosms, including treatments with both SMs and AMs (S&A), only SMs (SO) and only AMs (AO), were established to identify the performance of the new strategy. The results suggest that treatment S&A obtained REs of 88.9% for total nitrogen (TN) and 48.1% for chemical oxygen demand (COD); as comparison, treatments SO and AO obtained REs of 77.4% and 81.2% for TN and REs of -13.7% and 39.0% for COD, respectively. Compared with SO, the S&A treatment benefited SM growth in biomass, leaf chlorophyll concentration and root activity by inhibiting algae growth. In addition, compared with treatment AO, S&A increased the biofilm microbial biomass and the relative abundance of nitrifiers of families Nitrosomonadaceae and Nitrospira attached to AM surfaces. Therefore, by the mutual promotion of SMs and biofilms on AMs, the synergic application of SMs and AMs is a useful strategy for improving TN and COD REs in eutrophic water bodies such as rivers and constructed wetlands. A strategy was developed to increase nitrogen and COD removal in eutrophic water by the mutual promotion of submerged macrophytes and biofilms on artificial macrophytes.

Transcriptomic profiling of atrazine phytotoxicity and comparative study of atrazine uptake, movement, and metabolism in Potamogeton crispus and Myriophyllum spicatum

The accumulation of atrazine in sediments raises wide concern due to its potential negative effects on aquatic environments. Here we collected sediments and different submerged macrophytes to simulate natural shallow lakes and to measure atrazine levels and submerged macrophyte biomass. We determined gene expressions in submerged macrophytes treated with or without atrazine. We also examined atrazine concentrations and its metabolite structures in submerged macrophytes. When the initial concentration of atrazine in sediments ranged from 0.1 to 2.0 mg kg^-1 dry weight (DW), atrazine levels in the pore water of the sediments ranged from 0.003 to 0.05 mg L^-1 in 90 days. Atrazine did not show obvious long-term effects on the biomass of Potamogeton crispus and Myriophyllum spicatum (P > 0.05). On day 90, gene expressions related to cell wall in P. crispus were changed by atrazine phytotoxicity. Moreover, the decrease in the number genes controlling light-harvesting chlorophyll a/b-binding proteins verified the toxic effects of atrazine on the photosynthesis of M. spicatum. Compared with unexposed plants on day 90, ribosome pathway was significantly enriched with differentially expressed genes after submerged macrophytes were exposed to 2.0 mg kg^-1 DW atrazine (P < 0.05). In addition, shoots and roots of P. crispus and M. spicatum could absorb the equal amount of atrazine (P > 0.05). Once absorbed by submerged macrophytes, atrazine was degraded into 1-hydroxyisopropylatrazine, hydroxyatrazine, deethylatrazine, didealkylatrazine, cyanuric acid, and biuret, and some of its metabolites could conjugate with organic acids, cysteinyl β-alanine, and glucose. This study establishes a foundation for aquatic ecological risk assessments and the phytoremediation of atrazine in sediments.

Ecological damage of submerged macrophytes by fresh cyanobacteria (FC) and cyanobacterial decomposition solution (CDS)

To investigate the deleterious ecological effects of cyanobacteria on submerged macrophytes, this study investigated the effects of different concentrations of fresh cyanobacteria (FC) and cyanobacteria decomposition solution (CDS) on an experimental group of submerged macrophytes (Vallisneria natans (Lour.) Hara and Myriophyllum verticillatum Linn.). The results showed that FC and CDS not only lead to decrease in biomass and significant changes in enzyme activity and chlorophyll content in tissue, but also affected the permeability of cell membranes. The extent of damage was in the order CDS > FC, and the comprehensive stress resistance of Vallisneria natans (2.994) was more than that of Myriophyllum verticillatum (2.895). In addition, semi-permeable membranes can reduce plant damage by FC and CDS, but cannot completely prevent it. FC and CDS mainly affected the relative distribution of microbial genera on the surface of aquatic plants (p < 0.05). Furthermore, CDS caused irreversible damage to plant cells and induced programmed cell death (PCD) of plants to accelerate their decline. Therefore, FC and CDS may be one of the main reasons for the decline in submerged vegetation. This study provides a scientific basis for evaluating the harmful effects of cyanobacteria on submerged macrophytes.

