The effects of different doses of lanthanum-modified bentonite in combination with a submerged macrophyte (Vallisneria denseserrulata) on phosphorus inactivation and macrophyte growth: A mesocosm study.

The combination of chemical phosphorus (P) inactivation and submerged macrophyte transplantation has been widely used in lake restoration as it yields stronger effects than when applying either method alone. However, the dose effect of chemical materials on P inactivation when used in combination with submerged macrophytes and the influences of the chemicals used on the submerged macrophytes growth remain largely unknown. In this study, we investigated P inactivation in both the water column and the sediment, and the responses of submerged macrophytes to Lanthanum modified bentonite (LMB) in an outdoor mesocosm experiment where Vallisneria denseserrulata were transplanted into all mesocosms and LMB was added at four dosage levels, respectively: control (LMB-free), low dosage (570 g m-2), middle dosage (1140 g m-2), and high dosage (2280 g m-2). The results showed that the combination of LMB dosage and V. denseserrulata reduced TP in the water column by 32%-38% compared to V. denseserrulata alone, while no significant difference was observed among the three LMB treatments. Porewater soluble reactive P, two-dimensional diffusive gradient in thin films (DGT)-labile P concentrations, and P transformation in the 0-1 cm sediment layer exhibited similar trends along the LMB dosage gradient. Besides, LMB inhibited plant growth and reduced the uptake of mineral elements (i.e., calcium, manganese, iron, and magnesium) in a dosage-dependent manner with LMB. LMB may reduce plant growth by creating a P deficiency risk for new ramets and by interfering with the uptake of mineral elements. Considering both the dose effect of LMB on P inactivation and negative effect on macrophyte growth, we suggest a "small dosage, frequent application" method for LMB application to be used in lake restoration aiming to recover submerged macrophytes and clear water conditions.

The response of structure and nitrogen removal function of the biofilm on submerged macrophytes to high ammonium in constructed wetlands.

The ammonium exceedance discharge from sewage treatment plants has a great risk to the stable operation of subsequent constructed wetlands (CWs). The effects of high ammonium shocks on submerged macrophytes and epiphytic biofilms on the leaves of submerged macrophytes in CWs were rarely mentioned in previous studies. In this paper, the 16S rRNA sequencing method was used to investigate the variation of the microbial communities in biofilms on the leaves of Vallisneria natans plants while the growth characteristics of V. natans plants were measured at different initial ammonium concentrations. The results demonstrated that the total chlorophyll and soluble sugar synthesis of V. natans plants decreased by 51.45% and 57.16%, respectively, and malondialdehyde content increased threefold after 8 days if the initial NH4+-N concentration was more than 5 mg/L. Algal density, bacterial quantity, dissolved oxygen, and pH increased with high ammonium shocks. The average removal efficiencies of total nitrogen and NH4+-N reached 73.26% and 83.94%, respectively. The heat map and relative abundance analysis represented that the relative abundances of phyla Proteobacteria, Cyanobacteria, and Bacteroidetes increased. The numbers of autotrophic nitrifiers and heterotrophic nitrification aerobic denitrification (HNAD) bacteria expanded in biofilms. In particular, HNAD bacteria of Flavobacterium, Hydrogenophaga, Acidovorax, Acinetobacter, Pseudomonas, Aeromonas, and Azospira had higher abundances than autotrophic nitrifiers because there were organic matters secreted from declining leaves of V. natans plants. The analysis of the nitrogen metabolic pathway showed aerobic denitrification was the main nitrogen removal pathway. Thus, the nitrification and denitrification bacterial communities increased in epiphytic biofilms on submerged macrophytes in constructed wetlands while submerged macrophytes declined under ammonium shock loading.

Niche-Specific Restructuring of Bacterial Communities Associated with Submerged Macrophyte under Ammonium Stress.

