Clonal diversity and structure of the invasive aquatic plant Eichhornia crassipes in China

The information on diversity and spatial distribution of clones of an invasive clonal plant is crucial for the understanding of its clonal structure and invasive history. In this paper, random amplified polymorphic DNA (RAPD) markers were used to explore the clonal diversity and clonal structure of Eichhornia crassipes (Mart.) Solms in natural populations, and their possible effects on the plant success as an invader are also discussed. Five populations covering the entire distribution area in China were studied, sampling 43 individuals per population at an interval of 1 m in a sampling plot. Twelve RAPD primers produced 69 reproducible bands, with 22 being polymorphic. Only five RAPD phenotypes (clones) were detected in these five populations, but each population consisted of at least three clones, contrary to the traditional expectations that E. crassipes populations should be monoclonal. The diversity of clones within populations is thought to be mainly resulted from multiple introductions by humans. The evenness of distribution of clones varied slightly and most clones were widespread, suggesting clonal growth is the predominant mode of regeneration in all the populations. A single clone dominated each population and this clone might be the first one introduced into China or the genotype with a higher phenotypic plasticity, which could survive and reproduce via clonal growth in various habitats. The clones in each population were highly intermixed, especially in river populations, suggesting this species has a guerilla clonal structure which can be facilitated by water current.     

Influence of physico-chemical parameters of the aquatic medium on germination of Eichhornia crassipes seeds

The germination of seeds of Eichhornia crassipes in locations distant from the foci of infestation may be a means of dispersal of this invasive plant. Nonetheless, no modern studies have examined the influence of single components on germination, although the influence of temperature, oxygen and redox potential was examined in earlier studies. The effects of pH, conductivity, nitrate, phosphate, potassium, calcium, iron and boron on germination of E. crassipes were determined in seed germination tests. The results showed that external input of nutrients influences germination, since neither pH nor conductivity alone had any effect, but there was a significant increase in germination in growth media containing phosphorus at 3.95 mg·l(-1) (P/L; 95.5%) and boron at 10 mg·l(-1) (B/L; 97.5%); at higher concentrations, the latter was toxic. These findings contribute to knowledge of factors controlling the germination of E. crassipes seeds. Consequently, E. crassipes seeds would find very good conditions for germination in water classified as hypereutrophic, which may play a decisive role in expansion of this plant.     

Ion transport and metal sensitivity of vacuolar channels from the roots of the aquatic plant Eichhornia crassipes

Using the patch‐clamp technique, we investigated the transport properties of vacuolar ion channels from the roots of water hyacinth, Eichhornia crassipes (Mart. Solms, Pontederiacae). Eichhornia crassipes vacuoles displayed large voltage‐dependent rectifying slow‐vacuolar (SV) currents, which activated in a few seconds at positive potentials and deactivated at negative voltages in a few hundreds of millseconds. Similarly to SV channel previously identified in the tonoplast of terrestrial plants, SV currents in E. crassipes were activated by micromolar concentrations of Ca²⁺ and current slightly increased (25%) on addition (10 mm ) of the reducing agent dithiothreitol (DTT). Eichhornia crassipes SV channels were equally permeable to K⁺ and Na⁺. The permeability sequence derived from current values is: K⁺ ≈ Na⁺ > Rb⁺ > NH₄⁺ ≈ Cs⁺ >> TEA⁺. Excised membrane patches displayed single channel transitions typical of SV‐type single channel openings with a conductance of (83·0 ± 5·6) pS; a smaller channel with a conductance of (31·0 ± 2·7) pS was also identified. Metals such as Ni²⁺ and Zn²⁺ decreased the vacuolar current in a reversible manner. However, although Zn²⁺ inhibition is comparable to that induced by the same metal in vacuoles from the main root of sugar beet (Beta vulgaris L.), the inhibition of the SV currents by Ni²⁺ is not as substantial in E. crassipes as in sugar beet. To our knowledge, this is the first electrophysiological characterization of ionic transport in E. crassipes, a pervasive troublesome aquatic weed, which has exceptional absorption properties of several water contaminants such as heavy metals, pesticides and phenols.     