A field study on the effects of combined biomanipulation on the water quality of a eutrophic lake

Lake eutrophication has become a serious environmental problem in China. Manipulations covering more elements of trophic pyramid are methods for lakes to obtain clear water state and should be studied in detail. In the present study, Meishan Dongpo Lake was divided into two parts, and a combined biomanipulation project was conducted in one part (RLake), and the other part was used as a control (CLake). Species of submerged-plant, fish, macrobenthos, and zooplankton were screened and a certain number of them were added to adjust the eco-chain in RLake. After restoration, the coverage of submerged macrophytes reached >85%; zooplankton greater than 0.6 mm in size increased in number, and the ratio of zooplankton biomass to chlorophyll-a (Chl-a) concentration increased. The dominant fish species changed, and disturbance of the sediment was reduced. The average density of mollusks in RLake was 111.5 ± 19.8 ind m^-2, which was much higher than that in CLake (36.7 ± 2.1 ind m^-2). Water quality and clarity were substantially improved, and nutrient concentrations, particularly total phosphorus, total nitrogen, and Chl-a were significantly reduced. The aquatic community parameters were negatively correlated with the nutrient parameters and Chl-a. The ecological restoration have adjusted the aquatic ecosystem in RLake, and many positive feedback effects among the aquatic communities made them remove internal nutrients and Chl-a more efficiently.

The influence of flow rates and water depth gradients on the growth process of submerged macrophytes and the biomass composition of the phytoplankton assemblage in eutrophic water: an analysis based on submerged macrophytes photosynthesis parameters

Submerged macrophytes and phytoplankton assemblage play significant roles in the functioning of aquatic ecosystems. An experiment was carried out in Beijing in order to further evaluate the environmental factors that affect the growth of submerged macrophytes and phytoplankton assemblage. Submerged macrophytes (i.e., Vallisneria natans, Hydrilla verticillata, and Ceratophyllum demersum) constructed the growth system with some controllable influencing factors (i.e., the flow rate and water depth gradient). The flow rates were set separately as 4 L/h (1#), 6 L/h (2#), and 12 L/h (3#), while the water depth gradient was of 0.5-1.7 m in eutrophic water. Generally, all macrophytes could grow normally in the experiment, and the system could maintain and improve the effluent quality. The average removal rates of NH3-N, COD, NO3-N, TN, and TP were about 90%, 33%, 65%, 45%, and 40%, respectively. Seen from the results of the water depth gradient experiments, it is indicated that Vallisneria natans grows better in shallow water (0.5 m) and moderate shallow water (0.7 m) area, with an average relative growth rate (ARGA) of 57%. Hydrilla verticillata and Ceratophyllum demersum grow better in moderate deep water (1.2 m) and deep water (1.7 m) area (ARGA of 66% and 64%, respectively). Results of the flow rate experiments showed that the moderate flow rate (6 L/h) was the best for those three macrophytes' growth. As the fitting results of the rapid light curves (RLCs) showed that the utilization of light and the tolerance to strong light were different for these macrophytes, if they are ranked in the order of the utilization and the tolerance from strong to weak, they are Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans. Microbial analyses indicated that the overall system diversity of the experimental groups have been improved after cultivation of macrophytes. However, the accumulated Cyanobacteria caused by the low flow rate (1#) would lead to the suppression of microbial organics decomposition and nutrient metabolism in the macrophytes. To sum up, the results of this study provided theoretical guidance and technical support for the restoration of submerged macrophytes in eutrophic water.

