Duckweed Species Research Articles

Natural enemies of Lemna minuta in its native range and their potential as biological control agents for Europe

ABSTRACT Lemna minuta is native to North America but an invasive alien plant in Europe, where it poses significant threats to freshwater ecosystems. Explorations for biological control agents were conducted in two regions of the United States (Louisiana and California), revealing three candidate species. Subsequent laboratory investigations focused on the weevil Tanysphyrus lemnae and the fly Lemnaphila scotlandae as the most promising agents and confirmed that both the herbivorous insects attack L. minuta plants. To evaluate the host specificity of these two potential agents, insects were exposed to five species of duckweed commonly occurring in North America and Europe. Preliminary host-range testing indicated that T. lemnae develops on all evaluated duckweed species, including those from different genera (Lemna, Spirodela, Landoltia). Conversely, data revealed that feeding and development of the dipteran L. scotlandae are limited to species in the genus Lemna, but this includes L. minor, a native European species threatened in Europe due to the spread of L. minuta. No-choice and choice tests confirmed that neither larvae nor adults of L. scotlandae discriminate between the two Lemna species, except for pupation, which occurs more frequently in L. minor under choice conditions. We conclude that the broad host-range of T. lemnae and L. scotlandae render them unsuitable as biological control agents of L. minuta in Europe.

Preliminary studies of selected Lemna species on the oxygen production potential in relation to some ecological factors.

Dissolved oxygen is fundamental for chemical and biochemical processes occurring in natural waters and critical for the life of aquatic organisms. Many organisms are responsible for altering organic matter and oxygen transfers across ecosystem or habitat boundaries and, thus, engineering the oxygen balance of the system. Due to such Lemna features as small size, simple structure, vegetative reproduction and rapid growth, as well as frequent mass occurrence in the form of thick mats, they make them very effective in oxygenating water. The research was undertaken to assess the impact of various species of duckweed (L. minor and L. trisulca) on dissolved oxygen content and detritus production in water and the role of ecological factors (light, atmospheric pressure, conductivity, and temperature) in this process. For this purpose, experiments were carried out with combinations of L. minor and L. trisulca. On this basis, the content of oxygen dissolved in water was determined depending on the growth of duckweed. Linear regression models were developed to assess the dynamics of changes in oxygen content and, consequently, organic matter produced by the Lemna. The research showed that the presence of L. trisulca causes an increase in dissolved oxygen content in water. It was also shown that an increase in atmospheric pressure had a positive effect on the ability of duckweed to produce oxygen, regardless of its type. The negative correlation between conductivity and water oxygenation, obtained in conditions of limited light access, allows us to assume that higher water conductivity limits oxygen production by all combinations of duckweeds when the light supply is low. Based on the developed models, it was shown that the highest increase in organic matter would be observed in the case of mixed duckweed and the lowest in the presence of the L. minor species, regardless of light conditions. Moreover, it was shown that pleustophytes have different heat capacities, and L. trisulca has the highest ability to accumulate heat in water for the tested duckweed combinations. The provided knowledge may help determine the good habitat conditions of duckweed, indicating its role in purifying water reservoirs as an effect of producing organic matter and shaping oxygen conditions with the participation of various Lemna species.

Range expansion risk for a newly established invasive duckweed species in Europe and Canada

Range expansion risk for a newly established invasive duckweed species in Europe and Canada

Passeio de capivara: evidência de dispersão de plantas aquáticas inteiras

Abstract: The functioning of diverse ecosystems relies on the dispersal processes facilitated by animals, known as zoochory. This ecological process is the only way in which some aquatic species can move between aquatic systems through the terrestrial matrix. Despite its paramount importance, the dispersal mechanisms involving certain vectors, such as mammals, have remained relatively poorly understood. Based on observation of capybaras Hydrochoerus hydrochaeris emerging from a wetland with various aquatic plant species attached to their fur, we hypothesized that these mammals play a crucial role in dispersing aquatic plants. We conducted a controlled experiment and confirmed that capybaras disperse two species of duckweed, Lemna valdiviana and Wolffia columbiana, through both endozoochory and epizoochory. The discovery of entire plant dispersal is noteworthy because it is not dependent on the season and does not rely on the production of specific reproductive diaspores. This study presents pioneering documentation of capybaras capacity to disperse entire plants through their gastrointestinal passage and offers further evidence of their role in epizoochory within neotropical wetlands.