Submerged macrophytes and their epiphytic microbes form a "holobiont" that plays crucial roles in regulating the biogeochemical cycles of aquatic ecosystems but is sensitive to environmental disturbances such as ammonium loadings. Increasingly more studies suggest that plants may actively seek help from surrounding microbial communities whereby conferring benefits in responding to particular abiotic stresses. However, empirical evidence is scarce regarding how aquatic plants reconstruct their microbiomes as a "cry-for-help" against acute ammonium stress. Here, we investigated the temporal dynamics of the phyllosphere and rhizosphere bacterial communities of Vallisneria natans following ammonium stress and recovery periods. The bacterial community diversity of different plant niches exhibited opposite patterns with ammonium stress, that is, decreasing in the phyllosphere while increasing in the rhizosphere. Furthermore, both phyllosphere and rhizosphere bacterial communities underwent large compositional changes at the end of ammonium stress, significantly enriching of several nitrifiers and denitrifiers. Meanwhile, bacterial legacies wrought by ammonium stress were detected for weeks; some plant growth-promoting and stress-relieving bacteria remained enriched even after stress disappeared. Structural equation model analysis showed that the reshaped bacterial communities in plant niches collectively had a positive effect on maintaining plant biomass. Additionally, we applied an age-prediction model to predict the bacterial community's successional trajectory, and the results revealed a persistent change in bacterial community development under ammonium treatment. Our findings highlight the importance of plant-microbe interactions in mitigating plant stress and fostering a better understanding of the assembly of plant-beneficial microbes under ammonium stress in aquatic ecosystems. IMPORTANCE Increasing anthropogenic input of ammonium is accelerating the decline of submerged macrophytes in aquatic ecosystems. Finding efficient ways to release submerged macrophytes from ammonium stress is crucial to maintain their ecological benefits. Microbial symbioses can alleviate abiotic stress in plants, but harnessing these beneficial interactions requires a detailed understanding of plant microbiome responses to ammonium stress, especially over a continuous time course. Here, we tracked the temporal changes in bacterial communities associated with the phyllosphere and rhizosphere of Vallisneria natans during ammonium stress and recovery periods. Our results showed that severe ammonium stress triggers a plant-driven timely reshaping of the associated bacterial community in a niche-specific strategy. The reassembled bacterial communities could potentially benefit the plant by positively contributing to nitrogen transformation and plant growth promotion. These findings provide empirical evidence regarding the adaptive strategy of aquatic plants whereby they recruit beneficial microbes against ammonium stress.

Global historical trends and drivers of submerged aquatic vegetation quantities in lakes.

Submerged aquatic vegetation (SAV) in lake littoral zones is an inland water wetland type that provides numerous essential ecosystem services, such as supplying food and habitat for fauna, regulating nutrient fluxes, stabilizing sediments, and maintaining a clear water state. However, little is known on how inland SAV quantities are changing globally in response to human activities, where loss threatens the provisioning of these ecosystem services. In this study, we generate a comprehensive global synthesis of trends in SAV quantities using time series (>10 years) in lakes and identify their main drivers. We compiled trends across methods and metrics, integrating both observational and paleolimnological approaches as well as diverse measures of SAV quantities, including areal extent, density, or abundance classes. The compilation revealed that knowledge on SAV is mostly derived from temperate regions, with major gaps in tropical, boreal, and mountainous lake-rich regions. Similar to other wetland types, we found that 41% of SAV times series are largely decreasing mostly due to land use change and resulting eutrophication. SAV is, however, increasing in 28% of cases, primarily since the 1980s. We show that trends and drivers of SAV quantities vary regionally, with increases in Europe explained mainly by management, decreases in Asia due to eutrophication and land use change, and variable trends in North America consistent with invasive species arrival. By providing a quantitative portrait of trends in SAV quantities worldwide, we identify knowledge gaps and future SAV research priorities. By considering the drivers of different trends, we also offer insight to future lake management related to climate, positive restoration actions, and change in community structure on SAV quantities.

