Duckweed Research Articles

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.

Lemna as a Sustainable, Highly Nutritious Crop: Nutrient Production in Different Light Environments

Development of a nutritious, sustainable food source is essential to address worldwide deficiencies in human micronutrients. Aquatic floating plants (e.g., species in the family Lemnaceae, duckweeds) are uniquely suited for area-efficient productivity with exceptionally high rates of growth and nutritional quality. Here, we provide an overview of the role of dietary micronutrients (with a focus on carotenoids) in human health and the promise of Lemnaceae as sustainable crops. We examine the effect of growth light environment on plant biomass production and levels of the carotenoids zeaxanthin, lutein, and pro-vitamin A (β-carotene), as well as the antioxidant vitamin E (α-tocopherol), and protein. Data on each of these nutrients are reported on a plant dry biomass basis (as relevant for nutrition) as well as relative to the required input of light energy (as relevant to resource-use efficiency).

Improving biorefinery sustainability and profitability by cultivating aquatic plants on ozonized distillery effluents

Industrial production of biogas offers a way to manage distillery leachate. The waste is usually subjected to anaerobic digestion for producing biogas. However, the effluent from anaerobic processes has high chemical oxygen demand (COD) and is harmful to the environment. An effective method of lowering COD is ozonation. Effluent from biogas plants after ozonation has the potential for use in breeding grounds for plants of the Lemnaceae family. Thus, they can provide a valuable additional source of biomass for the production of bioethanol. Lemna minor L. and Spirodela polyrhiza cultures were grown in media with the addition of 2.5% PFE, which had been treated by ozonation for between 6 and 50 min. Using ozonated effluent was an effective cultivation technique in all variants. The analyzed parameters were plant growth, chlorophyll index, fresh plant weight and photosynthetic traits (net photosynthesis, stomatal conductance, transpiration and concentration of intercellular CO2). The best growth of Lemna minor L. was observed in the media with PFE treated for 12 min. Similar effects were obtained for S. polyrhiza, with ozone treatment for 12 and 25 min. The results show the potential of using ozone-treated post-fermentation leachate as a supplement in culture media.

Total Active Compounds and Mineral Contents in Wolffia globosa

Wolffia globosa, or watermeal, is an aquatic plant belonging to the Lemnaceae family that is consumed as food and sold in local markets of Thailand. The aim of this study was to quantify selected active compounds and minerals in W. globosa ethanolic extract and evaluate its antioxidant activity. Total phenolic, flavonoid, and anthocyanin contents were analyzed. High-performance liquid chromatography was used for the determination of beta-carotene, ferulic acid, luteolin-7-O-β-D-glucoside, and kaempferol. Mineral contents (iron, potassium, calcium, magnesium, zinc, and sodium) were determined by atomic absorption spectroscopy. Antioxidative activity was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azobis (3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging assays. The beta-carotene, ferulic acid, luteolin-7-O-β-D-glucoside, and kaempferol contents of the extract were 2.52 ± 0.10, 1.40 ± 0.10, 2.42 ± 0.50, and 1.57 ± 0.14 mg/g extract, respectively. The highest mineral content in the W. globosa extract was magnesium. The wet extract of W. globosa showed higher amounts of all minerals than the dry extract. Freshly prepared and boiled W. globosa extracts showed radical scavenging activity at 1000 µg/milliliter with 75.77 ± 0.93% and 67.10 ± 0.20% inhibition of DPPH and 70.40 ± 7.20% and 59.78 ± 3.16% inhibition of ABTS, respectively. This plant is a promising novel source of natural phytochemical constituents and antioxidants and has potential for development as a plant-based nutraceutical product for the treatment of diseases caused by free radicals.

