Plant Lemna Research Articles

A preharvest finishing procedure for Lemna to produce high levels of zeaxanthin that is retained post-high-light exposure

Development of a productive, nutritious, and low-input food source is needed for humanity's expanding population on Earth and for long-duration crewed space missions. The exceptionally protein- and micronutrient-rich members of the aquatic plant family Lemnaceae are uniquely suited for both purposes. We here introduce a protocol to accumulate large quantities of the carotenoid zeaxanthin that are retained post-high-light exposure. The function of the essential human micronutrients zeaxanthin, lutein, vitamin E (α-tocopherol), and pro-vitamin A (β-carotene) are briefly reviewed. Attention is given to the role of zeaxanthin in opposing oxidants (reactive oxygen species), the production of which is further enhanced by space radiation. We report a new preharvest finishing procedure – sudden transfer of Lemna plants grown in low light (200 µmol photons m-2 s-1) to high light (1000 µmol photons m-2 s-1) for six hours, which rapidly increased and stabilized zeaxanthin content. Unlike terrestrial crops, Lemna possessed a uniquely high protein content when grown in low light and did not experience any adverse effects of the abrupt five-fold increase in light intensity. These findings provide additional justification for Lemnaceae as food crops with applications on Earth as well as for future long-duration human space missions.

Chemical Characteristics of Zirconium Chloride and Zirconium Oxide Nanoparticles Driving Toxicity on Lemna minor

The increasing global production and utilization of zirconium (Zr) compounds, including zirconium chloride (ZrCl4) and zirconium oxide nanoparticles (NPs-ZrO2), raises concerns about their potential environmental impact. This study investigated the toxicity mechanisms of ZrCl4 and NPs-ZrO2 on the aquatic plant Lemna minor. The physicochemical properties of NPs-ZrO2 in the test medium were characterized, revealing concentration-dependent changes in the hydrodynamic diameter, zeta potential, and solubility over time. The analysis of Zr speciation showed the predominance of Zr(OH)4(aq) species from ZrCl4. Plants of L. minor exposed to ZrCl4 and NPs-ZrO2 exhibited differential Zr bioaccumulation, growth inhibition, oxidative stress, and antioxidant responses. ZrCl4 induced a higher toxicity than NPs-ZrO2, with bioaccumulation strongly correlating with adverse effects. The differential toxicity impact between these two Zr-compounds was also determined by the lowest observed-effect doses for growth and biochemical parameters. The scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed internalization of NPs-ZrO2 and Zr uptake in the L. minor plant. Therefore, these findings highlighted the importance of chemical speciation, environmental transformations, and biological responses in assessing the ecological impact of Zr-compounds for effective risk assessment and management strategies for protecting aquatic ecosystems.

Impacts of Fulvic Acid on the Toxicity of the Herbicide Atrazine to Lemna minor.

Fulvic acids (FA) are environmentally prevalent components of dissolved organic carbon. Little research has evaluated their potential influence on the bioavailability of herbicides to non-target aquatic plants. This study evaluated the potential impacts of FA on the bioavailability of atrazine (ATZ) to the aquatic plant Lemna minor. Plants were exposed to 0, 15, 30, 60, 125, and 750µg/L ATZ in media containing three FA concentrations (0, 5, and 15mg/L) in a factorial study under static conditions. Fronds were counted after 7- and 14-days exposure and intrinsic growth rates (IGR) and total frond yields were calculated for analysis. Atrazine NOAECs and LOAECs within each FA treatment series (0, 5, or 15mg/L) were identified and EC50s were estimated. NOAEC/LOAECs for yield and IGR were 60/125 µg/L except for yield in the 0mg/L-FA series (30/60) and IGR in the 5mg/L-FA series (30/60). NOAEC/LOAECs were 30/60 µg/L for all treatments and both endpoints after 14 days exposure. EC50s ranged from 88.2 to 106.1µg/L (frond production 7 DAT), 158.0-186.0µg/L (IGR, 7 DAT), 74.7-86.3µg/L (frond production, 14 DAT), and 144.1-151.3µg/L (IGR, 14 DAT). FA concentrations did not influence the toxicity of ATZ.