On the rise: Development of a multi-tiered, indoor duckweed cultivation system.

Duckweed species (Lemnaceae) are suitable for remediation and valorization of agri-feed industry wastewaters and therefore can contribute to a more sustainable, circular economy where waste is a resource. Industrial applications will, however, require space efficient cultivation methods that are not affected by prevailing weather conditions. Here, the development and operation of a multi-tiered duckweed bioreactor is described. The developed prototype bioreactor depicted in this paper is composed of four cultivation layers (1m2 each) with integrated LED lighting (generating up to 150 μmol m-2 s-1 ), a system of pumps and valves to manage the recirculatory flow (2.5Lmin-1 ) of wastewater, and an automatic harvesting system. Using a nutrient poor medium, good growth of the duckweed species Lemna minor was achieved in the bioreactor, and this was matched by strong nutrient depletion from the medium, especially for phosphorus (45-mg total phosphorus [TP] removed per m-2 day-1 ). A fully automatic harvesting arm reliably captured similar amounts of duckweed biomass across multiple harvesting cycles, revealing a future scenario whereby labor and interventions by human operators are minimized. Further developments to advance the system towards fully automated operation will include, for example, the use of specific nutrient sensors to monitor and control medium composition. It is envisaged that multi-tiered, indoor bioreactors can be employed in the agri-feed industry where wastewaters are, in many cases, continuously generated throughout the year and need remediating immediately to avoid costly storage. Given the extensive use of automation technology in conventional wastewater treatment plants, multi-tiered duckweed bioreactors can be realistically integrated within the operating environment of such treatment plants. PRACTITIONER POINTS: Duckweed is suitable for remediation and valorization of agri-feed wastewater. Industrial duckweed applications require space efficient cultivation methods. Development and operation of a multi-tiered duckweed bioreactor is detailed. Flow dynamics and automatic harvesting in the bioreactor are optimized. It is concluded that a multi-tiered bioreactor can be used in industry.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Population genetic structure of two cryptic duckweed species (Lemna minor &L. turionifera) in Alberta using a genotyping-by-sequencing approach

Identifying population genetic structure is important for the development of species-specific management plans. Investigating the population genetics of cryptic species is even more critical. Here we focus on two cryptic duckweed species easily mistaken for one another, Lemna minor L. and L. turionifera Landolt, which have overlapping ranges in our study region of Alberta, Canada, and elsewhere. We used genotyping-by-sequencing to determine the population genetic structure of both duckweed species. A total of 192 samples was sequenced. After filtering, 16,007 single nucleotide polymorphisms were used to examine patterns of genetic diversity between and within L. minor and L. turionifera. The two species showed clear differentiation. When examining L. minor singly, we discovered at least three genetically distinct populations among the 30 samples from eight sites, even though these were from a small geographic area. In contrast, when examining L. turionifera singly, we found no evidence of genetically distinct populations among 67 samples from 43 sites. We also examined the relationship between surface water quality variables and the distribution of the two Lemna species. The sites containing L. turionifera had a wider range of water chemistry variables suggesting they are more tolerant of different environmental conditions. In contrast, each of the three genetically distinct L. minor groups had different water chemistry profiles. Large differences between L. minor and L. turionifera in their regional distributions and degrees of genetic differentiation highlight the importance of documentation and careful monitoring of Lemna species within Alberta, and in other regions where they co-occur.

DNA barcoding and biomass accumulation rates of native Iranian duckweed species for biotechnological applications.

