Effects of Aquatic Plant Coverage on Diversity and Resource Use Efficiency of Phytoplankton in Urban Wetlands: A Case Study in Jinan, China

With the acceleration of urbanization, biodiversity and ecosystem functions of urban wetlands are facing serious challenges. The loss of aquatic plants in urban wetlands is becoming more frequent and intense due to human activities; nevertheless, the effects of aquatic plants on wetland ecosystems have received less attention. Therefore, we conducted field investigations across 10 urban wetlands in Jinan, Shandong Province, as a case in North China to examine the relationships between aquatic plant coverage and phytoplankton diversity, as well as resource use efficiency (RUE) in urban wetlands. Multivariate regression and partial least squares structural equation modeling (PLS-SEM) were used to analyze the water quality, phytoplankton diversity, and RUE. The results demonstrate that the increase in aquatic plant coverage significantly reduced the concentration of total nitrogen and suspended solids' concentrations and significantly increased the phytoplankton diversity (e.g., species richness and functional diversity). The aquatic plant coverage significantly affected the composition of phytoplankton functional groups; for example, functional groups that had adapted to still-water and low-light conditions became dominant. Furthermore, the increase in phytoplankton diversity improved phytoplankton RUE, highlighting the importance of aquatic plants in maintaining wetland ecosystem functions. This study may provide a scientific basis for the management strategy of aquatic plants in urban wetlands, emphasizing the key role of appropriate aquatic plant cover in maintaining the ecological stability and ecosystem service functions of wetlands.

Climate Change Potentially Leads to Habitat Expansion and Increases the Invasion Risk of Hydrocharis (Hydrocharitaceae)

Climate change is a crucial factor impacting the geographical distribution of plants and potentially increases the risk of invasion for certain species, especially for aquatic plants dispersed by water flow. Here, we combined six algorithms provided by the biomod2 platform to predict the changes in global climate-suitable areas for five species of Hydrocharis (Hydrocharitaceae) (H. chevalieri, H. dubia, H. laevigata, H. morsus-ranae, and H. spongia) under two current and future carbon emission scenarios. Our results show that H. dubia, H. morsus-ranae, and H. laevigata had a wide range of suitable areas and a high risk of invasion, while H. chevalieri and H. spongia had relatively narrow suitable areas. In the future climate scenario, the species of Hydrocharis may gain a wider habitat area, with Northern Hemisphere species showing a trend of migration to higher latitudes and the change in tropical species being more complex. The high-carbon-emission scenario led to greater changes in the habitat area of Hydrocharis. Therefore, we recommend strengthening the monitoring and reporting of high-risk species and taking effective measures to control the invasion of Hydrocharis species.

Genomic analysis of the emergent aquatic plant Sparganium stoloniferum provides insights into its clonality, local adaptation and demographic history

Clonal propagation and extensive dispersal of seeds and asexual propagules are two important features of aquatic plants that help them adapt to aquatic environments. Accurate measurements of clonality and effective clonal dispersal are essential for understanding the evolution of aquatic plants. Here, we first assembled a high-quality chromosome-level genome of a widespread emergent aquatic plant Sparganium stoloniferum to provide a reference for its population genomic study. We then performed high-depth resequencing of 173 individuals from 20 populations covering different basins across its range in China. Population genomic analyses revealed three genetic lineages reflecting the northeast (NE), southwest (SW) and northwest (NW) of its geographical distribution. The NE lineage diverged in the middle Pleistocene while the SW and NW lineages diverged until about 2400 years ago. Clonal relationship analyses identified nine populations as monoclonal population. Dispersal of vegetative propagules was identified between five populations covering three basins in the NE lineage, and dispersal distance was up to 1041 km, indicating high dispersibility in emergent aquatic plant species. We also identified lineage-specific positively selected genes that are likely to be involved in adaptations to saline wetlands and high-altitude environments. Our findings accurately measure the clonality, determine the dispersal range and frequency of vegetative propagules, and detect genetic signatures of local adaptation in a widespread emergent aquatic plant species, providing new perspectives on the evolution of aquatic plants.

Using explainable machine learning methods to evaluate vulnerability and restoration potential of ecosystem state transitions

Ecosystem state transitions can be ecologically devastating or be a restoration success. State transitions are common within aquatic systems worldwide, especially considering human-mediated changes to land use and water use. We created a transferable conceptual framework to enable multiscale assessments of state resilience and early warnings of state transitions that can inform strategic restorations and avoid ecosystem collapse. The conceptual framework integrated machine learning predictions with ecosystem state concepts (e.g., state classification, gradients of vulnerability, and recovery potential leading to state transitions) and was devised to investigate possible environmental drivers. As an application of the framework, we generated prediction probabilities of submersed aquatic vegetation (SAV) presence at nearly 10,000 sites in the Upper Mississippi River (United States). Then, we used an interpretability method to explain model predictions to gain insights into possible environmental drivers and thresholds or linear responses of SAV presence and absence. Model accuracy was 89% without spatial bias. Average water depth, suspended solids, substrate, and distance to nearest SAV were the best predictors and likely environmental drivers of SAV habitat suitability. These environmental drivers exhibited nonlinear, threshold-type responses for SAV. All the results are also presented in an online dashboard to explore results at many spatial scales. The habitat suitability model outputs and prediction explanations from many spatial scales (4 m to 400 km of river reach) can inform research and restoration planning.

Chemical Composition, Market Survey, and Safety Assessment of Blue Lotus (Nymphaea caerulea Savigny) Extracts

Blue lotus, also known as Nymphaea caerulea (Nymphaeaceae), is a water lily found globally in lakes and rivers. With its long history of use in Egyptian culture, blue lotus has been associated with spiritual rituals and health benefits. Nowadays, blue lotus is still consumed as a tea or tincture to induce relaxation and heightened spiritual awareness. In this study, six authentic N. caerulea extracts from trusted sources and eleven commercial products were analyzed using gas chromatography-mass spectrometry (GC-MS). Authentic blue lotus extracts were produced in industrial settings. Overall, the extracts were a mixture of aliphatic hydrocarbons, aromatic alcohols, fatty acids, phenyl derivatives, diterpenoids, phytosterols, and stigmastanes. Apomorphine and nuciferine, which are responsible for psychoactive effects of the blue lotus flower, were virtually absent from the authentic blue lotus extract. Although blue lotus has a long history of use, the safety data on the plant and its extracts is limited; however, together with the analytical data, the available information does not indicate major safety concerns for the topical application of authentic blue lotus flower concrete or absolute when diluted as a fragrance ingredient.

Differential Morpho-Physiological and Biochemical Responses of Duckweed Clones from Saudi Arabia to Salinity

Salinity affects the morphological, physiological, and biochemical characteristics of several plant species. The current study was conducted to investigate differential salt tolerance potentials among ten duckweed clones under different salt-stress conditions. Morphological and physiological parameters, including fronds length, fronds number, root length, root number, Na+/K+, chlorophyll, proline contents, and fresh harvest weight, were recorded for each of the ten duckweed clones collected from different Saudi Arabia regions. Additionally, the expression patterns of seven salt-related genes were monitored in a salt-tolerant duckweed genotype. The results show that the Madinah-2 (Spirodela polyryiza) and Al-Qassim (Landoltia punctata) clones presented higher performances for all the tested morphological and physiological parameters compared to other genotypes under salt-stress conditions. At concentrations greater than 150 mM NaCl, these aforementioned traits were affected for all the genotypes tested, except Madinah-2 (S. polyryiza) and Al-Qassim (L. punctata) clones, both of which exhibited high tolerance behavior under high salt conditions (200 mM and 250 mM NaCl). The principal component analysis (PCA) showed that the first five principal components accounted for 94.8% of the total variance among the studied traits. Morphological and physiological traits are the major portions of PC1. Moreover, the expression pattern analysis of NHX, BZIP, ST, and KTrans transcript revealed their upregulation in the Al-Qassim clone under salt-stress conditions, suggesting that these genes play a role in this clone's tolerance to salt-induced stress. Overall, this study indicates that the Al-Qassim clone could be used in a brackish-water duckweed-based treatment program with a simultaneous provision of valuable plant biomass.