Novel wet-solid states serial anaerobic digestion process for enhancing methane recovery of aquatic plant biomass

Aquatic plant biomass is characterised by high moisture content and a lignocellulose structure. To apply the anaerobic digestion (AD) treatment to aquatic plants, the simultaneous achievement of high methane (CH₄) recovery per biomass volume and high biodegradability have been a challenge owing to these characteristics. Herein, we propose a novel two-stage serial wet- and solid-state AD (SS-AD) system that quickly digests the labile cytoplasm fraction in the first wet AD reactor in a short retention time while slowly digesting the lignocellulosic fraction in the later SS-AD with long retention time. In this study, the effect of this serial AD on CH₄ recovery and chemical oxygen demand (COD) balance from aquatic plant biomass was examined in a semi-continuous operation. Elodea nuttallii, which grows excessively in the southern basin of Lake Biwa, Japan, was used as the substrate. For comparison, single-stage AD with different hydraulic retention times (HRTs) (30 d and 15 d) was performed. The CH₄ conversion efficiency in single-stage AD deteriorated from 47.6 to 33.1% COD with shortened HRT, probably owing to the low degradability of slowly degrading fraction (i.e. lignocellulose) in the short retention time. In contrast, the serial AD under the same HRT (15 d) as a single-stage AD exhibited higher CH₄ conversion efficiency of 65.1% COD, mainly owing to the enhanced degradation of slowly degrading fraction because of the prolonged solid retention time (52.2 d) of the entire system. The CH₄ recovery from the wet AD alone in the serial AD system surpassed that from the 30 d-HRT of the single-stage AD, possibly due to the appropriate HRT for labile fraction and/or the microbial recirculation. The serial wet and SS-AD was suggested as a suitable technology for the treatment of aquatic plant biomass with recalcitrant cell walls and a labile cytoplasm.

Community composition and correlations between bacteria and algae within epiphytic biofilms on submerged macrophytes in a plateau lake, southwest China

Epiphytic biofilms are complex matrix-enclosed communities comprising large numbers of bacteria and algae, which play an important role in the biogeochemical cycles in aquatic systems. However, little is known about the correlations that occur between these communities or the relative impact of environmental factors on their composition. In this study, epiphytic biofilms on three different aquatic plants were sampled in a typical plateau lake (Caohai, southwest China) in July and November of 2018. Bacterial diversity was assessed using Miseq sequencing approaches and algal communities were assessed using light microscopy. Gammaproteobacteria (54.64%), Bacteroidetes (17.50%) and Firmicutes (13.99%) were the dominant bacterial taxa and Chlorophyta (47.62%), Bacillariophyta (28.57%) and Euglenophyta (19.05%) were the dominant algae. The alpha diversity values of the epiphytic bacterial and algal communities were greater during the macrophyte decline period (November) than during the growth period (July). Microbial community composition was significantly affected by abiotic factors (water temperature, NH₄⁺, pH or TP) and biotic factors (algae or bacteria). Interestingly, in July and November, the epiphytic algal community dissimilarity was stronger than that observed for bacterial community dissimilarity, suggesting that bacterial community dissimilarity may increase more slowly with environmental change than algal community dissimilarity. Furthermore, association network analysis revealed complex correlations between algal biomass and bacteria phylotype, and that 67.83% of correlations were positive and 32.17% were negative. This may indicate that facilitative correlations between algae and bacteria are predominant in epiphytic biofilms. These results provide new information on algal-bacterial correlations as well as the possible mechanisms that drive variations in the microbial community in epiphytic biofilms in freshwater lakes.

How many submerged macrophyte species are needed to improve water clarity and quality in Yangtze floodplain lakes?

Successful re-establishment and maintenance of submerged macrophytes is a pivotal problem for the restoration of shallow eutrophic lakes, since submerged macrophytes can facilitate a shift of lake ecosystems from a turbid water state to a clear water state through their structuring roles. However, little is known about the optimal number of macrophyte species (species richness) needed for the recovery of shallow eutrophic lakes. Here, we investigated 19 shallow eutrophic lakes along the mid-lower reaches of the Yangtze River to reveal the underlying interrelations among water clarity, water quality and species richness. Our results showed positive correlations of water nutrients (TN and TP) with K_d and Red/Blue light ratio, suggesting that bad water quality can significantly lower water clarity. The results of path analysis indicated that the underwater light climate directly affects morphological and physiological traits and species richness of submerged macrophytes. Changes in functional traits also affected significantly the species richness of submerged macrophytes. Moreover, the presence of submerged macrophytes not only had positive effects on the underwater light climate (water clarity), but also on water quality. Most importantly, the assemblage of three or more submerged macrophyte species can significantly improve water clarity in these sampled eutrophic lakes, but not water quality. Additionally, the basic species assemblage of Myriophyllum spicatum and Vallisneria natans can be used for restoration of submerged macrophytes in shallow eutrophic Yangtze floodplain lakes. It is concluded that species richness and species assemblage are critical for recovery of submerged macrophytes in shallow eutrophic lakes.