The Lemnaceae family (duckweed) consists of at least three recognized genera with six reported species in Iran that are distributed in wetlands. Duckweeds are the simplest and smallest flowering aquatic monocots with free-floating fronds that can reproduce asexually every 2-3 days. Duckweed could be a major source of balanced amino acids and high protein content, which is increasingly promising for biotechnological applications. For molecular classification and species identification of the collected samples, DNA barcoding was performed using two standard chloroplast markers, the spacer region between the ATP synthase subunits F and H (atpF-atpH) and the intron region of the ribosomal protein S16 (rps16). The results confirm the presence of four species belonging to the two genera Lemna and Spirodela. In addition, L. turionifera was detected for the first time in Iran. Due to the high growth rates of duckweed, measurement of biomass accumulation and doubling time are important factors in determining growth potential, especially for native species. The relative growth rates (RGR), doubling times (DT), biomass accumulation, and relative weekly yields (RY) of 40 distinct duckweed clones were determined under standard cultivation conditions. The dry weight-based RGR ranged from 0.149 to more than 0.600 per day, DT from 1.12 to 9 days, and RY from 7 to 108.9 per week. All values are comparable with previous studies. RGR and RY of selected clones are higher than the growth potential for a wide range of wild plants and common crops. These data support that native duckweed has high productivity value and should be further investigated as a potentially rich protein source for alternative human food, livestock feed, and recombinant protein production.

Transcriptome analysis reveals genes expression pattern of Spirodela polyrhiza response to heat stress

With global warming, high-temperature stress has become an essential abiotic factor affecting plant growth and survival. However, little knowledge was available of the molecular mechanism that aquatic plants respond to this stress. In the present study, we explore the adaptation mechanism of Spirodela polyrhiza, a surface-water-grown duckweed species broadly distributed worldwide to high temperatures, and analyze its gene expression pattern of S. polyrhiza under heat stress. Three temperature stress treatments, including room temperature group (CK), middle high-temperature group (MTS), and high-temperature group (45 °C, HTS) were set. The results showed that the contents of SOD first increased and then decreased, and those of MDA showed an upward trend under elevated high-temperature stress. According to the transcriptome data, 3145, 3487, and 3089 differently expressed genes (DEGs) were identified between MTS and CK, HTS and CK, and HTS and MTS, respectively. The transcription factors (TFs) analysis showed that 14 deferentially expressed TFs, including HSF, ERF, WRKY, and GRAS family, were responsive to heat stress, suggesting they might play vital roles in improving resistance to heat stress. In conclusion, S. polyrhiza could resist high temperatures by increasing SOD activity and MDA at the physiological level. Several transcription factors, energy accumulation processes, and cell membranes were involved in high-temperature stress at the molecular level. Our findings are helpful in better grasping the adaptation rules of some aquatic plants to high temperatures.

Cultivation of Lemna Minor on Industry-Derived, Anaerobically Digested, Dairy Processing Wastewater.

The growth and nutrient uptake capacity of a common duckweed (Lemnaceae) species, Lemna minor "Blarney", on dairy processing wastewater pre-treated by an anaerobic digester (AD-DPW) was explored. L. minor was cultivated in small stationary vessels in a controlled indoor environment, as well as in a semi-outdoor 35 L recirculatory system. The use of AD-DPW as a cultivation medium for L. minor offers a novel approach to dairy wastewater treatment, evolving from the current resource-intensive clean-up of wastewaters to duckweed-based valorisation, simultaneously generating valuable plant biomass and remediating the wastewater.

