Myriophyllum Spicatum Research Articles

Bioturbation Affects Bioaccumulation: PFAS Uptake from Sediments by a Rooting Macrophyte and a Benthic Invertebrate.

Despite the widespread presence of per- and polyfluoroalkyl substances (PFAS) in freshwater environments, only a few studies have addressed their bioaccumulation in macrophytes and benthic invertebrates. This study therefore aimed at investigating the presence of 40 PFAS in sediments, assessing their bioaccumulation in a rooting macrophyte (Myriophyllum spicatum) and a benthic invertebrate (Lumbriculus variegatus) and examining the effects of the presence and bioturbation activity of the invertebrate on PFAS bioaccumulation in the plants. The macrophytes were exposed to sediments originating from a reference and a PFAS-contaminated site. The worms were introduced in half of the replicates, and at the end of the experiment, PFAS were quantified in all environmental compartments. Numerous targeted PFAS were detected in both sediments and taken up by both organisms, with summed PFAS concentrations in organisms largely exceeding concentrations in the original sediments. Bioaccumulation differed between organisms and the two sediments. The presence of the worms significantly reduced the PFAS concentrations in the plant tissues, but for some compounds, root bioaccumulation increased in the presence of the worms. This effect was most prominent for the degradable PFAS precursors. It is concluded that organisms affect the environmental fate of PFAS, emphasizing that contaminant-macroinvertebrate interactions are two-sided.

Findings of Aquatic Vascular Plants on the Sakhalin Island

Investigations of South-western geobotanical district of Sakhalin Island, which is classified as a separate subzone of dark coniferous forests with an admixture of broad-leaved species and corresponds to Krillon floristic district, revealed a number of new aquatic vascular plant species for that area (Lemna turionifera, Myriophyllum verticillatum, Potamogeton gramineus, P. manchuriensis, Stuckenia pectinata, Utricularia minor, U. × ochroleuca). There is also a novelty for the South-Sakhalin lowland geobotanical district (Myriophyllum spicatum). All these taxa are known from other geobotanical districts of Sakhalin. The additions to the flora of the South-western district, which is well surveyed by botanists, indicate not floristic uniqueness of the subzone of dark coniferous forests with an admixture of broad-leaved species, but rather a poor knowledge of the Sakhalin Island aquatic flora.

Differential photosynthetic yield across a wide range of temperatures for Northern and invasive Watermilfoils

Eurasian watermilfoil (Myriophyllum spicatum) is one of the most challenging invasive aquatic plant species in Minnesota. Eurasian watermilfoil has hybridized with the native Northern watermilfoil (Myriophyllum sibiricum), creating a more complex issue when it comes to invasions. The hybridization of watermilfoil has increased difficulty for management and an underlying biological mechanism explaining this difficulty has yet to be determined. We compared the photosynthetic temperature response of the parental Northern and Eurasian parental genotypes to five hybrid watermilfoils using pulse amplitude modulated (PAM) chlorophyll fluorometry to determine if there are intrinsic physiological differences in photosynthesis between genotypes. We examined both the ratio of variable to maximal fluorescence (Fv/Fm) and light-adapted quantum yield of photosystem II (PSII) electron transfer (ΦPSII) every 5 °C from 0 to 45 °C representing sub- to supraoptimal water temperatures. On average, hybrids had 6% and 8% higher Fv/Fm and ΦPSII values respectively, than parental genotypes across all temperatures. In both parental and hybrid genotypes Fv/Fm values were consistent from 0 to 35 °C and declined 36% as water temperature approached 45 °C. Optimal water temperature for ΦPSII was between 25-35 °C and hybrids had 17% higher values for suboptimal temperatures between 5-15 °C. Our findings indicate that although the many strains of watermilfoil are morphologically similar, they differ in their photosynthetic capacity and may indicate heterosis. Innate differences between parental strains and hybrids could impact overall primary productivity, life history characteristics, and overall invasiveness. These factors could also be contributing to the documented management failures seen in field populations.

