Individual architecture and photosynthetic performance of the submerged form of Drosera intermedia Hayne.

Drosera intermedia grows in acidic bogs in parts of valleys that are flooded in winter, and that often dry out in summer. It is also described as the sundew of the most heavily hydrated habitats in peatlands, and it is often found in water and even underwater. This sundew is the only one that can tolerate long periods of submersion, and more importantly produces a typical submerged form that can live in such conditions for many years. Submerged habitats are occupied by D. intermedia relatively frequently. The aim of the study was to determine the environmental conditions and architecture of individuals in the submerged form of D. intermedia. The features of the morphological and anatomical structure and chlorophyll a fluorescence of this form that were measured were compared with analogous ones in individuals that occurred in emerged and peatland habitats. The submerged form occurred to a depth of 20 cm. Compared to the other forms, its habitat had the highest pH (4.71-4.92; Me = 4.71), the highest temperature and substrate hydration, and above all, the lowest photosynthetically active radiation (PAR; 20.4-59.4%). This form differed from the other forms in almost all of the features of the plant's architecture. It is particularly noteworthy that it had the largest main axis height among all of the forms, which exceeded 18 cm. The number of living leaves in a rosette was notable (18.1 ± 8.1), while the number of dead leaves was very low (6.9 ± 3.8). The most significant differences were in the shape of its submerged leaves, in which the length of the leaf blade was the lowest of all of the forms (0.493 ± 0.15 mm; p < 0.001) and usually the widest. The stem cross-sectional area was noticeably smaller in the submerged form than in the other forms, the xylem was less developed and collaterally closed vascular bundles occurred. Our analysis of the parameters of chlorophyll fluorescence in vivo revealed that the maximum quantum yield of the primary photochemistry of photosystem II is the highest for the submerged form (Me = 0.681), the same as the maximum quantum yield of the electron transport (Me φE0 = 0.183). The efficiency of energy use per one active reaction center of photosystem II (RC) was the lowest in the submerged form (Me = 2.978), same as the fraction of energy trapped by one active RC (Me = 1.976) and the non-photochemical energy dissipation (DI0/RC; Me = 0.916). The ET0/RC parameter, associated with the efficiency of the energy utilization for electron transport by one RC, in the submerged plant reached the highest value (Me = 0.489). The submerged form of D. intermedia clearly differed from the emerged and peatland forms in its plant architecture. The submerged plants had a thinner leaf blade and less developed xylem than the other forms, however, their stems were much longer. The relatively high photosynthetic efficiency of the submerged forms suggests that most of the trapped energy is utilized to drive photosynthesis with a minimum energy loss, which may be a mechanism to compensate for the relatively small size of the leaf blade.

Characterization of the cryptic interspecific hybrid Lemna×mediterranea by an integrated approach provides new insights into duckweed diversity.

Lemnaceae taxonomy is challenged by the particular morphology of these tiny free-floating angiosperms. Although molecular taxonomy has helped clarify the phylogenetic history of this family, some inconsistency with morphological data leads to frequent misclassifications in the genus Lemna. Recently, the finding that Lemna japonica is an interspecific hybrid between Lemna minor and Lemna turionifera provided a clear explanation for one such taxonomic question. Here we demonstrated that L. minor is also capable of hybridizing with Lemna gibba, generating a cryptic but widespread taxon in the Mediterranean area. The nothotaxon Lemna ×mediterranea is described and compared with clones of the putative parental species L. minor and L. gibba. Genetic analysis by nuclear and plastid markers, as well as genome size measurement, revealed that two different cytotypes, diploid and triploid, originated by at least two independent hybridization events. Despite high overall similarity, morphometrical, physiological, and biochemical analyses showed an intermediate position of L. ×mediterranea between its parental species in most qualitative and quantitative characters, and also separation of the two hybrid cytotypes by some criteria. These data provide evidence that hybridization and polyploidization, driving forces of terrestrial plant evolution, contribute to duckweed genetic diversity and may have shaped the phylogenetic history of these mainly asexual, aquatic plants.

Tolerance to mild shading levels in cattail as related to increased photosynthesis and changes in its leaf area and anatomy.