Co-pyrolysis of paper mill sludge and textile dyeing sludge with high calorific value solid waste: Pyrolysis kinetics, products distribution, and pollutants transformation

Paper mill sludge (PMS) and printing and textile dyeing sludge (TDS) are two typical industrial sludge with high calcium content, high ash content and low calorific value. To attain effective removal of industrial solid waste, in this study, PMS and TDS are first pyrolyzed independently to study their thermochemical behavior. Results show that 600 °C is the optimal pyrolysis temperature for both PMS and TDS from the perspective of organics degradation. However, the yield and quality of pyrolysis oil and gas are still at low level due to the characteristics of high ash content and low organic content, which is not suitable for fuel recovery. Two kinds of organic solid wastes with high calorific value, duckweed (DW) and waste tire (WT), are co-pyrolyzed with PMS and TDS, which can effectively reduce activation energy and increase the yield of liquid and gas products. The most prominent is P1D1 pyrolysis gas, the production of CH4 and C2-C3 increased from 10.80 L/kg and 3.89 L/kg to 20.16 L/kg and 15.58 L/kg respectively, and the high calorific value also increased to 230.93 kJ/kg. The quality of pyrolysis liquid has been improved significantly as the declined N and O-heteroatom content (especially for P1D1 and T1W1) due to the inhibition effect of co-pyrolysis on the N/O migration into pyrolytic liquid. The solid residue from the co-pyrolysis of PMS and DW contains rich N-functional groups and can promote the conversion of pyridinic-N and pyrrolic-N to quaternary-N. Compared with independent pyrolysis, co-pyrolysis can promote the degradation of harmful organic matter in sludge. The addition of DW and WT co-pyrolysis reduced the solid residue yield of PMS by 19.9 wt% and 14.9 wt% (13.4 wt% and 10.5 wt% for TDS). This work provides inspiration for further understanding the safe disposal of PMS and TDS by pyrolysis.

Graphene/hydroxyapatite nano-composite for enhancement of hydrogen productivity from delignified duckweed

The incredible growth of the duckweed (DW) in the water ecosystem causes severe environmental problems and reduces biodiversity. Harvesting and valorization of such plants represents a challenge due to its richness with organics. Hydrogen productivity (HP) from dark fermentation of delignified duckweed (DDW) is the main objective of current research. The anaerobes cultures were immobilized on the Graphene/hydroxyapatite nano-composite (nG/HAP) for enhancement of hydrogen yield (HY) and enzymes activities. The HP of 13.5 ± 0.78 mL was obtained from the fermentation of native DW and significantly increased up to 208.9 ± 12.6 mL for delignified one. This was linked to an increase of the hydrogenase enzyme (HE) activities from 0.02 ± 0.0003 to 0.109 ± 0.004 mg M.B reduced/min. The HP was further increased up to 387.1 ± 13.6 mL for batches containing 80 mg/gVS of nG/HAP. nG/HAP inhibited the competitors and promoted the cooperators for the Firmicutes hydrogen producers.

A Machine-Learning Method to Assess Growth Patterns in Plants of the Family Lemnaceae.

Numerous new technologies have been implemented in image analysis methods that help researchers draw scientific conclusions from biological phenomena. Plants of the family Lemnaceae (duckweeds) are the smallest flowering plants in the world, and biometric measurements of single plants and their growth rate are highly challenging. Although the use of software for digital image analysis has changed the way scientists extract phenomenological data (also for studies on duckweeds), the procedure is often not wholly automated and sometimes relies on the intervention of a human operator. Such a constraint can limit the objectivity of the measurements and generally slows down the time required to produce scientific data. Herein lies the need to implement image analysis software with artificial intelligence that can substitute the human operator. In this paper, we present a new method to study the growth rates of the plants of the Lemnaceae family based on the application of machine-learning procedures to digital image analysis. The method is compared to existing analogical and computer-operated procedures. The results showed that our method drastically reduces the time consumption of the human operator while retaining a high correlation in the growth rates measured with other procedures. As expected, machine-learning methods applied to digital image analysis can overcome the constraints of measuring growth rates of very small plants and might help duckweeds gain worldwide attention thanks to their strong nutritional qualities and biological plasticity.