Water hyacinth (Eichhornia crassipes) to biomonitor genotoxicity of low levels of mercury in aquatic environment

The mitotic cell-cycle duration of root meristematic cells of Eichhornia crassipes as determined by the colchicine labelling method was approximately 24 h at 30 +/- 1 degrees C. In one experiment the intact root meristems of E. crassipes were subjected to 1 h acute exposure to water contaminated with maleic hydrazide (MH), 56 ppm, or methyl mercuric chloride (MMCl), 0.1-0.5 ppm, followed by recovery in tap water for 4-48 h. In a second experiment the roots were subjected to 96 h exposure to water contaminated with MH, 56 ppm, or MMCl, 0.0001-0.1 ppm. In both experiments the cytological end-point measured was the frequency of cells with micronuclei (MNC). In the first experiment, while in the MH-exposed root meristems the frequency of MNC was significant at 40 h of recovery, MMCl induced significant MNC at 12, 20, 24, 40, and 40 h of recovery depending on the concentration. In the second experiment both test chemicals induced MNC which was concentration-dependent in case of MMCl. The highest ineffective concentration tested (HICT) and lowest effective concentration tested (LECT) for MMC determined in this experiment were 0.0005 ppm and 0.001 ppm, respectively. The present work provides evidence that E. crassipes could be a promising in situ environmental biomonitoring assay system.     

Genotoxicological studies in aquatic organisms: an overview

Substantial progress has been made in the lat two decades to evaluate the impact of physical and chemical genotoxins in aquatic organisms. This overview (a) summarises the major high lights in this stimulating area of research, (b) compares the developments in this field with the developments in mammalian genotoxicological studies, where appropriate, (c) introduces 18 different articles presented in this special issue of Mutation Research in the backdrop of main advances and , (d) hypothesises on future directions of research in this exciting field.     

Molecular characterization of Vibrio cholerae O139 bengal isolated from water and the aquatic plant Eichhornia crassipes in the River Ganga,Varanasi, India

A collection of ten strains of Vibrio cholerae O139, comprising six isolates from Eichhornia crassipes, two from water of the River Ganga, and one each from a well and a hand pump, were characterized. All the strains carried the CTX genetic element (ctxA, zot, and ace) except for the st gene and carried structural and regulatory genes for toxin-coregulated pilus (tcpA, tcpI, and toxR), adherence factor (ompU), and accessory colonization factor (acfB); all produced cholera toxin (CT). These strains were resistant to trimethoprim, sulfamethoxazole, streptomycin, and to the vibriostatic agent pteridine. Results obtained by ribotyping and enterobacterial repetitive intergenic consensus sequence-PCR fingerprint analysis indicate that multiple clones of toxigenic-pathogenic V. cholerae O139 were present in the aquatic environment.     

Anaerobic digestion of harvested aquatic weeds: water hyacinth (Eichhornia crassipes), cabomba (Cabomba Caroliniana) and salvinia (Salvinia molesta)

The aim of this study was to explore the potential of three aquatic weeds, water hyacinth, cabomba, and salvinia, as substrates for anaerobic digestion. A set of four pilot-scale, batch digestions were undertaken to assess the yield and quality (% methane) of biogas from each plant species, and the rate of degradation. A set of 56 small-scale (100 mL) biological methane potential (BMP) tests were designed to test the repeatability of the digestions, and the impact of drying and nutrient addition.The results of the pilot-scale digestions show that both water hyacinth and cabomba are readily degradable, yielding 267 L biogas kg^?1 VS and 221 L biogas kg^?1 VS, respectively, with methane content of approximately 50%. There is evidence that the cabomba fed reactor leaked midway through the digestion therefore the biogas yield is potentially higher than measured in this case. Salvinia proved to be less readily degradable with a yield of 155 L biogas kg^?1 VS at a quality of 50% methane.The BMPs showed that the variability was low for water hyacinth and cabomba but high for salvinia. They also showed that the addition of nutrient solution and manure did not significantly increase the biogas yields and that drying was detrimental to the anaerobic degradability of all three substrates.Based on these results treatment of both water hyacinth and cabomba by anaerobic digestion can be recommended. Anaerobic digestion of Salvinia cannot be recommended due to the low biogas yields and high variability for this substrate.     

High-rate composting-vermicomposting of water hyacinth (Eichhornia crassipes,Mart. Solms)

In an attempt to develop a system with which the aquatic weed water hyacinth (Eichhornia crassipes, Mart. Solms) can be economically processed to generate vermicompost in large quantities, the weed was first composted by a 'high-rate' method and then subjected to vermicomposting in reactors operating at much larger densities of earthworm than recommended hitherto: 50, 62.5, 75, 87.5, 100, 112.5, 125, 137.5, and 150 adults of Eudrilus eugeniae Kinberg per litre of digester volume. The composting step was accomplished in 20 days and the composted weed was found to be vermicomposted three times as rapidly as uncomposted water hyacinth [Bioresource Technology 76 (2001) 177]. The studies substantiated the feasibility of high-rate composting-vermicomposting systems, as all reactors yielded consistent vermicast output during seven months of operation. There was no earthworm mortality during the first four months in spite of the high animal densities in the reactors. In the subsequent three months a total of 79 worms died out of 1650, representing less than 1.6% mortality per month. The results also indicated that an increase in the surface-to-volume ratio of the reactors might further improve their efficiency.     