Shading is an environmental factor that has been little investigated regarding its effects on emergent aquatic plants. Typha domingensis Pers. is an emergent macrophyte that demonstrates some plasticity for self-shading, and as it can shade other species in the same area, the effect of shading on its traits deserves further investigation. The objective of the present study was to evaluate the gas exchange, leaf anatomy, and growth of T. domingensis cultivated under increasing shading intensities. The plants were collected and propagated in a greenhouse, and the clones were subjected to four shading intensities: 0% (unshaded), 35%, 73%, and 83% shading created by black nets. Growth traits, clonal production, photosynthesis, transpiration, and leaf anatomy were evaluated. The 73% and 83% shading promoted the death of all plants, but all plants survived in the 35% and unshaded treatments. Compared with the unshaded treatment, the 35% shading treatment promoted a higher photosynthetic rate and greater transpiration, supporting increased growth and production of clones. The increase in the photosynthetic rate in the 35% shading was related to the increase in leaf area which increased the photosynthesis of the whole plant. The 73% and 83% treatments inhibited the development of photosynthetic parenchyma and stomata in T. domingensis, leading to a drastic reduction in photosynthesis and energy depletion. Therefore, T. domingensis does not tolerate intense shading, but its photosynthetic characteristics and growth are favored by mild shading, a factor that may be of great importance for its competitiveness and invasive behavior.

Predation risk-mediated indirect effects promote submerged plant growth: Implications for lake restoration.

Biological manipulation, involving fish stockings, is commonly used to counteract the deterioration of submerged vegetation in eutrophic lakes. Nevertheless, the non-consumptive effects (NCEs) of stocked carnivorous fish are often overlooked. Using a controlled experimental system, we investigated the NCEs of a native carnivorous fish, snakehead (Channa argus), on two key biological factors, herbivore-dominated grass carp (Ctenopharyngodon idella) and disturbance-dominated loach (Misgurnus anguillicaudatus), influencing submerged plants growth. Additionally, we conducted a meta-analysis on predation risk and primary productivity. The results reveal that predation risk induces oxidative stress damage and affects grass carp growth. Non-significant changes in cortisol and glucose may be linked to predation risk prediction. Simultaneously, predation risk reduces fish feeding and disturbance behavior, relieving pressure on submerged plants to be grazed and disturbed, thereby supporting plant development. The presence of submerged plants, in turn, enhances loach activity and influences water body characteristics through negative feedback. Furthermore, the meta-analysis results indicate the facilitative effect of predation risk on primary producers. Our findings contribute to the understanding of biological manipulation theory. We demonstrate that the predation risk associated with introducing carnivorous fish can promote the growth of submerged plants through behaviorally mediated indirect effects. This highlights the potential utility of predation risk in lake restoration efforts.

Shoots and Turions of Aquatic Plants as a Source of Fatty Acids.

BACKGROUND: Fatty acids are essential for human health. Currently, there is a search for alternative sources of fatty acids that could supplement such sources as staple crops or fishes. Turions of aquatic plants accumulate a variety of substances such as starch, free sugars, amino acids, reserve proteins and lipids. Our aim is to see if turions can be a valuable source of fatty acids. METHODS: Overwintering shoots and turions of aquatic carnivorous plants were collected. The plant material was extracted with hexane. The oils were analyzed using a gas chromatograph with mass spectrometer. RESULTS: The dominant compound in all samples was linolenic acid. The oil content was different in turions and shoots. The oil content of the shoots was higher than that of the turions, but the proportion of fatty acids in the oils from the shoots was low in contrast to the oils from the turions. The turions of Utricularia species were shown to be composed of about 50% fatty acids. CONCLUSIONS: The turions of Utricularia species can be used to obtain oil with unsaturated fatty acids. In addition, the high fatty acid content of turions may explain their ability to survive at low temperatures.

Genetic diversity and gene expression diversity shape the adaptive pattern of the aquatic plant Batrachium bungei along an altitudinal gradient on the Qinghai-Tibet plateau.

It is an intriguing issue of evolutionary biology how genetic diversity and gene expression diversity shape the adaptive patterns. Comparative transcriptomic studies of wild populations in extreme environments provide critical insights into the relative contribution of genetic and expressive components. In this study, we analyzed the genetic diversity and gene expression diversity of 20 populations of the aquatic plant Batrachium bungei along elevations ranging from 2690 to 4896 m on the Qinghai-Tibet plateau (QTP). Based on single nucleotide polymorphisms (SNPs) and gene expression data from 100 individuals of B. bungei, we found that variation in genetic sequence was more sensitive to detect weak differentiation than gene expression. Using 292,613 high-quality SNPs, we documented a significant phylogeographical structure, a low within-population genetic diversity, and a high inter-population genetic differentiation in B. bungei populations. Analysis of relationship between geographic distance, genetic distance, and gene expression similarity showed that geographic isolation shaped gene flow patterns but not gene expression patterns. We observed a negative relationship between genetic diversity and gene expression diversity within and among B. bungei populations, and we demonstrated that as environmental conditions worsen with increasing altitude, genetic diversity played an increased role in maintaining the stability of populations, while the corresponding role of gene expression diversity decreased. These results suggested that genetic diversity and gene expression diversity might act as a complementary mechanism contributing to the long-term survival of B. bungei in extreme environments.