Conquering Space with Crops That Produce Ample Oxygen and Antioxidants

Sustainable long-term space missions require regenerative life support from plants. Traditional crop plants lack some features desirable for use in space environments. The aquatic plant family Lemnaceae (duckweeds) has enormous potential as a space crop, featuring (i) fast growth, with very high rates of O2 production and CO2 sequestration, (ii) an exceptional nutritional quality (with respect to radiation-fighting antioxidants and high-quality protein), (iii) easy propagation and high productivity in small spaces, and (iv) resilience to the stresses (radiation, microgravity, and elevated CO2) of the human-inhabited space environment. These traits of Lemnaceae are placed into the context of their unique adaptations to the aquatic environment. Furthermore, an overview is provided of the challenges of galactic cosmic radiation to plant and human physiology and the mechanisms involved in oxidative injury and the prevention/mitigation of such effects by antioxidant micronutrients. A focus is placed on the carotenoid zeaxanthin accumulated by Lemnaceae in unusually high amounts and its role in counteracting system-wide inflammation, cognitive dysfunction, and other oxidative injuries in humans.

Biodiversity of Duckweed (Lemnaceae) in Water Reservoirs of Ukraine and China Assessed by Chloroplast DNA Barcoding

Monitoring and characterizing species biodiversity is essential for germplasm preservation, academic studies, and various practical applications. Duckweeds represent a group of tiny aquatic plants that include 36 species divided into 5 genera within the Lemnaceae family. They are an important part of aquatic ecosystems worldwide, often covering large portions of the water reservoirs they inhabit, and have many potential applications, including in bioremediation, biofuels, and biomanufacturing. Here, we evaluated the biodiversity of duckweeds in Ukraine and Eastern China by characterizing specimens using the two-barcode protocol with the chloroplast atpH–atpF and psbK–psbI spacer sequences. In total, 69 Chinese and Ukrainian duckweed specimens were sequenced. The sequences were compared against sequences in the NCBI database using BLAST. We identified six species from China (Spirodela polyrhiza, Landoltia punctata, Lemna aequinoctialis, Lemna minor, Lemna turionifera, and Wolffia globosa) and six from Ukraine (S. polyrhiza, Lemna gibba, Lemna minor, Lemna trisulca, Lemna turionifera, and Wolffia arrhiza). The most common duckweed species in the samples from Ukraine were Le. minor and S. polyrhiza, accounting for 17 and 15 out of 40 specimens, respectively. The most common duckweed species in the samples from China was S. polyrhiza, accounting for 15 out of 29 specimens. La. punctata and Le. aequinoctialis were also common in China, accounting for five and four specimens, respectively. According to both atpH–atpF and psbK–psbI barcode analyses, the species identified as Le. aequinoctialis does not form a uniform taxon similar to other duckweed species, and therefore the phylogenetic status of this species requires further clarification. By monitoring duckweeds using chloroplast DNA sequencing, we not only precisely identified local species and ecotypes, but also provided background for further exploration of native varieties with diverse genetic backgrounds. These data could be useful for future conservation, breeding, and biotechnological applications.

Grouping the Potential Local Feed Ingredients for Ornamental Fish Feed based on their Nutrient Composition, Cost, and Availability

