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Eutrophication of water bodies causes the disappearance of submerged macrophytes and frequent blooms of phytoplankton, which leads to changes in the underwater light environment in the aspect of light intensity and light quality. However, compared with underwater light intensity, only few studies have been concentrated in the effect of light quality on submerged macrophytes. The effect of light quality on plants is heterogeneous, and there are two absorption peaks in red and blue wavelengths. Thus, we carried out a mesocosm experiment to study the effects of a series of red and blue light ratios (red/blue light ratio = 1/8, 1/4, 1/1, 4/1, and 8/1) on two submerged macrophyte species, Hydrilla verticillata and Vallisneria natans. We hypothesized that functional traits (growth strategy, morphological, photosynthetic, and nutritional traits) of submerged macrophytes will be modified by different red/blue light ratios. With the increase of red/blue light ratio, plant height of the two submerged macrophytes decreased, while tillers number increased. We could not completely verify our hypothesis, but we found species-specific differences. The leaf area of H. verticillata under 8/1 red/blue light ratio was significantly higher than that under 1/8 red/blue light ratio, whereas the leaf area of V. natans under 4/1 red/blue light ratio was lower than that under 1/8 red/blue light ratio. Our results are helpful to understand the disappearance mechanism of submerged macrophytes in eutrophic lakes and devise more appropriate measures for the recovery of submerged macrophytes. [ABSTRACT FROM AUTHOR]

Macrobenthic communities in a lake are affected by the type of bottom cover such as macrophytes or algae. In the southern basin of Lake Biwa, mats of the benthic cyanobacteria (BC) Microseira wollei widely cover the lake bottom and are interspersed with submerged macrophytes (SMs). Because different macrobenthos species appear to occur at those bottoms, we investigated the composition of the communities. Furthermore, as M. wollei is supposed to be inedible to consumer organisms owing to its hard sheath and toxins, the food possibility of the cyanobacteria and macrophytes for macrobenthos was analyzed. In this study, macrobenthos were collected, identified molecularly, counted in the BC and SM zones, and analyzed for carbon and nitrogen stable‐isotopic compositions. In the BC zone, asellids and amphipods dominated the macrobenthic community, while chironomids dominated the SM zone. The stable‐isotope analysis revealed that M. wollei was a minor food source for macrobenthos and other higher‐level consumers, with some macrophytes, particulate organic matter and bottom sediment potentially being a major source. The dominance of crustacean macrobenthos in M. wollei mats suggested that they provided a refuge from predation for crustaceans, whereas SMs were not sufficiently abundant to achieve this. Although different macrobenthic communities in the BC and SM zones were likely supported by common food sources, with the exeption of M. wollei, the present study was conducted over a short period and lacked advanced methods for gut content analysis. Therefore, further monitoring and food web analysis are required. [ABSTRACT FROM AUTHOR]

The consequences of non-native species invasion may depend on the characteristics of the invaded ecosystem, such as abiotic environmental conditions and biological community structure. Invasive herbivores can have a substantial adverse impact on the abundance of submerged macrophytes and trigger declines in water quality. Although previous research has posited that shallow lakes with higher nutrient conditions might exhibit greater susceptibility to non-native herbivores, empirical support for this claim remains limited. In this study, we employed 24 mesocosms to simulate shallow water ecosystems, with the primary objective of assessing the influence of invasive herbivorous apple snails (Pomacea canaliculata) on submerged macrophyte and phytoplankton abundance under two distinct nutrient conditions. Our findings indicate that moderate nutrient enrichment alone promoted submerged macrophyte growth, leading to a 156% increase in total biomass in the nutrient-enriched treatment compared to the control (low-nutrient conditions without apple snails). However, the introduction of apple snails caused a significant reduction in submerged macrophyte biomass in both nutrient conditions, approximately 100% loss in low-nutrient conditions and a roughly 50% loss in moderately nutrient-enriched conditions. Additionally, the presence of apple snails slightly increased phytoplankton abundance (~ 57 chl-a μg/l for phytoplankton and ~ 2 μg/l chl-a for cyanobacteria) under low-nutrient conditions, while triggering a shift to a turbid state dominated by planktonic algae (~ 270 chl-a μg/l for phytoplankton and ~ 36 μg/l chl-a for cyanobacteria) under moderately nutrient-enriched conditions. These results emphasize the need for effective management strategies to control invasive herbivores and decrease nutrient inputs. [ABSTRACT FROM AUTHOR]

