Free-floating Aquatic Plant Research Articles

Characterization of flower-inducing compound in Lemna paucicostata exposed to drought stress

A flower-inducing compound, LDS1, was isolated from a free-floating aquatic plant, Lemna paucicostata. The chemical structure and the absolute stereochemistry of LDS1 were determined as (9R,13R,11E,15Z)-9,13-dihydroxy-10-oxooctadeca-11,15-dienoic acid for its most abundant diastereomer. LDS1 was enzymatically produced when the plant was exposed to drought stress, and induced flowering at a concentration of 10 nM.

Water hyacinth, Eichhornia crassipes (Pontederiaceae), reduces benthic macroinvertebrate diversity in a protected subtropical lake in South Africa

The socio-economic impacts of the free-floating aquatic plant water hyacinth, Eichhornia crassipes (Pontederiaceae), on aquatic systems are well documented, yet the impacts on aquatic biodiversity, particularly invertebrate biodiversity, are less well understood. This study aimed to determine whether the presence of water hyacinth altered the diversity and assemblage structure of benthic macroinvertebrates in a conservation area. The benthic macroinvertebrate assemblage was sampled over 1 year at five sites under water hyacinth mats and at five sites without water hyacinth at Lake Nsezi—Nseleni River in the vicinity of Richards Bay, KwaZulu-Natal, South Africa. Artificial substrates were placed beneath water hyacinth mats or in the open water to allow for colonization by freshwater macroinvertebrates, and left for a period of 6 weeks, repeated on seven occasions. Twenty nine families comprising 18,797 individuals were collected, 817 (13 families) individuals were from under water hyacinth mat sites compared to 17,980 (27 families) individuals from open water sites. Ninety-eight percent of individuals collected were, however, the invasive snail, Tarebia granifera. Open water samples were separated from samples beneath the water hyacinth mat by non-metric Multidimensional Scaling, indicating reduced biodiversity associated with the presence of water hyacinth. Exclusion of the dominant Thiaridae from the analysis did not alter the groupings. Family richness(s) and abundance (N) were significantly higher in open water communities(S: H3 = 21.09; P = 0.0001; N: H3 = 22.58; P = 0.00001), while evenness (J’) was higher under water hyacinth mats (H3 = 20.13; P = 0.0002). The presence of water hyacinth had a significantly negative impact on aquatic macroinvertebrate biodiversity in a conservation area, and therefore the control of this invasive aquatic plant must play a major role in catchment management.

Development of a micro-XRF system for biological samples based on proton-induced quasimonochromatic X-rays

We have developed a micro-XRF system based on a proton-induced quasimonochromatic X-ray (QMXR) microbeam for in vivo measurement of biological samples. A 2.5-MeV proton beam impinged normally on a Cu foil target that was slightly thicker than the proton range. The emitted QMXR behind the Cu target was focused with a polycapillary X-ray half lens. For application to analysis of wet or aquatic samples, we prepared a QMXR beam with an incident angle of 45° with respect to the horizontal plane by using a dipole magnet in order to bend the primary proton beam downward by 45°. The focal spot size of the QMXR microbeam on a horizontal sample surface was evaluated to be 250×350μm by a wire scanning method. A microscope camera with a long working distance was installed perpendicular to the sample surface to identify the analyzed position on the sample. The fluorescent radiation from the sample was collected by a Si-PIN photodiode X-ray detector. Using the setup above, we were able to successfully measure the accumulation and distribution of Co in the leaves of a free-floating aquatic plant on a dilute Co solution surface.