Regeneration and colonization abilities of submerged macrophytes under different fragment types and lengths: comparison of the invasive species Myriophyllum aquaticum and the native species Myriophyllum spicatum

Abstract Alien invasive species usually have strong regeneration and colonization abilities. However, whether invasive species have advantages in term of regeneration and colonization ability over native species requires further exploration. In this study, the effects of fragment types (with and without apical tips) and lengths (5, 10, and 15 cm) on the regeneration and colonization abilities of the invasive Myriophyllum aquaticum (M. aquaticum) and native Myriophyllum spicatum (M. spicatum) in China were studied. Fragments of M. aquaticum and M. spicatum without apical tips had an advantage in branch formation, and their regeneration ability was stronger than that of fragments with apical tips. With longer initial fragments, the root length of M. aquaticum were longer and its colonization ability was stronger. This resulted in an increase in plant length, stem node number, and biomass, with an increase in fragment length. But the colonization ability of M. spicatum do not stronger with longer fragment. On the whole, native M. spicatum had stronger regeneration and colonization abilities than the invasive species M. aquaticum. However, M. aquaticum had a higher survival rate and plant length, enabling it to quickly occupy living spaces. Our results suggest that management needs to strengthened for both M. aquaticum and M. spicatum to avoid biological invasion.

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.

Scaling up the Natural Mode of Action of Macrophyte Allelochemicals and Their Effect on Toxic Cyanobacteria Using a Nitrogen-Limited Chemostat

This study investigates the inhibitory and hormetic effects of Myriophyllum spicatum extract on Microcystis aeruginosa in a controlled, continuous culture environment. To address the global challenge posed by harmful algal blooms, we used a range of extract concentrations to delineate the growth response patterns. At very low concentrations (6.25 and 12.5 mg/L), the addition of M. spicatum extract shows no discernible reduction in M. aeruginosa cell density or growth rate; instead, a slight increase is observed during exposure, suggesting a hormetic effect. However, at higher concentrations (75 and 100 mg/L), there is a drastic reduction of more than 50% in cell density and growth rate at 75 mg/L, with complete inhibition at 100 mg/L, leading to pronounced oxidative stress, damage to antioxidant defense systems, and increased cell mortality. Increased levels of malondialdehyde, catalase, and superoxide dismutase activities indicate the involvement of these enzymes in combating oxidative stress. Furthermore, intracellular and extracellular microcystins were significantly decreased at higher extract concentrations (50, 75, and 100 mg/L) in a dose-dependent manner. Our results indicate a dose-dependent response and provide insight into the potential application of natural water treatment solutions. Implications for ecological management and future research directions are discussed.

Native macrophyte community response to water-level manipulation for an invasive species

Disturbance regimes related to water level fluctuation play an important role in the structuring of aquatic macrophyte communities. In managed systems, winter water level drawdowns have shown promise in controlling populations of nuisance macrophytes, however, drawdowns may have unintended negative consequences on erosion, fauna, and non-target plant species. The Chippewa Flowage, located in Sawyer County, WI, has implemented targeted winter water level drawdowns with the goal of reducing nuisance levels of Myriophyllum spicatum. To evaluate the effects of water level drawdowns on Myriophyllum spicatum and the native macrophyte community, we conducted repeated full lake surveys of aquatic macrophytes at 2018 points under drawdown and normal water level management in 2005/06, 2015, and 2017. We supplemented these efforts with downscaled surveys in 2007, 2010, and 2016. Surveys revealed a statistically significant decline in both Myriophyllum spicatum occurrence and abundance, and average macrophyte abundance during active drawdown management. Kernel distributions of change in point-specific c-value between the two time periods showed a significant increase under drawdown conditions, and a decrease under normal management (D = 0.41, P ≤0.0001). Drawdown management appeared to successfully control Myriophyllum spicatum abundance and allowed for improvements in the floristic quality of the macrophyte community but resulted in reduced macrophyte abundance overall.

Establishment of a Flow-Through System for the Macrophyte Growth Inhibition Test (OECD 239) Including Photosynthetic Activity Measurement to Determine Early Effects.