Because of the high growth rates often achieved by invasive alien macrophytes, their establishment in recipient ecosystems may alter the abundance and composition of litter entering detrital pathways, representing a significant—but often overlooked—ecological effect of these invasions. Crassula helmsii (Kirk) Cockayne (New Zealand pygmyweed) is an invasive alien macrophyte, notorious for its profuse growth in invaded waterbodies. C. helmsii is perennial and often forms dense stands, producing abundant detritus. To investigate whether some of C. helmsii's impacts are mediated by this detritus, we conducted an 85-day litterbag experiment comparing decomposition of C. helmsii with that of Callitriche stagnalis Scop. (water-starwort), a commonly co-occurring native macrophyte. Macroinvertebrate assemblage composition was comparable between macrophyte species throughout the experiment, but shifted as plants decayed. Litterbags were initially dominated by the invasive shredder Crangonyx pseudogracilis Bousfield, 1958 and later by Euglesa casertana (Poli, 1791), an interstitial suspension feeder. C. helmsii litter decomposed more slowly, with proportionally less invertebrate-mediated breakdown, but was ultimately colonised by more abundant macroinvertebrates, including more C. pseudogracilis. Decomposition may be slowed by C. helmsii's high carbon: nitrogen ratio. These results suggest that C. helmsii invasion may impact macroinvertebrate assemblages via the production of long-lasting and relatively unpalatable detritus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Disinfection by-products (DBPs) such as chloroacetic acids (CAAs) and N-Nitrosodimethylamine (NDMA) are prevalent pollutants in surface waters, particularly with the increasing use of chlorine-based disinfectants. The entry of these DBPs into water bodies may increase accordingly, posing ecological risks to aquatic life. To assess the toxic effects of CAAs and NDMA on submerged macrophytes, Vallisneria natans was exposed to different concentrations of CAAs (1.0, 10.0, and 100.0 μg L−1) and NDMA (0.1, 1.0, and 10.0 μg L−1). A RI value of <1 indicates that simultaneous exposure to CAAs and NDMA can produce an antagonistic effect. Both CAAs and NDMA adversely affect the photosynthetic system of plants. In the NDMA treatment group, chlorophyll a content decreases with increasing concentration, accounting for 96.03%, 60.80%, and 58.67% of the CT group, respectively. Additionally, it effectively triggers the plant's antioxidant response, with significant increases in SOD, POD, and GSH levels. Among these, the combined treatment group AN2 (10 + 1 μg L−1) showed the most significant change in SOD activity, reaching 3.57 times that of the CT group. Ultrastructural changes also revealed stress responses in leaf cells and damage to organelles. Furthermore, metabolomics provided insights into the metabolic responses induced by CAAs or NDMA in V. natans leaves, where the composition and metabolism of lipids, fatty acids, cofactors and vitamins, amino acids, nucleotides, and some antioxidants were regulated, affecting plant growth. This study provides preliminary information for the ecological risk assessment of submerged plants by complex contamination with the disinfection by-products CAA and NDMA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• High initial ammonium harmed the growth of Vallisneria natans if NH4+-N concentration exceeded 5 mg/L. • High initial ammonium imposed the algal growth to produce hydrogen. • Autotrophic nitrifiers and heterotrophic nitrification aerobic denitrification bacteria enriched in biofilms could enhance the nitrification and denitrification functions of the biofilm. • Autotrophic denitrifiers in biofilms appeared to use hydrogen to denitrify nitrate and nitrite. 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 NH 4 +-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 NH 4 +-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. [ABSTRACT FROM AUTHOR]

ABSTRACT Macrobenthic communities in a lake are affected by the type of bottom cover such as macrophytes or algae. In the southern basin of Lake Biwa, mats of the benthic cyanobacteria (BC) Microseira wollei widely cover the lake bottom and are interspersed with submerged macrophytes (SMs). Because different macrobenthos species appear to occur at those bottoms, we investigated the composition of the communities. Furthermore, as M. wollei is supposed to be inedible to consumer organisms owing to its hard sheath and toxins, the food possibility of the cyanobacteria and macrophytes for macrobenthos was analyzed. In this study, macrobenthos were collected, identified molecularly, counted in the BC and SM zones, and analyzed for carbon and nitrogen stable‐isotopic compositions. In the BC zone, asellids and amphipods dominated the macrobenthic community, while chironomids dominated the SM zone. The stable‐isotope analysis revealed that M. wollei was a minor food source for macrobenthos and other higher‐level consumers, with some macrophytes, particulate organic matter and bottom sediment potentially being a major source. The dominance of crustacean macrobenthos in M. wollei mats suggested that they provided a refuge from predation for crustaceans, whereas SMs were not sufficiently abundant to achieve this. Although different macrobenthic communities in the BC and SM zones were likely supported by common food sources, with the exeption of M. wollei, the present study was conducted over a short period and lacked advanced methods for gut content analysis. Therefore, further monitoring and food web analysis are required.

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.

Globally intensified lake eutrophication, attributed to excessive anthropogenic nitrogen loading, emerges as a significant driver of submerged vegetation degradation. Consequently, the impact of nitrogen on the decline of submerged macrophytes has received increasing attention. However, a functional trait-based approach to exploring the response of submerged macrophytes to nitrogen loading and its environmental feedback mechanism was unclear. Our study utilized two different growth forms of submerged macrophytes (canopy-forming Myriophyllum spicatum, and rosette-forming Vallisneria natans) to established “submerged macrophytes-water–sediment” microcosms. We assessed the influence of nitrogen loading, across four targeted total nitrogen concentrations (original control, 2, 5, 10 mg/L), on plant traits, water parameters, sediment properties, enzyme activities, and microbial characteristics. Our findings revealed that high nitrogen (10 mg/L) adversely impacted the relative growth rate of fresh biomass and total chlorophyll content in canopy-forming M. spicatum, while the chlorophyll a/b and free amino acid content increased. On the contrary, the growth and photosynthetic traits of resource-conservative V. natans were not affected by nitrogen loading. Functional traits (growth, photosynthetic, and stoichiometric) of M. spicatum but not V. natans exhibited significant correlations with environmental variables. Nitrogen loading significantly increased the concentration of nitrogen components in overlying water and pore water. The presence of submerged macrophytes significantly reduced the ammonia nitrogen and total nitrogen both in overlying water and pore water, and decreased total organic carbon in pore water. Nitrogen loading significantly inhibited sediment extracellular enzyme activities, but the planting of submerged macrophytes mitigated their negative effects. Furthermore, rhizosphere bacterial interactions were less compact compared to bare control, while eukaryotic communities exhibited increased complexity and connectivity. Path modeling indicated that submerged macrophytes mitigated the direct effects of nitrogen loading on overlying water and amplified the indirect effects on pore water, while also attenuating the direct negative effects of pore water on extracellular enzymes. The findings indicated that the restoration of submerged vegetation can mitigate eutrophication resulting from increased nitrogen loading through species-specific changes in functional traits and direct or indirect feedback mechanisms in the water–sediment system.