Temperature dependence and genetic variation in resource acquisition strategies in a model freshwater plant

Abstract Understanding how competition varies with environmental stress is critical to anticipating species and community responses to rapid environmental change. While the stress‐gradient hypothesis predicts the strength of competition to decrease with increasing stress, our understanding of how competition varies with stress is limited by a lack of mechanistic understanding of how resource‐use traits underlying competitive dynamics respond to stress. Here, we use duckweeds in the Lemna species complex to measure how phenotypic and genetic variation in R* (a resource acquisition trait representing the minimum resource requirement for positive population growth) varies with high‐temperature stress to better understand how stress alters competitive ability for essential resources. We found that heat stress increased the R* of Lemna plants for nitrogen acquisition. Because lower R* values predict dominance in competitive dynamics where resources are limiting, this indicates that under stressful, high temperatures, plants could experience reduced competitive ability due to the higher resources required to sustain positive population growth rates. We found minimal genetic variation in R* across 11 local genotypes within the Lemna species complex, indicating that selection on resource acquisition strategies for essential resources such as nitrogen may be constrained in nature. The expression of genetic variation in R* for nitrogen was further reduced under heat stress, suggesting that the response to selection for R* could be particularly constrained under high‐temperature stress. Contrary to predictions drawn from the gleaner–opportunist trade‐off, we did not find evidence for a trade‐off in resource acquisition strategies under benign conditions or high‐temperature stress. Plants with lower R* (i.e. higher growth rates under lower nitrogen levels) were not constrained to have lower growth rates under higher nitrogen levels, possibly because the chosen genotypes have not diverged across resource acquisition strategies or because Lemna spp. has escaped this constraint. Importantly, our work indicates that high‐temperature stress could increase sensitivity to competition through an increased requirement for resources while reducing the evolutionary potential for Lemna species to respond to selection for resource traits. This study acts as a key step to understanding the mechanistic traits behind competitive dynamics in resource‐limited and stressful environments. Read the free Plain Language Summary for this article on the Journal blog.

Peracetic acid activated by nickel cobaltite as effective oxidizing agent for BPA and its analogues degradation

The presented research concerns the use of nickel cobaltite nanoparticles (NiCo2O4 NPs) for the heterogeneous activation of peracetic acid and application of NiCo2O4-PAA system for degradation 10 organic micropollutants from the group of bisphenols. The bisphenols removal (initial concentration 1 μM) process was optimized by selecting the appropriate process conditions. The optimal amount of catalyst (115 mg/L), peracetic acid (PAA) concentration (7 mM) and pH (7) were determined using response surface analysis in the Design of Experiment. Then, NiCo2O4 NPs were used to check the possibility of reuse in subsequent oxidation cycles. The work also attempts to explain the mechanism of oxidation of the studied micropollutants. The participation of the sorption process on the catalyst was excluded and based on the experiments with radical scavengers it can be concluded that the oxidation proceeds in a radical pathway, mainly with participation of O2•- radicals. Experiments conducted in real water matrices exhibit low impact on degradation efficiency. Toxicity tests with green alga Acutodesmus obliquus and aquatic plant Lemna minor showed that post-reaction mixture influenced growth and the content of photosynthetic pigments in concentration dependent manner.

Effects of two pharmaceuticals: Doxycycline and norfloxacin on plant and animal organisms living in the freshwater