AMONG-SPECIES VARIATION IN FLOWER SIZE DETERMINES FLORIVORY IN THE LARGEST SEASONALLY FLOODED TROPICAL WETLAND

PREMISES OF THE STUDY

Floral damage caused by florivores often has negative consequences for plant reproduction. However, the factors affecting plant-florivore interactions are still poorly understood, especially the role of abiotic factors and interspecific variation in florivory within ecosystems. Thus, it is largely required to investigate the patterns of florivory levels and its consequences for plant communities.

METHODS

We assessed the influence of abiotic factors related to climatic seasonality, of phylogenetic relationships among plants, and of functional attributes associated with attractiveness to pollinators on florivory levels (incidence and intensity) in the Pantanal, the world's largest tropical wetland. Between December 2020 and November 2021, the percentage of both flowers attacked (incidence) and area removed from petals (intensity) by florivores were examined in 51 species from 25 families, considering flowering season, the substrate where the plants occur, and floral attributes as potentially determining factors on florivory levels.

KEY RESULTS

Phylogeny and environmental factors did not have a significant influence on florivory. The only determinant of interspecific variation in florivory incidence and intensity was flower size, where larger flowers experienced higher florivory levels regardless of season and substrate, while flower arrangement and color were not significant factors.

CONCLUSIONS

Our study is one of the first to estimate the community-wide effects of biotic and abiotic factors on both the incidence and the intensity of florivory. The magnitude of this plant-florivore interaction may reduce reproductive success and entail selective pressures on plant attractiveness to pollinators. This article is protected by copyright. All rights reserved.

Algal Extracts for Green Synthesis of Zinc Oxide Nanoparticles: Promising Approach for Algae Bioremediation

Zinc oxide nanoparticles (ZnO-NPs) possess unique properties, making them a popular material across various industries. However, traditional methods of synthesizing ZnO-NPs are associated with environmental and health risks due to the use of harmful chemicals. As a result, the development of eco-friendly manufacturing practices, such as green-synthesis methodologies, has gained momentum. Green synthesis of ZnO-NPs using biological substrates offers several advantages over conventional approaches, such as cost-effectiveness, simplicity of scaling up, and reduced environmental impact. While both dried dead and living biomasses can be used for synthesis, the extracellular mode is more commonly employed. Although several biological substrates have been successfully utilized for the green production of ZnO-NPs, large-scale production remains challenging due to the complexity of biological extracts. In addition, ZnO-NPs have significant potential for photocatalysis and adsorption in the remediation of industrial effluents. The ease of use, efficacy, quick oxidation, cost-effectiveness, and reduced synthesis of harmful byproducts make them a promising tool in this field. This review aims to describe the different biological substrate sources and technologies used in the green synthesis of ZnO-NPs and their impact on properties. Traditional synthesis methods using harmful chemicals limit their clinical field of use. However, the emergence of algae as a promising substrate for creating safe, biocompatible, non-toxic, economic, and ecological synthesis techniques is gaining momentum. Future research is required to explore the potential of other algae species for biogenic synthesis. Moreover, this review focuses on how green synthesis of ZnO-NPs using biological substrates offers a viable alternative to traditional methods. Moreover, the use of these nanoparticles for industrial-effluent remediation is a promising field for future research.

Hydrocharis laevigata in Europe

Hydrocharis laevigata (Humb. & Bonpl. ex Willd.) Byng & Christenh. [= Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine], Hydrocharitaceae, is a floating-leaf aquatic plant that is native to inland South America. It is an invasive species in several parts of the world. Reports of its presence in Europe have been recently published: naturalised populations occur in three locations on the Iberian Peninsula. The literature also contains records of the species in Hungary and Poland. In addition, it has been observed in Sweden, Belgium, and the Netherlands. H. laevigata is highly adaptable and can profoundly transform habitat conditions in its invasive range, causing major issues for ecosystem conservation and human activities. Until recently, H. laevigata was not to be found in natural environments in Europe. Factors explaining its spread include its use as an ornamental plant, the eutrophication of inland waters, and the effects of global warming. With a focus on Europe, this short communication provides information on the species' distribution, taxonomy, biology, habitat, and negative impacts.

Macrophytes in Inland Waters: From Knowledge to Management

The huge biodiversity of inland waters and the many different aquatic habitats or ecosystems occurring there are particularly threatened by human impacts. In this Special Issue, ten articles have been collected that show new data on the distribution and ecology of some rare aquatic macrophytes, including both vascular plants and charophytes, but also on the use of these organisms for the monitoring, management, and restoration of wetlands.

Clear phylogeographical structures shed light on the origin and dispersal of the aquatic boreal plant Hippuris vulgaris

Aquatic plants are an important ecological group in the arctic flora; however, their evolutionary histories remain largely unknown. In order to deepen our understanding of the evolution of these plants, we explored the phylogeographical structure of an aquatic boreal plant Hippuris vulgaris in a broad geographical sampling from Eurasia and North America using the chloroplast intergenic spacer psbA-trnH and seven nuclear microsatellite loci. Two closely-related species H. lanceolata and H. tetraphylla were also included because of their taxonomic controversy. Both chloroplast DNA sequences and nuclear microsatellite data revealed three genetic lineages with distinct distribution ranges. Incongruence between nuclear and chloroplast DNA lineages occurred in 14 samples from Russian Far East and Europe caused by inter-lineage hybridization. No private haplotypes or independent genetic clusters were evident in H. lanceolata or H. tetraphylla, suggesting that these two species should be considered conspecific ecotypes of H. vulgaris. Analysis using Approximate Bayesian Computation-Random Forest approach suggests that Hippuris vulgaris originated in China, followed by dispersal into Russia plus Northeast China, then successively westwards into Europe and North America, and finally into the Russian Far East from both North America and Russia plus Northeast China. This study is the first to elucidate the historical dispersal processes of a circumarctic aquatic plant across the entirety of its range.

Genome-Wide Analysis of the Growth-Regulating Factor (GRF) Family in Aquatic Plants and Their Roles in the ABA-Induced Turion Formation of Spirodela polyrhiza

Growth-regulating factors (GRFs) are plant-specific transcription factors that play essential roles in regulating plant growth and stress response. The GRF gene families have been described in several terrestrial plants, but a comprehensive analysis of these genes in diverse aquatic species has not been reported yet. In this study, we identified 130 GRF genes in 13 aquatic plants, including floating plants (Azolla filiculoides, Wolffia australiana, Lemna minuta, Spirodela intermedia, and Spirodela polyrhiza), floating-leaved plants (Nymphaea colorata and Euryale ferox), submersed plants (Zostera marina, Ceratophyllum demersum, Aldrovanda vesiculosa, and Utricularia gibba), an emergent plant (Nelumbo nucifera), and an amphibious plant (Cladopus chinensis). The gene structures, motifs, and cis-acting regulatory elements of these genes were analyzed. Phylogenetic analysis divided these GRFs into five clusters, and ABRE cis-elements were highly enriched in the promoter region of the GRFs in floating plants. We found that abscisic acid (ABA) is efficient at inducing the turion of Spirodela polyrhiza (giant duckweed), accompanied by the fluctuated expression of SpGRF genes in their fronds. Our results provide information about the GRF gene family in aquatic species and lay the foundation for future studies on the functions of these genes.

Substrates, Plants, and Their Combinations for Water Purification of Urban Household Aquaponics Systems

To make full use of urban household balcony space, an urban aquaponics system for balconies was constructed to investigate the purification effects of four different substrates (volcanic stone, ceramic pellets, ceramic rings, and nanorods) and six plants (mung bean sprouts, hollow cabbage, water celery, lettuce, leek, and water chestnut) on fish culture wastewater. Through the determination of contaminants such as nitrogen and phosphorus and through the use of 16SrDNA sequencing technology, the substrate material and plant combinations with the best purification effects were screened. The results show that volcanic stone and nanorods have strong purification capacities. Compared to the other substrate types, there were more unique bacterial species on the surface of volcanic stone, among which amoeba species were the most dominant (92.42%). Among the six tested plant species, mung bean sprouts had the highest contribution to nitrogen uptake (94.96%), and water chestnut had the highest contribution to phosphorus uptake at 12.07%. Finally, the combination of nanorods and water celery was the best at purifying the wastewater. This study provides a theoretical basis and new ideas for the construction of urban aquaponics systems on balconies, which will help to achieve green farming and the efficient utilization of water resources.

Bubbles help male flowers overcome obstacles during pollination in Hydrilla verticillata

PREMISE

Pollination in many aquatic plants takes place on the water surface, and the male flowers or stamens often produce gas bubbles underwater; however, the generation mechanism and function of these bubbles are unknown.