Light intensity is a determinant for submerged macrophytes. Little is known about their molecular responses to low‐light exposure, despite more informative and responsive than morphological traits. For erect‐type submerged macrophytes, the stem is more crucial relative to the leaf in acclimation to low‐light stress, but receives less attention. We determined morphological and stem transcriptomic responses/acclimations of Hydrilla verticillata to extremely and mildly low light (7.2 and 36 μmol photons m−2 s−1, respectively), that is, EL and ML, with the radiation intensity of 180 μmol photons m−2 s−1 as the control. Low‐light exposure continued for 9 days, followed by a 7‐day recovery phase (180 μmol photons m−2 s−1). At the exposure phase, the low‐light treatments, in particular the EL, decreased the relative growth ratio, but induced greater height and longer stem internode distance and epidermal cell. Such responses/acclimations continued into the recovery phase, despite more or less changes in the magnitude. Transcriptome showed that the photosynthetic system was inhibited at the exposure phase, but the macrophyte adjusted hormone synthesis relating to cell division and elongation. Moreover, the EL activated cell stress responses such as DNA repair. Following light recovery, the macrophyte exhibited a strong‐light response, although energy metabolism enhanced. Especially, the EL enriched the pathways relating to anthocyanin synthesis at such phase, indicating an activation of photoprotective mechanism. Our findings suggest that negative influences of low light occur at both low‐light exposure and recovery phases, but submerged macrophytes would acclimate to light environments. Transcriptome can show molecular basis of plant responses/acclimations, including but not limited to morphology. This study establishes a bridge connecting morphological and molecular responses/acclimations. [ABSTRACT FROM AUTHOR]

Abstract Light intensity is a determinant for submerged macrophytes. Little is known about their molecular responses to low‐light exposure, despite more informative and responsive than morphological traits. For erect‐type submerged macrophytes, the stem is more crucial relative to the leaf in acclimation to low‐light stress, but receives less attention. We determined morphological and stem transcriptomic responses/acclimations of Hydrilla verticillata to extremely and mildly low light (7.2 and 36 μmol photons m−2 s−1, respectively), that is, EL and ML, with the radiation intensity of 180 μmol photons m−2 s−1 as the control. Low‐light exposure continued for 9 days, followed by a 7‐day recovery phase (180 μmol photons m−2 s−1). At the exposure phase, the low‐light treatments, in particular the EL, decreased the relative growth ratio, but induced greater height and longer stem internode distance and epidermal cell. Such responses/acclimations continued into the recovery phase, despite more or less changes in the magnitude. Transcriptome showed that the photosynthetic system was inhibited at the exposure phase, but the macrophyte adjusted hormone synthesis relating to cell division and elongation. Moreover, the EL activated cell stress responses such as DNA repair. Following light recovery, the macrophyte exhibited a strong‐light response, although energy metabolism enhanced. Especially, the EL enriched the pathways relating to anthocyanin synthesis at such phase, indicating an activation of photoprotective mechanism. Our findings suggest that negative influences of low light occur at both low‐light exposure and recovery phases, but submerged macrophytes would acclimate to light environments. Transcriptome can show molecular basis of plant responses/acclimations, including but not limited to morphology. This study establishes a bridge connecting morphological and molecular responses/acclimations.

Constructing multispecies submerged vegetation systems and maintaining stable seasonal succession is crucial for restoring shallow eutrophic lakes. However, little is known about the interactions between successional and existing species of different growth forms, particularly under the low light and high nutrient conditions of eutrophic lakes. We measured the functional traits of mature Vallisneria natans (Lour.) Hara plants and Potamogeton crispus L. shoots in monoculture and mosaic patterns under different light and nutrient conditions. The effect of light on functional traits of the submerged macrophyte species was more significant than that of nutrients, but the reverse was true for P. crispus biomass allocation. Moreover, interspecific interactions affected only the submerged macrophytes under the low light condition and varied with species. Specifically, the interaction of P. crispus to V. natans was biased towards competition, while the interaction of V. natans to P. crispus was converted from facilitation to competition by eutrophication, particularly in the homogenous mosaic growth pattern. This study demonstrates that sufficient light is a prerequisite and patch planting is an effective means to form a multispecies submerged vegetation system. In addition, we emphasize that the coexistence of eutrophication and low light will likely result in a competition between submerged macrophytes thus simplifying the vegetation, even if their growth forms and growing seasons are different. These findings help explain the collapse of multispecies submerged vegetation and guide the restoration of aquatic plants in eutrophic lakes. [ABSTRACT FROM AUTHOR]

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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-benefi- cial microbes under ammonium stress in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Article Highlights Environmental factors had different effects on different forms of phosphorus transformation. The submerged macrophytes affected the migration and transformation of phosphorus by increasing pH, oxidation-redox potential and dissolved oxygen in the overlying water. H. verticillata and P. crispus acted on the different forms of phosphorus through environmental factors.

To study the response of the Vallisneria natans morphological and physiology to water level change, seedlings were placed in a submerged condition at depths ranging from 50 cm to 135 cm and set the rising and declining water levels respectively (0.2 cm/d, 0.5 cm/d, 0.8 cm/d, 1.1 cm/d, 1.4 cm/d, 1.7 cm/d). After 50 days of simulation experiment, we observed the effects on plant height, the number of blades, root activity, biomass, chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (a + b) (Chl a + b), carotenoid (Car), soluble protein (SP) and soluble sugar (SS) of V. natans under different water level change rates. The results showed that (1) plant height and the number of blades showed an overall upward trend under the condition of high-rate water level change, while the low-rate change of water level showed a trend of first rising and then decreasing. (2) the root activity of 0.5–1.7 cm/d groups increased with the test time at rising water level, and the declining water level showed a trend of increasing and then decreasing. The total biomass showed an upward trend with the extension of the test time. (3) Chl a, Chl b, Chl (a + b), and Car showed a multi-peak downward trend with the extension of the test time. (4) the response of SP and SS to the test time showed a trend of first increase and then decrease with water level changes. In conclusion, our study demonstrates that the morphological and physiology of V. natans could adapt to water level changes, but it could be stressed if the water level exceeded the suitable range.