La végétation aquatique submergée (VAS) dans la zone littorale des lacs fait partie des milieux humides des eaux continentales et soutient plusieurs services écologiques, tels que fournir un habitat pour la faune, réguler les flux de nutriments et stabiliser les sédiments. Cependant, comment les changements des quantités de VAS varient mondialement en réponse aux activités humaines demeurent peu connu, alors que leur perte menace le maintien de ces services écologiques. Dans cette étude, nous avons généré une synthèse globale des séries temporelles des quantités de VAS dans les lacs et avons identifié leurs tendances et leurs facteurs explicatifs. Nous avons compilé les tendances à travers les méthodes et les métriques, intégrant à la fois les approches observationnelles et paléolimnologiques ainsi que des mesures diverses de quantité de VAS, telles que la superficie de couverture, la densité et les classes d'abondance. La compilation a révélé que les connaissances sur la VAS proviennent surtout des régions tempérées, avec peu d'information dans les régions boréales, tropicales et montagneuses riches en lacs. Comme pour les autres types de milieux humides, nous avons trouvé que la VAS est largement en déclin, tel que reporté dans 41% des séries temporelles principalement à cause des changements d'utilisation du territoire et de l'eutrophisation. La VAS est cependant en augmentation dans 28 % des cas, surtout depuis les années 1980. Nous montrons que les tendances de la VAS et les facteurs explicatifs varient par région. En Europe, les augmentations sont expliquées principalement par la gestion, en Asie, le déclin est fonction de l'eutrophisation et des changements d'utilisation du territoire, alors qu'en Amérique du Nord les tendances variables sont associées à l'arrivée de nouvelles espèces. En fournissant un portrait quantitatif des tendances de VAS à travers le monde, nous indiquons des lacunes dans les connaissances et les futures priorités de recherche. En se penchant sur les facteurs explicatifs, nous offrons des informations sur l'influence du climat, des actions de restauration positives et du changement de la structure des communautés sur la VAS qui pourront informer les gestionnaires des lacs.

Controlling internal nutrients loading at low temperature using oxygen-loading zeolite and submerged macrophytes enhances environmental resilience to subsequent high temperature.

Nutrients releasing from anoxic sediment can be enhanced in summer because the dissolved oxygen (DO) consumption, nitrogen (N) and phosphorus (P) migration are susceptible to temperature. Herein, we proposed a method to hinder the aquatic environmental deterioration in warm seasons through consecutive application of oxygen- and lanthanum-modified zeolite (LOZ) and submerged macrophytes (V. natans) at low temperature scenario (5 °C, with depleted DO in water), and the effect was examined with drastic increasing the ambient temperature to 30 °C. The investigation was conducted in a microcosm scale including sediment cores (with a diameter of 11 cm, height of 10 cm) and overlying water (with depth of 35 cm). During the 60 days experiment, application of LOZ at 5 °C facilitated slower releasing and diffusion of oxygen from LOZ and the growth of V. natans. Thereby, when the temperature was increased to 30 °C and maintained for 35 days, the DO reached 10.01 mg/L, and the release of P and N from the sediment was reduced by 86% and 92%, respectively. This was achieved from the joint efforts of adsorption, biological conversion, chemical inactivation, and assimilation. Also, the LOZ inhibited 80% N2O, 75% CH4, and 70% CO2 emissions primary by promoting V. natans growth and reshaping microbiota. Meanwhile, the colonization of V. natans benefited the sustainable improvement in the water quality. Our results addressed the time that the remediation of anoxic sediment can be applied.

Heterogeneity of molecular-level and photochemical of dissolved organic matter derived from decomposing submerged macrophyte and algae.

Aquatic macrophytes and algae are the most important sources of autochthonous dissolved organic matter (DOM), and their transformation and reuse significantly affect aquatic ecosystem health. In this study, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to identify the molecular features between submerged macrophyte-derived DOM (SMDOM) and algae-derived DOM (ADOM). The photochemical heterogeneity between SMDOM and ADOM by UV254-irradiation and their molecular mechanism were also discussed. The results showed that the molecular abundance of SMDOM was dominated by lignin/CRAM-like structures, tannins, and concentrated aromatic structures (sum of 91.79%), while that of ADOM was dominated by lipids, proteins, and unsaturated hydrocarbons (sum of 60.30%). UV254-radiation resulted in a net reduction of tyrosine-like, tryptophan-like and terrestrial humic-like, and conversely a net production of marine humic-like. The light decay rate constants obtained by the multiple exponential function model fitting revealed that both tyrosine-like and tryptophan-like components of SMDOM could be rapidly and directly photodegraded, while the photodegradation of tryptophan-like in ADOM depended on the production of photosensitizers. The photo-refractory fractions of both SMDOM and ADOM were as follows: humic-like > tyrosine-like > tryptophan-like. Our results provide new insights into the fate of autochthonous DOM in aquatic ecosystems where "grass-algae" coexist or evolve.

