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The effects of eutrophication on the growth and phenotypic performance of macrophytes have been widely studied. Experimental evidence suggests that an increase in the water nutrient level would promote the performance of several invasive free-floating macrophytes. However, few studies have focused on how a shift in water nutrient (nitrogen and phosphorus) stoichiometric regimes may influence the performance of invasive free-floating macrophytes. In the present study, two exotic invasive plant species, free-floating Eichhornia crassipes and Pistia stratiotes , were subjected to different water nutrient stoichiometric regimes, and their phenotypic performance was studied. We found that the two species converged in several resource use traits and diverged in lateral root length. This implied that their similarities in fitness-correlated traits and their underwater niche differentiation probably contribute to their stable coexistence in the field. Additionally, the eutrophic conditions in the different N:P regimes scarcely altered the performance of both species compared to their performance in the oligotrophic condition. Based on previous studies, we predicted that moderate eutrophication with slight overloading of nitrogen and phosphorus would not improve the performance of several invasive free-floating plants and thus would scarcely alter the invasive status of these species. However, moderate eutrophication may cause other problems, such as the growth of phytoplankton and algae and increased pollution in the water.

Free-floating aquatic plants Pistia stratiotes and Eichhornia crassipes are well-known invasive species in the tropics and subtropics. The aim of this study was to utilize the plants as cost-effective and environmentally friendly oil sorbents. Multilevel wrinkle structure of P. stratiotes leaf (PL), rough surface of E. crassipes leaf (EL), and box structure of E. crassipes stalk (ES) were observed using the scanning electron microscope. The natural hydrophobic structures and capillary rise tests supported the idea to use P. stratiotes and E. crassipes as oil sorbents. Experiments indicated that the oil sorption by the plants was a fast process. The maximum sorption capacities for different oils reached 5.1–7.6, 3.1–4.8, and 10.6–11.7 g of oil per gram of sorbent for PL, EL, and ES, respectively. In the range of 5–35 °C, the sorption capacities of the plants were not significantly different. These results suggest that the plants can be used as efficient oil sorbents.

This study aimed at testing the hypothesis that free-floating plants may facilitate the growth of submerged plants under hypertrophic conditions and intermediate plant density. The effects of Lemna presence on the growth of two submerged plants ( Elodea nuttallii and Ceratophyllum demersum ) over a nitrogen gradient were experimentally investigated. This was complemented with analysing the presence of C. demersum and E. nuttallii in Hungary and in Germany in relation to the density of free-floating plants. Results showed a negative exponential pattern between underwater light intensity and Lemna cover. Ceratophyllum and Elodea relative growth rate decreased with increasing nitrogen concentrations and additional low Lemna density stimulated Ceratophyllum and suppressed Elodea . Elodea decreased linearly with Lemna density while Ceratophyllum showed a unimodal response. Total algal biomass (epiphytic and planktonic) was higher in Ceratophyllum than in Elodea treatments and decreased rapidly with increasing Lemna density. The field studies showed a positive relationship between Ceratophyllum and a negative one between Elodea and free-floating plant cover. This study clearly showed that free-floating plants can have either facilitating or inhibiting impact on the growth of submerged plants depending on cover density and macrophyte species. The facilitating effect on Ceratophyllum is most likely due to suppressing epiphytic algal growth.

This data paper describes the native vascular aquatic plant floras of 268 Japanese lakes recorded from 1899–2011. The data were compiled from 201 literature sources, most of which were written in Japanese and published in local journals or individual reports rather than in major scientific journals. The literature was searched using web-based services (i.e., Google Scholar, http://scholar.google.com/ ; CiNii, http://ci.nii.ac.jp/en ; JDreamII, http://pr.jst.go.jp/jdream2/ ; and ISI, http://apps.webofknowledge.com ) and by private communication with experts or local governments. Scientific names were consolidated under currently-accepted nomenclature. Four datasets, FloraDB, LakeDB, SpeciesDB, and LiteratureDB, were created to include records of the flora of each lake in each year, the names and locations of the lakes, the scientific names and synonyms of the aquatic vascular plants, and a literature list, respectively. These data can be used to study long-term changes in the species composition and/or richness of aquatic plants in Japanese lakes.

Water hyacinth ( Eichhornia crassipes ) is considered a prospective free-floating aquatic plant potentially used to address current issues on food, energy, and the environment. It can grow quickly and easily in various tropical and subtropical environments as long as it has access to adequate light and water to support photosynthetic growth. Ecosystems are threatened by their invasive growth and remarkable capacity for adaptation. However, managing this plant can result in valuable products. This paper demonstrates particle technologies that might be used to utilize water hyacinths, including brake pads, fertilizer, bioenergy, animal feed, phytoremediation agents, bioplastics, and adsorbents. This study is accompanied by a discussion based on the conducted experiments and currently available literature, providing readers with a clearer understanding. Water hyacinth's capacity to absorb macro- and micro-nutrients, nitrogen, and phosphorus makes it a good plant for phytoremediation. The prospect of producing cellulose makes it prospective as a biomass energy source and livestock feeding. Further, it can be transformed into high-cellulose content particles for applications in bioplastics, brake pads, and adsorbents. The current reports regarding education of water hyacinth to student also were added. Finally, issues and suggestions for future development related to the use of water hyacinths are discussed. This study is expected to provide comprehensive knowledge on how to turn invasive water hyacinth plants into valuable products.