Maintaining constant exposure concentrations during ecotoxicological studies while testing rapidly degradable substances is a challenge. To achieve stable concentrations during exposure, flow-through systems are used. To assess the impact of substances on higher aquatic plants, the 14-day macrophyte water-sediment Myriophyllum spicatum growth inhibition test (Organisation for Economic Co-operation and Development [OECD, 2014a] test guideline 239) only includes a static or a semistatic test design. The main aim of our study was to investigate the applicability of a flow-through system for M. spicatum. The standard OECD test design was miniaturized, and a flow-through system with spill-over was developed to achieve stable exposure concentrations of a rapidly degrading substance. The main endpoints were total shoot length and fresh and dry weight. Photosynthetic activity was used as an endpoint for the identification of early effects using the noninvasive Image-Producing Pulse Amplitude Modulation (IMAGING-PAM) procedure. Atorvastatin (AV; fast degrading) and bentazone (BT; photosynthesis inhibitor) were used as model substances to observe differences of the effect concentration depending on the test design. At higher exposure levels of AV, stronger necrosis combined with lower effect concentrations was observed in the flow-through test compared with the semistatic test, indicating the applicability of the flow-through test for evaluating degradable substances. The test with BT demonstrated a concentration-dependent decrease in the photosynthetic yield (Y(II)) from day 3 onward even before macroscopically visible changes occurred. Our results show that the flow-through system in the macrophyte growth inhibition test (OECD test guideline 239; 2014a) is a suitable alternative when one is testing rapidly degradable substances such as AV. In addition, we showed that photosynthetic yield can serve as a supplementary endpoint, when one is testing substances with photosynthesis inhibition as a mode of action. Environ Toxicol Chem 2024;00:1-12. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Mechanisms of ammonium detoxification in submerged macrophytes under shade conditions

Excessive ammonium disrupts the biological and physical characteristics of aquatic freshwater ecosystems, causing nutrient imbalances and toxicity. Different macrophytes exhibit varying tolerance levels to ammonium stress, influenced by species-specific adaptations. However, eutrophic water bodies not only have high nutrient loads but also exhibit low light transparency, necessitating an understanding of how submerged macrophytes cope with both high ammonium concentrations and low light conditions. In this study, we explored the tolerance of submerged macrophytes under these challenging conditions by testing various ammonium concentrations and light intensities. Our findings reveal that Myriophyllum spicatum demonstrates high ammonium tolerance under both optimal and low light intensities. Specifically, under optimal light, the primary ammonium assimilation pathway is catalyzed by NADH-GDH (Nicotinamide Adenine Dinucleotide-dependent Glutamate Dehydrogenase), with its activity increasing 4-fold at 50 mg L−1 [NH4+-N] compared to the control. Conversely, under low light intensity, the GS (Glutamine Synthetase)-catalyzed pathway becomes predominant, with GS activity rising 3-fold at 50 mg L−1 [NH4+-N] compared to the control. These results provide new insights into the adaptive mechanisms of M. spicatum, highlighting its flexible strategies for ammonium assimilation and its potential application in water restoration efforts. This study offers valuable information on the enzymatic pathways involved in ammonium detoxification, which is essential for developing effective strategies to manage and restore eutrophic aquatic systems.

Inorganic carbon utilization strategies of plateau aquatic plants in response to native habitats.

Aquatic plants are a crucial component of the aquatic ecosystem in the Tibetan Plateau region. Researching the adaptability of plateau aquatic plants in photosynthesis to the plateau environment can enhance understanding of the operational mechanisms of plateau ecosystems, thereby providing a scientific basis for the protection and management of plateau aquatic ecosystems. This study presents an investigation of photosynthetic inorganic carbon utilization strategies and photosynthetic efficiency of 17 aquatic plants under natural growing conditions in Niyang River basin on the Tibetan Plateau. In pH-drift experiments, 10 of 17 species were able to utilize HCO3-, and environmental factors like water pH were shown to have a significant effect on the ability of the tested species to utilize HCO3-. Titratable acidity in the leaves of Stuckenia filiformis, Zannichellia palustris, Batrachium bungei, and Myriophyllum spicatum showed significant diurnal fluctuations at certain sampling sites, indicating the presence of CAM. In B. bungei, water pH positively correlated with CAM activity, while CO2 concentration negatively correlated with CAM activity. The chlorophyll fluorescence analysis revealed that aquatic plants inhabiting the Tibetan Plateau exhibited photosynthetic adaptations. In conclusion, the aquatic plants on the Tibetan Plateau employ diverse strategies for utilizing inorganic carbon during photosynthesis, exhibiting their flexible adaptability to the native high-altitude habitats of the Tibetan Plateau.