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. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) is considered a contaminant of emerging concern and interferes with the normal activities of living organisms. The toxicity of BPA is evident in animals and terrestrial plants. However, the response of aquatic plants to low BPA concentrations is still unclear. In the present study, effects of varying BPA loadings (targeting at 0.01, 0.1, and 1 mg/L) on the growth and reproductive traits of the dioecious annual submerged macrophyte Vallisneria natans were assessed through a 5-month experiment. The results showed that BPA inhibited the elongation of V. natans leaves but resulted in an increase in leaf number and ramet number under the highest BPA loading treatment (targeting at 1 mg/L). In addition, detectable biochemical changes in the total carbon and soluble sugar contents were found, which both were significantly higher at the highest BPA loading treatment. However, the total biomass did not alter significantly after the BPA treatments, indicating that BPA did not induce direct toxic effects on the growth of V. natans. At the highest BPA loading treatment, female individuals of V. natans allocated less number for ramet than male ones, showing a clear sexual dimorphism. No significant differences between the five treatments were found for the flower or fruit traits, while the germination rate was significantly inhibited for the seeds collected from the highest BPA loading treatment. In conclusion, V. natans tolerated low concentrations of BPA by making a trade-off between ramet (leaf) number and leaf elongation, as well as modulating the total carbon and soluble sugar contents. However, serious consequence of decline in seed viability implied that the impact of BPA on plant reproduction were usually underestimated. [ABSTRACT FROM AUTHOR]

Degradation of lake ecosystem is a common problem existing in many countries. Remediation of degraded lake is urgently needed in order to maintain water safety and lake ecosystem health. Restoration of submerged macrophyte is considered as an important measure of ecological remediation of shallow lakes after pollution loading get effectively controlled. Nowadays, enclosures resembling those used in aquaculture historically are widely used for submerged macrophyte restoration. Although submerged macrophyte can be successfully restored in enclosure, it's contribution to the whole lake ecological remediation is limited. Fish manipulation, which reduces fish stock and adjusts fish community structure, was found able to improve water quality and promote submerged macrophyte restoration in many lakes. However, the role of fish in ecological restoration do not receive enough attention in many ecological remediation projects. Future studies are required to better understand the role of fish in lake nutrient cycle and the influence on submerged macrophyte to help develop theory that better guide the fish manipulation for the ecological remediation in shallow lakes. In the end, we want to point out that manipulation of fish community structure following by natural restoration and/or artificial planting of submerged macrophyte could be an effective strategy for whole lake ecological remediation of shallow lakes, and suggest that fish manipulation measure should be tested in more ecological remediation projects of shallow lakes worldwide. [ABSTRACT FROM AUTHOR]

The effect of biodiversity on ecosystem productivity has been a controversial issue in ecological research. The species richness–productivity relationship is highly variable in natural ecosystems, with a positive relationship being one of the most commonly observed relationships. Previous regional studies from terrestrial ecosystems have demonstrated that environmental gradients can regulate the species richness–productivity relationship. However, how this relationship varies in freshwater ecosystems across spatial environment gradients remains unclear. In this study, we propose that the species richness–productivity relationship can be modulated by the water depth. Here, we surveyed the submerged macrophyte community structure by establishing 24 transects and 642 quadrats in Erhai Lake, Yunnan Plateau, China. Our findings highlight that the species richness–productivity relationship gradually changed from slightly positive to strongly positive as the environment became more light-limited with the increasing water depth, supporting the stress-gradient hypothesis. The results from this study provide new insights into the biodiversity–ecosystem functioning relationships and in managing lake macrophyte communities and productivity.

Interspecific interaction are playing vital roles in shaping phytoplankton structure and affecting the food webs in freshwater ecosystems. However, the responses of green algae to allelochemically competition with submerged macrophytes were mainly focused on the growth, whereas, the algal morphology changes were usually ignored. In the present study, according to co-cultivation experimentation of submerged macrophyte Egeria densa and green alga Scenedesmus obliquus with gradient initial algal density, it was demonstrated that E. densa could allelochemically suppress the growth of S. obliquus, but the shading effects should also be considered when the algal density was low. In addition, small colonies of S. obliquus with large amount were induced in the presence of E. densa. The suppressing expression of photosynthesis-related genes LhcbM and PS II D1 might lead the reduction of cell division in S. obliquus. The small but not large colonies formation might be interpreted as the inhibitory cell division and promotion of polysaccharide by allelochemicals from E. densa. Owing to the ecological significance, much more emphasis should be placed on the morphological changes induced by interspecific competition. The results would be of great help in the prediction of phytoplankton composition and structure in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