The main reason for the appearance of pharmaceutical compounds in the aquatic environment is their regular excretion by humans and animals in an unchanged form or slightly metabolized. Pharmaceuticals limit the habitable living environment for aquatic organisms, because they can be toxic not only to bacteria but also to non-target organisms. Plants of the Lemnoideae subfamily and crustaceans Daphniindae family are widely used as bioindicators in freshwater environmental risk assessments. This study aimed to use biotests (Lemna test and Daphtoxkit) to determine the effect of two pharmaceuticals: antibiotic – Doxycycline (DOX) and semi-synthetic chemotherapeutic drug – Norfloxacin (NOR) on plants Lemna minor and crustaceans Daphnia magna. Standard Lemna test was extended to include pharmaceutical effects on plant chlorophyll content (LCC) and fluorescence (Fo, Fm, and Fv/Fm), and the confirmation of drug toxicity was the biotest Daphtoxkit assessing the immobilization (IM) of organisms. Studies have shown that DOX was more toxic than NOR on tested aquatic organisms: plants and crustaceans. The lowest observed effect concentration (EC20) of DOX and NOR reduced by 20 % LCC and Iy of L. minor was 2.14 and 8.11 mg × L−1, respectively. The LCC was an early and sensitive indicator of the phytotoxic effects of DOX in L. minor before morphological changes were observed. Confirmation of drug toxicity was the Daphtoxkit. The EC20 (180. min) of DOX and NOR, IM of daphnia by 20 % was 117.18 and 215.42 mg × L−1, respectively. In conclusion, DOX and NOR in aquatic environments may have significant implications for tested organisms and their ecosystems.

Occurrence and distribution of azole antifungal agents in eight urban Romanian waste water treatment plants

Azole compounds are utilized to combat fungal infections in plants to protect them and also used for treating mycosis in humans. The LC-MS/MS method is a technique that combines liquid chromatography with tandem mass spectrometry for analysis of twelve azole compounds from wastewater (influent, effluent) and sewage sludge. The compounds were isolated from waste water using automatic extraction in the solid phase. Sludge samples were dried by lyophilization, after which they were subjected to ultrasound extraction with methanol. The quantification limits ranged from 0.3 ng/L (clotrimazole-CLO and prochloraz-PRO) to 1.5 ng/L (tetraconazole-TEB and penconazole-PEN), for wastewater samples and for sewage sludge, the LOQs ranged from 0.1 ng/g to 0.6 ng/g. High concentrations of climbazole-CLI (207–391 ng/L), tebuconazole (92–424 ng/L), and clotrimazole (6.9–93-ng/L) were observed in influent samples of the 8 urban wastewater treatment plants, followed by fluconazole (49.3–76.8 ng/L), and prochloraz (7.3–72 ng/L). The ∑Azoles had a maximum of 676 ng/L in the Galati effluent, followed by the Bucharest station 357 ng/L, and 345 ng/L in the Braila effluent. The highest value of the daily mass loading (input) level was observed for climbazole, 265 mg/day/1000 in Iasi station, followed by tebuconazole, 238 mg/day/1000 people in the Bucharest station, and 203 mg/day/1000 people for climbazole in the Targoviste station. The daily mass emission presented values between 0.7 and 247 mg/day/1000 people. The highest emissions were observed for climbazole, 247 mg/day/1000 people in Braila station; 174 mg/day/1000 people in the Iasi station and 129 mg/day/1000 people in the Bucharest station. The concentrations of climbazole detected in the effluent can present a high risk for the plants Lemna minor and Navicula pelliculosa. Clotrimazole may present a high risk to the plant Desmodesmus subspicatus and to the invertebrate Daphnia magna. PRO may present high risk to the invertebrate Mysidopsis Bahia.

Effects of biodegradable P3HB on the specific growth rate, root length and chlorophyll content of duckweed, Lemna minor

The extensive production and use of plastics have led to widespread pollution of the environment. As a result, biodegradable polymers (BDPs) are receiving a great deal of attention because they are expected to degrade entirely in the environment. Therefore, in this work, we tested the effect of two fractions (particles <63 μm and particles from 63 to 125 μm) of biodegradable poly-3-hydroxybutyrate (P3HB) at different concentrations on the specific growth rate, root length, and photosynthetic pigment content of the freshwater plant Lemna minor. Microparticles with similar properties made of polyethylene terephthalate (PET) were also tested for comparison. No adverse effects on the studied parameters were observed for either size fraction; the only effect was the root elongation with increasing P3HB concentration. PET caused statistically significant root elongation only in the highest concentration, but the effect was not as extensive as for P3HB. The development of a biofilm on P3HB particles was observed during the experiment, and the nutrient sorption experiment showed that the sorption capacity of P3HB was greater than PET's. Therefore, depleting the nutrients from the solution could force the plant to increase the root surface area by their elongation. The results suggest that biodegradable microplastics may cause secondary nutrient problems in the aquatic environment due to their biodegradability.