Eurasian watermilfoil (Myriophyllum spicatum) alters its root topology but conserves its root branching in response to freshwater cultural eutrophication

Cultural eutrophication is the main cause of the decline of submerged plants in freshwater ecosystems. While many studies have focused on the nutrient uptake by the roots of these plants, less attention has been given to the effects of eutrophication on root structure. We designed a mesocosm experiment with Eurasian watermilfoil (Myriophyllum spicatum), a submerged plant indigenous to the Eurasian continent. The responses of plant functional traits, including growth traits, morphological traits and root topological indices, to different nitrogen (N) and phosphorus (P) concentrations were elucidated. We found that high P concentrations suppressed all the morphological traits and reduced the root topological traits, whereas N concentrations had a comparatively minor effect. Although the root branching of M. spicatum did not change, its root topology became more dichotomous with fewer exterior root links being formed in nutrient-rich habitats, and the root form changed from deep and thin to shallow and dense with increasing P concentrations. The root nutrient absorption ability of M. spicatum may decrease with cultural eutrophication, and this change most likely reduces its anchoring ability and increases its sensitivity to dislodge from the sediment if disturbed by hydraulic forces.

SedaDNA reveals mid-to late Holocene aquatic plant and algae changes in Luanhaizi Lake on the Tibetan Plateau

Aquatic plants and algae are the primary producers in lake ecosystems, providing the organic matter and oxygen necessary for the nutrients and energy of most organisms. Climatic and environmental changes may have irreversible impacts on aquatic plants and algae communities, while direct observation and experiments can only provide a short-term perspective. As a record of the long-term variation of the ecosystem, sedimentary ancient DNA (sedaDNA) could offer evidence about aquatic plants and algae change over extended time scales and improve the taxonomic resolution than the traditional morphology methods such as pollen and macrofossil. In this study, we employed metagenomics in sedaDNA from Luanhaizi Lake (northeastern Tibetan Plateau) since 8.2 cal kyr BP, to characterize the aquatic plant and algae communities' response to the climatic and environmental change over an extended historical timeline. The results demonstrate that during 8130–4620 cal yr BP, pondweed (Stuckenia) was the dominating aquatic plant in Luanhaizi Lake, with a generally low diversity of aquatic plants and algae. During 3670–2290 cal yr BP, Luanhaizi Lake had an increased diversity and triggered a shift from Stuckenia to Eurasian watermilfoil (Myriophyllum). During 1810–50 cal yr BP, with the warming process, cyanobacteria appeared and diversity peaked. Correlation and redundancy analyses show that this process might be related to climatic and environmental changes, such as decreased salinity, increased temperature, and higher water levels. Our results signify that aquatic plants and algae communities are sensitive to paleoclimatic and environmental change, in the context of global warming, the studies on the past dynamics of aquatic plants and algae will help predict the potential changes of the lake ecosystem on the northeastern Tibetan Plateau in the future.

Nutrient enrichment, propagule pressure, and herbivory interactively influence the competitive ability of an invasive alien macrophyte Myriophyllum aquaticum.