In the ornamental fish industry, there is a growing concern about the higher freight cost of feed ingredients. The present study aimed to cluster the locally available ingredients based on their nutrient contents, price, and availability. A total of 15 ingredients; fish meal (FM), by-catches (BC), soybean seeds (Soy), maize (Ma), duckweed (DW), Azolla pinnata (Az), rice bran (RB), shrimp shells (SS), palmyrah fruit pulp (PFP), red seaweed (RS), wheat flour (WF), cassava flour (CF), cornflour (CoF), coconut copra waste (CCC), and groundnut cake (GNC) were selected as locally available ingredients. Principal Component Analysis (PCA) was performed by grouping the ingredients based on their nutrient contents, price, and availability using Minitab 16. In PCA, the two first components accounted for 57.50% of the total variance in the initial data. Protein, calcium, phosphorus, and price contribute positively with component 1, whereas carbohydrate content is related negatively to this component. Calcium and ash content correlated positively with component 2 and fat, gross energy, and availability were linked negatively to it. The PCA allowed the clustering the ingredients into four groups. Ingredients in Group 1, including Az, SS, RB, DW, and RS showed a positive correlation with component 2 and they contain more fiber although, they are not accessible throughout the year. Ingredients of Group 2, PFP, WF, CoF, and CF are excellent sources of starch but contained less protein content (0.94%, 11.00%, 0.00%, and 2.80% respectively). CCC, Ma, GNC, and SB pertain to group 3 correlating poorly with component 2. They are an excellent source of protein with the advantage that they are relatively affordable and easy to available than the other groups. Ingredients in group 4 incorporated BC and FB. Although they are high in protein, they are expensive and very poor in carbohydrates. Therefore, it is recommended that the ingredients in group 3 are the best choice for feed formulation with balanced nutrition at a low cost for fish feed preparation.

Septage effluent treatment using floating constructed wetland with Spirodela polyrhiza: Response of biochar addition in the support matrix

Amendments and modifications in conventional methods are continuously required to make wastewater treatment cost-effective, easy to handle, and eco-friendly. Given that, the present study aimed to investigate the efficacy of duckweed (Spirodela polyrhiza)-based multilayer floating constructed wetland (CW) with wood biochar (BC), as carbon stock in the support matrix for treatment of septage effluent. For that four different setups: S+BC+DW (sand + BC + duckweed), S+BC (sand + BC); S (sand); DW (duckweed) were prepared using PVC plastic columns (30 cm length × 11 cm Ø) filled with support matrix and changes in effluent parameters i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), ammonium N (NH4+-N), nitrate (NO3-N), phosphate (PO4−3), and sulphate (SO4−2) were monitored after each 24 h interval for 168 hr HRT. The maximum reduction in PO4−3, TN, NH4+-N, BOD, COD, SO4−2 and NO3-N load was found to be 68.43 %, 64.29 %; 66.41 %, 81.87 %, 58.02 %, 60.48 %, and 64.45%, respectively in S+BC+DW setup. The performance of the studied CW setups was in the order: S+BC+DW> S+BC > S > DW. Phytoremediation assisted by BC-meditated adsorption and chemical oxidation could be the major mechanisms for septage effluent treatment in different CW setups. The results of the study could be beneficial for developing nature-based-low-cost septage treatment setups for rural areas under the decentralized wastewater treatment tools.

Wolffia, a minimalist plant and synthetic biology chassis.

A highly simplified species for genome engineering would facilitate rational design of a synthetic plant. A candidate species is the aquatic, non-grass monocot wolffia (Wolffia australiana) in the Lemnaceae family. Commonly known as watermeal, wolffia is a rootless ball of several thousand cells the size of a pinhead and the fastest growing plant known on Earth. Its extreme morphological reduction is coupled to transposon-mediated streamlining of its transcriptome, which represents a core set of nonredundant protein coding genes. Despite its body plan and transcriptome being highly specialized for continuous growth, wolffia retains cell types relevant to higher plants. Systems level studies with this species could enable the creation of a defined biological chassis for synthetic plant construction.

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.

REPLACING OF SOYA BEANS BY DUCK WEED (LEMNA GIBBA) IN THE DIETS OF FRY OF COMMON CARP (CYPRINUS CARPIO)

Soya bean was replaced in ratio of 20% and 40% by a dry duck weed in the diet of common carp fry under laboratory conditions. The results showed that the fry which fed on duck weeds gives a final total length of 40.15mm, final wet weight of 1.105 gm and final increase of weight was 0.966gm. The group of larvae which fed on soya bean recorded 37.230 mm, 0.750 gm and 0.618 gm respectively.