Monitoring Duckweeds (Lemna minor) in Small Rivers Using Sentinel-2 Satellite Imagery: Application of Vegetation and Water Indices to the Lis River (Portugal)

Duckweed species, particularly Lemna minor, are widely found in freshwaters all over the world. This macrophyte provides multiple ecosystems’ functions and services, but its excessive proliferation can have negative environmental impacts (including ecological and socio-economic impacts). This work explores the use of remote sensing tools for mapping the dynamics of Lemna minor in open watercourses, which could contribute to identifying suitable monitoring programs and integrated management practices. The study focuses on a selected section of the Lis River (Portugal), a small river that is often affected by water pollution. The study approach uses spatiotemporal multispectral data from the Sentinel-2 satellite and from 2021 and investigates the potential of remote sensing-based vegetation and water indices (Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Aquatic Vegetation Index (NDAVI), Green Red Vegetation Index (GRVI), Normalized Difference Water Index (NDWI)) for detecting duckweeds’ infestation and its severity. The NDAVI was identified as the vegetation index (VI) that better depicted the presence of duckweeds in the surface of the water course; however, results obtained for the other VIs are also encouraging, with NDVI showing a response that is very similar to NDAVI. Results are promising regarding the ability of remote sensing products to provide insight into the behavior of Lemna minor and to identify problematic sections along small watercourses.

Nutritional Content and Growth Ability of Duckweed Spirodela polyrhiza on Various Culture Media

Giant duckweed (Spirodela polyrhiza) is one species of duckweed, distributed cosmopolitanly in stagnant freshwater. The duckweed has several potential uses such as for animal and fish feeds. However, its biological information in Indonesia is rare. A research was conducted in June to July 2019 to explore its nutritional content and growth ability. The growth ability experiment was done with two replications at The Research Center for Limnology, Indonesia Institute of Sciences laboratory. The indoor experiments used 3 types of culture media, namely P (mixture of Urea, NPK, and Gandasil); Q (water waste from catfish cultivation), and R (hydroponic fertilizer). Spirodela polyrhiza has a protein content of 24.10%; fat 1.74%; ash 1.78%, crude fiber 14.47%, and nitrogen-free extract of 57.89%. There were 15 types of amino acids observed in the biomass, made of as much as 13.1% w/w. The highest growth was obtained in R culture media with a specific growth rate (SGR): 8.54–16.53 % and productivity of 15.62–51.32 g/day/m2. Outdoor trials using the R media have a SGR value of 10.17–11.16% and productivity of 54.82–84.1 g/day/m2. Spirodela polyrhiza can be developed and have the potential to be used as an alternative natural feed source for aquaculture or another purpose. Further research is needed.

Pace and shape of senescence in three species of duckweed.

Senescence is progressive bodily deterioration associated with declines in survival and fecundity in older age classes. There is great diversity in patterns of senescence across species, but these patterns can be difficult to compare formally due to variation in the absolute time scales in which species live and die: members of some species live for a matter of days, others for millennia. To address this issue, the “pace‐shape” approach was developed to decouple absolute time from analyses and instead standardize life history traits in terms of average life expectancy, facilitating intra‐ and interspecific comparisons. Here, we use this approach to distinguish the generic form of demographic trajectories (shape) from the time scale on which the trajectories occurred (pace) in three species of tiny, free‐floating aquatic plants known as duckweeds (Lemna gibba L., L. minor L., and L. turionifera Landolt), which have mean lifespans of less than a month under typical lab conditions, and exhibit age‐related declines in survivorship and reproduction. Using a randomized block design in which we tracked a final total of 430 individuals, we report differences in pace and shape among the three species. Specifically, the largest, least‐fecund, and typically longest‐lived species, L. gibba, tended to exhibit more rapid decreases in time‐standardized survivorship and fecundity compared with the other two species. This study emphasizes variation in aging patterns that can be found among plant species, including those in the same genus, and provides further validation for the utility of applying the pace and shape approach in interspecific comparisons.