Freshwater ecosystems are susceptible to invasion by alien macrophytes due to their connectivity and various plant dispersal vectors. These ecosystems often experience anthropogenic nutrient enrichment, favouring invasive species that efficiently exploit these resources. Propagule pressure (reflecting the quantity of introduced individuals) and habitat invasibility are key determinants of invasion success. Moreover, the enemy release hypothesis predicts that escape from natural enemies, such as herbivores, allows alien species to invest more resources to growth and reproduction rather than defense, enhancing their invasive potential. Yet, the combined impact of propagule pressure, herbivory, and nutrient enrichment on the competitive dynamics between invasive alien macrophytes and native macrophyte communities is not well understood due to a paucity of studies. We conducted a full factorial mesocosm experiment to explore the individual and combined effects of herbivory, nutrient levels, propagule pressure, and competition on the invasion success of the alien macrophyte Myriophyllum aquaticum into a native macrophyte community comprising Vallisneria natans, Hydrilla verticillata, and Myriophyllum spicatum. This setup included varying M. aquaticum densities (low vs. high, simulating low and high propagule pressures), two levels of herbivory by the native snail Lymnaea stagnalis (herbivory vs no-herbivory), and two nutrient conditions (low vs. high). Myriophyllum aquaticum was also grown separately at both densities without competition from native macrophytes. The invasive alien macrophyte M. aquaticum produced the highest shoot and total biomass when simultaneously subjected to conditions of high-density intraspecific competition, no herbivory, and low-nutrient availability treatments. Moreover, a high propagule pressure of M. aquaticum significantly reduced the growth of the native macrophyte community in nutrient-rich conditions, but this effect was not observed in nutrient-poor conditions. These findings indicate that M. aquaticum has adaptive traits enabling it to flourish in the absence of herbivory (supporting the enemy release hypothesis) and in challenging environments such as intense intraspecific competition and low nutrient availability. Additionally, the findings demonstrate that when present in large numbers, M. aquaticum can significantly inhibit the growth of native macrophyte communities, particularly in nutrient-rich environments. Consequently, reducing the propagule pressure of M. aquaticum could help control its spread and mitigate its ecological impact. Overall, these findings emphasize that the growth and impacts of invasive alien plants can vary across different habitat conditions and is shaped by the interplay of biotic and abiotic factors.

Endothall and 2,4-D Activity in Milfoil Hybrid (Myriophyllum spicatum × M. sibiricum) when Applied Alone and in Combination

Abstract Eurasian watermilfoil (Myriophyllum spicatum L.) is an invasive aquatic plant that can hybridize with the native Northern watermilfoil (Myriophyllum sibiricum Kom.). These milfoil hybrids (M. spicatum × M. sibiricum) are becoming more prevalent in many lakes where the invasive and the native milfoil co-occur. Hybrid plants are more vigorous than either parent with a faster growth rate and lower sensitivity to some herbicides. The aquatic herbicides, endothall and 2,4-D, provide two effective modes of action (MOA) for management of the hybrids. For more than a decade, these two herbicides have been used in combination as an effective control option and a resistance management strategy. How this combination impacts herbicide movement and efficacy is unknown. Therefore, the objective of this research was to determine the activity of endothall and 2,4-D combined compared to activity applied alone. Absorption and translocation of endothall, 2,4-D and the combination was determined in hybrid plants over a 96-h time course. Endothall bioaccumulation was not impacted when these herbicides were applied in combination; however, 2,4-D accumulation increased by 80%, relative to when 2,4-D was applied alone. Endothall translocation from shoots to roots decreased by almost 50% when applied in combination with 2,4-D (alone = 16.7% ± 2.6; combination = 9.2% ± 1.2). Shoot-to-root translocation of 2,4-D also decreased when the two herbicides were applied in combination (24.8% ± 2.6 when applied alone to only 3.93% ± 0.4 when in the presence of endothall). This research demonstrates that combining herbicides can significantly impact herbicide activity in plants. Future research is needed to determine if this reduced translocation negatively impacts operational effectiveness when these herbicides applied in combination.

High diversity of macrophytes in the »green river« Krka (Slovenia)