Among-species variation in flower size determines florivory in the largest tropical wetland.

PREMISE: Flower 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, the patterns of florivory levels and its consequences for plant communities need to be investigated further. 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 incidence and intensity in the Pantanal, the world's largest tropical wetland. Between December 2020 and November 2021, the percentage of flowers attacked (incidence) and petal area removed (intensity) by florivores were examined in 51 species from 25 families, considering flowering season, the substrate where the plants occur, and flower attributes as potentially determining factors on florivory levels. 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.

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.

Métodos de aprendizaje automático para evaluar la vulnerabilidad y el potencial de restauración de las transiciones de estados de los ecosistemas Resumen Las transiciones de estado de los ecosistemas pueden tener consecuencias ecológicas graves o ser un éxito de restauración. Estas transiciones son comunes en los sistemas acuáticos, especialmente si consideramos los cambios mediados por humanos en el uso del suelo y del agua. Generamos un marco conceptual transferible para permitir las evaluaciones multiescalares de la resiliencia del estado y las alertas tempranas de la transición de estado que sirvan para guiar las restauraciones estratégicas y evitar el colapso del ecosistema. Este marco integró predicciones de aprendizaje automático a los conceptos de estado del ecosistema (p. ej.: clasificación del estado, gradientes de vulnerabilidad y potencial de restauración que lleve a transiciones de estado) y fue diseñado para investigar los posibles factores ambientales. Para aplicar el marco, generamos probabilidades de predicción de la presencia de vegetación acuática sumergida (VAS) en casi 10,000 sitios del Alto Río Mississippi en los Estados Unidos. Después usamos un método de interpretabilidad para explicar las predicciones del modelo y obtener información de los posibles factores ambientales y umbrales o respuestas lineales de la presencia y ausencia de la VAS. La precisión del modelo fue de 89% sin sesgo espacial. Los mejores pronosticadores y probables factores ambientales de la idoneidad de hábitat de la VAS fueron la profundidad promedio del agua, los sólidos suspendidos, el sustrato y la distancia a la VAS más cercana. Estos factores ambientales exhibieron respuestas no lineales de tipo umbral para la VAS. Todos los resultados también están presentados en un tablero virtual para explorar los resultados a varias escalas espaciales. Los resultados del modelo de idoneidad de hábitat y las explicaciones de las predicciones de varias de las escalas espaciales (4 m-400 km de alcance del río) pueden guiar la investigación y la planeación de la restauración.

Phylogeny of Alisma (Alismataceae) revisited: implications for polyploid evolution and species delimitation.

Alisma L. is a genus of aquatic and wetland plants belonging to family Alismataceae. At present, it is thought to contain ten species. Variation in ploidy level is known in the genus, with diploids, tetraploids and hexaploids recorded. Previous molecular phylogenetic studies of Alisma have generated a robust backbone that reveals important aspects of the evolutionary history of this cosmopolitan genus, yet questions remain unresolved about the formation of the polyploid taxa and the taxonomy of one particularly challenging, widely distributed species complex. Here we directly sequenced, or cloned and sequenced, nuclear DNA (nrITS and phyA) and chloroplast DNA (matK, ndhF, psbA-trnH and rbcL) of multiple samples of six putative species and two varieties, and conducted molecular phylogenetic analyses. Alisma canaliculatum and its two varieties known in East Asia and A. rariflorum endemic to Japan possess closely related but heterogeneous genomes, strongly indicating that the two species were generated from two diploid progenitors, and are possibly siblings of one another. This evolutionary event may have occurred in Japan. Alisma canaliculatum var. canaliculatum is segregated into two types, each of which are geographically slightly differentiated in Japan. We reconstructed a single phylogeny based on the multi-locus data using Homologizer and then applied species delimitation analysis (STACEY). This allowed us to discern A. orientale as apparently endemic to the Southeast Asian Massif and distinct from the widespread A. plantago-aquatica. The former species was most likely formed through parapatric speciation at the southern edge of the distribution of the latter.

Short-term effects of macrophyte removal on aquatic biodiversity in rivers and lakes.