Glutamate dehydrogenase plays an important role in ammonium detoxification by submerged macrophytes

Ammonium is a paradoxical chemical because it is a nutrient but also damages ecosystems at high concentration. As the most eco-friendly method of water restoration, phytoremediation technology still faces great challenges. To provide more theoretical support, we exploited six common submerged macrophytes and selected the most ammonium-tolerant and -sensitive species; then further explored and compared the mechanisms underlying ammonium detoxification. Our results showed the activity of glutamate dehydrogenase (GDH) in the ammonium-tolerant species Myriophyllum spicatum leaves performed a dose-response curve (increased 169% for NADH-dependent GDH and 103% for NADPH-dependent GDH) with the [NH₄⁺-N] increasing from 0 to 100 mg/L while glutamine synthetase (GS) activity slightly changed. But for the ammonium-sensitive species, Potamogeton lucens, the activity of GDH recorded no major changes, while the GS increased slightly (17%). Based on this, we conclude that the alternative pathway of GDH is more important than the pathway catalyzed by GS in determining the tolerance of submerged macrophytes to high ammonium concentration (up to 100 mg N/L). Our present study identifies submerged macrophytes that are tolerant of high concentrations of ammonium and provides mechanistic support for practical water restoration by aquatic plants.

Impact of upstream landslide on perialpine lake ecosystem: An assessment using multi-temporal satellite data

Monitoring freshwater and wetland systems and their response to stressors of natural or anthropogenic origin is critical for ecosystem conservation. A multi-temporal set of 87 images, acquired by Sentinel-2 satellites over three years (2016-2018), provided quantitative information for assessing the temporal evolution of key ecosystem variables in the perialpine Lake Mezzola (northern Italy), which has suffered from the impacts of a massive landslide that took place upstream of the lake basin in summer 2017. Sentinel-2 derived products revealed an increase in lake turbidity triggered by the landslide that amounted to twice the average values scored in the years preceding and following the event. Hotspots of turbidity within the lake were in particular highlighted. Moreover, both submerged and riparian vegetation showed harmful impacts due to sediment deposition. A partial loss of submerged macrophyte cover was found, with delayed growth and a possible community shift in favor of species adapted to inorganic substrates. Satellite-derived seasonal dynamics showed that exceptional sediment load can overwrite climatic factors in controlling phenology of riparian reed beds, resulting in two consecutive years with shorter than normal growing season and roughly 20% drop in productivity, according to spectral proxies. Compared to 2016, senescence came earlier by around 20 days on average in 2017 season, and green-up was delayed by up to 50 days (20 days, on average) in 2018, following the landslide. The approach presented could be easily implemented for continuous monitoring of similar ecosystems subject to external pressures with periods of high sediment loads.

Generalized additive models for biomass simulation of submerged macrophytes in a shallow lake

Submerged macrophytes are widely distributed primary producer that play important roles in maintaining healthy aquatic ecosystems. Generally, the relationships between macrophytes and environmental factors are complicated, so nonlinear nonparametric models with relatively flexible structures are optimal for macrophyte habitat simulation. In this study, generalized additive model (GAM) was used to evaluate the response of the submerged macrophytes biomass to water environmental factors in the Baiyangdian Lake. Forward stepwise method was used to implement model optimization. Likelihood ratio test was used to determine whether adding a variable enhances the model performance. Four individual variables (water depth, transparency, total nitrogen, and total phosphorus) and two interaction terms (water depth × transparency and water depth × total phosphorus) were included in the optimal GAM. The optimal model explained 70.5% of the biomass variation with a relatively low residual deviance value (22.40). There was a significant correlation between the measured and predicted data (R² = 0.716, p = 0.0004). The response lines generated by the model indicated that macrophyte biomass had a positive correlation with transparency but negative correlations with total nitrogen and nitrite nitrogen in water. The response patterns of macrophyte biomass to water depth and total phosphorus were unimodal. The biomass reached the maximum value when the water depth was about 2.1 m and the total phosphorus concentration was 0.07 mg/L. Water depth and transparency, which affect light availability, are critical physical variables affecting the conditions associated with the submerged macrophytes, and excess nitrite and phosphorus limiting macrophyte biomass.