METHODS

A common submerged plant, Hydrilla verticillata, was used as experimental material to observe the structure of male flowers, analyze the process of bubble generation, and simulate the movement process of the male flower with attached gas bubble in water.

RESULTS

The aerenchyma inside the male plants of H. verticillata transported the gas produced by the plant's branches during photosynthesis to the male flower, and the formed gas bubbles became attached to the edge of the perianth. The gas accumulation rate in the attached bubbles increased with light intensity. Once the bubble diameter increased to approximately 3.3 mm, the male flowers with the bubble detached from the plant and floated to the water surface. The removal of the attached bubbles did not affect the male flower detached from the plant; however, the surfacing of male flowers without gas bubbles was easily prevented by the plant's branches in the water, and they could not reach the water surface to complete pollen dispersal.

CONCLUSIONS

The gas bubbles produced by male flowers of H. verticillata came from the gas produced by branches under light. These bubbles can help ascending male flowers bypass the obstacles in water and reach the surface to complete pollination.

Macroevolutionary dynamics in the transition of angiosperms to aquatic environments

Angiosperm lineages in aquatic environments are characterized by high structural and functional diversity, and wide distributions. A long-standing evolutionary riddle is what processes have caused the relatively low diversity of aquatic angiosperms compared to their terrestrial relatives. We use diversification and ancestral reconstruction models with a comprehensive > 10 000 genus angiosperm phylogeny to elucidate the macroevolutionary dynamics associated with transitions of terrestrial plants to water. Our study reveals that net diversification rates are significantly lower in aquatic than in terrestrial angiosperms due to lower speciation and higher extinction. Shifts from land to water started early in angiosperm evolution, but most events were concentrated during the last c. 25 million years. Reversals to a terrestrial habitat started only 40 million years ago, but occurred at much higher rates. Within aquatic angiosperms, the estimated pattern is one of gradual accumulation of lineages, and relatively low and constant diversification rates throughout the Cenozoic. Low diversification rates, together with infrequent water transitions, account for the low diversity of aquatic angiosperms today. The stressful conditions and small global surface of the aquatic habitat available for angiosperms are hypothesized to explain this pattern.

Possibility of Metal Accumulation in Reed Canary Grass (Phalaris arundinacea L.) in the Aquatic Environment of South-Western Polish Rivers

A four-year research study was conducted on aquatic plants (reed canary grass) growing in the beds of three rivers and their tributaries in Lower Silesia, Poland. Metal contents (Cu, Cd, Ni, Pb, Zn, Fe, Mn) were determined in plant samples, metal accumulation in water (BCFw) and sediment (BCFB), Metal Pollution Index (MPI) and Enrichment Factor (EF) were calculated. The highest contents of copper, lead, nickel and cadmium were found in reed canary grass sampled from the Nysa Szalona River. The highest values were recorded for zinc in the Bystrzyca River, and for iron and manganese in the Strzegomka River. The series of metals were as follows: Nysa Szalona and Strzegomka: Cd < Ni < Pb < Cu < Zn < Mn < Fe, Bystrzyca: Cd < Ni < Cu < Pb < Zn < Mn < Fe. Throughout the study period, the lowest values of metals in plants were recorded in 2015 and 2018, and the highest in 2017. The general picture of MPI in aquatic plants is arranged in the series Bystrzyca < Strzegomka < Nysa Szalona. These values classify the studied material at a high level of pollution in all rivers. In the comparison of the two extreme sites, i.e., source−mouth, higher values were found at the mouth of the reservoir, which suggests that metals move with the water current and accumulate more with the direction of the river flow, which is most likely a consequence of the influence of the catchment area as the source of metals. The series of EF enrichment factor values were as follows: Bystrzyca—Ni < Cd < Fe < Cu < Zn < Mn < Pb, Nysa Szalona—Ni < Fe < Zn < Cd < Mn < Cu < Pb, Strzegomka—Ni < Cd < Fe < Zn < Cu < Pb < Mn. For all the samples studied, the values found in spring were much higher than in autumn, which indicates the great importance for research in that area. The levels of copper and iron were within the range of moderate values, lead and manganese reached very high and exceptionally high values, and the remaining metals were within the values described as significant. Bioaccumulation of metals determined relative to bottom sediments was highest in 2017 and lowest in 2018, while bioaccumulation relative to water was highest in 2018 and lowest in 2016. The four-year study found that the metal content in reed canary grass was mostly within the range of mean values presented in the literature from moderately polluted areas. Also, no significant deviation was found from levels that have been recorded for the same rivers for more than two decades.

Effects of Partial Substitution of Conventional Protein Sources with Duckweed (Lemna minor) Meal in the Feeding of Rainbow Trout (Oncorhynchus mykiss) on Growth Performances and the Quality Product

Duckweed (Lemna minor) meal was included in the formulation of three experimental feeds (L1, L2, L3) for rainbow trout at 10%, 20%, 28% of the protein source, respectively. Increasing the duckweed inclusion, the other protein sources were adjusted to get isonitrogenous (41%) and isolipidic (20%) diets, as the control diet (LC). 540 fish (mean body weight 124.5 ± 0.7 g) were randomly allocated in 12 tanks divided equally among the four different diets. After 90 days, fish were weighed and the most important productive performances, fillet quality and fatty acid profile were determined. The final body weight in L1 (340.53 g) and L2 (339.42 g) was not different from LC (348.80 g); L3 trout significantly (p < 0.05) exhibited the lowest one (302.16 g). Similar trends were found in final mean length, weight gain, specific growth rate, food conversion rate. Somatic indices were affected by duckweed inclusion. Diets had not significant effects on the proximate composition and fatty acids of the fillet in L1, L2, L3 respect to LC. Based on this study, duckweed meal derived from Lemna minor can be included in the feed for the rainbow trout without negative effects on the growth performances at 20% of the protein substitution.

Direct and indirect effects of climate change on distribution and community composition of macrophytes in lentic systems

Macrophytes are an important part of freshwater ecosystems and they have direct and indirect roles in keeping the water clear and providing structure and habitats for other aquatic organisms. Currently, climate change is posing a major threat to macrophyte communities by altering the many drivers that determine macrophyte abundance and composition. We synthesise current literature to examine the direct effects of climate change (i.e. changes in CO₂, temperature, and precipitation patterns) on aquatic macrophytes in lakes as well as indirect effects via invasive species and nutrient dynamics. The combined effects of climate change are likely to lead to an increased abundance and distribution of emergent and floating species, and a decreased abundance and distribution of submerged macrophytes. In small shallow lakes, these processes are likely to be faster than in deep temperate lakes; with lower light levels, water level fluctuations and increases in temperature, the systems will become dominated by algae. In general, specialized macrophyte species in high‐latitude and high‐altitude areas will decrease in number while more competitive invasive species are likely to outcompete native species. Given that the majority of endemic species reside in tropical lakes, climate change, together with other anthropogenic pressures, might cause the extinction of a large number of endemic species. Lakes at higher altitudes in tropical areas could therefore potentially be a hotspot for future conservation efforts for protecting endemic macrophyte species. In response to a combination of climate‐change induced threats, the macrophyte community might collapse, which will change the status of lakes and may initiate a negative feedback loop that will affect entire lake ecosystems.

Pollen in water of unstable salinity: Evolution and function of dynamic apertures in monocot aquatics

PREMISE

The sporoderm of seed-plant pollen grains typically has apertures in which the outer sporopollenin-bearing layer is relatively sparse. The apertures allow regulation of the internal volume of the pollen grain during desiccation and rehydration (harmomegathy) and also serve as sites of pollen germination. A small fraction of angiosperms undergo pollination in water or at the water surface, where desiccation is unlikely. Their pollen grains commonly lack apertures, though with some notable exceptions. We tested a hypothesis that in some angiosperm aquatics that inhabit water of unstable salinity, the pollen apertures accommodate osmotic effects that occur during pollination in such conditions.

METHODS

Pollen grains of the tepaloid clade of the monocot order Alismatales, which contains ecologically diverse aquatic and marshy plants, were examined using light microscopy and scanning electron microscopy. We used Ruppia as a model to test pollen grain response in water of various salinities. Pollen aperture evolution was also analyzed using molecular tree topologies.