滇池水葫芦固液分离后的沼气发酵研究

在常温下,分离水葫芦为水葫芦渣和水葫芦汁,水葫芦渣与猪粪结合进行批量发酵试验,研究了产气量及原料半纤维素、纤维素、木质素的降解,结果表明原料的产气率为504.04 L/g TS,甲烷含量65%,半纤维素、纤维素降低,木质素升高.对水葫芦汁厌氧发酵的产气及COD降解情况进行了研究,结果表明水葫芦汁的产气潜力为2.192 mL/g,COD降解率达到91.27%.     

Recovery in aquatic ecosystems: an overview of knowledge and needs

This article summarizes the views of scientists asked to address some of the critical unanswered questions concerning recovery in aquatic systems. Spatial and temporal variability were emphasized because of their implications for our abilities to distinguish between recovered and non-recovered ecosystems and the consequent effects such variability has on the statistical precision of developed recovery metrics. There was also consensus that pre-disturbance ecosystem states may not be re-established in the absence of a disturbance event and that better data sets will be required to separate the influences of natural variability from disturbance event induced fluctuations in many biological measures. Although discussions tended to focus at the population or community level, evidence from physiological-based measures of recovery indicates divergent rates of recovery at varying levels of biological organization, a fact which suggests a role for biomarkers in developing a complete understanding of recovery. Critical questions concerning the determination and understanding of recovery that remain to be answered are identified. This revised version was published online in July 2006 with corrections to the Cover Date.     

凤眼莲及其根际微生物共同代谢和协同降酚机理的研究

研究表明凤眼莲在苯酚浓度不超过１５０μｇ·ｍｌ－１的水体中,不但可以在体内富集酚,而且可以通过多酚氧化酶、过氧化物酶、酚糖苷等途径降解水体中的酚类化合物;其根际微生物可以通过ｍｅｔａ或ｏｒｔｈ途径降酚,起到共同降酚的作用．当两者结合构成生物系统,便会产生协同效应,其降酚效果可达９７．５％,大大超过两者分别降酚效果之和（含酚５０μｇ·ｍｌ－１的培养液中,１０ｈ内,无菌凤眼莲降酚仅为１．９％,假单胞菌Ｎｏ．５降酚３７．９％）．     

Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System

A natural wetland in Mexico City Metropolitan Area is one of the main suppliers of crops and flowers, and in consequence its canals hold a high concentration of organochlorine (OC) and organophosphorus (OP) pesticides. There is also an extensive population of water hyacinth (Eichhornia crassipes), which is considered a plague; but literature suggests water hyacinth may be used as a phytoremediator. This study demonstrates bioaccumulation difference for the OC in vivo suggesting their bioaccumulation is ruled by their log K_ow, while all the OP showed bioaccumulation regardless of their log K_ow. The higher bioaccumulation factors (BAF) of the accumulated OC pesticides cannot be explained by their log K_ow, suggesting that the OC pesticides may also be transported passively into the plant. Translocation ratios showed that water hyacinth is an accumulating plant with phytoremediation potential for all organophosphorus pesticides studied and some organochlorine pesticides. An equation for free water surface wetlands with floating macrophytes, commonly used for the construction of water-cleaning wetlands, showed removal of the pesticides by the wetland with room for improvement with appropriate management.     

Arsenic toxicity: cell signalling and the attenuating effect of nitric oxide in Eichhornia crassipes

Nitric oxide (NO) is an important molecule involved in the perception of stress induced by toxic compounds such as arsenic (As). The present study investigated the role of NO applied as sodium nitroprusside (SNP) in cell signalling and the ability of NO to attenuate the toxic effects of As (in the form of sodium arsenate) in water hyacinth (Eichhornia crassipes). Water hyacinth plants were collected and assigned to one of the following treatments: control; 100 μM SNP; 20 μM As; or 20 μM As + 100 μM SNP. The plants remained under these conditions for 0, 4, 12, and 24 h. After each time interval, the plants were collected and As absorption, production of reactive oxygen species (ROS), integrity of membranes, and antioxidant enzyme activities were evaluated. The plants were able to absorb and accumulate large amounts of As, even after only four hours of exposure to the pollutant. The absorption and bioaccumulation factor of As was even greater when plants were exposed to both As and SNP. The accumulation of As triggered increases in ROS production and cell membrane damage. In the presence of SNP, the tolerance index to As increased and damage was mitigated. Therefore, from the present work, it was possible to conclude that exogenous NO influenced the ability of plants to tolerate As; this finding has implications for phytoremediation in areas contaminated by As.     