Mass development of macrophytes is an increasing problem in many aquatic systems worldwide. Dense mats of macrophytes can negatively affect activities like boating, fishing or hydropower production and one of the management measures often applied is mechanical removal. In this study, we analyzed the effect of mechanical macrophyte removal on phytoplankton, zooplankton, and macroinvertebrate (pelagic and benthic samples) assemblages. Our study covered five sites in four countries in Europe and Africa with highly variable characteristics. In all sites, dense mats of different macrophyte species (Juncus bulbosus in a river in Norway; a mix of native macrophytes in a German river, Elodea nuttallii in a lake in Germany, Ludwigia spp. In a French lake and Pontederia crassipes in a South African lake) are problematic and mechanical removal was applied. In every country, we repeated the same BACI (Before-After-Control-Impact) design, including "before", "one week after", and "six weeks after" sampling in a control and an impact section. Repeating the same experimental design at all sites allowed us to disentangle common effects across all sites from site-specific effects. For each taxonomic group, we analyzed three structural and three functional parameters, which we combined in a scoring system. Overall, the removal of macrophytes negatively affected biodiversity, in particular of zooplankton and macroinvertebrate assemblages. In contrast, plant removal had positive effects on the phytoplankton assemblages. Effects were more pronounced one week after removal than six weeks after. Consequently, we suggest a stronger consideration of the effect of plant removal on biodiversity to arrive at more sustainable management practices in the future.

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.

Endophytic microbiota of floating aquatic plants: recent developments and environmental prospects.

Plant-associated microorganisms play a critical role in plant survival and functional attributes. There are many studies on the taxonomical and functional aspects of microorganisms associated with terrestrial plants. However, the microbiome of aquatic plants is not much explored. This work details the studies on microbiomes and diversity in microbial communities inhabiting the three common free-floating aquatic plants of tropical regions viz. duckweed, water hyacinth and water lettuce, widely implicated for their bioremediation potential. Studies conducted till date reveal the prevalence and dominance of different Bacillus sp. Other genera, including Rhodanobacter, Pseudomonas, Rhizobium, Achromobacter, Serratia, Actinobacteria, Proteobacter, Klebsiella and Acidobacteria, have also been prominently reported. This lesser explored niche offers great bioprospecting opportunities to obtain taxonomically diverse and functionally distinct microorganisms. Bacterial endophytes from these aquatic plants have been primarily studied for their ability to produce indole acetic acid and degrade phenol. Limited studies reveal some fungal endophytes to have promising herbicidal effect. Not much is known on other functional attributes and hence microbial studies on these plants holds much promise for obtaining novel isolates or isolates with novel functions that would impact both aquatic and terrestrial ecosystems. This study proposes the need for exploring the role of endophytes as biocontrol agents and their potential to provide a pragmatic and robust solution to the aquatic weed menace in freshwater bodies. Bioprospecting of this lesser studied ecological niche hence is a promising field of research that has both environmental and economic potential.

Identification for the species of aquatic higher plants in the Taihu Lake basin based on hyperspectral remote sensing.

Aquatic plants are crucial for aquatic ecosystems and their species and distribution reflect aquatic ecosystem health. Remote sensing technology has been used to monitor plant distributions over large scales. However, the fine identification of the species of aquatic higher plants is challenging due to large temporal-spatial changes in optical water body properties and small spectral differences among plant species. Here, an aquatic plant identification method was developed by constructing a decision tree file in the C4.5 algorithm based on the canopy spectra of eight plants in the Changguangxi Wetland water area from hyperspectral remote sensing technology. The method was used to monitor the distribution of different plants in the Changguangxi Wetland area and two other water areas. The results showed that the spectral characteristics of plants were enhanced by calculating their spectral index, thereby improving the comparability among different species. The total recognition accuracy of the constructed decision tree file for eight types of plants was 85.02%. Nymphaea tetragona, Pontederia cordata, and Nymphoides peltatum had the highest recognition accuracy and Eichhornia crassipes was the lowest. The specific species and distributions of aquatic plants were consistent with the water quality in the area. The results can provide a reference for the accurate identification of aquatic plants in the same type of water area.

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.

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.

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.

Influence of glyphosate and its metabolite aminomethylphosphonic acid on aquatic plants in different ecological niches.