Exposure of Lemna minor (Common Duckweed) to Mixtures of Uranium and Perfluorooctanoic Acid (PFOA).

A variety of processes, both natural and anthropogenic, can have a negative impact on surface waters, which in turn can be detrimental to human and environmental health. Few studies have considered the ecotoxicological impacts of concurrently occurring contaminants, and that is particularly true for mixtures that include contaminants of emerging concern (CEC). Motivated by this knowledge gap, the present study considers the potential ecotoxicity of environmentally relevant contaminants in the representative aquatic plant Lemna minor (common duckweed), a model organism. More specifically, biological effects associated with exposure of L. minor to a ubiquitous radionuclide (uranium [U]) and a fluorinated organic compound (perfluorooctanoic acid [PFOA], considered a CEC), alone and in combination, were monitored under controlled laboratory conditions. Lemna minor was grown for 5 days in small, aerated containers. Each treatment consisted of four replicates with seven plants each. Treatments were 0, 0.3, and 3 ppb PFOA; 0, 0.5, and 5 ppb U; and combinations of these. Plants were observed daily for frond number and signs of chlorosis and necrosis. Other biological endpoints examined at the conclusion of the experiment were chlorophyll content and antioxidant capacity. In single-exposure experiments, a slight stimulatory effect was observed on frond number at 0.3 ppb PFOA, whereas both concentrations of U had a detrimental effect on frond number. In the dual-exposure experiment, the combinations with 5 ppb U also had a detrimental effect on frond number. Results for chlorophyll content and antioxidant capacity were less meaningful, suggesting that environmentally relevant concentrations of PFOA and U have only subtle effects on L. minor growth and health status. Environ Toxicol Chem 2023;42:2412-2421. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Phytoremediation, recovery and toxic effects of ionic gadolinium using the free-floating plant Lemna gibba

The biosorption and recovery of ionic gadolinium (Gd) from contaminated water by the free-floating duckweed Lemna gibba was studied. The highest non-toxic concentration range was determined as (6.7 mg L-1). The concentration of Gd in the medium and in the plant biomass was monitored and a mass balance was established. Tissue Gd concentration of Lemna increased with increasing Gd concentration of the medium. The bioconcentration factor was up to 1134 and in nontoxic concentrations up to 2.5 g kg-1 Gd tissue concentration was reached. Lemna ash contained 23.2 g Gd kg-1. Gd removal efficiency from the medium was 95%, however, only 17–37% of the initial Gd content of the medium accumulated in Lemna biomass, an average of 5% remained in the water, and 60–79% was calculated as a precipitate. Gadolinium-exposed Lemna plants released ionic Gd into the nutrient solution when they were transferred to a Gd-free medium. The experimental results revealed that in constructed wetlands, L. gibba is able to remove ionic Gd from the water and can be suitable for bioremediation and recovery purposes.

Presence of microbiome decreases fitness and modifies phenotype in the aquatic plant Lemna minor.

Plants live in close association with microbial organisms that inhabit the environment in which they grow. Much recent work has aimed to characterize these plant-microbiome interactions, identifying those associations that increase growth. Although most work has focused on terrestrial plants, Lemna minor, a floating aquatic angiosperm, is increasingly used as a model in host-microbe interactions and many bacterial associations have been shown to play an important role in supporting plant fitness. However, the ubiquity and stability of these interactions as well as their dependence on specific abiotic environmental conditions remain unclear. Here, we assess the impact of a full L. minor microbiome on plant fitness and phenotype by assaying plants from eight natural sites, with and without their microbiomes, over a range of abiotic environmental conditions. We find that the microbiome systematically suppressed plant fitness, although the magnitude of this effect varied among plant genotypes and depended on the abiotic environment. Presence of the microbiome also resulted in phenotypic changes, with plants forming smaller colonies and producing smaller fronds and shorter roots. Differences in phenotype among plant genotypes were reduced when the microbiome was removed, as were genotype by environment interactions, suggesting that the microbiome plays a role in mediating the plant phenotypic response to the environment.