Occurrence and habitat preference of aquatic macrophytes in a large river channel

This paper explores correlations between macrophyte occurrence and environmental characteristics recorded in a more than 350 rkm long segment of the main Danube channel in Hungary. The selected river section belongs entirely to the lowland part of the Middle Danube, but it is separated into the mostly gravelly upper and the sandy lower river sections. Two markedly different groups of macrophytes correlated with this separation; the mostly perennial, rooting species (Myriophyllum spicatum, Potamogeton crispus, P. nodosus, P. pectinatus, P. perfoliatus and Zannichellia palustris) preferred the gravelly habitats, while the non-rooting, free-floating macrophytes (Ceratophyllum demersum, Lemna minor, Salvinia natans and Spirodela polyrhiza) occurred mainly in the sandy stretches. Based on current velocity and Secchi transparency, these stretches seemed to provide “more lotic” and “rather lentic” habitats. Data evaluation also revealed that the closer are the river stretches to a water course discharging upstream the more free-floating aquatic plants occur in the main Danube channel.

Utilization of two invasive free-floating aquatic plants (Pistia stratiotes and Eichhornia crassipes) as sorbents for oil removal

Free-floating aquatic plants Pistia stratiotes and Eichhornia crassipes are well-known invasive species in the tropics and subtropics. The aim of this study was to utilize the plants as cost-effective and environmentally friendly oil sorbents. Multilevel wrinkle structure of P. stratiotes leaf (PL), rough surface of E. crassipes leaf (EL), and box structure of E. crassipes stalk (ES) were observed using the scanning electron microscope. The natural hydrophobic structures and capillary rise tests supported the idea to use P. stratiotes and E. crassipes as oil sorbents. Experiments indicated that the oil sorption by the plants was a fast process. The maximum sorption capacities for different oils reached 5.1-7.6, 3.1-4.8, and 10.6-11.7g of oil per gram of sorbent for PL, EL, and ES, respectively. In the range of 5-35°C, the sorption capacities of the plants were not significantly different. These results suggest that the plants can be used as efficient oil sorbents.

A co-beneficial system using aquatic plants: bioethanol production from free-floating aquatic plants used for water purification

A co-beneficial system using constructed wetlands (CWs) planted with aquatic plants is proposed for bioethanol production and nutrient removal from wastewater. The potential for bioethanol production from aquatic plant biomass was experimentally evaluated. Water hyacinth and water lettuce were selected because of their high growth rates and easy harvestability attributable to their free-floating vegetation form. The alkaline/oxidative pretreatment was selected for improving enzymatic hydrolysis of the aquatic plants. Ethanol was produced with yields of 0.14-0.17 g-ethanol/ g-biomass in a simultaneous saccharification and fermentation mode using a recombinant Escherichia coli strain or a typical yeast strain Saccharomyces cerevisiae. Subsequently, the combined benefits of the CWs planted with the aquatic plants for bioethanol production and nutrient removal were theoretically estimated. For treating domestic wastewater at 1,100 m(3)/d, it was inferred that the anoxic-oxic activated sludge process consumes energy at 3,200 MJ/d, whereas the conventional activated sludge process followed by the CW consumes only 1,800 MJ/d with ethanol production at 115 MJ/d.

Assessing the potentials of Lemna minor in the treatment of domestic wastewater at pilot scale

Water crisis is one of the most serious problems faced by the world today. Phytoremediation is one of the serious efforts towards sustainability. Macrophyte-based wastewater treatment systems have several potential advantages compared with conventional treatment systems. Duckweeds (Lemna spp., Spirodela spp., Wolffia spp.) are small, green freshwater, free-floating aquatic plants. The primary objective of this work was to analyze the role of duckweeds in organic waste and nutrient removal from domestic wastewater being generated from hostels of Birla Institute of Technology, Mesra, Ranchi (India). Interesting results were obtained in which the BOD value reduced by 94.45% and the level of orthophosphate at the end of the work was found to be reduced by 79.39%. The duckweeds flourished well during the experimental period in the pH range of 7 to 8; it can be said that, other factors remaining favorable, the optimum pH for duckweed growth ranges from 7 to 8. Therefore, it can be concluded that this treatment can be successfully carried out on a large scale. Also, it is a low-cost solution to wastewater treatment problems and could satisfy the discharge standards.