RESULTS

Phylogenetic optimizations demonstrated an evolutionary loss and two subsequent regains of the aperturate condition in the tepaloid clade of Alismatales. Both of the taxa that have reverted to aperturate pollen (Ruppia, Ruppiaceae; Althenia, Potamogetonaceae) are adapted to changeable water salinity. Direct experiments with Ruppia showed that the pollen apertures have a role in a harmomegathic response to differences in water salinity.

CONCLUSIONS

Our results showed that the inferred regain of pollen apertures represents an adaptation to changeable water salinity. We invoke a loss-and-regain scenario, prompting questions that are testable using developmental genetics and plant physiology.

Aluminum Bioaccumulation in Reed Canary Grass (Phalaris arundinacea L.) from Rivers in Southwestern Poland

This study aimed to determine aluminum levels in reed canary grass Phalaris arundinacea L.) in rivers in southwestern Poland—Bystrzyca, Strzegomka, and Nysa Szalona, together with their tributaries. The samples were collected in spring and autumn 2015−2018. The highest amounts of aluminum were recorded in the Nysa Szalona, and the lowest in the Bystrzyca. During the four-year cycle of studies, the highest values were recorded in the last year, and the lowest in the first year. The highest amounts of aluminum were found in all three rivers in the lowland tributaries. In the main rivers, higher amounts of aluminum were found at the mouth of the Nysa Szalona and Strzegomka reservoirs, while the opposite situation was found for the Bystrzyca. Higher aluminum contents were recorded in autumn than in spring, and the values of BCFW (aluminum bioaccumulation factor in relation to water) and BCFB (aluminum bioaccumulation factor in relation to bottom sediments) coefficients were also higher. The MPI (metal pollution index) was arranged in a series: Bystrzyca < Strzegomka < Nysa Szalona, while the degree of pollution was high for Bystrzyca and very high for the other two rivers. The variability in Al levels may be attributed to pollution level in the catchments, but also to successive modernization works carried out in the beds of the main rivers and their tributaries. All these works were carried out in a variable way and often covered only a fragment of the riverbed; therefore, the consequences of activity may have been visible in the catchment but not necessarily in the same vegetation cycles.

Effect of Pb-Contaminated Water on Ludwigia stolonifera (Guill. & Perr.) P.H. Raven Physiology and Phytoremediation Performance

A laboratory experiment was led to examine the lead bioaccumulation capacity of Ludwigia stolonifera (Guill. & Perr.) exposed to various Pb concentrations (0, 10, 25, 50, and 100 mg/L) for 1, 3, 5, and 7 days. The lead accumulation increased as the metal concentrations in the solution increased and over time, to an extreme accretion of 6840 mg/kg DW(dry weight) at 100 mg/L of lead on the 10 days exposure. The proportion removal efficiency, translocation factor, and bioconcentration factor of the plant were assessed. The maximum bioconcentration factor values (1981.13) indicate that the plant was a Pb hyperaccumulator, and translocation factor values (1.85), which are >1, indicate fit of L. stolonifera for eliminating Pb in Pb-contaminated water. Photosynthetic pigments were decreased with increase of Pb concentration and time exposure. Total chlorophyll content and Chl a/b ratio lowered to between 46 and 62% at 100 mg/L Pb after 10 days exposure. Protein content and soluble carbohydrate indicated a similar trend, which showed the highest decrease (7.26 and 36.2 mg/g FW(fresh weight), respectively) at 100 mg/L of Pb after 10 days. The activity of the antioxidant enzymes superoxide dismutase, ascorbate, and peroxidase was increased significantly in comparison to the control. The results indicate that L. stolonifera is a newly recognized Pb hyperaccumulator (6840 mg/kg DW), but physiological status indicates that the plant is not tolerant to high Pb concentrations.

Heavy Metal Accumulation in Rice and Aquatic Plants Used as Human Food: A General Review

Aquatic ecosystems are contaminated with heavy metals by natural and anthropogenic sources. Whilst some heavy metals are necessary for plants as micronutrients, others can be toxic to plants and humans even in trace concentrations. Among heavy metals, cadmium (Cd), arsenic (As), chromium (Cr), lead (Pb), and mercury (Hg) cause significant damage to aquatic ecosystems and can invariably affect human health. Rice, a staple diet of many nations, and other aquatic plants used as vegetables in many countries, can bioaccumulate heavy metals when they grow in contaminated aquatic environments. These metals can enter the human body through food chains, and the presence of heavy metals in food can lead to numerous human health consequences. Heavy metals in aquatic plants can affect plant physicochemical functions, growth, and crop yield. Various mitigation strategies are being continuously explored to avoid heavy metals entering aquatic ecosystems. Understanding the levels of heavy metals in rice and aquatic plants grown for food in contaminated aquatic environments is important. Further, it is imperative to adopt sustainable management approaches and mitigation mechanisms. Although narrowly focused reviews exist, this article provides novel information for improving our understanding about heavy metal accumulation in rice and aquatic plants, addressing the gaps in literature.

The impact of raindrops on Salvinia molesta leaves: effects of trichomes and elasticity

The floating leaves of the aquatic fern Salvinia molesta are covered by superhydrophobic hairs (=trichomes) which are shaped like egg-beaters. These trichomes cause high water repellency and stable unwettability if the leaf is immersed. Whereas S. molesta hairs are technically interesting, there remains also the question concerning their biological relevance. S. molesta has its origin in Brazil within a region exposed to intense rainfall which easily penetrates the trichome cover. In this study, drop impact on leaves of S. molesta were analysed using a high-speed camera. The largest portion of the kinetic energy of a rain drop is absorbed by elastic responses of the trichomes and the leaf. Although rain water is mostly repelled, it turned out that the trichomes hamper swift shedding of rain water and some residual water can remain below the 'egg-beaters'. Drops rolling over the trichomes can, however, 'suck up' water trapped beneath the egg-beaters because the energetic state of a drop on top of the trichomes is-on account of the superhydrophobicity of the hairs-much more favourable. The trichomes may therefore be beneficial during intense rainfall, because they absorb some kinetic energy and keep the leaf base mostly free from water.

Cable bacteria at oxygen-releasing roots of aquatic plants: a widespread and diverse plant-microbe association

Cable bacteria are sulfide-oxidising, filamentous bacteria that reduce toxic sulfide levels, suppress methane emissions and drive nutrient and carbon cycling in sediments. Recently, cable bacteria have been found associated with roots of aquatic plants and rice (Oryza sativa). However, the extent to which cable bacteria are associated with aquatic plants in nature remains unexplored. Using newly generated and public 16S rRNA gene sequence datasets combined with fluorescence in situ hybridisation, we investigated the distribution of cable bacteria around the roots of aquatic plants, encompassing seagrass (including seagrass seedlings), rice, freshwater and saltmarsh plants. Diverse cable bacteria were found associated with roots of 16 out of 28 plant species and at 36 out of 55 investigated sites, across four continents. Plant-associated cable bacteria were confirmed across a variety of ecosystems, including marine coastal environments, estuaries, freshwater streams, isolated pristine lakes and intensive agricultural systems. This pattern indicates that this plant-microbe relationship is globally widespread and neither obligate nor species specific. The occurrence of cable bacteria in plant rhizospheres may be of general importance to vegetation vitality, primary productivity, coastal restoration practices and greenhouse gas balance of rice fields and wetlands.

Portable Measurement System for in situ Estimation of Oxygen and Carbon Fluxes of Submerged Plants

The metabolism of submerged plants is commonly characterized by oxygen development. The turnover rates of carbon dioxide and other inorganic carbon species, however, are assessed only at distinct points in time after incubation or calculated through shifts in pH and total alkalinity. A novel three parameter measurement system was developed in order to improve this issue and to gain a better understanding of the metabolism of aquatic plants. It allows the simultaneous and continuous assessment of oxygen concentration, partial pressure of carbon dioxide and pH with optical sensors without the need of taking water samples. Plants or plant parts can be enclosed in a chamber, while the surrounding water is either flushed through or circulated within the system. The method was evaluated in regards to measurement time and possible stress reactions during measurement. Its applicability in situ was confirmed with Elodea nuttallii and Ceratophyllum demersum. The measurement system will enable deeper insights into the metabolism and response of aquatic plants to changing environmental conditions, especially related to carbon fixation.

A New Species of Pseudostrandesia Savatenalinton and Martens, 2009 (Ostracoda, Crustacea) Collected from Two Pet Shops in Central Japan: an Alien Species?