Influence of water temperature and water depth on macrophyte-bacterioplankton interaction in a groundwater-fed river

Biotic interactions shape the community structure and function of ecosystems and thus play an important role in ecosystem management and restoration. To investigate how water temperature (related to the season) and water depth (related to spatial patterns of river morphology) affect macrophyte-bacterioplankton interactions in a groundwater-fed river, we conducted the structural equation modeling on datasets grouped by hydrological conditions. In addition to direct effects on macrophyte growth and/or bacterioplankton development, water temperature and water depth could both regulate the role of different nutrients (inorganic and organic) on affecting these biological indicators. Deeper water depth intensified the positive relationship between macrophytes and bacterioplankton, while higher temperature switched the relationship from being positive to negative. Our study provides empirical evidences that abiotic variables, even with relatively low fluctuations, play a critical role in regulating the patterns and strengths of interaction between macrophytes and bacterioplankton.

The abundance of nirS-type denitrifiers and anammox bacteria in rhizospheres was affected by the organic acids secreted from roots of submerged macrophytes

Excessive nitrogen has been a global concern to cause lake eutrophication. The denitrification and anammox processes are considered to be effective biological pathways for nitrogen removal. Submerged macrophytes also play a key role in the nitrogen cycle of lakes. However, the mechanism of submerged macrophytes on regulating biological nitrogen removal pathways has not been well quantified. Therefore, this study investigated the impacts of submerged macrophytes on the community structures and abundance of the nirS-type denitrifiers and anammox bacteria in the rhizospheres. The qPCR results indicated that the abundance of two bacteria in the near-rhizospheres of submerged macrophytes was significantly lower than the root compartments and non-rhizospheres, while the concentrations of organic acids in the near-rhizospheres were higher than those of the root compartments and non-rhizospheres. Redundancy analysis results illustrated that concentrations of NO₃^--N, NO₂^--N, citric acid and oxalic acid were the key environmental indicators which had the significant impact on the microbial community. The concentrations of citric acid and oxalic acid were negatively correlated with the nirS-type denitrifiers abundance, and the oxalic acid concentrations were negatively correlated with the anammox bacteria abundance. These results indicated that submerged macrophytes could reduce the abundance of nirS-type denitrifiers and anammox bacteria by releasing organic acids. In addition, the highest diversity of denitrifier community were found in the rhizosphere of the Hydrilla verticillata, while the highest diversity of anammox community were found in the Potamogeton maackianus rhizosphere. These results indicate that the impacts of submerged macrophytes on the biological nitrogen removal pathways were species-dependent.

The dissipation and risk alleviation mechanism of PAHs and nitrogen in constructed wetlands: The role of submerged macrophytes and their biofilms-leaves

The role of submerged macrophytes (Vallisneria natans, Hydrilla verticillata and artificial plant) and their biofilms-leaves for the dissipation and risk alleviation mechanism of PAHs (phenanthrene and pyrene) and nitrogen in constructed wetland systems with PAH-polluted sediments were investigated. Biofilms-leaves/surface might contribute to PAHs degradation, which was positively correlated with PAHs degrading bacteria. Nitrogen-fixing bacteria in biofilms on surface might cause total nitrogen in sediment (TNs) increasing by 4% from 14th d to 28th d indirectly when suffering PAHs pollution. The relative abundance of nitrogen-fixing bacteria significantly increased with the increase of PAHs concentrations in early period (p < 0.01), which might lead to risk of nitrogen accumulation further. Heat maps showed that the relative abundance of functional bacteria were influenced in order of attached surface > incubation time > spiking concentration of PAHs. Interestingly, differences of deduced bacterial functions were affected in order of incubation time > attached surface > spiking concentration. Thus, submerged macrophytes and their biofilms on leaves not only played an important role in PAHs degradation, but also regulated the nitrogen cycling in constructed wetland systems, which could reduce these pollutants risk for natural environment, organisms and human health.