Effects of NH 4+ concentration on growth, morphology and NH 4+ uptake kinetics of Salvinia natans

Many plants develop toxicity symptoms and have reduced growth rates when supplied with ammonium (NH 4 +) as the only source of inorganic nitrogen. In the present study, the growth, morphology, NH 4 + uptake kinetics and mineral concentrations in the tissues of the free-floating aquatic plant Salvinia natans (water fern) supplied exclusively with NH 4 +–N at concentrations of 0.25–15 mM were investigated. S. natans grew well, with relative growth rates of c. 0.25 g g −1 d −1 at external NH 4 + concentrations up to 5 mM, but at higher levels growth was suppressed and the plants had small leaves and short roots with stunted growth. The high-affinity transport system (HATS) that mediate NH 4 + uptake at dilute NH 4 + levels was downregulated at high NH 4 + concentrations with lower velocities of maximum uptake ( V max) and higher half-saturation constants ( K 1/2). High NH 4 + levels also barely affected the concentrations of mineral cations and anions in the plant tissue. It is concluded that S. natans can be characterized as NH 4 +-tolerant in line with a number of other species of wetland plants as growth was unaffected at NH 4 + concentrations as high as 5 mM and as symptoms of toxicity at higher concentrations were relatively mild. Depolarization of the plasma membrane to the equilibrium potential for NH 4 + at high external concentrations may be a mechanism used by the plant to avoid excessive futile transmembrane cycling. S. natans is tolerant to the high NH 4 + levels that prevail in domestic and agricultural wastewaters, and the inherent high growth rate and the ease of biomass harvesting make S. natans a primary candidate for use in constructed wetland systems for the treatment of various types of nitrogen-rich wastewaters.

Ethanol production from candidate energy crops: Water hyacinth ( Eichhornia crassipes) and water lettuce ( Pistia stratiotes L.)

Fermentation modes and microorganisms related to two typical free-floating aquatic plants, water hyacinth and water lettuce, were investigated for their use in ethanol production. Except for arabinose, sugar contents in water lettuce resembled those in water hyacinth leaves. Water lettuce had slightly higher starch contents and lower contents of cellulose and hemicellulose. A traditional strain, Saccharomyces cerevisiae NBRC 2346, produced 14.4 and 14.9 g l −1 ethanol, respectively, from water hyacinth and water lettuce. Moreover, a recombinant strain, Escherichia coli KO11, produced 16.9 and 16.2 g l −1 ethanol in the simultaneous saccharification and fermentation mode (SSF), which was more effective than the separated hydrolysis and fermentation mode (SHF). The ethanol yield per unit biomass was comparable to those reported for other agricultural biomasses: 0.14–0.17 g g-dry −1 for water hyacinth and 0.15–0.16 g g-dry −1 for water lettuce.

Phytotoxic effects of cyanobacteria extract on the aquatic plant Lemna gibba: Microcystin accumulation, detoxication and oxidative stress induction

The occurrence of toxic cyanobacteria in the aquatic environment constitutes a serious risk for the ecological balance and the functioning of ecosystems. The presence of cyanotoxins in ecosystems could have eventual adverse effects on aquatic plants, which play an important biological role as primary producers. The original aim of this study was to investigate microcystin (MC) accumulation, detoxication and oxidative stress induction in the free-floating aquatic vascular plant Lemna gibba (Duckweed, Lemnaceae). Experiments were carried out with a range of MC levels, obtained from toxic Microcystis culture extracts (0.075, 0.15, 0.22 and 0.3 μg equiv. MC-LR mL −1). During chronic exposure of the plant to MC, we examined the growth, photosynthetic pigment contents and also the physiological behavior related to toxin accumulation, possible biodegradation and stress oxidative processes of L. gibba. For the last reason, changes in peroxidase activity and phenol compound content were determined. This is a first report using phenol compounds as indicators of biotic stress induced by MC contamination in aquatic plants. Following MC exposure, a significant decrease of plant growth and chlorophyll content was observed. Also, it was demonstrated that L. gibba could take up and bio-transform microcystins. A suspected MC degradation metabolite was detected in treated Lemna cells. In response to chronic contamination with MCs, changes in the peroxidase activity and qualitative and quantitative changes in phenolic compounds were observed after 24 h of plant exposure. The physiological effects induced by chronic exposure to microcystins confirm that in aquatic ecosystems plants coexisting with toxic cyanobacterial blooms may suffer an important negative ecological impact. This may represent a sanitary risk due to toxin bioaccumulation and biotransfer through the food chain.