An undescribed species of freshwater ostracod belonging to the genus Pseudostrandesia Savatenalinton and Martens, 2009 was collected from two pet shops in the Kanto region of central Japan. This species, herein named Pseudostrandesia tenebrarum sp. nov., is similar to four species previously reported from Southeast Asia, but can be distinguished by carapace and appendage features. It is the second species of the genus for which males are known. Of the nine previously described species in the genus, one is exclusively known from Turkey, and the others are found in Southeast Asia and the vicinity, one of which is also recorded in India and east China. There are two scenarios to explain the existence of Pseudostrandesia tenebrarum sp. nov. in pet shops in Japan: it is either native to Japan but has yet to be discovered in its natural habitat, or it is an alien species, perhaps unwittingly imported with plants or fish for the pet trade. We review the likelihood of both scenarios, and conclude that although there is insufficient evidence to be sure, it is potentially an alien species in Japan. The most likely origin is Southeast Asia, as evidenced by its close morphological resemblance to particular Southeast Asian species. Juveniles as well as adults were recovered, indicating that this species is reproducing in the pet trade, supporting the notion that it has invasive potential to areas outside of its natural range. The description and report of this species highlights a possible introduction of an alien species to Japan, and facilitates further monitoring.

Depth diversity gradients of macrophytes: Shape, drivers, and recent shifts

Investigating diversity gradients helps to understand biodiversity drivers and threats. However, one diversity gradient is rarely assessed, namely how plant species distribute along the depth gradient of lakes. Here, we provide the first comprehensive characterization of depth diversity gradient (DDG) of alpha, beta, and gamma species richness of submerged macrophytes across multiple lakes. We characterize the DDG for additive richness components (alpha, beta, gamma), assess environmental drivers, and address temporal change over recent years. We take advantage of yet the largest dataset of macrophyte occurrence along lake depth (274 depth transects across 28 deep lakes) as well as of physiochemical measurements (12 deep lakes from 2006 to 2017 across Bavaria), provided publicly online by the Bavarian State Office for the Environment. We found a high variability in DDG shapes across the study lakes. The DDGs for alpha and gamma richness are predominantly hump-shaped, while beta richness shows a decreasing DDG. Generalized additive mixed-effect models indicate that the depth of the maximum richness (D max) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (R max) is significantly influenced by lake area only. Most observed DDGs seem generally stable over recent years. However, for single lakes we found significant linear trends for R max and D max going into different directions. The observed hump-shaped DDGs agree with three competing hypotheses: the mid-domain effect, the mean-disturbance hypothesis, and the mean-productivity hypothesis. The DDG amplitude seems driven by lake area (thus following known species-area relationships), whereas skewness depends on physiochemical factors, mainly water transparency and layering depth. Our results provide insights for conservation strategies and for mechanistic frameworks to disentangle competing explanatory hypotheses for the DDG.

Characterization of the Complete Chloroplast Genome of Hygroryza aristata (Retz.) Nees ex Wight & Arn. (Zizaniinae, Poaceae)

The complete chloroplast genome sequence of Hygroryza aristata was sequenced, assembled and published for the first time here. The chloroplast genome was 135,681 bp in length and comprised of a large single-copy (LSC, 81,532 bp) region and a small single-copy (SSC, 12,383 bp) region interspersed by two inverted repeats (IRs, 20,883 bp). Gene annotation resulted in the identification of 113 unique genes including 79 protein-coding genes, 30 transfer RNA (tRNA) genes, and four ribosomal RNA (rRNA) genes. In addition, 118 simple sequence repeats (SSRs) and 47 long repeats were identified. Phylogenetic analysis based on maximum likelihood analysis (ML) resolved the placement of H. aristata sister to a clade of Rhynchoryza subulata and Zizania.

Purification Efficiency of Three Combinations of Native Aquatic Macrophytes in Artificial Wastewater in Autumn

Water pollution caused by excessive nutrient and biological invasion is increasingly widespread in China, which can lead to problems with drinking water as well as serious damage to the ecosystem if not be properly treated. Aquatic plant restoration (phytoremediation) has become a promising and increasingly popular solution. In this study, eight native species of low-temperature-tolerant aquatic macrophytes were chosen to construct three combinations of aquatic macrophytes to study their purification efficiency on eutrophic water in large open tanks during autumn in Guangzhou City. The total nitrogen (TN) removal rates of group A (Vallisneria natans + Ludwigia adscendens + Monochoria vaginalis + Saururus chinensis), group B (V. natans + Ipomoea aquatica + Acorus calamus + Typha orientalis), and group C (V. natans + L. adscendens + Schoenoplectus juncoides + T. orientalis) were 79.10%, 46.39%, and 67.46%, respectively. The total phosphorus (TP) removal rates were 89.39%, 88.37%, and 91.96% in groups A, B, and C, respectively, while the chemical oxygen demand (COD) removal rates were 93.91%, 96.48%, and 92.78%, respectively. In the control group (CK), the removal rates of TN, TP, and COD were 70.42%, 86.59%, and 87.94%, respectively. The overall removal rates of TN, TP, and COD in the plant groups were only slightly higher than that in CK group, which did not show a significant advantage. This may be related to the leaf decay of some aquatic plants during the experiment, whereby the decay of V. natans was the most obvious. The results suggest that a proper amount of plant residue will not lead to a significant deterioration of water quality.

Plant and Animal-Type Feedstuff Shape the Gut Microbiota and Metabolic Processes of the Chinese Mitten Crab Eriocheir sinensis

In animals, growth and development are strongly correlated with the gut microbiota and metabolic profiles. In this study, gut microbiome communities, metabolic profiles, and growth performance of Eriocheir sinensis under three dietary feed types based on waterweed plants only, freshwater snails only, and waterweed plants combined with freshwater snails were studied by using 16S rRNA gene sequencing and liquid chromatography-mass spectrometry. Results indicated that different feed types dramatically affected the growth performances of E. sinensis by altering the gut microbiota and metabolic profiles. Aquatic plants, such as waterweeds, played essential roles in shaping gut microbiome communities, and the optimal Bacteroides-to-Firmicutes ratio might strongly promote growth performance. Waterweed plants also helped decrease maleficent Proteobacteria caused by excess animal-type feedstuff, such as freshwater snails, and might have positive roles in antibacterial functions in gut. A diet based on waterweeds only resulted in lipid metabolism disorders, which significantly retarded the growth of E. sinensis. In summary, E. sinensis cultured with a diet of waterweeds and freshwater snails showed superior growth performance due to their healthy gut microbiota and metabolic homeostasis. Our findings unveiled the roles of aquatic plants and animal-type food such as freshwater snail in shaping the gut microbiota and metabolic processes and provided guidance for the aquaculture of E. sinensis in future.

Genetic Diversity of Aquatic Ranunculus (Batrachium, Ranunculaceae) in One River Basin Caused by Hybridization

Aquatic Ranunculus (sect. Batrachium) include homophyllous and heterophyllous plants. The development of floating leaves may be induced by genetic mechanisms or/and environmental conditions and this fact complicates the morphologically based identification of species. DNA-based studies provide the opportunity to expand the knowledge of this complicated group. We studied heterophyllous Ranunculus with well-developed capillary and intermediate leaves and visually homophyllous plants with capillary leaves from a single river basin, with the aim to evaluate their genetic polymorphism and taxonomic status-whether the plants with well-developed and weakly expressed intermediate leaves belong to different forms (taxa) or if they just express morphological variation of one or two taxa in a specific, very variable river environment. The studied heterophyllous and homophyllous plants from different rivers showed high genetic differentiation and a low level of genetic diversity within these groups. The molecular analysis did not reveal any inter simple sequence repeat (ISSR) polymorphism associated with the development of intermediate leaves. An analysis of nuclear ribosomal internal transcribed spacers ITS1-2 sequences revealed several ribotypes, which indicated the genetic heterogeneity of studied plants and indirectly confirmed the hybrid origin of some of them. Sterile plants originated from crossing of R. circinatus and R. penicillatus were discovered in the Skroblus River; however, identification of the parental species was impeded by the polymorphism detected. For this reason, cytological studies were performed and allowed confirmation of the hybrid origin of these plants.