Phytoremediation of mercury from water by monocultures and mixed cultures pleustophytes

Mercury pollution is a global environmental problem. An alternative to the chemical method of removing mercury from the aquatic environment is the phytoremediation process, based on phytofiltration, phytoextraction, and phytovolatilization techniques. The study showed the effectiveness of phytoremediation with plants Lemna minor and Salvinia natans carried out in monoculture systems and mixed cultures. We used Hoagland's mercury-contaminated liquid medium: 0.15 mgHg/dm3, 0.20 mgHg/dm3 and 0.30 mgHg/dm3. The relative growth rate of plants in the control samples was 0.04–0.07 g/gd. In the presence of mercury for monocultures, observed a toxic effect in the form of growth stimulation, and the relative growth rate reached 0.12 g/gd. The bioconcentration factor was the highest on the 7th day of mercury exposure and was 216–856. The efficiency of mercury removal from the substrate in the phytoremediation process was 96 %. The total protein was increased for Lemna minor by 34 %, Salvinia natans by 84 %, and in mixed culture by up to 99 %. Also, the total chlorophyll increased for Lemna minor by 14 % and for the mixed culture by up to 60 %. For Salvinia natans, the total chlorophyll decreased by 53 %. The biochemical changes may have been a toxic effect of mercury in the environment.

Comprehensive Ecotoxicity Studies on Quaternary Ammonium Salts Synthesized from Vitamin B3 Supported by QSAR Calculations.

Lately, ionic forms (namely, quaternary ammonium salts, QASs) of nicotinamide, widely known as vitamin B3, are gaining popularity in the sectors developing novel pharmaceuticals and agrochemicals. However, the direct influence of these unique QASs on the development of various terrestrial plants, as well as other organisms, remains unknown. Therefore, three compounds comprising short, medium, and long alkyl chains in N-alkylnicotinamide were selected for phytotoxicity analyses, which were conducted on representative dicotyledonous (white mustard) and monocotyledonous (sorghum) plants. The study allowed the determination of the impact of compounds on the germination capacity as well as on the development of roots and stems of the tested plants. Interestingly, independently of the length of the alkyl chain or plant species, all QASs were established as non-phytotoxic. In addition, QSAR simulations, performed using the EPI Suite™ program pack, allowed the determination of the products' potential toxicity toward fish, green algae, and daphnids along with the susceptibility to biodegradation. The obtained nicotinamide derivative with the shortest chain (butyl) can be considered practically non-toxic according to GHS criteria, whereas salts with medium (decyl) and longest (hexadecyl) substituent were included in the 'acute II' toxicity class. These findings were supported by the results of the toxicity tests performed on the model aquatic plant Lemna minor. It should be stressed that all synthesized salts exhibit not only a lack of potential for bioaccumulation but also lower toxicity than their fully synthetic analogs.

Multigenerational effects of microplastic fragments derived from polyethylene terephthalate bottles on duckweed Lemna minor: Size-dependent effects of microplastics on photosynthesis

The 2019 global coronavirus disease pandemic has led to an increase in the demand for polyethylene terephthalate (PET) packaging. Although PET is one of the most recycled plastics, it is likely to enter the aquatic ecosystem. To date, the chronic effects of PET microplastics (MPs) on aquatic plants have not been fully understood. Therefore, this study aimed to investigate the adverse effects of PET MP fragments derived from PET bottles on the aquatic duckweed plant Lemna minor through a multigenerational study. We conducted acute (3-day exposure) and multigenerational (10 generations from P0 to F9) tests using different-sized PET fragments (PET0–200, < 200 μm; PET200–300, 200–300 μm; and PET300–500, 300–500 μm). Different parameters, including frond number, growth rate based on the frond area, total root length, longest root length, and photosynthesis, were evaluated. The acute test revealed that photosynthesis in L. minor was negatively affected by exposure to small-sized PET fragments (PET0–200). In contrast, the results of the multigenerational test revealed that large-sized PET fragments (PET300–500) showed substantial negative effects on both the growth and photosynthetic activity of L. minor. Continuous exposure to PET MPs for 10 generations caused disturbances in chloroplast distribution and inhibition of plant photosynthetic activity and growth. The findings of this study may serve as a basis for future research on the generational effects of MPs from various PET products.