Effect of submerged plant coverage on phytoplankton community dynamics and photosynthetic activity in situ.

Restoration of submerged plants in eutrophic lakes can reduce nutrients and phytoplankton biomass in the water body. However, the effect of submerged plants on phytoplankton communities and their photosynthetic activity in situ are still poorly understood. Here, we studied the response of phytoplankton community structure and fluorescence parameters to different submerged plants coverage, the relationship of phytoplankton community and fluorescence parameters with submerged plants coverage and water physicochemical parameters were analysed in sampling area of Hangzhou West Lakes. The results showed that the coverage and biomass of submerged plants were negatively correlated with nitrogen and phosphorus contents in water body but positively correlated with total phenol content. The ratio of nitrogen to phosphorus in the study site changed greatly (32.25-124.54). In spring and summer, Oscillatoria and Leptolyngbya (Cyanophyta) were the dominant species, while in autumn and winter, the dominant species were Cyclotella (Chlorophyta), and Melosira and Cymbella (Bacillariophyta). Compared with Chlorophyta and Bacillariophyta, fluorescence parameters of Cyanophyta were more sensitive to total phosphorus, N:P ratio, total phenols, pH, and electric conductivity. Fluorescence parameters of Chlorophyta and Bacillariophyta were only affected by underwater light. Total phosphorus (TP) and N:P had a negative effect on the maximum photochemical electron yield of Cyanophyta. Furthermore, Cyanophyta was inhibited by total phenols from submerged plants. When phytoplankton were under stress, photochemical electron yield decreased significantly, whereas non-photochemical quenching increased. The structural equation model showed that the coverage of submerged plants might indirectly affect the fluorescence parameters of Cyanophyta by affecting nitrogen, phosphorus, and total phenol contents in the water body. These findings contribute to the understanding of the mechanisms underlying the impact of submerged plant restoration on phytoplankton community dynamics in subtropical eutrophic shallow lakes and provide a theoretical basis for the management of lakes.

Effects of Submerged Macrophytes on the Growth, Morphology, Nutritional Value, and Flavor of Cultured Largemouth Bass (Micropterus salmoides).

Aquaculture environment plays important roles in regulating the growth, morphology, nutrition, and flavor of aquatic products. The present study investigated growth, morphology, nutrition, and flavor formation in largemouth bass (Micropterus salmoides) cultured in the ponds with (EM group) and without (M group) the submerged macrophytes (Elodea nuttallii). Fish in the EM group showed a significantly greater body length, higher growth rate, and lower hepatosomatic index than those in the M group (p< 0.05). Moreover, compared with fish in the M group, those in the EM group showed improved muscle quality with significantly elevated levels of crude protein, total free and hydrolysable amino acids, and polyunsaturated fatty acids (p < 0.05). Specifically, certain amino acids related to flavor (Glu, Asp, Ala, and Arg) and valuable fatty acids (C18:2, C18:3n3, C20:3n3, and C22:6) were more abundant in the EM group (p < 0.05). In addition, the levels of 19 volatile (p < 0.05) were significantly higher in the EM group than in the M group. Therefore, E. nuttallii significantly improved growth, morphological traits, nutritional components, and characteristic flavor in largemouth bass, indicating the superior nutritional value and palatability of fish cultured with submerged macrophytes.

Dynamic nutrient removal potential of a novel submerged macrophyte Rotala rotundifolia, and its growth and physiological response to reduced light available.