Zinc pollution in zones dominated by algae and submerged macrophytes in Lake Taihu

Zinc (Zn) contamination in lake zones dominated by algae and macrophytes in Lake Taihu was analyzed through diffusive gradient in thin films (DGT) and dialysis (HR-Peeper) methods. It was found that in both zones Zn contamination varied by season. In July and October, dissolved Zn was present in high concentrations, and in July, high concentrations of labile Zn were found in sediments. In July, reductive dissolutions of Fe/Mn oxides likely played a key role in the release of Zn, which was confirmed by both zones having the lowest percentage of the reducible fraction of Zn in July. Complexation of dissolved organic matter (DOM) with Zn may be responsible for the observed increase in the dissolved Zn concentration in October. This conclusion was supported by noting that October had the highest percentages of Zn-DOM complexes (25.3% and 34.4%) in the algae- and macrophytes-dominated zones, respectively. However, in January, low dissolved and labile Zn contents were observed in sediments in the two zones, suggesting that the decrease of Zn in sediments was caused by the adsorption of Fe/Mn oxides.

Association between submerged aquatic vegetation and elevated levels of Escherichia coli and potential bacterial pathogens in freshwater lakes

Fecal indicator bacteria such as Escherichia coli have been reported to persist and potentially grow in a wide variety of secondary habitats, such as water, beach sand, sediment, periphyton and some algae. However, little is known about their association with submerged macrophytes and how this may influence water quality. In this study, we examined the association of E. coli and potential bacterial pathogens with Eurasian watermilfoil (EWM), an invasive, submerged, macrophyte that has spread across thousands of lakes in North America. EWM samples were collected from 10 lakes in Minnesota, once a month, for six consecutive months from early summer to late fall. Microbiota associated with EWM were examined using membrane filtration, quantitative PCR targeting various bacterial pathogens and host-associated marker genes, and high-throughput DNA sequencing. E. coli densities were generally elevated on EWM samples, and peaked during warmer months. Moreover, our results showed that EWM could serve as a temporal source for transmission of microbiota to the water column. Several potential pathogenic groups, including Aeromonas, Enterobacteriaceae, and Clostridium were present in significantly greater relative abundance on EWM than in water, and waterfowl was predicted to be the major source of fecal contamination. These findings have water quality implications with respect to the potential for submerged macrophytes to harbor and disperse E. coli and other bacterial pathogens in a large number of waterbodies.

Responses of propagule germination and sexual reproduction of submerged macrophytes exposed to cadmium

Submerged macrophytes are considered the main primary producers in shallow lakes. Recently, they have experienced a decline due to increasing environmental impacts, e.g., excessive heavy metal loads. Compared to extensive studies on vegetative growth, reports on effects of heavy metals on propagule germination and reproduction remain scarce. In this study, three experiments were conducted to investigate the effects of cadmium (Cd) on the propagule germination and sexual reproduction of submerged macrophytes. In Experiment I, six Cd concentrations were used (0, 0.05, 0.5, 1, 2.5, and 5 mg L^-1), with seed germination found to be marginally affected by Cd treatment. In Experiment II, Cd exposure (5 d) at the six Cd concentrations was performed 15, 30, 60, 90, and 120 d prior to the designated germination date for turions/tubers. The Vallisneria spinulosa tubers did not germinate at ≥ 2.5 mg Cd L^-1 when exposed to Cd 90 and 120 d prior to germination, whereas the Potamogeton crispus turions remained viable but with a low germination rate at ≥ 2.5 mg Cd L^-1. In Experiment III, with an increase from 0 to 0.5 Cd mg L^-1, the fruit weight of Ottelia alismoides and V. spinulosa decreased, whereas the fruit number increased for O. alismoides but not for V. spinulosa. Furthermore, the phenology of sexual reproduction for both species advanced under Cd exposure. In summary, Cd exposure affected the germination of asexual propagules and sexual reproduction of submerged macrophytes, with seeds found to be tolerant of Cd treatment up to 5 mg L^-1.