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

Tropical freshwater wetlands are subject to multiple stressors but there is little information on which stressors cause wetland degradation. Increased turbidity is considered a major cause of degradation, but the effects of introduced fish are often overlooked. Tilapia are frequently introduced in tropical regions, especially species in the genus Oreochromis, and the ecological effects of introducing tilapia are poorly studied. We used enclosure experiments in a shallow lake in Madagascar to assess the effects of tilapia and turbidity on macrophytes and benthic invertebrates, and to test management interventions designed to increase both. Tilapia at high and low stocking densities had negative effects on survival of Charophyte algae and water lilies, but no direct effect on benthic invertebrate abundance or diversity. Invertebrate abundance was highest on submerged Charophytes, so herbivory by tilapia indirectly affected invertebrates. Turbidity affected Charophyte survival, and abundance and diversity of non-Dipteran insects. As a complication, tilapia may increase turbidity by re-suspending the lake sediment. Our results suggest that herbivory by tilapia is a plausible cause of the removal of macrophytes from the lake and an impediment to their re-establishment. Tilapia are widely introduced in tropical areas as a food resource. Our results demonstrate serious consequences to these introductions. [ABSTRACT FROM AUTHOR]

Aquatic macrophytes, especially Vallisneria nana , provide essential spawning habitat and food resources for the threatened Australian lungfish (Neoceratodus forsteri). The availability of V. nana for lungfish has been dramatically reduced in some areas due to flood disturbances and macrophyte recovery is inhibited by reduced hydrochory due to river fragmentation by dams. Active transplanting of macrophytes may be a feasible restoration strategy to increase abundance of macrophytes, however, in the presence of macro-herbivorous aquatic animals, replanted beds may not persist due to intensive grazing. In this study, we analyzed the effects of environmental conditions on growth and expansion of transplanted V. nana in six 60 m2 herbivore exclosures in the mid-Brisbane River in subtropical south-east Queensland. Following establishment, we also quantified the impact of aquatic herbivores on different patch sizes (15 m2 or 45 m2) of restored V. nana to test the hypothesis that larger patch sizes may confer greater resistance to grazing using a paired control/treatment design. After initial planting, V. nana grew and spread rapidly throughout the exclosure plots, with mean % cover increasing from 5% to 71% on average and mean leaf length increasing from 20 cm to 54 cm on average over 161 days. Transplanted V. nana cover was significantly positively associated with water depth and finer substrate sizes and leaf length was significantly positively associated with water depth and water velocity but was unrelated to substrate size. Exposure to grazing significantly reduced cover of V. nana , however there was no significant effects of macrophyte patch size, grazing intensity, or environmental factors on changes in V. nana cover. Complete removal of exclosure fencing resulted in near complete loss of macrophytes within 7–22 days at all plots, indicating the macrophyte beds (15 m2–60 m2) were of insufficient size to resist grazing pressure. Our findings suggest that transplanting is a viable restoration method with exclusion of grazing, which is critical for creating resistant beds to disturbances and driving future macrophyte recovery. Further research is required to evaluate the feasibility and efficacy of alternative macrophyte restoration strategies in rivers to foster hydrochory and natural regeneration processes following flood disturbance. • Greater water depth and finer substrate increased Vallisneria nana coverage. • Water velocity and depth influenced increased leaf length. • Restoration exposed to grazing significantly reduced macrophyte coverage. • First video evidence of wild Australian lungfish eating Vallisneria nana. • Removal of exclosures resulted in rapid destruction of Vallisneria nana beds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atmospheric CO 2 absorption and CH 4 emission occurred in 4 habitats in Lake Taihu. • Various seasonal fluctuations in CH 4 emissions were found in different habitats. • Highest CO 2 absorption & CH 4 emission occurred at high-density phytoplankton site. • CH 4 emissions counteracted 7–69% of CO 2 absorption across four lake habitats. • This large eutrophic lake confirmed to be a total CO 2 -eq sink. Lakes are a crucial component of global carbon cycling and play a key role in the global CO 2 and CH 4 budgets. Intensified anthropogenic activity contributes to eutrophication, and reduces macrophytes while increasing phytoplankton in shallow lakes. However, the information on how the CO 2 and CH 4 fluxes at water–air interface temporally varies across habitats dominated by various primary producers in lakes and how CH 4 emission counteracts CO 2 adsorption is limited. In this study, in situ fluxes of CO 2 and CH 4 were measured monthly for one year at four sites in Lake Taihu, China. These sites had contrasting habitats dominated by high-density phytoplankton, low-density phytoplankton, floating-leaved macrophytes, and submerged macrophytes. We found that the CO 2 fluxes ranged from − 439 ± 385 to − 106 ± 348μmol m−2h−1 and the CH 4 fluxes ranged from 1.96 ± 3.79 to 10.7 ± 14.8μmol m−2h−1. The fluxes of CO 2 and CH 4 were mainly regulated by water pH, phosphorus levels, and sediment organic carbon. All four habitats acted as sinks of atmospheric CO 2 and sources of atmospheric CH 4 , and the habitats with high-density phytoplankton showed the highest CO 2 absorption and strongest CH 4 emission. Generally, the CH 4 emission counteracted 7–69 % of the atmospheric CO 2 absorption in the four sites. These results collectively revealed that in a large, shallow eutrophic lake, habitats dominated by various primary producers consistently adsorb atmospheric CO 2 , even being counteracted by CH 4 emission. These findings provide valuable insights for understanding carbon cycling and CO 2 and CH 4 dynamics across the water–air interface in shallow lakes. [ABSTRACT FROM AUTHOR]