Tolerance of Landoltia punctata to arsenate: an evaluation of the potential use in phytoremediation programs

Plants used in phytoremediation should accumulate and tolerate a specific pollutant. Here, we aimed at evaluating a possible arsenic (As) accumulation and mechanisms of tolerance against As-induced damage in Landoltia punctata to explore this species for phytoremediation. Plants were subjected to increasing As levels. As absorption was higher with increasing As levels. The activity of superoxide dismutase and glutathione reductase as well as anthocyanin levels increased with As levels. Catalase and peroxidase activities increased in plants subjected to As levels up to 1.0 mg L^-1 and decreased at higher levels. Due to the antioxidant system, higher levels of reactive oxygen species were restrained in plants under low levels of As. However, the levels of superoxide anion, hydrogen peroxide, and lipid peroxidation increased in response to the impaired antioxidant system induced by the highest As levels. Biomass decreased in plants exposed to As and scanning electron microscopy revealed root structural damage in the root cap of plants under 3.0 mg L^-1As. This work highlights that L. punctata can be considered a hyperaccumulator species and has potential for As phytoremediation when levels are lower than 1.0 mg L^-1-a concentration 100-fold higher than that recommended for drinking water. Novelty Statement: Landoltia punctata can be considered a hyperaccumulator species and has the potential for arsenic phytoremediation when levels are lower than 1.0 mg L^-1.

Life in the Current: Anatomy and Morphology of Utricularia neottioides

Rheophytism is extremely rare in the Utricularia genus (there are four strictly rheophytic species out of a total of about 260). Utricularia neottioides is an aquatic rheophytic species exclusively growing attached to bedrocks in the South American streams. Utricularia neottioides was considered to be trap-free by some authors, suggesting that it had given up carnivory due to its specific habitat. Our aim was to compare the anatomy of rheophytic U. neottioides with an aquatic Utricularia species with a typical linear monomorphic shoot from the section Utricularia, U. reflexa, which grows in standing or very slowly streaming African waters. Additionally, we compared the immunodetection of cell wall components of both species. Light microscopy, histochemistry, scanning, and transmission electron microscopy were used to address our aims. In U. neottioides, two organ systems can be distinguished: organs (stolons, inflorescence stalk) which possess sclerenchyma and are thus resistant to water currents, and organs without sclerenchyma (leaf-like shoots), which are submissive to the water streaming/movement. Due to life in the turbulent habitat, U. neottioides evolved specific characters including an anchor system with stolons, which have asymmetric structures, sclerenchyma and they form adhesive trichomes on the ventral side. This anchor stolon system performs additional multiple functions including photosynthesis, nutrient storage, vegetative reproduction. In contrast with typical aquatic Utricularia species from the section Utricularia growing in standing waters, U. neottioides stems have a well-developed sclerenchyma system lacking large gas spaces. Plants produce numerous traps, so they should still be treated as a fully carnivorous plant.

The rhizosphere of aquatic plants is a habitat for cable bacteria

Cable bacteria belonging to the family Desulfobulbaceae couple sulfide oxidation and oxygen reduction by long-distance electron transfer over centimeter distances in marine and freshwater sediments. In such habitats, aquatic plants can release oxygen into the rhizosphere. Hence, the rhizosphere constitutes an ideal habitat for cable bacteria, which have been reported on seagrass roots recently. Here, we employ experimental approaches to investigate activity, abundance, and spatial orientation of cable bacteria next to the roots of the freshwater plant Littorella uniflora. Fluorescence in situ hybridization (FISH), in combination with oxygen-sensitive planar optodes, demonstrated that cable bacteria densities are enriched at the oxic–anoxic transition zone next to roots compared to the bulk sediment in the same depth. Scanning electron microscopy showed cable bacteria along root hairs. Electric potential measurements showed a lateral electric field over centimeters from the roots, indicating cable bacteria activity. In addition, FISH revealed that cable bacteria were present in the rhizosphere of Oryza sativa (rice), Lobelia cardinalis and Salicornia europaea. Hence, the interaction of cable bacteria with aquatic plants of different growth forms and habitats indicates that the plant root–cable bacteria interaction might be a common property of aquatic plant rhizospheres.

Extensive interlineage hybridization in the predominantly clonal Hydrilla verticillata

PREMISE

The submersed aquatic plant Hydrilla verticillata ("hydrilla") is important ecologically and economically due to its aggressive growth in both indigenous and nonindigenous regions. Substantial morphological variation has been documented in hydrilla, including the existence of monoecious and dioecious "biotypes." Whereas plastid sequence data have been used previously to explore intraspecific diversity, nuclear data have yet to be analyzed in a phylogenetic context. Molecular and morphological analyses were used to evaluate the genetic diversity and phylogenetic relationships of native and introduced populations.

METHODS

Nuclear (internal transcribed spacer-ITS; phytoene desaturase-PDS) and plastid (trnL-F) sequence data were evaluated phylogenetically using likelihood and Bayesian methods. Leaf morphologies were compared among clades that were identified in phylogenetic analyses.

RESULTS

Data from both ITS and PDS show multiple instances of polymorphic sequences that could be traced to two or more lineages, including both invasive biotypes in the Americas. Leaf morphological data support the distinctness of lineages and provide a metric for distinguishing monoecious and dioecious biotypes in the United States.

CONCLUSIONS

Nuclear molecular data indicate far greater genetic diversity than could be estimated using plastid markers. Substantially divergent copies of nuclear genes, found in multiple populations worldwide, likely result from interlineage hybridization. Invasive monoecious and dioecious hydrilla biotypes in the Americas are genetically distinct, with both biotypes resulting from admixture among Eurasian progenitors. Genetic similarity to populations in India and South Korea, respectively, implicates these as likely origins for the dioecious and monoecious biotypes.

[Removal of Nitrogen and Phosphorus from Water by Biomass Carbon of Aquatic Plants]

In the bioremediation of eutrophic water, a large number of aquatic plants will be produced. How to continue the reasonable disposition is the question that needs to be solved. In this paper, biomass carbon was prepared from aquatic plants, and the adsorption capacity of the biomass carbon on nitrogen and phosphorus in water was improved by magnesium modification. The characterization results of material properties showed that magnesium modification not only formed nanometer MgO sheets on the surface of biomass carbon to increase the specific surface area, but also introduced hydroxyl functional groups to promote the adsorption of ammonium nitrogen. The adsorption processes of modified biomass carbon on nitrates and ammonium nitrogen belonged to multi-layer adsorption, and the adsorption isotherms conformed to the Freundlich model. The adsorption mechanism of modified biomass carbon changed from single layer adsorption to multi-layer diffusion. The maximum adsorption capacity of the modified biomass carbon on nitrate nitrogen, ammonium nitrogen, and phosphorus were 5.66, 62.53, and 90.92 mg·g^-1, respectively. The adsorption capacity of the modified biomass carbon on ammonium nitrogen is 178 times that of unmodified biomass carbon. When phosphorus, nitrate nitrogen, and ammonium nitrogen coexist, the adsorption amounts of modified biomass carbon increase by 79.1%, 67.5%, and 47.1%, respectively. The results of this paper showed that the preparation of biomass carbon can realize the resource recovery of aquatic plants, and can be used for the removal of nitrogen and phosphorus pollution from water, which has good prospects for application.

Climatic Niche Shift during Azolla filiculoides Invasion and Its Potential Distribution under Future Scenarios

In order to prevent future biological invasions, it is crucial to know non-native species distributions. We evaluated the potential global distribution of Azolla filiculoides, a free-floating macrophyte native to the Americas by using species distribution models and niche equivalency tests to analyze the degree of niche overlap between the native and invaded ranges of the species. The models were projected under two future emission scenarios, three global circulation models and two time periods. Our results indicate a possible niche shift between the distribution ranges of the species, indicating that A. filiculoides can adapt to novel environmental conditions derived from climatic differences during the invasion process. Our models also show that the future potential distribution of A. filiculoides will decrease globally, although the species could colonize new vulnerable regions where it is currently absent. We highlight that species occurrence records in the invaded area are necessary to generate accurate models, which will, in turn, improve our ability to predict potential invasion risk areas.

Does Soil Nutrient Heterogeneity Improve the Growth Performance and Intraspecific Competition of the Invasive Plant Myriophyllum aquaticum?