AbstractThe presence, abundance, and distribution of aquatic macrophytes and their growth forms in the river Krka in Slovenia were studied. The studied slow‐flowing lowland River Krka is also called a »green river« since it is overgrown with macrophytes from its source to its outflow to the river Sava. The environmental parameters of the river ecosystem were also assessed using the modified version of the RCE (Riparian, Channel, and Environmental Inventory) method. Within 24 sections reaching from 100 to 250 m, 23 taxa of macrophytes were found. Sections were distributed noncontinuously from the source to the outflow more or less equally along the river course. The invasive alien species Elodea canadensis reached the highest relative abundance, followed by Ranunculus trichophyllus, Potamogeton crispus, Myriophyllum spicatum, Ceratophyllum demersum, and Potamogeton nodosus. Potamogeton crispus was present in most of the studied sections followed by Nasturtium officinale and M. spicatum. The river offers suitable conditions for the high diversity of macrophytes regarding the type of substrate, low flow velocity, heterogeneity of habitats, and relatively high concentrations of nutrients. In comparison to the survey performed in 2003, when the river Krka was surveyed continuously from the source to the outflow, we found that seven of the submerged and natant macrophytes were not detected in 2020. Macrophytes, growing in the river Krka, indicated meso‐ to eutrophic conditions. Five species recorded in the river Krka are listed on the Red list of endangered species in Slovenia, indicating the need to conserve the river ecosystem.

Foundation species stabilize an alternative eutrophic state in nutrient-disturbed ponds via selection on microbial community.

Eutrophication due to nutrient addition can result in major alterations in aquatic ecosystem productivity. Foundation species, individually and interactively, whether present as invasive species or as instruments of ecosystem management and restoration, can have unwanted effects like stabilizing turbid eutrophic states. In this study, we used whole-pond experimental manipulations to investigate the impacts of disturbance by nutrient additions in the presence and absence of two foundation species: Dreissena polymorpha (a freshwater mussel) and Myriophyllum spicatum (a macrophyte). We tracked how nutrient additions to ponds changed the prokaryotic and eukaryotic communities, using 16S, 18S, and COI amplicon sequencing. The nutrient disturbance and foundation species imposed strong selection on the prokaryotic communities, but not on the microbial eukaryotic communities. The prokaryotic communities changed increasingly over time as the nutrient disturbance intensified. Post-disturbance, the foundation species stabilized the prokaryotic communities as observed by the reduced rate of change in community composition. Our analysis suggests that prokaryotic community change contributed both directly and indirectly to major changes in ecosystem properties, including pH and dissolved oxygen. Our work shows that nutrient disturbance and foundation species strongly affect the prokaryotic community composition and stability, and that the presence of foundation species can, in some cases, promote the emergence and persistence of a turbid eutrophic ecosystem state.

Which Has a Greater Impact on Plant Functional Traits: Plant Source or Environment?

The deterioration of water quality caused by human activities has triggered significant impacts on aquatic ecosystems. Submerged macrophytes play an important role in freshwater ecosystem restoration. Understanding the relative contributions of the sources and environment to the adaptive strategies of submerged macrophytes is crucial for freshwater restoration and protection. In this study, the perennial submerged macrophyte Myriophyllum spicatum was chosen as the experimental material due to its high adaptability to a variable environment. Through conducting reciprocal transplant experiments in two different artificial environments (oligotrophic and eutrophic), combined with trait network and redundancy analysis, the characteristics of the plant functional traits were examined. Furthermore, the adaptive strategies of M. spicatum to the environment were analyzed. The results revealed that the plant source mainly influenced the operational pattern among the traits, and the phenotypic traits were significantly affected by environmental factors. The plants cultured in high-nutrient water exhibited a higher plant height, longer leaves, and more branches and leaves. However, their physiological functions were not significantly affected by the environment. Therefore, the adaptation strategy of M. spicatum to the environment mainly relies on its phenotypic plasticity to ensure the moderate acquisition of resources in the environment, thereby ensuring the stable and efficient operation of plant physiological traits. The results not only offered compelling evidence on the adaptation strategies of M. spicatum in variable environments but also provided theoretical support for the conservation of biodiversity and sustainable development.