Distinguishing the diets of coexisting fossil theridomyid and glirid rodents using carbon isotopes

Carbon isotope analyses were conducted on the teeth of four species of rodents and associated plant fossils from the Late Eocene–Early Oligocene Solent Group of the Hampshire Basin, UK. Results indicate that there is no detectable difference in the overall mean δ13C values between permanent cheek teeth of the two species of theridomyid, Thalerimys fordi and Isoptychus sp. This accords with their very similar teeth that indicate comparable diets. However, the teeth of the two species of glirid (dormouse), Glamys priscus and Glamys fordi, have distinctly more negative mean δ13C values than those of either T. fordi or Isoptychus sp., with which they co-existed. This indicates that both glirids had diets significantly different from those of the theridomyids. This dietary distinction is consistent in all three levels studied spanning at least 3 million years. Carbon isotope analysis of associated plant fossils combined with independent evidence from dental morphology and gnaw marks on Stratiotes seeds shows that seeds of the open water, free-floating aquatic plant Stratiotes formed a significant proportion of the diet of G. priscus and by inference that of G. fordi. In contrast calculated dietary δ13C values of T. fordi and Isoptychus sp. overlap the δ13C values of marginal freshwater aquatic plant seeds and thick-walled plant tissues. This evidence, combined with independent taphonomic and palaeoecological information, suggests that these theridomyids and glirids foraged in close association with large water bodies. This supports the use of tooth enamel from these rodents as a proxy for freshwater oxygen isotope values, in palaeoclimate reconstruction.

Axenic culture of Pistia stratiotes for use in plant biochemical studies

Free-floating aquatic plants are useful in studies of plant biochemistry. Their value lies in the fact that they are naturally adapted to growth on liquid media which can be precisely manipulated. Critical biochemical studies require axenic plants free of contaminating organisms which contribute unwanted chemical products or bind/metabolize added compounds. Axenic plants of Lemna, Spirodela, and Wolffiella species have been available for some time. Access to axenic cultures of the free-floating aquatic plant, Pistia stratiotes L., Araceae, (water lettuce) would provide a model more representative of higher and terrestrial plants (leaves, stems, stolons, multiple roots). Our choice of P. stratiotes focuses on its value as a model to study oxalic acid formation and calcium regulation as related to calcium oxalate production. To this end, we have developed axenic Pistia cultures and compared non-axenic plants grown in greenhouse conditions to the axenic plants in terms of organic acid content and morphology/anatomy. Axenic Pistia were comparable to greenhouse-grown plants, the only difference being the smaller size of axenic plants. This study demonstrates the suitability of axenic Pistia for biochemical research and also indicates that such plants will be very useful in studies of bioremediation and other processes in aquatic systems.

The effect of Amazon water type on acetate metabolism by species of Salvinia and Limnobium

The uptake and incorporation of [1-14C]acetate was studied in two species of free-floating aquatic plants incubated in three different Amazon water types. Waters from the Rio Negro, the Rio Solimoes, and a local lake were used. The plants, species of Salvinia and Limnobium, were collected from the local lake. The results demonstrate that in September, the water of the Rio Negro and Rio Solimoes have similar effects on acetate metabolism by the lake plants and markedly different effects from those of the plants' home waters. Although the Rio Negro and Rio Solimoes are considered to be totally different water types, this study indicates they may cause similar biochemical responses in aquatic plants.