Effects of parental age on salt stress tolerance in an aquatic plant

Parental age influences components of offspring fitness in many species. The ability to tolerate stress also affects fitness, but less is known regarding changes in offspring stress tolerance with increasing parental age, especially in plants. We examined first and fifth‐born clonal offspring (using birth order as a proxy for parental age), and compared their fitness in several sub‐lethal concentrations of salt (NaCl), to investigate the interactive effects of birth order and salt stress on the offspring of the aquatic plant Lemna minor L. We found that increasing salt concentration reduced reproduction particularly at early ages, which detrimentally affected fitness, as measured by the intrinsic rate of natural increase. Fifth offspring had greater fitness than first offspring, potentially due to the hump‐shaped relationship between offspring fitness and birth order observed in other studies on Lemna, with fifth offspring near the peak of the hump. We found no interactive effect of birth order and salt concentration on offspring fitness; however, there were interactive effects on the time to first reproduction and the size of fronds. Specifically, first offspring exposed to increasing salt concentrations exhibited longer delays to first reproduction and grew to a greater size, while fifth offspring showed little change in either variable with increasing salt concentration. Thus, variation in birth order affected offspring response to salt stress, although not in terms of fitness. These results help illuminate factors impacting the age‐specific strength of natural selection and stress responses, and may be environmentally relevant in the context of environmental salinization.

Effects of Microplastic Contamination on the Aquatic Plant Lemna minuta (Least Duckweed)

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP's impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.

Aquatic Ecological Risk Evaluation of Chiral Triazole Fungicide Prothioconazole and Its Metabolite Prothioconazole-Desthio on Lemna minor

The potential risk posed by the chiral triazole fungicide prothioconazole and its metabolite, prothioconazole-desthio to aquatic ecosystems has attracted attention. At present, the aquatic toxicity of prothioconazole is focused on aquatic animals, and the study of aquatic plants is limited. In this work, the acute toxicity of prothioconazole (PTZ) and its metabolite, prothioconazole-desthio (PTD), to the aquatic plant Lemna minor (L. minor) was evaluated at the enantiomer level. The effects of the prothioconazole and its metabolite enantiomer on the physiological and biochemical indices, including growth rate, photosynthetic pigment content, and antioxidant-defense-enzymes activity, of L. minor were measured to evaluate the potential risk. The results showed that prothioconazole and prothioconazole-desthio possessed obvious stereoselective toxicity to Lemna minor with an LC50 (7 days) of 0.76–5.63 mg/L. The toxicity order was S-PTD &gt; Rac-PTD &gt; S-PTZ &gt; R-PTD &gt; Rac-PTZ &gt; R-PTZ. The S-PTZ, which had the highest toxicity, obviously inhibited the biosynthesis of photosynthetic pigments and the activity of antioxidant-defense enzymes (malondialdehyde, catalase and superoxide dismutase), leading to an increase in MDA content and oxidative damage. The results further confirmed that the metabolism of PTZ in aquatic ecosystems increased its exposure risk, providing data support and a theoretical basis for the risk assessment of PTZ.