Rotala rotundifolia is a novel submerged macrophyte able to survive across the winter under temperature as low as 4 °C. Dynamic nutrient removal potential of R. rotundifolia was estimated using the Eco-tank system simulating natural eutrophic waters. The growth and physiological response of R. rotundifolia by cutting and division propagation to light (100%, 60%, and 20% natural light) were investigated. The results showed that R. rotundifolia was superior in removing N and P from eutrophic waters. As influent concentrations of NH4+-N and total phosphorus (TP) were 4.81-5.87 and 0.61-0.78 mg L-1, effluent concentrations of NH4+-N, total nitrogen (TN), and TP were separately 0.06-1.10, 0.40-1.59, and 0.05-0.17 mg L-1, with removal efficiencies of 93.6%, 84.6%, and 82.5% at a flow rate of 200 L d-1. The growth and morphology of the plant under two propagation patterns were influenced by light and the responses were quite different. The biomass of the plant by cutting was higher at low light conditions, and the plant allocated more biomass on above ground. However, there was no significant difference in the height. By division, the plant preferred to high light. The biomass and height were significantly higher at 100% natural light. The peroxidase (POD), superoxide dismutase (SOD) and root activities of plant by cutting showed a trend of decrease and followed by an increase with light reduction, while by division, they increased with reduced light available. Variations of chlorophyll and soluble protein of the plant by cutting and division were contrary to the changes of POD activity. These results suggest that R. rotundifolia can be used to effectively remove nitrogen and phosphorus in eutrophic waters, and high light promotes the growth of the plant by division, while suitable shade is needed for the plant by cutting.

Response of the submerged macrophytes Vallisneria natans to snails at different densities.

The study investigated the responses of the submerged macrophyte Vallisneria natans (V. natans) to snails (Bellamya aeruginosa) at different densities, with changes in physiological parameters, morphology, leaf-epiphytic bacteria community and water quality parameters examined. The changes of water quality parameters (pH, total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC)) indicated that snails secreted nutrients into water. Changes in morphological and physiological parameters (fresh weight, root length, shoot height, chlorophyll, malondialdehyde (MDA), activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) demonstrated that the presence of snails were beneficial to the growth of submerged macrophytes. Microbial diversity analyses indicated that snails could decrease microbial community richness and diversity. At medium densities (340 ind. m-2), an increase in snail density was beneficial to the growth of submerged macrophytes. The results of this study provide theoretical guidance and technical support for the maintenance and restoration of submerged macrophytes.

Response of submerged macrophytes and periphyton biofilm to water flow in eutrophic environment: Plant structural, physicochemical and microbial properties.

The integrated effects of water flow on submerged macrophytes (Vallisneria natans) and leaf biofilms were comprehensively investigated in eutrophic microcosm. Changes in aquatic environmental factors were analyzed and water flow was found to elevate eutrophic water quality, especially in terms of TP removal. The removal efficiency of TP reached 78.95% in flowing water, which was more than 10-fold higher than in static water. Water flow altered the morphological and physiological characteristics of plants, decreasing the cell wall thickness and rate of photosynthesis, while promoting the accumulation of soluble sugar and protein in leaves. The starch content also increased with water flow, and significantly larger starch granules were observed in chloroplast. Furthermore, oxidative damage was evidenced by the consistently higher content of malondialdehyde in flowing water. Superoxide dismutase (SOD), peroxidase (POD) and Catalase (CAT) were induced in plants exposed to water flow, as an antioxidant stress response. The results of 16S rRNA high-throughput sequencing analysis showed that the structure of the biofilm microbial community changed in response to water flow. These results expand our understanding of the effects of water flow on submerged macrophytes and periphyton biofilms in eutrophic environments.

The response of epiphytic bacteria on Vallisneria natans (Lour.) Hara (Hydrocharitaceae) to increasing nutrient loadings.