Dilution rates of cattle slurry affect ammonia uptake and protein production of duckweed grown in recirculating systems

Duckweed is a potential collector of nitrogen from animal liquid manure and a source of protein suitable as feed for livestock and fish. Therefore, it provides opportunities for circular economy systems. Two duckweed species, Spirodela polyrhiza and Landoltia punctata, were grown in five recirculating systems each connected to a reservoir tank filled with water and graded organic cattle slurry concentrations. Fresh and dry biomass, protein production and amino acid profiles among the nitrogen removal were evaluated. Spirodela polyrhiza showed a significantly higher fresh biomass production but L. punctata dry matter content was generally higher resulting in similar dry biomass production for both species This study shows clearly that the crude protein content, ranging between 29.3 and 37.9% of dry matter, was positively correlated to slurry and total ammonia nitrogen (TAN) concentration of the substrate, independent of the duckweed species. Total crude protein yield was in the range of 1.37–1.95 g m−2 d−1, following a quadratic function regarding slurry and TAN concentrations, with marginal differences between species. Biomass and crude protein yields were optimal for both duckweed species at a TAN concentration of 19 mg l−1, which corresponded to a slurry dilution of 1:8. The results of this study provide important information for operation of recirculating duckweed production systems on slurry and operators should aim to keep TAN concentrations in that range for optimization of protein production in conjunction with TAN removal.

Whole structures, core taxa, and functional properties of duckweed microbiomes

The microbiomes of 15 duckweed species in five Lemnaceae genera cultivated in two microbial sources were analyzed using a bacterial 16S rRNA gene sequencing. The structure of duckweed microbiomes resembled each other. Seven families, including Comamonadaceae, Caulobacteraceae, Methylophilaceae, Oxalobacteraceae, Sphingomonadaceae, Rhizobiaceae, and Rhodospirillaceae, accounted for 56.1% to 96.3% of total bacterial communities and were identified as the core taxa conserved among the Lemnaceae family for the first time. Prediction of duckweed microbiome functional properties revealed that the selective recruitment and enrichment of core and other taxa on duckweed surfaces were likely due to superior colonization abilities, such as motility, chemotaxis, and flagellar assembly. These findings will assist in the exploration of duckweed-microbial associations/interactions and their effective use in wastewater treatment and valuable biomass production.

Duckweeds as Promising Food Feedstocks Globally

Duckweeds are the smallest flowering plants on Earth. They grow fast on water’s surface and produce large amounts of biomass. Further, duckweeds display high adaptability, and species are found around the globe growing under different environmental conditions. In this work, we report the composition of 21 ecotypes of fourteen species of duckweeds belonging to the two subfamilies of the group (Lemnoideae and Wolffioideae). It is reported the presence of starch and the composition of soluble sugars, cell walls, amino acids, phenolics, and tannins. These data were combined with literature data recovered from 85 publications to produce a compiled analysis that affords the examination of duckweeds as possible food sources for human consumption. We compare duckweeds compositions with some of the most common food sources and conclude that duckweed, which is already in use as food in Asia, can be an interesting food source anywhere in the world.

Auxin-Producing Bacteria from Duckweeds Have Different Colonization Patterns and Effects on Plant Morphology.

The role of auxin in plant–microbe interaction has primarily been studied using indole-3-acetic acid (IAA)-producing pathogenic or plant-growth-promoting bacteria. However, the IAA biosynthesis pathway in bacteria involves indole-related compounds (IRCs) and intermediates with less known functions. Here, we seek to understand changes in plant response to multiple plant-associated bacteria taxa and strains that differ in their ability to produce IRCs. We had previously studied 47 bacterial strains isolated from several duckweed species and determined that 79% of these strains produced IRCs in culture, such as IAA, indole lactic acid (ILA), and indole. Using Arabidopsis thaliana as our model plant with excellent genetic tools, we performed binary association assays on a subset of these strains to evaluate morphological responses in the plant host and the mode of bacterial colonization. Of the 21 tested strains, only four high-quantity IAA-producing Microbacterium strains caused an auxin root phenotype. Compared to the commonly used colorimetric Salkowski assay, auxin concentration determined by LC–MS was a superior indicator of a bacteria’s ability to cause an auxin root phenotype. Studies with the auxin response mutant axr1-3 provided further genetic support for the role of auxin signaling in mediating the root morphology response to IAA-producing bacteria strains. Interestingly, our microscopy results also revealed new evidence for the role of the conserved AXR1 gene in endophytic colonization of IAA-producing Azospirillum baldaniorum Sp245 via the guard cells.