Short-term test for the toxicogenomic assessment of ecotoxic modes of action in Myriophyllum spicatum

In environmental risk assessment of substances, the 14-day growth inhibition test following OECD test guideline 239 is employed to assess toxicity in the macrophyte Myriophyllum spicatum. Currently, this test evaluates physiological parameters and does not allow the identification of the mode of action (MoA) by which adverse effects are induced. However, for an improved ecotoxicity assessment of substances, knowledge about their ecotoxic MoA in non-target organisms is required. It has previously been suggested that the identification of gene expression changes can contribute to MoA identification. Therefore, we developed a shortened three-day assay for M. spicatum including the transcriptomic assessment of global gene expression changes and applied this assay to two model substances, the herbicide and photosynthesis inhibitor bentazone and the pharmaceutical and HMG-CoA reductase inhibitor atorvastatin. Due to the lack of a reference genome for M. spicatum we performed a de novo transcriptome assembly followed by a functional annotation to use the toxicogenomic results for MoA discrimination. The gene expression changes induced by low effect concentrations of these substances were used to identify differentially expressed genes (DEGs) and impaired biological functions for the respective MoA. We observed both concentration-dependent numbers and differentiated patterns of DEGs for both substances. While bentazone impaired genes involved in the response to reactive oxygen species as well as light response, and also genes involved in developmental processes, atorvastatin exposure led to a differential regulation of genes related to brassinosteroid response as well as potential metabolic shifts between the mevalonate and methyl erythritol 4-phosphate pathway. Based on these responses, we identified biomarker candidates for the assessment of MoA in M. spicatum. Utilizing the shortened assay developed in this study, the investigation of the identified biomarker candidates may contribute to the development of future MoA-specific screening approaches in the ecotoxicological hazard prediction using aquatic non-standard model organisms.

Different seasonal dynamics of contrasting aquatic plants and the consequences for the submerged macrophyte biodiversity

Global warming shifts climate zones to the north, resulting in changes in biodiversity. One of the species adaptation strategies to survive is to change their phenology. In temperate climate, most aquatic plants show their peak of biomass in summer. In our study, we hypothesised that the rare charophyte Lychnothamnus barbatus and the partially invasive vascular plant Myriophyllum spicatum may apply a different seasonality and cause a decrease in the biodiversity of submerged macrophytes. The object of our study was a mesotrophic temperate lake in Western Poland with abundant submerged vegetation, where macrophyte seasonality was studied from November 2015 to November 2019 (autumn, spring, summer). Altogether, 29 taxa of plants were recorded, including 13 species of charophytes (40 % of the Polish charophyte flora) but only four species co-dominated, two eutrophic vascular plants, Ceratophyllum demersum and M. spicatum, and two charophytes, the rare mesotrophic L. barbatus and common Nitellopsis obtusa. M. spicatum due to its expansiveness in the shallow littoral decreased biodiversity in the study lake. Moreover, C. demersum negatively affected the endangered L. barbatus by direct competition for habitats in the lake. L. barbatus and M. spicatum dominated in vegetation in autumn while the further two species co-dominated in summer. L. barbartus and M. spicatum seem to avoid high competition in summer, which proves a high adaptive potential with respect to climate warming. However, further study in other lakes is needed to verify the relevance of our findings in terms of the conservation of rare macrophyte species.

Monitoring the Extraordinary Ephemeral Emergence of Myriophyllum spicatum L. in the Coastal Lagoon Albufera of Valencia (Spain) and Assessing the Impact of Environmental Variables Using a Remote Sensing Approach

The Albufera of Valencia, a Mediterranean coastal lagoon, has been in a turbid state since 1974, with only four episodes of temporary water transparency in spring. Despite its average depth of 1 m and oligohaline waters, excessive turbidity, fish grazing, and toxic compounds have inhibited submerged macrophyte growth. In spring 2018, a significant area of Myriophyllum spicatum emerged and exhibited significant density until its complete disappearance in August 2018. Using Sentinel-2 and Landsat-8 imagery, we monitored water quality variables and vegetation density during these months. Our study revealed the first unique occurrence of M. spicatum in more than 40 years. A period of increased transparency from summer 2017 compared to previous years seems to be the cause of this appearance, while high summer temperatures caused its disappearance. While improving water quality may help restore submerged macrophyte meadows, our results suggest that summer maximum temperatures may inhibit recovery. Remote sensing, particularly the NDVI index, proved successful in monitoring aquatic vegetation and understanding species-environment relationships. This methodology can enhance future monitoring efforts for macrophyte colonization and expand knowledge of their occurrence and causes of disappearance in this and other similar areas.