Glyphosate and its metabolite aminomethylphosphonic acid (AMPA) draw great concern due to their potential threat to aquatic ecosystems. The individual and combined effects of glyphosate and AMPA on aquatic plants in different ecological niches need to be explored. This study aimed to investigate the ecotoxicity of glyphosate and AMPA on the emergent macrophyte Acorus calamus, phytoplankton Chlorella vulgaris, and submerged macrophyte Vallisneria natans after their exposure to glyphosate and AMPA alone and to their mixture. Medium and low concentrations of glyphosate (≤ 0.5 mg L-1) significantly inhibited the growth of V. natans and promoted the growth of C. vulgaris (P < 0.05) but had no significant effect on the growth of A. calamus (P > 0.05). AMPA (≤ 5.0 mg L-1) did not significantly influence the relative growth rate (except C. vulgaris) or malonaldehyde levels but significantly altered the expression levels of chlorophyll-related genes and superoxide dismutase [Cu-Zn] genes in the aquatic plants examined. AMPA mainly affected the oxidative phosphorylation pathway in V. natans and not those in other two plants, indicating that V. natans was more sensitive to AMPA-induced oxidative damage. Moreover, antagonistic effects on plant growth were observed when plants were exposed to low concentrations of glyphosate + AMPA (≤ 0.1 + 0.1 mg L-1). When the concentration of glyphosate + AMPA reached 0.5 + 0.5 and 5.0 + 5.0 mg L-1, the growth of the submerged macrophyte was additively or synergistically inhibited, but the growth of the emergent macrophyte and phytoplankton was antagonistically inhibited. Our results indicated that both the individual and combined effects of glyphosate and AMPA might alter the vertical structure of shallow lakes and accelerate the conversion of shallow lakes from grass-based to algal-based lakes.

Genome-wide identification and comparative analysis of the WRKY gene family in aquatic plants and their response to abiotic stresses in giant duckweed (Spirodela polyrhiza).

WRKY is one of the largest transcription factor families across higher plant species and is involved in important biological processes and plant responses to various biotic/abiotic stresses. However, only a few investigations on WRKYs have been conducted in aquatic plants. This study first systematically analyzed the gene structure, protein properties, and phylogenetic relationship of 693 WRKYs in nine aquatic and two wetland plants at the genome-wide level. The pattern of WRKY groups in two aquatic ferns provided new evidence for the origin and evolution of WRKY genes. ARE cis-regulatory elements show an unusual high frequency in the promoter region of WRKY genes, indicating the adaptation to the aquatic habitat in aquatic plants. The WRKY gene family experienced a series of gene loss events in aquatic plants, especially group III. Further studies were conducted on the interaction network of SpWRKYs, their target genes, and non-coding RNAs. The expression profile of SpWRKYs under phosphate starvation, cold, and submergence conditions revealed that most SpWRKYs are involved in the response to abiotic stresses. Our investigations lay the foundation for further study on the mechanism of WRKYs responding to abiotic stresses in aquatic plants.

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.

Removal effects of aquatic plants on high-concentration phosphorus in wastewater during summer.

Aquatic plants are widely used in depth treatment of wastewater; however, the phosphorus (P) removal mechanisms of aquatic plants at high temperatures in summer are not well understood. Eight aquatic plants, including two floating species (Ludwigia peploides and Hydrocharis dubia) and six emergent species (Lythrum salicaria, Sagittaria sagittifolia, Canna indica, Sparganium stoloniferum, Rotala rotundifolia, and Ludwigia ovalis), were treated with five P solutions (3.0, 3.5, 4.0, 4.5, and 5.5 mg L-1) for 5 weeks in a greenhouse during summer at air temperatures ranging from 25 to 35 °C. H. dubia, L. peploides, L. salicaria, and S. sagittifolia showed high water P removal efficiencies (exceeded 95%). Furthermore, their corresponding residual P concentrations in water were almost lower than the limit value of 0.2 mg L-1 of Grade III in the Chinese Environmental Quality Atandards for Surface Water (GB3838-2002). Plants have different water P removal paths. For example, H. dubia enriched more P with water P concentration increasing significantly. As the culture time increased, the water pH fluctuated significantly in the fall, and then H. dubia used the produced H+ enrich P. L. peploides did not enrich P, but proliferated rapidly, to remove P from water by increasing its fresh weight (FW). L. salicaria and S. sagittifolia showed two paths of enrich-P and FW increase. During the growth process of L. salicaria, the stem diameter and leaf length increased with an increase in P concentration in water or plant or both; however, the height and root length of L. peploides were reduced. Moreover, SOD and CAT activities responded to high P concentrations in water or high temperatures or both, which protected against oxidative damage. These findings could offer theoretical foundation and practical guidance for selection of aquatic plant species in depth treatment of wastewater during summer.