Interspecific divergence of circadian properties in duckweed plants.

The circadian clock system is widely conserved in plants; however, divergence in circadian rhythm properties is poorly understood. We conducted a comparative analysis of the circadian properties of closely related duckweed species. Using a particle bombardment method, a circadian bioluminescent reporter was introduced into duckweed plants. We measured bioluminescence circadian rhythms of eight species of the genus Lemna and seven species of the genus Wolffiella at various temperatures (20, 25, and 30°C) and light conditions (constant light or constant dark). Wolffiella species inhabit relatively warm areas and lack some tissues/organs found in Lemna species. Lemna species tended to show robust bioluminescence circadian rhythms under all conditions, while Wolffiella species showed lower rhythm stability, especially at higher temperatures. For Lemna, two species (L. valdiviana and L. minuta) forming a clade showed relatively lower circadian stability. For Wolffiella, two species (W. hyalina and W. repanda) forming a clade showed extremely long period lengths. These analyses reveal that the circadian properties of species primarily reflect their phylogenetic positions. The relationships between geographical and morphological factors and circadian properties are also suggested.

Duckweed as a future food: Evidence from metabolite profile, nutritional and microbial analyses

Duckweed species are nutritionally meaningless plant which grow wildly in unattended areas. Therefore, understanding the metabolites content in duckweed species is essential for designing a future food products. Here, we report an untargeted Gas Chromatography-Mass Spectrometry (GC-MS)-based metabolomics approach for comprehensively discriminating between Lemna minor and Wolffia globosa of duckweeds species using principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA). Ten differential metabolites levels were tentatively identified between L. minor and W. globosa. Relative to W. globosa, L. minor appeared to enrich with 5-Hydroxyl-L-tryptophan, Tocopheryl acetate, Naringenin, α-linolenic acid and glutamic acid. Furthermore, the nutritional and microbial analyses of ice cream formulated with dried L. minor were investigated. The nutritional analysis results show that relative to control, the ice cream with 2% dried L. minor had significantly increased protein, fiber and ash content. In addition, total plate count (TPC) for microbial analysis of duckweed ice cream was performed. The result suggested that the small amount of bacteria (3.82 cfu/g) was traced in formulated ice cream with 2% dried L. minor. Overall, the metabolites profile, nutritional and microbial analyses of food used L. minor plant indicate that duckweed is a good candidate for future food.

Species interactions in three Lemnaceae species growing along a gradient of zinc pollution.

Duckweeds (Lemnaceae) are increasingly studied for their potential for phytoremediation of heavy‐metal polluted water bodies. A prerequisite for metal removal, however, is the tolerance of the organism to the pollutant, e.g., the metal zinc (Zn). Duckweeds have been shown to differ in their tolerances to Zn; however, despite them most commonly co‐occurring with other species, there is a lack of research concerning the effect of species interactions on Zn tolerance. Here, we tested whether the presence of a second species influenced the growth rate of the three duckweed species Lemna minor, Lemna gibba, and Lemna turionifera. We used four different Zn concentrations in a replicated microcosm experiment under sterile conditions, either growing the species in isolation or in a two‐species mixture. The response to Zn differed between species, but all three species showed a high tolerance to Zn, with low levels of Zn even increasing the growth rates. The growth rates of the individual species were influenced by the identity of the competing species, but this was independent of the Zn concentration. Our results suggest that species interactions should be considered in future research with duckweeds and that several duckweed species have high tolerance to metal pollution, making them candidates for phytoremediation efforts.