Spatial heterogeneity in soil nutrient availability is considered to play an important role in promoting plant invasion success and can affect interspecific competition. Although some clonal plants have been demonstrated to be correlated with resource heterogeneity in terrestrial systems, little is known about how soil nutrient heterogeneity affects the growth of invasive aquatic plants or their population structure. A greenhouse experiment was therefore conducted to study the response of the invasive aquatic plant Myriophyllum aquaticum to the spatial heterogeneity of soil nutrients under three plant densities (one, four, or twelve plants 0.28 m2) with a constant amount of soil nutrients. The results showed that soil nutrient heterogeneity significantly increased the number of shoots in the single-plant density treatment. However, heterogeneous soil nutrient treatment significantly increased the number of shoots at the expense of total biomass and aboveground biomass in the twelve-plant density treatment. The heterogeneous soil nutrient treatment had low effects on other growth traits and intraspecific competition under different plant density treatments. These results indicate that spatial heterogeneity in soil nutrient availability may facilitate the spread of M. aquaticum.

A global growth-form database for 143,616 vascular plant species

For the majority of plant species in the world, we know little about their functional ecology, and not even one of the most basic traits-the species' growth habit. To fill the gap in availability of compiled plant growth-form data, we have assembled what is, to our knowledge, the largest global database on growth-form as a plant trait. We have, with extensive error checking and data synthesis, assembled a growth-form database from 163 data sources for 143,616 vascular plant species from 445 different plant families. This is 38.6% of the currently accepted vascular plant diversity. For our database, we have chosen seven categories to cover the majority of the diversity in plant growth forms: aquatic plants, epiphytes, hemiepiphytes, climbing plants, parasitic plants, holo-mycoheterotrophs, and freestanding plants. These categories were used because we were able to reconcile the wealth of existing definitions and types of growth-form information available globally to them clearly and unequivocally, and because they are complementary with existing databases. Plants in the database were designated into a category if their adult growth form fit the criterion. We make available two databases: first, the complete data set, including species for which there is currently conflicting information, and second, a consensus data set, where all available information supports one categorization. Of the plant species for which we found information, 103,138 (72%) are freestanding, 21,110 (15%) are epiphytes, and 4,046 (3%) are parasites. Our growth-form data can be used to produce useful summary statistics by clade. For example, current data suggests that half of pteridophytes are epiphytic, that all hemiepiphytes are eudicots, and that there are no parasitic monocots, gymnosperms, or pteridophytes. Growth form is a crucial piece of fundamental plant-trait data with implications for each species' ecology, evolution, and conservation, and thus this data set will be useful for a range of basic and applied questions across these areas of research. No copyright or proprietary restrictions are associated with the use of this data set, other than citation of the present Data Paper. A static version of this dataset is provided as Supporting Information, and a living and updating version of the dataset is available in a GitHub repository.

Heavy Metal Accumulation in Common Aquatic Plants in Rivers and Lakes in the Taihu Basin

We investigated the concentrations of 10 heavy metals in Potamogeton malaianus, Nymphoides peltata, Eichhornia crassipes, and Hydrilla verticillata to evaluate their potential to bioaccumulate heavy metals and related influencing factors in Taihu Lake. Enrichment factor (EF) values of Cu, Cr, Mn, Ni, Zn, Co, Pb, and V were above 2.0, indicating moderate to significant contamination in sediment. Most of Ti, V, Cr, Mn, and Ni in P. malaianus, E. crassipes, and H. verticillata and V in N. peltata were within excess/toxic level in plants, but higher than normal level. Even though no aquatic plants in this study were identified as a hyperaccumulator, relatively higher concentrations in aquatic plants were found in Taihu Lake than have been found in other previous studies. Heavy metal in submerged plants, especially in their stems, seemed to be more closely related to metals in water and sediment than those in floating-leaf plants. Ratios of metals in stem versus leaves in all plants ranged from 0.2 to 25.8, indicating various accumulation capabilities of plant organs. These findings contribute to the application of submerged aquatic plants to heavy metal removal from moderately contaminated lakes.

Rewilding wetlands: beaver as agents of within-habitat heterogeneity and the responses of contrasting biota

Ecosystem engineers can increase biodiversity by creating novel habitat supporting species that would otherwise be absent. Their more routine activities further influence the biota occupying engineered habitats. Beavers are well-known for transforming ecosystems through dam building and are therefore increasingly being used for habitat restoration, adaptation to climate extremes and in long-term rewilding. Abandoned beaver ponds (BP) develop into meadows or forested wetlands that differ fundamentally from other terrestrial habitats and thus increase landscape diversity. Active BP, by contrast, are superficially similar to other non-engineered shallow wetlands, but ongoing use and maintenance might affect how BP contribute to aquatic biodiversity. We explored the 'within-habitat' effect of an ecosystem engineer by comparing active BP in southern Sweden with coexisting other wetlands (OW), using sedentary (plants) and mobile (water beetles) organisms as indicators. BP differed predictably from OW in environmental characteristics and were more heterogeneous. BP supported more plant species at plot (+15%) and site (+33%) scales, and plant beta diversity, based on turnover between plots, was 17% higher than in OW, contributing to a significantly larger species pool in BP (+17%). Beetles were not differentiated between BP and OW based on diversity measures but were 26% more abundant in BP. Independent of habitat creation beaver are thus significant agents of within-habitat heterogeneity that differentiates BP from other standing water habitat; as an integral component of the rewilding of wetlands re-establishing beaver should benefit aquatic biodiversity across multiple scales.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Treatment efficiency of a hybrid constructed wetland system for municipal wastewater and its suitability for crop irrigation

Design and implementation of wastewater treatment is inevitable due to toxic effects of wastewater irrigation on crops, soil and human health. Current investigation is the pioneer attempt on full-scale hybrid constructed wetland system (HCWS) built for municipal wastewater treatment from Pakistan. HCWS was comprised of vertical sub-surface flow constructed wetland (VSSF-CW) and five phyto-treatment ponds connected in series. Higher environmental risk was associated with untreated municipal wastewater usage in irrigation as estimated through discharge of metals to recipient soils. Treatment efficiency percentages recorded for HCWS reclaimed water quality parameters were, i.e., EC (56.68), TDS (56.86), alkalinity (39.67), chloride (39.68), sulfate (46.73), Na (28.80), Mn (65.24), Cr (78.07), Ni (81.02), BOD (68.74), total hardness (19.56), Fe (70.09), phosphate (55.40), Pb (80.48), COD (63.64), Mg (17.24), K (60.05), Co (100), Cu (67.73), Zn (59.97), Cd (100), and Ca (21.47) respectively. Wastewater treatment in HCWS was due to aquatic plants [Phragmites australis Cav. Trin. ex Steud., Canna indica L. Typha latifolia L., and Hydrocotyle umbellata L.], microbial activities and substrate based wetland processes. The HCWS treated water was well under irrigation standards and recommended for safer crop production in water scarce regions.

Variations in Species-Level N:P Stoichiometry of Charophytes and Aquatic Angiosperms on the Tibetan Plateau

The variations in nitrogen (N) and phosphorus (P) stoichiometry between species and along environmental gradients reflects plant growth and survival under certain conditions. Exploring the determinants of plant N and P stoichiometry at species level could help us understand the mechanisms of plant distribution. Temperature is considered a driving factor in forming the geographical patterns of plant N and P stoichiometry at the community level. Here we selected four common aquatic plants to explore the divergence of plant N and P stoichiometry between species and the species-level variations across large geographical gradients on the Tibetan Plateau. We found that plant N and P concentrations and N:P ratios were significantly different among the four species/groups. Charophytes had the lowest N and P concentrations, but the N:P ratio did not differ significantly from those of angiosperms. All four species/groups plant N concentrations were positively correlated with P concentrations. The temperature was also the primary explanatory variable, while the habitats properties showed weak and inconsistent effects on plant N and P stoichiometry. Plant N and P concentrations increased, but N:P ratios decreased, with decreasing temperature. Altitude, rather than latitude, determined the environmental patterns of plant N and P stoichiometry by affecting the temperature. These findings indicated that, after removing the influences of species replacement at the community level, temperature still plays a primary role in forming the geographical patterns of plant N and P stoichiometry at species level. Plants of each species could optimize their investment strategies of elements under different environmental conditions. The Tibetan Plateau is recognized as an area that is sensitive to global warming. Our results provided evidence, in terms of N and P stoichiometry, of potential variations among aquatic plants in nutrient absorption and element cycling under climatic warming.