A Review on the application of Macrophytes in Phytoremediation of Heavy metal Polluted water

Heavy metal pollution is a major source of pollution in the environment. Heavy metal pollution in ground and surface water threatens human health and the aquatic ecology. Traditional treatment approaches for removing pollutants from wastewater are typically expensive, time-consuming, harmful to the environment and inefficient. Phytoremediation is a low-cost, environmentally sustainable, emerging technology with a long-term application. The most important part of successful phytoremediation is plant species selection. Organic and inorganic contaminants are removed with great efficiency by aquatic macrophytes. Metal accumulator plants such as water hyacinth, water lettuce and duck weed as well as a few other aquatic plants, are commonly used to treat heavy-metal polluted water. In order to show the extensive applicability of phytoremediation, a comprehensive review about the aquatic macrophytes in phytoremediation has been compiled.

Pectin from Duckweed (Lemnaceae) As Potential Commercial Pectin and Its Gelling Function in Food Production: A Review

Duckweed, a small flowering plant which comes from Lemnaceae family, has been rising in popularity to many researches and applications for its numerous valuable functional properties. One of its special features is fast growing plant and easily adapted to various types of regions which makes it attractive to be manipulated in many applications including in biofuel production, waste water treatment and also for pharmaceutical and medicinal purposes. Pectin is the common component found in plant cell wall and it has been used as food additive for its capability to gel, emulsify and stabilize food products. Several requirements for commercial pectin such as galacturonic acid content (GalA) and degree of amidation have been regulated. Studies have proven that duckweed have significant amount of pectin which make it as a potential source of gelling agent in food industry. However, the structural properties of pectin from duckweed need to be investigated, in order to ensure if they meet the regulated requirements for industrial production. It is also to determine the suitability of duckweed pectin utilization in different type of food products since pectin of different sources have different structural characteristics, thus exhibit different gelling capability. This present review discusses on the potential of pectin from duckweed species to be utilized as food additive with gelling function in food products. Several extraction methods also have been reviewed, which each of them showed different efficiency and affect the extracted pectin characteristics.

Pectin from Duckweed (Lemnaceae) As Potential Commercial Pectin and Its Gelling Function in Food Production: A Review

Duckweed, a small flowering plant which comes from Lemnaceae family, has been rising in popularity to many researches and applications for its numerous valuable functional properties. One of its special features is fast growing plant and easily adapted to various types of regions which makes it attractive to be manipulated in many applications including in biofuel production, waste water treatment and also for pharmaceutical and medicinal purposes. Pectin is the common component found in plant cell wall and it has been used as food additive for its capability to gel, emulsify and stabilize food products. Several requirements for commercial pectin such as galacturonic acid content (GalA) and degree of amidation have been regulated. Studies have proven that duckweed have significant amount of pectin which make it as a potential source of gelling agent in food industry. However, the structural properties of pectin from duckweed need to be investigated, in order to ensure if they meet the regulated requirements for industrial production. It is also to determine the suitability of duckweed pectin utilization in different type of food products since pectin of different sources have different structural characteristics, thus exhibit different gelling capability. This present review discusses on the potential of pectin from duckweed species to be utilized as food additive with gelling function in food products. Several extraction methods also have been reviewed, which each of them showed different efficiency and affect the extracted pectin characteristics.

Poly(lactic acid)/thermoplastic cassava starch blends filled with duckweed biomass