Differential phytotoxic effect of silver nitrate (AgNO3) and bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) on Lemna plants (duckweeds)

Duckweeds are aquatic plants often used in phytotoxic studies for their small size, simple structure, rapid growth, high sensitivity to pollutants and facility of maintaining under laboratory conditions. In this paper, induced phytotoxic effects were investigated in Lemna minor and Lemna minuta after exposition to silver nitrate (AgNO3) and silver nanoparticles stabilized with sodium citrate and L-Cysteine (AgNPs-Cit-L-Cys) at different concentrations (0, 20 and 50 mg/L) and times (7 and 14 days). Lemna species responses were evaluated analyzing plant growth (mat thickness, fresh and dry biomass, relative growth rate – RGR) and physiological parameters (chlorophyll – Chl, malondialdehyde – MDA, ascorbate peroxidase – APX and catalase - CAT). Ag content was measured in the fronds of the two Lemna species by inductively coupled plasma optical emission spectrometry. AgNO3 and AgNPs-Cit-L-CYs produced phytotoxic effects on both duckweed species (plant growth and Chl reduction, MDA increase) that enhanced in response to increasing concentrations and exposure times. AgNPs-Cit-L-Cys caused much less alteration in the plants compared to AgNO3 suggesting that the presence of bifunctionalized AgNPs-Cit-L-Cys have a reduced phytotoxic effect as compared to Ag+ released in water. Based on the physiological performance, L. minuta plants showed a large growth reduction and higher levels of chlorosis and stress in respect to L. minor plants, probably due to greater Ag+ ions accumulation in the fronds. Albeit with some differences, both Lemna species were able to uptake Ag+ ions from the aqueous medium, especially over a period of 14 days, and could be considered adapt as phytoremediation agents for decontaminating silver ion-polluted water.

Harnessing plant-microbiome interactions for bioremediation across a freshwater urbanization gradient

Urbanization impacts land, air, and water, creating environmental gradients between cities and rural areas. Urban stormwater delivers myriad co-occurring, understudied, and mostly unregulated contaminants to aquatic ecosystems, causing a pollution gradient. Recipient ecosystems host interacting species that can affect each others’ growth and responses to these contaminants. For example, plants and their microbiomes often reciprocally increase growth and contaminant tolerance. Here, we identified ecological variables affecting contaminant fate across an urban-rural gradient using 50 sources of the aquatic plant Lemna minor (duckweed) and associated microbes, and two co-occurring winter contaminants of temperate cities, benzotriazole and salt. We conducted experiments totalling >2,500 independent host-microbe-contaminant microcosms. Benzotriazole and salt negatively affected duckweed growth, but not microbial growth, and duckweeds maintained faster growth with their local, rather than disrupted, microbiota. Benzotriazole transformation products of plant, microbial, and phototransformation pathways were linked to duckweed and microbial growth, and were affected by salt co-contamination, microbiome disruption, and source sites of duckweeds and microbes. Duckweeds from urban sites grew faster and enhanced phytotransformation, but supported less total transformation of benzotriazole. Increasing microbial community diversity correlated with greater removal of benzotriazole, but taxonomic groups may explain shifts across transformation pathways: the genus Aeromonas was linked to increasing phototransformation. Because benzotriazole toxicity could depend on amount and type of in situ transformation, this variation across duckweeds and microbes could be harnessed for better management of urban stormwater. Broadly, our results demonstrate that plant-microbiome interactions harbour manipulable variation for bioremediation applications.

Circadian-period variation underlies the local adaptation of photoperiodism in the short-day plant Lemna aequinoctialis

SummaryPhenotypic variation is the basis for trait adaptation via evolutionary selection. However, the driving forces behind quantitative trait variations remain unclear owing to their complexity at the molecular level. This study focused on the natural variation of the free-running period (FRP) of the circadian clock because FRP is a determining factor of the phase phenotype of clock-dependent physiology. Lemna aequinoctialis in Japan is a paddy field duckweed that exhibits a latitudinal cline of critical day length (CDL) for short-day flowering. We collected 72 strains of L. aequinoctialis and found a significant correlation between FRPs and locally adaptive CDLs, confirming that variation in the FRP-dependent phase phenotype underlies photoperiodic adaptation. Diel transcriptome analysis revealed that the induction timing of an FT gene is key to connecting the clock phase to photoperiodism at the molecular level. This study highlights the importance of FRP as a variation resource for evolutionary adaptation.