The preservation of biodiversity is crucial for sustaining ecosystem functioning, and recently the ongoing loss of biodiversity in lake ecosystems due to human activities has raised significant concerns. This study aimed to assess the impact of human activities on the biodiversity of aquatic plants through long-term empirical evidence. By comparing species composition and genetic diversity of submerged macrophyte within last decade, this research focused on the long-term changes of submerged macrophyte biodiversity resulting from human disturbances and restoration efforts. Three plateau lakes - Lake Erhai, Lake Fuxianhu, and Lake Jianhu - were selected as study sites, exhibiting varying biodiversity alterations in response to different levels of human disturbance and restoration activities. The oligotrophic Lake Fuxianhu demonstrated a stable level of both biodiversity levels, and the eutrophic Lake Jianhu exhibited a significant reduction in species diversity and genetic diversity. Meanwhile, the strong restoration measures in Lake Erhai between the 2010s and the 2020s effectively safeguard species diversity and alleviate declines in genetic diversity due to eutrophication during the last decade. We also found that improper use of alien species and the transplantation of clones of aquatic plant may pose ecological risks to biodiversity. Given the importance of aquatic plant re-establishment for the long-term recovery of plateau lakes, conservation strategies could prioritize large-scale propagation of aquatic plant materials through local seed banks. • This research focused on the alterations in biodiversity of submerged macrophyte in three plateau lakes over the last decade. • Lake Erhai have experienced well-preserved biodiversity and reduced losses in genetic variation. • Introducing exotic species inappropriately could lead to ecological consequences. • The use of local seed banks to propagate aquatic plants in targeted lakes to conserve biodiversity was suggested. [ABSTRACT FROM AUTHOR]

Attempts to control massive proliferations of invasive alien aquatic plants (IAAP) are often ineffective. A renewed interest for dye treatment is emerging aiming to control the submerged macrophyte Myriophyllum heterophyllum in France. We aimed to understand the effects of dye on this plant knowing about its adaptation to low light. In a 2 × 2 factorial design experiment, we assessed the effect of a dye mixture based on Brilliant Blue (E133) and Allura Red (E129) at high and low light intensities on light quantity and quality and how this might affect the plant's performance by measuring morphological and physiological traits. A multivariate analysis identified three groups – high light (HL) plants, plants in high light with dye (HLD) or low light (LL), and low light with dye (LLD) plants. HL plants performed well but showed stress signs, with a reduced main shoot length, a higher leaf dry matter content (LDMC) and a lower nitrogen content (N), not observed in plants grown in HLD or LL. HLD and LL plants exhibited a comparable total length growth rate to those in HL, but had lower LDMC and higher N contents. LLD plants performed poorly with the lowest growth and signs of physiological stress. Dye-induced changes in light quality only marginally affected the absorbance range of chlorophyll b , which apparently did not affect photosynthesis. Commercially available dyes currently used to control nuisance aquatic plants thus seem to have little or no effect on submerged macrophytes. The presence of dye may exacerbate negative effects of very low light intensities on the plant's growth. However, these very low intensities would only be reached during high-water levels or in winter, periods where the dye would rapidly be diluted. During summer, however, the application of dye may protect the plant from damaging light intensities and thus not be a good management strategy to control low light adapted invasive submerged macrophytes. • Dye treatments are used to control massive developments of aquatic alien plants. • Dye treatment had very different effects on plants at high or low light intensities. • Dye-induced changes in light quality only marginally affected plant performance. • M. heterophyllum benefited from dye application at high light. • Recommendation to avoid dye treatment of low-light adapted macrophytes. [ABSTRACT FROM AUTHOR]

To study the response of the Vallisneria natans morphological and physiology to water level change, seedlings were placed in a submerged condition at depths ranging from 50 cm to 135 cm and set the rising and declining water levels respectively (0.2 cm/d, 0.5 cm/d, 0.8 cm/d, 1.1 cm/d, 1.4 cm/d, 1.7 cm/d). After 50 days of simulation experiment, we observed the effects on plant height, the number of blades, root activity, biomass, chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (a + b) (Chl a + b), carotenoid (Car), soluble protein (SP) and soluble sugar (SS) of V. natans under different water level change rates. The results showed that (1) plant height and the number of blades showed an overall upward trend under the condition of high-rate water level change, while the low-rate change of water level showed a trend of first rising and then decreasing. (2) the root activity of 0.5–1.7 cm/d groups increased with the test time at rising water level, and the declining water level showed a trend of increasing and then decreasing. The total biomass showed an upward trend with the extension of the test time. (3) Chl a, Chl b, Chl (a + b), and Car showed a multi-peak downward trend with the extension of the test time. (4) the response of SP and SS to the test time showed a trend of first increase and then decrease with water level changes. In conclusion, our study demonstrates that the morphological and physiology of V. natans could adapt to water level changes, but it could be stressed if the water level exceeded the suitable range. [ABSTRACT FROM AUTHOR]

Context: Submerged macrophytes develop great phenotypic plasticity responding to light stress. However, the light effects on carbon (C), nitrogen (N) and phosphorus (P) stoichiometry of submerged macrophytes are unknown. Aims: To determine the stoichiometric response of Myriophyllum spicatum and Vallisneria natans to a light gradient. Methods: We determined the C, N and P stoichiometry of two aquatic plants grown in pots subjected to an incident light gradient ranging from 100 to 17% of incident light. Key results: The C, N and P stoichiometry of V. natans (except C:N of root) were not significantly different among the light treatments, whereas those of M. spicatum (except leaf element concentrations and root element ratios) showed significant differences across the light gradient. The analysis of variance results implied that the species, plant organs and their interactions explained more than 75% of total variance of all measured indices (except C). Conclusions: The C, N and P stoichiometry of the two studied submerged macrophytes are more affected by plant organs and species than by light irradiance. Implication: Although C, N and P stoichiometry of submerged macrophytes was little affected by light irradiance, whether the stoichiometry of submerged macrophytes is stable under other environmental factors should be focused on in future investigation. We determined the C, N and P stoichiometry of two aquatic plants grown in pots subjected to an incident light gradient ranging from 100 to 17% of incident light. Whereas the C, N and P stoichiometry of V. natans and M. spicatum were little influenced across the light gradient, they were more affected by plant organs and species than by light irradiance. [ABSTRACT FROM AUTHOR]