Duckweed (DW) is a highly small, free-floating aquatic plant. It grows and reproduces rapidly, comprises mainly protein and carbohydrate, and has substantial potential as a feedstock to produce bioplastics due to its renewability and having very little impact on the food chain. The aim of this work was to analyze the effect of DW biomass on the characteristics and properties of bio-based and biodegradable plastics based on a poly(lactic acid)/thermoplastic cassava starch (PLA/TPS) blend. Various amounts of DW biomass were compounded with PLA and TPS in a twin-screw extruder and then converted into dumbbell-shaped specimens using an injection molding machine. The obtained PLA/TPS blends filled with DW biomass exhibited a lower melt flow ability, higher moisture content, and increased surface hydrophilicity than the neat PLA/TPS blend. Incorporation of DW with low concentrations of 2.3 and 4.6 wt% increased the tensile strength, Young's modulus, and hardness of the PLA/TPS blend. Moisture and glycerol from DW and TPS played important roles in reducing the Tg, Tcc, Tm, and Td of PLA in the blends. The current work demonstrated that DW could be used as a biofiller for PLA/TPS blends, and the resulting PLA/TPS blends filled with DW biomass have potential in manufacturing injection-molded articles for sustainable, biodegradable, and short-term use.

Azolla as a Green Fodder Feed Supplent of Cross Breed Cows in District- Sehore (M.P.)

Background: Azolla is a floating fern also known as duck weed is belongs to the family Salviniaceae. Azolla is a good source of protein and contains almost all essential amino acids and minerals such as iron, calcium, magnesium, potassium, phosphorus, manganese etc. Methods: In the present dairy business, the cost of milk production is increasing due to market based feed management and lack of green fodder. In the context of which, Krishi Vigyan Kendra, District- Sehore (M.P.) were conducted 20 no of trais in the field of farmers during 2014-15 and 2015-16. KVK, Sehore assessed the technology is Dry fodder 4 Kg/ Day/ Animal + Green Fodder @ 20 Kg/ Day/ Animal + 2 Kg Concentrate feed/Day/Animal for body maintenance alongwith additional 1 Kg Concentrate feed/Day/Animal in every 3 litre Milk yield + 50 gm mineral mixture/ Day/ Animal. Result: Under the assessed technology, farmers found 12.5 per cent milk enhancement in assessed technology 2 as compared to farmers practice (Assessed technology-1) and 26.04 per cent higher milk yield in assessed technology 3 as compared to farmers practice (Assessed technology-1) likewise 4.76 per cent enhance the fat per cent in assessed technology 2 as compared to farmers practice (Assessed technology-1) and 9.24 per cent enhance the fat per cent in assessed technology 3 as compared to farmers practice (Assessed technology-1).

Light intensity drives different growth strategies in two duckweed species: Lemna minor L. and Spirodela polyrhiza (L.) Schleiden.

Duckweed species Lemna minor and Spirodela polyrhiza are clonal plants with vegetative organs reduced to a frond and a root in L. minor or a frond and several roots in S. polyrhiza. They reproduce vegetatively by relatively rapid multiplication of their fronds. The habit of S. polyrhiza (large fronds with up to 21 roots) makes it a strong competitor among representatives of the family Lemnaceae, probably due to different resource-use strategies compared to small duckweed. In our study, light was the resource that affected the plants before and during the laboratory experiment. We sampled the plants from natural habitats differing in light conditions (open and shady) and grew them for 16 days in a thermostatic growth room at 22 °C under a 16:8 photoperiod and three light intensities (125, 236, 459 µmol photons m–2 s–1) to investigate the trade-off between frond enlargement and multiplication. Both species from the open habitat had higher growth rates based on the frond numbers and on surface area of fronds compared to plants from the shady habitat. They adopted different species-specific strategies in response to the experimental light conditions. The species size affected the growth rates in L. minor and S. polyrhiza. Spirodela polyrhiza grew slower than L. minor, but both species grew fastest at medium light intensity (236 µmol m–2 s–1). Lemna minor maintained the growth rates at high light intensity, while S. polyrhiza slowed down. Spirodela polyrhiza responded to deteriorating light conditions by increasing its frond surface area, thus optimising light capture. Lemna minor from the shady habitat enhanced light harvest by increasing chlorophyll a concentration, but did not invest more in frond enlargement than L. minor from the open habitat. Under shady conditions, S. polyrhiza is likely to achieve an advantage over L. minor due to the larger frond size of the former. Our findings suggest the existence of a trade-off between size and number in duckweed.