To investigate the effects of water column nutrient loading on epiphytic bacteria, we determined the abundance and community composition of epiphytic bacteria on the submerged macrophyte Vallisneria natans (Lour.) Hara during the growth season (June-October) under four different nutrient concentrations (nitrogen (N)-phosphorus (P) in mg L(-1) : 0.5-0.05, 1.0-0.1, 5.0-0.5, 10.0-1.0; hereafter NP-1, NP-2, NP-3, NP-4, respectively), using epifluorescence microscopy method and terminal restriction fragment length polymorphism (T-RFLP) analysis, respectively. Relative to low nutrient conditions (NP-1), there was no significant effect on the epiphytic bacterial community, and even a decrease in the number of epiphytic bacteria, which linked to the well growth status of host macrophytes at moderate nutrient conditions (NP-2). However, further nutrient enrichment induced significant increase in the abundance of epiphytic bacteria, and marked changes in the community structures of epiphytic bacteria. Furthermore, at high nutrient conditions, epiphytic bacterial communities varied widely temporally, and were not stable compared with those at the lower nutrient conditions. These results indicated that the effects of nutrient enrichment on epiphytic bacteria were nonlinear and dependent on the nutrient concentrations in the water.

A restoration-promoting integrated floating bed and its experimental performance in eutrophication remediation.

Numerous studies on eutrophication remediation have mainly focused on purifying water first, then restoring submerged macrophytes. A restoration-promoting integrated floating bed (RPIFB) was designed to combine the processes of water purification and macrophyte restoration simultaneously. Two outdoor experiments were conducted to evaluate the ecological functions of the RPIFB. Trial 1 was conducted to compare the eutrophication purification among floating bed, gradual-submerging bed (GSB) and RPIFB technologies. The results illustrated that RPIFB has the best purification capacity. Removal efficiencies of RPIFB for TN, TP, NH(+)4-N, NO(-)3-N, CODCr, Chlorophyll-a and turbidity were 74.45%, 98.31%, 74.71%, 88.81%, 71.42%, 90.17% and 85%, respectively. In trial 2, influences of depth of GSB and photic area in RPIFB on biota were investigated. When the depth of GSB decreased and the photic area of RPIFB grew, the height of Potamogeton crispus Linn. increased, but the biomass of Canna indica Linn. was reduced. The mortalities of Misgurnus anguillicaudatus and Bellamya aeruginosa in each group were all less than 7%. All results indicated that when the RPIFB was embedded into the eutrophic water, the regime shift from phytoplankton-dominated to macrophyte-dominated state could be promoted. Thus, the RPIFB is a promising remediation technology for eutrophication and submerged macrophyte restoration.

Sedimentary organic matter load influences the ecological effects of submerged macrophyte restoration through rhizosphere metabolites and microbial communities.

Organic matter (OM) accumulation in lake sediments has doubled owing to human activities over the past 100 years, which has negatively affected the restoration of submerged vegetation and ecological security. Changes in the pollution structure of sediments caused by plant recovery and rhizosphere chemical processes under different sediment OM levels are the theoretical basis for the rational application of plant rehabilitation technology in lake management. This study explored how Vallisneria natans mediates changes in sediment N and P through rhizospheric metabolites and microbial community and function under low (4.94 %) and high (17.35 %) sediment OM levels. V. natans promoted the accumulation of NH4-N in the high-OM sediment and the transformation of Fe/Al-P to Ca-P in the low-OM sediment. By analyzing 63 rhizospheric metabolites and the sediment microbial metagenome, the metabolites lactic acid and 3-hydroxybutyric acid and the genus Anammoximicrobium were found to mediate NH4-N accumulation in the high-OM sediment. Additionally, 3-hydroxy-decanoic acid, adipic acid, and the genus Bdellovibrionaceae mediated the transformation of Fe/Al-P to Ca-P in the low-OM sediment. The growth of V. natans enriched the abundance of functional genes mediating each step from nitrate to ammonia and the genes encoding urease in the high-OM sediment, and it up-regulated three genes related to microbial phosphorus uptake in the low-OM sediment. This study revealed the necessity of controlling endogenous pollution by recovering submerged macrophytes under high- and low-OM conditions from the perspective of the transformation of inorganic nitrogen and phosphorus.

Does invasive submerged macrophyte diversity affect dissimilatory nitrate reduction processes in sediments with varying microplastics?