Field studies evidence shifts between phytoplankton and free-floating plant regimes; yet, it is unclear what drives these shifts and if they are critical transitions (alternative stable states). In this review, we synthesized field and experimental data on free-floating plants (of varying size and phylogenies) and phytoplankton regimes, to assess the effects of these producers on the environment. Nutrient-rich environments promote free-floating plants dominance—regardless of life form—which causes dark and anoxic environments, and nutrient release from sediments. This reinforces free-floating plants dominance, but controls phytoplankton biomass by strong shading (despite high nutrients and low grazing). Phytoplankton dominance renders turbid and oxygen-rich (when producing) environments. We also searched for case studies of regime shifts for free-floating plants and phytoplankton dominance. Most studies showed that when free-floating plants dominance was interrupted, phytoplankton biomass (usually Cyanobacteria) rose steeply. Likewise, when phytoplankton-dominated, the development of dense mats of free-floating plants covers usually controlled phytoplankton. Field evidence that suggests critical transitions include abrupt regime transitions in time and space; yet, evidence including indoor controlled experiments and mathematical models is needed for conclusive evidence of alternative stable states to be drawn.

Numerous studies note the overwhelming influence of functional diversity on ecosystem functioning. It remains unclear how functional diversity affects the productivity of aquatic plant communities with different life-forms. We constructed free-floating plant communities dominated by Salvinia natans and submerged plant communities dominated by Vallisneria natans to explore the effects of disturbance (clonal fragmentation) on functional diversity-productivity relationships under different nutrient availability. Results showed that, in free-floating plant communities, disturbance had significant impacts on three community-weighted means traits (average leaf length, average leaf width and average root length), functional evenness (FEve) and productivity under high nutrient conditions. Three single-trait indices and FEve showed reverse correlations with productivity. In submerged plant communities, disturbance-induced considerable variations of single- and multi-trait indices and inapparent variation of productivity. Functional evenness was negatively related to community productivity under low nutrient conditions. Our results suggest that mechanisms of mass ratio and niche complementarity can simultaneously explain variations in free-floating plant community productivity under high nutrient conditions. Niche complementarity had a weak explanatory power for variations in submerged plant community productivity under low nutrient conditions. Our study provides the first evidence for the non-negligible role of nutrients and life-forms in functional diversity-productivity relationships of aquatic plant communities.

Hydroponic root mats (HRMs) are ecotechnological wastewater treatment systems where aquatic vegetation forms buoyant filters by their dense interwoven roots and rhizomes, sometimes supported by rafts or other floating materials. A preferential hydraulic flow is created in the water zone between the plant root mat and the bottom of the treatment system. When the mat touches the bottom of the water body, such systems can also function as HRM filter; i.e. the hydraulic flow passes directly through the root zone. HRMs have been used for the treatment of various types of polluted water, including domestic wastewater; agricultural effluents; and polluted river, lake, stormwater and groundwater and even acid mine drainage. This article provides an overview on the concept of applying floating HRM and non-floating HRM filters for wastewater treatment. Exemplary performance data are presented, and the advantages and disadvantages of this technology are discussed in comparison to those of ponds, free-floating plant and soil-based constructed wetlands. Finally, suggestions are provided on the preferred scope of application of HRMs.

Shallow lakes have become the archetypical example of ecosystems with alternative stable states. However, since the early conception of that theory, the image of ecosystem stability has been elaborated for shallow lakes far beyond the simple original model. After discussing how spatial heterogeneity and fluctuation of environmental conditions may affect the stability of lakes, we review work demonstrating that the critical nutrient level for lakes to become turbid is higher for smaller lakes, and seems likely to be affected by climatic change too. We then show how the image of just two contrasting states has been elaborated. Different groups of primary producers may dominate shallow lakes, and such states dominated by a particular group may often represent alternative stable states. In tropical lakes, or small stagnant temperate waters, free-floating plants may represent an alternative stable state. Temperate shallow lakes may be dominated alternatively by charophytes, submerged angiosperms, green algae or cyanobacteria. The change of the lake communities along a gradient of eutrophication may therefore be seen as a continuum in which gradual species replacements are interrupted at critical points by more dramatic shifts to a contrasting alternative regime dominated by different species. The originally identified shift between a clear and a turbid state remains one of the more dramatic examples, but is surely not the only discontinuity that can be observed in the response of these ecosystems to environmental change.

Although studies on microplastics are increasing every year, still very little is known about their toxicity. Especially for plant species, even studies of uptake of microplastics are only few, not to mention phytotoxicity of microplastics. Therefore, we conducted a pilot study on the phytotoxicity of 1-μm-sized fluorescent microplastics (FMPs) on the free-floating aquatic plants Spirodela polyrhiza and Salvinia natans and the emergent aquatic plant Phragmites australis using 0.1% and 0.01% FMP treatment. Furthermore, uptake of FMPs by plants was verified by detecting fluorescence of FMPs by laser. A free-floating aquatic plant S. polyrhiza and emergent aquatic plant P. australis showed significantly decreased harvested biomass after 3 weeks indicating phytotoxicity of FMPs, but S. natans did not show any differences of harvested biomass or chlorophyll contents among treatments. Detection of fluorescence from plant leaves provided evidence of active FMPs uptake by plants. The emission spectra of plant leaves in 0.1% FMP treatment showed similar peaks to those of free fluorescent microplastics, providing a firm evidence of FMPs uptake by plants. This study is one of the pioneering studies to explore fluorescent microplastic uptake and toxicity in aquatic plants and therefore provides a baseline for further studies.