Due to climate change and increasing anthropogenic activities, lakes are disturbed frequently, usually by press (e.g., diffused pollution, rising temperatures) or pulse (e.g., storms, rainfall, pollution events) disturbances. Both press and pulse disturbances can affect abiotic and biotic environments, changing the structure of ecosystems and affecting ecosystem services. To confront with the effects of climate change and increasing anthropogenic activities, understanding the different effects of press and pulse disturbances on lake ecosystems is essential. This study assessed the effect of press and pulse disturbances of phosphorus on a microcosmic aquatic ecosystem by measuring the total phosphorus (TP), algae density, and physiological indicators of submerged macrophytes. We found that the microcosmic aquatic ecosystem responded differently to press and pulse disturbances. Our results suggested that it had a lower resistance to pulse phosphorus disturbances than to press phosphorus disturbances. There were significantly higher nutrient concentrations and algal densities in the pulse treatment than in the press treatment. Positive feedback was found between the biomass of submerged macrophytes and the water quality. There was a higher submerged macrophytes biomass at low TP concentration and algal density. In the context of climate change, press and pulse disturbances could have severe impacts on lake ecosystems. Our findings will provide some insight for further research and lake management. [ABSTRACT FROM AUTHOR]

Abstract Rosette‐type submerged macrophytes are widely distributed across a range of water depths in shallow lakes and play a key role in maintaining ecosystem structures and functions. However, little is known about the rapid adaptive responses of such macrophytes to variations in water depth, especially at the juvenile stage. Here, we conducted a short‐term in situ mesocosm experiment, in which the juveniles of Vallisneria natans were exposed to a water depth gradient ranging from 20 to 360 cm. Twenty‐two leaf‐related traits were examined after 4 weeks of growth in a shallow lake. Most (18) traits of V. natans generally showed high plasticity in relation to water depth. Specifically, juveniles allocated more biomass to leaves and had higher specific leaf area, leaf length‐to‐width ratio, chlorophyll content, and carotenoids content in deep waters, displaying trait syndrome associated with high resource acquisition. In contrast, V. natans juveniles in shallow waters had higher leaf dry matter content, leaf soluble carbohydrate content, carotenoids per unit chlorophyll, and peroxidase activity, pertaining to resource conservation. Notably, underwater light intensity was found to be the key factor explaining the trait plasticity along the water depth gradient, and 1.30 mol photons m−2 d−1 (at 270 cm) could be the optimal irradiance level based on the total biomass of V. natans juveniles. The present study highlights the significance of leaf trait plasticity for rosette‐type macrophytes in response to variations in water depth and sheds new light on the differences between trade‐offs in deep‐ and shallow‐water areas.

Abstract Due to climate change and increasing anthropogenic activities, lakes are disturbed frequently, usually by press (e.g., diffused pollution, rising temperatures) or pulse (e.g., storms, rainfall, pollution events) disturbances. Both press and pulse disturbances can affect abiotic and biotic environments, changing the structure of ecosystems and affecting ecosystem services. To confront with the effects of climate change and increasing anthropogenic activities, understanding the different effects of press and pulse disturbances on lake ecosystems is essential. This study assessed the effect of press and pulse disturbances of phosphorus on a microcosmic aquatic ecosystem by measuring the total phosphorus (TP), algae density, and physiological indicators of submerged macrophytes. We found that the microcosmic aquatic ecosystem responded differently to press and pulse disturbances. Our results suggested that it had a lower resistance to pulse phosphorus disturbances than to press phosphorus disturbances. There were significantly higher nutrient concentrations and algal densities in the pulse treatment than in the press treatment. Positive feedback was found between the biomass of submerged macrophytes and the water quality. There was a higher submerged macrophytes biomass at low TP concentration and algal density. In the context of climate change, press and pulse disturbances could have severe impacts on lake ecosystems. Our findings will provide some insight for further research and lake management.

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. [ABSTRACT FROM AUTHOR]

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ABSTRACT Submersed macrophytes have important ecological roles but non-native invasive species may affect biodiversity and water uses. We investigated the native macrophyte Egeria najas and the invasive Hydrilla verticillata and measured their maximum colonization depth and its relationship with Secchi disk depth, their biomass along the depth gradient and their preferred depths of occurrence. The Itaipu Reservoir was monitored for seven years, during which maximum colonization depth and Secchi disk depth were measured. During a separate sampling, plants were collected to determine biomass along the depth gradient. Ancova showed that the maximum colonization depth of both species increased with increasing Secchi disk depth, but the maximum colonization depth of H. verticillata increased faster with increasing water transparency than did that of E. najas. Quadratic regression revealed that the biomass of each species peaks at intermediate depths. Hydrilla verticillata colonizes deeper regions than does E. najas. The patterns found in the present study can be explained by underwater light and, probably, wave disturbances. The preference of H. verticillata for deeper sites indicates that the ecological niches of the two macrophytes differ, and that H. verticillata has great potential to spread and accumulate biomass in reservoirs.