Nitrogen removal is essential for restoring eutrophic lakes. Microorganisms and aquatic plants in lakes are both crucial for removing excess nitrogen. However, microplastic (MP) pollution and the invasion of exotic aquatic plants have become increasingly serious in lake ecosystems due to human activity and plant-dominant traits. This field mesocosm study explored how the diversity of invasive submerged macrophytes affects denitrification (DNF), anammox (ANA), and dissimilatory nitrate reduction to ammonium (DNRA) in lake sediments with varying MPs. Results showed that invasive macrophytes suppressed DNF rates, but DNRA and ANA were less sensitive than DNF to the diversity of invasive species. Sediment MPs increased the biomass of invasive species more than native species, but did not affect microbial processes. The effects of MPs on nitrate dissimilatory reduction were process-specific. MPs increased DNF rates and the competitive advantage of DNF over DNRA by changing the sediment environment. The decoupling of DNF and ANA was also observed, with increased DNF rates and decreased ANA rates. The study findings suggested new insights into how the invasion of exotic submerged macrophytes affects the sediment nitrogen cycle complex environments.

Cumulative effects of fish disturbance and vegetative propagules reduce the growth advantage of Vallisneria natans.

Benthivorous fish disturbance and density-dependent competition from adjacent macrophytes are two important biotic factors that significantly impact the growth of submerged macrophyte pioneer species, which is crucial for the success of eutrophication lake restoration. We conducted an outdoor mesocosm experiment to explore the individual and combined effects of these two factors on water quality and the growth of Vallisneria natans. The experiment involved two levels of fish (Misgurnus anguillicaudatus) disturbance crossed with two levels of Hydrilla verticillata vegetative propagule (shoot) intensity. The results showed that fish disturbance significantly increased the water column total nitrogen (TN), ammonia nitrogen (N-NH4), total phosphorus (TP), and phosphate­phosphorus (P-PO4). V. natans exhibited restricted plant height elongation and decreased soluble carbohydrate (SC) and starch concentration in fish treatments. Fish disturbance inhibited the growth advantage of V. natans by increasing the extinction coefficient of the water column. There was no statistical significance in total biomass between the two macrophytes in increased vegetative propagule and fish treatments. H. verticillata exhibited a higher relative growth rate (RGR) and summed dominance ratio (SDR3) than V. natans in four treatments and the treatment with three shoots of H. verticillata and one M anguillicaudatus, respectively. Fish disturbance and vegetative propagules showed cumulative effects that negatively affected the RGR_V.H (V. natans relative to H. verticillata). Our findings indicated that benthivorous fish disturbance and vegetative propagules could individually and cumulatively reduce the growth advantage of the pioneer species, V. natans. Our study sheds light on the accumulated effects of multiple disturbances that simultaneously occur in lakes, which holds theoretical and practical importance for lake restoration efforts.

The Genetic Diversity of the Macrophyte Ceratophyllum demersum in Backwaters Reflects Differences in the Hydrological Connectivity and Water Flow Rate of Habitats.

Macrophytes often live in fluvial backwaters that have a variety of hydrological connections to a main river. Since the ability of these plants to adapt to changing environments may depend on the genetic diversity of the populations, it is important to know whether it can be influenced by habitat characteristics. We examined the microsatellite polymorphism of the submerged macrophyte Ceratophyllum demersum from various backwaters and showed that the genetic diversity of this plant clearly reflects habitat hydrological differences. The greatest genetic variability was found in a canal system where constant water flow maintained a direct connection between the habitats and the river. In contrast, an isolated backwater on the protected side of the river had the lowest plant genetic diversity. Oxbows permanently connected to the branch system with static or flowing water, and former river branches temporarily connected to the main bed contained populations with moderately high or low genetic variability. The results demonstrate that habitat fragmentation can be a result not only of the loss of direct water contact, but also of the lack of flowing water. Adverse hydrological changes can reduce the genetic diversity of populations and thus the ability of this macrophyte to adapt to changing environments.

Response of submerged macrophytes of different growth forms to multiple sediment remediation measures for hardened sediment.