Landscape- and Local-Scale Actions Are Essential to Conserve Regional Macrophyte Biodiversity

Regional-scale pond diversity is supported by high variation in community composition. To effectively and efficiently conserve pond regional diversity, it is essential to recognize the community types in a focal region and the scales of the factors influencing the occurrence of respective community types. Based on a flora survey and GIS analysis of 367 ponds in western Japan, we developed a multinomial regression model that describes the relationship between aquatic macrophyte community type (based on cluster analysis) and five environmental factors that differ in the spatial scale at which they operate (i.e., landscape or local scale) and origin (i.e., natural or anthropogenic). A change in topographic configuration resulted in a transition of the community types with high species richness. Increasing urban and agricultural area around ponds resulted in a decrease in species-rich community occurrence; an increase in urban area increased the probability of a pond having no macrophytes, whereas that of paddy field increased the probability of a pond having only a few macrophytes. Pond surface area and proportion of artificial embankment significantly defined the pond community: greater embankment proportions increased the probability of ponds having few or no macrophytes. Our results suggest that conserving regional pond biodiversity will require actions not only at a local scale but also at a sufficiently large spatial scale to cover the full gradient of topographic configurations that influence the macrophyte species composition in ponds.

[Characteristics of N2O Release and Influencing Factors in Grass-type and Algae-type Zones of Taihu Lake During Summer]

Spatial heterogeneity of N₂O generation and emissions in multi-ecotype lakes limited the accurate estimation of the N₂O fluxes in lakes, but few studies on the characteristics of N₂O generation and emissions have been conducted. In this study, N₂O flux at the water-gas interface, dissolved N₂O concentration in the water column, and N₂O flux at the sediment-water interface in typical grass-type and algal-type zones of Taihu Lake were analyzed during summer, and indoor micro-environment experiments were conducted to illustrate the main factors affecting the generation and emissions of N₂O. The results showed that the N₂O fluxes at the water-gas interface, dissolved N₂O concentration, and N₂O fluxes at the sediment-water interface of the emergent macrophyte type area was higher than the algae-type area and submerged macrophyte area during the summer., with N₂O fluxes at the water-gas interface of (115.807±7.583), (79.768±1.842), and (3.685±0.295) μmol ·(m² ·h)^-1, respectively. The dissolved N₂O concentration in the water column were (0.051±0), (0.029±0.001), and (0.018±0) μmol ·L^-1, respectively; and the N₂O fluxes at the sediment-water interface were (178.275±3.666), (160.685±0.642), and (75.665±1.016) μmol ·(m² ·h)^-1, respectively. The spatial difference could be attributed to dominant plants and the concentration of inorganic nitrogen in the water column. The results of micro-environment experiments showed that nitrate and organic carbon sources could significantly increase the N₂O production potential of sediments, the high concentration of NH₄⁺-N in the water column might inhibit the N₂O production in sediments, and the production rates of N₂O in the sediment increased remarkably when the incubation temperature increased, suggesting that the generation and emissions of N₂O were mainly restricted by nitrate, organic carbon, and temperature in summer.

Finding the pond through the weeds: eDNA reveals underestimated diversity of pondweeds

PREMISE OF THE STUDY

The detection of environmental DNA (eDNA) using high-throughput sequencing has rapidly emerged as a method to detect organisms from environmental samples. However, eDNA studies of aquatic biomes have focused on surveillance of animal species with less emphasis on plants. Pondweeds are important bioindicators of freshwater ecosystems, although their diversity is underestimated due to difficulties in morphological identification and monitoring.

METHODS

A protocol was developed to detect pondweeds in water samples using atpB-rbcL and ITS2 markers. The water samples were collected from the Grand River within the rare Charitable Research Reserve, Ontario (RARE). Short fragments were amplified using primers targeting pondweeds, sequenced on an Ion Torrent Personal Genome Machine, and assigned to the taxonomy using a local DNA reference library and GenBank.

RESULTS

We detected two species earlier documented at the experimental site during ecological surveys (Potamogeton crispus and Stuckenia pectinata) and three species new to the RARE checklist (P. foliosus, S. filiformis, and Zannichellia palustris).

DISCUSSION

Our targeted approach to track the species composition of pondweeds in freshwater ecosystems revealed underestimation of their diversity. This result suggests that eDNA is an effective tool for monitoring plant diversity in aquatic habitats.

Associations between Macrophyte Life Forms and Environmental and Morphometric Factors in a Large Sub-tropical Floodplain

Macrophyte assemblages are composed of species with different life forms and various ecological functions. Our aim was to investigate the potential environmental determinants of changes in the biomass of individual life forms and of the composition of the macrophyte assemblage in terms of life forms diversity. We sampled 23 waterbodies at low and high water levels in the Middle Paraná River floodplain. Macrophyte biomass samples were collected and classified in terms of life forms. We performed a redundancy analysis using the biomass of the various life forms to assess the importance of environmental variables to the composition of macrophyte life forms. Linear regressions were applied to investigate the environmental determinants of the biomasses of individual life forms. The degree of connectivity and the combination of depth, hydrology and nitrate were the main determinants of the composition in terms of life forms. The biomass of each individual life form was explained by different combinations of environmental variables, but the connectivity was the most important one. Our study shows that groups of species with similar life forms respond to environmental factors in particular ways, which might alter the biomass composition of life forms. Given that the ecosystem functioning depends on the functional characteristics of local communities, our findings about the relation between environmental changes and the community composition in terms of life forms (or functional composition) can be a helpful tool for predicting changes on ecosystem processes (such as nutrient cycling) against possible future scenarios.

The Dangers of Being a Small, Oligotrophic and Light Demanding Freshwater Plant across a Spatial and Historical Eutrophication Gradient in Southern Scandinavia

European freshwater habitats have experienced a severe loss of plant diversity, regionally and locally, over the last century or more. One important and well-established driver of change is eutrophication, which has increased with rising population density and agricultural intensification. However, reduced disturbance of lake margins may have played an additional key role. The geographical variation in water chemistry, which has set the scene for - and interacted with - anthropogenic impact, is much less well understood. We took advantage of some recently completed regional plant distribution surveys, relying on hundreds of skilled citizen scientists, and analyzed the hydrophyte richness to environment relations in five contiguous South-Scandinavian regions. For three of the regions, we also assessed changes to the freshwater flora over the latest 50-80 years. We found a considerable variation in background total phosphorus concentrations and alkalinity, both within and between regions. The prevalence of functional groups differed between regions in accordance with the environmental conditions and the species' tolerance to turbid waters. Similarly, the historical changes within regions followed the same trend in correspondence to the altered environmental conditions over time. Small submerged species decreased relative to tall submerged and floating-leaved species along the regional and historical eutrophication gradients. These changes were accompanied by systematically greater relative abundance of species of higher phosphorus prevalence. We conclude that species traits in close correspondence with anthropogenic impacts are the main determinants of local, regional and historical changes of species distribution and occupancy, while pure biogeography plays a minor role. Conservation measures, such as re-oligotrophication and re-established disturbance regimes through grazing and water level fluctuations, may help reduce the tall reed vegetation, restore the former richness of the freshwater flora and safeguard red-listed species, although extended time delays are anticipated in nutrient-rich regions, in which species only survive at minute abundance in isolated refugia.

Phytoremediation capabilities of Spirodela polyrhiza, Salvinia molesta and Lemna sp. in synthetic wastewater: A comparative study

Macrophytes have been used to mitigate eutrophication and upgrade effluent quality via their nutrient removal capability. However, the available data are influenced by factors such as microbial activities, weather, and wastewater quality, making comparison between nutrient removal performance of different macrophytes almost impossible. In this study, phytoremediation by Spirodela polyrhiza, Salvinia molesta and Lemna sp. were carried out axenically in synthetic wastewater under controlled condition to precisely evaluate nutrient removal efficiency of NO₃^--N, PO₄^3-, NH₃-N, COD and pH in the water sample. The results showed that ammonia removal was rapid, significant for S. polyrhiza and Lemna sp., with efficiency of 60% and 41% respectively within 2 days. S. polyrhiza was capable of reducing 30% of the nitrate. Lemna sp. achieved the highest phosphate reduction of 86% at day 12 to mere 1.07 mg/L PO₄^3--P. Correlation was found between COD and TC, suggesting the release of organic substances by macrophytes into the medium. All the macrophytes showed biomass increment. S. polyrhiza outperformed other macrophytes in nutrient removal despite lower biomass production. The acquired nutrient removal profiles can serve as a guideline for the selection of suitable macrophytes in wastewater treatment and to evaluate microbial activity in non-aseptic phytoremediation system.