Abstract Spatiotemporal variation in community composition is of considerable interest in ecology. However, few studies have focused on seasonal variation patterns in taxonomic and functional community composition at the fine scale. As such, we conducted seasonal high‐density sampling of the submerged macrophyte community in Hongshan Bay of Erhai Lake in China and used the generalized dissimilarity model (GDM) to evaluate the effects of environmental factors and geographic distance on taxonomic and functional beta diversity as well as corresponding turnover and nestedness components. At the fine scale, taxonomic turnover and nestedness as well as functional turnover and nestedness showed comparable contributions to corresponding taxonomic and functional beta diversity, with different importance across seasons. All taxonomic and functional dissimilarity metrics showed seasonal variation. Of note, taxonomic beta diversity was highest in summer and lowest in winter, while functional beta diversity showed the opposite pattern. Taxonomic and functional turnover showed similar change patterns as taxonomic and functional beta diversity. Taxonomic nestedness was low in summer and high in winter. Functional nestedness was also lower in summer. These results suggest that under extreme environmental conditions, both turnover and nestedness can exist at the fine scale and seasonal community composition patterns in submerged macrophytes should be considered. Future investigations on community assembly mechanisms should pay greater attention to long‐term dynamic characteristics and functional information.

• Restoration of submerged vegetation mitigated nutrient loads in sediment-water systems. • Submerged vegetation reduced the abundance of most nitrogen cycling genes and increased that of phosphorus cycling genes. • Diversity differently affects sediment nutrients and microbiomes, mainly due to plant life cycles. The release of nitrogen and phosphorus from sediments, known as internal nutrient loading, plays a crucial role in determining the eutrophic state of lakes and the timeframe for their ecological recovery. The restoration of submerged macrophytes is considered an effective measure to improve lake eutrophication. However, the impact of submerged macrophytes restoration on the storage and transformation mechanisms of nitrogen and phosphorus in lake sediment-water systems has not yet been systematically studied. This study constructed two submerged macrophyte communities with species richness of either two or five and monitored the physicochemical characteristics, nitrogen and phosphorus dynamics, and the structural and functional changes of sediment microbiomes in the plant-water-sediment system during three growth stages of the plants (May, July, and October). Our results demonstrated that the presence of submerged vegetation effectively reduced the nitrogen and phosphorus loads in the sediment-water system, encompassing their chemical forms, active concentrations, and release fluxes. Simultaneously, the restoration of submerged vegetation altered the composition of sediment microbial communities and the nitrogen and phosphorus cycling functions. Following the restoration, the abundance of functional genes associated with nitrogen fixation, organic nitrogen metabolism, nitrate reduction, and nitrification exhibited an average decrease of 2.95 %. In contrast, the abundance of genes involved in denitrification and nitrogen limitation response regulation increased by 20.24 %, while those related to phosphorus cycling processes showed a 7.29 % increase. Additionally, submerged macrophyte communities with varying richness differentially affected lake nitrogen and phosphorus loads, as well as the structure and function of sediment microbiomes, primarily related to the life cycle stages of the submerged macrophytes. These findings highlight the crucial role of submerged plants in maintaining lake nutrient balance and sediment microbiomes, providing valuable insights into how the restoration of submerged vegetation affects nutrient cycling in aquatic ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Background The effects of biodiversity on community function and services are frequently studied in the history of ecology, while the response of individual species to biodiversity remains great elusive. In this study, we determined the biodiversity effects on community productivity as well as species level plant mass and carbon (C) and nitrogen (N) metabolism of eight submerged plants. These macrophytes in Lake Erhai were selected and planted in a water depth of one meter along a diversity gradient of 1, 2, 4 or 8 species. Then, the community productivity or species level plant mass, soluble protein, free amino acid and soluble carbohydrate were correlated to species richness to determine the biodiversity effects on community and single species. Results The results showed that the community level biomass was positively correlated to plant species richness although the species level plant mass of individual species responded differently to the overall plant species richness. Namely, only one plant mass positively correlated to species richness and the others decreased or showed no significant correlation with the increase of species richness. The soluble proteins of most macrophytes were positively correlated to species richness; however, both the free amino acid and soluble carbohydrate of the plants were negatively or not significantly correlated to species richness. Conclusions These results indicated that the selection effects might dominate in our aquatic communities and the negative impacts of biodiversity on C and N metabolism of the macrophytes increased with the increase of species richness, which might result from the strong competition among the studied species. The biodiversity effects on the plant mass, and C and N metabolism of individual submerged species were first reported in this study, while more such field and control experiments deserve further research.

• Toxicity of recycled and pristine PVC-MPs were compared under four Cd levels. • Recycled PVC-MPs had more adverse effects on physiological traits than the pristine. • Recycled PVC-MPs affected growth more negatively than the pristine at high Cd levels. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • LMA capping combined with macrophyte (Vallisneria natans) enhanced the immobilization of P in sediments. • A new sediment–water interface was generated after LMA capping, which promoted the growth of Vallisneria natans roots. • Mobile P in black odorous sediments had the highest reduction rates when capping with LMA. As a kind of phosphorus (P) inactivating agent, lanthanum-modified attapulgite (LMA) has effectively been used for controlling the release of P from sediments. However, the effects of LMA on sediments from different types of ecological environments, especially in the rhizosphere of macrophyte, have not yet been studied. In this study, sediments from black-odor rivers (Black-S), cyanobacteria blooms-dominated lake (Algal-S) and macrophyte-dominated lake (Phytic-S) were collected for laboratory-scale microcosmic experiments. The results indicated that LMA had a good inactivation effect on mobile P (sum of Labile-P, Fe-P and organic-P) in three types of sediments, and significantly reduced soluble and labile P in pore water. The rates of reduction of mobile P in Black-S and Algal-S were much higher than that in Phytic-S. LMA capping generated a new sediment water interface, which significantly promoted the growth of roots, the release of oxygen from Vallisneria natans , and the secretion of organic acids to improve the rate of utilization of P in sediments. Meanwhile, the addition of LMA increased the relative abundance of Sideroxydans in the rhizosphere of Vallisneria natans. The study provides a new insight into the applications of LMA capping combined with macrophyte in the restoration of sediments obtained from different ecological settings. [ABSTRACT FROM AUTHOR]