Climate change and intensified human activities have disrupted the natural hydrological regime and rhythm of river-connected lakes, extending the dry season, increasing water loss, and exposing previously submerged lake floors. This exposure has led to significant sediment hardening, which directly impacts submerged macrophytes. However, strategies to mitigate the negative effects of hardened sediments and promote the growth and development of submerged macrophytes remain largely unexplored. In this study, we selected typical hardened sediment from Dongting Lake to investigate the response of different growth forms of submerged macrophytes to multiple sediment remediation measures (loosening and litter addition) using a mesocosm experiment. The results indicated that loosening alone uniformly benefited all submerged macrophytes by increasing total biomass, relative growth rate (RGR), and the root/shoot ratio. Additionally, loosening altered the root traits of submerged macrophytes, promoting maximum root length (MRL) while reducing average root diameter (ARD). Moreover, different submerged macrophytes exhibited species-specific responses to the combination of loosening and litter addition. Notably, the combination of loosening and adding Miscanthus lutarioriparius litter had an antagonistic effect on the growth of Potamogeton wrightii and Myriophyllum spicatum. The response of functional traits of submerged macrophytes with similar growth forms to the same treatment was consistent. Our findings suggest that future sediment remediation efforts should consider matching specific treatments with the growth forms of submerged macrophytes to achieve optimal outcomes.

Epiphytic bacterial community composition on four submerged macrophytes in different regions of Taihu Lake.

The epiphytic bacteria in aquatic ecosystems, inhabiting a unique ecological niche with significant ecological function, have long been the subject of attention. Habitat characteristics and plant species are believed to be important in controlling the assembly of epiphytic bacteria. However, the underlying principle governing the assembly of the epiphytic bacterial community on macrophytes is far from clear. In this study, we systematically compared the diversity and community composition of epiphytic bacteria both in different habitats and on different species of macrophytes where they were attached. Results suggested that neither the plant species nor the habitat had a significant effect on the diversity and community of epiphytic bacteria independently, indicating that the epiphytic bacterial community composition was correlated to both geographical distance and individual species of macrophytes. Furthermore, almost all of the abundant taxa were shared between different lake regions or macrophyte species, and the most abundant bacteria belonged to Proteobacteria and Firmicutes. Our results demonstrated that the competitive lottery model may explain the pattern of epiphytic bacterial colonization of submerged macrophyte surfaces. This research could provide a new perspective for exploring plant-microbe interaction in aquatic systems and new evidence for the lottery model as the mechanism best explaining the assembly of epiphytic bacteria.

Are recyclable plastics eco-friendly? Recycled PVC microplastics show higher toxicity than pristine PVC on Vallisneria natans, regardless of Cadmium.

As environmental awareness increases, the use of recyclable plastics has risen. However, it is currently unclear whether recycled microplastics (MPs) pose a lesser or greater environmental risk than pristine MPs. Cadmium (Cd), known for its toxicity to most organisms, can bind with MPs and accumulate in sediments. Few studies have explored the environmental risks posed by the coexistence of recycled MPs and pristine MPs with Cd to rooted macrophytes. We investigated the effects of recycled PVC MPs (R-PVC-MPs) and pristine PVC MPs (PVC-MPs) on Vallisneria natans in the presence and absence of Cd. Results showed that at moderate and high Cd levels, R-PVC-MPs reduced plant Cd enrichment. Despite this, the fresh weight of V. natans exposed to R-PVC-MPs was significantly lower than those exposed to PVC-MPs. Furthermore, R-PVC-MPs had more negative impacts on the physiological traits of V. natans than PVC-MPs, as chlorophyll was significantly reduced across all Cd levels. At high Cd levels, both R-PVC-MPs and PVC-MPs caused significantly high oxidative stress, with no significant differences observed. The PCoA plot showed that different MPs cause noticeable variations within the same Cd concentration. The trait network diagrams illustrated strong interactions among traits, with R-PVC-MPs showing the highest complexity. Lower average degree and decreased edge density indicate that traits of plants with R-PVC-MPs addition are more independent of each other. Our findings suggest that recycled PVC MPs pose a greater environmental risk than pristine PVC MPs, offering reference for assessing the risks of recycled plastics in freshwater ecosystems.