Productivity and nutrient uptake of water hyacinth,Eichhornia crassipes I. Effect of nitrogen source

Water hyacinth,Eichhornia crassipes, growth and nutrient uptake rates, as influenced by different N sources and N transformations, were measured using microcosm aquaculture systems. Net productivity was highest in the system receiving equal amounts of NH₄ ⁺ and NO₃ ^- (at 10 mg N 1^-1 each) and decreased in the order of NO₃ ^-, NH₄ ⁺, urea (added at 20 mg N 1^-1 each), and methane digestor effluent (at 6 mg N 1^-1). During the first 7-wk study (average ambient air temperature was 26–28°C), biomass yields were in the range of 19–53 g dry wt m^-2 day^-1, while between the 8th and 12th wk (average ambient air temperature was 16–22°C), biomass yields were in the range of 10–33 g dry wt m^-2 day^-1. In the systems with either NH₄ ⁺ or NO₃ ^-, or both added in equal proportions, about 14–20% of the total yield was contributed by roots, whereas in the system with urea and digestor effluent, roots contributed about 23 and 44% of the total yield, respectively. Nitrogen and P uptake per unit area followed trends similar to biomass yields. Nitrogen uptake rates were in the range of 533–2, 161 mg N m^-2 day^-1 for the systems receiving NH₄ ⁺, NO₃ ^-, and urea, while uptake rates were in the range of 124–602 mg N m^-2 day^-1 for the system receiving methane digestor effluent. Phosphorus uptake rates were found to be in the range of 59–542 mg P m^-2 day^-1. Under the most favorable conditions, maximum recorded biomass yield was 53 g dry wt m^-2 day^-1, with N and P removal rate of 2,161 mg N m^-2 day^-1 and 542 mg P m^-2 day^-1, indicating the potential of water hyacinth to produce large amounts of biomass which can be potentially used as a feedstock to produce methane.     

Extraction and retrieval of potassium from water hyacinth (Eichhornia crassipes)

Studies were carried out on extraction and retrieval of potassium from water hyacinth (Eichhornia crassipes). The stem and leaf were subjected to 13 treatments. The highest rate of K removal following HCl treatment was 69.7% K. Most effective removal of suspended organic substances, Ca2+ and Mg2+ were achieved at pH approximately 13, when 88.0% of K remained in filtrate. Maximum K in precipitate following this step was achieved with tartaric acid additions at n(C4H6O6)/n(K+) of 1.72 when precipitating at 4 degrees C for 3h, which resulted in 72.3% of K removal from the solution. Over the entire process, 44.3% of K in the dried stem-leaf sample of water hyacinth was retrieved in the form of KC4H5O6. This process demonstrated the potential for use of water hyacinth as a resource of potassium to produce potassium salts and provide a valuable end use for the plant, which could be highly invasive in aquatic ecosystems.     

Development of secretory cells and crystal cells in Eichhornia crassipes ramet shoot apex

The distribution and development of secretory cells and crystal cells in young shoot apexes of water hyacinth were investigated through morphological and cytological analysis. The density of secretory cells and crystal cells were high in parenchyma tissues around the vascular bundles of shoot apexes. Three developmental stages of the secretory cells can be distinguished under transmission electron microscopy. Firstly, a large number of electron-dense vesicles formed in the cytoplasm, then fused with the tonoplast and released into the vacuole in the form of electron-dense droplets. As these droplets fused together, a large mass of dark material completely filled the vacuole. To this end, a secretion storage vacuole (SSV) formed. Secondly, an active secretion stage accompanied with degradation of the large electron-dense masses through an ill-defined autophagic process at periphery and in the limited internal regions of the SSV. Finally, after most storage substances were withdrawn, the materials remaining in the spent SSV consisted of an electron-dense network structure. The distribution and development of crystal cells in shoot apical tissue of water hyacinth were also studied by light and electron microscopy. Crystals initially formed at one site in the vacuole, where tube-like membrane structures formed crystal chambers. The chamber enlarged as the crystal grew in bidirectional manner and formed needle-shaped raphides. Most of these crystals finally occurred as raphide bundles, and the others appeared as block-like rhombohedral crystals in the vacuole. These results suggest that the formation of both secretory cells and crystal cells are involved in the metamorphosis of vacuoles and a role for vacuoles in water hyacinth rapid growth and tolerance.     

Distribution of cytokinin-like activity in different plant parts of the water hyacinth, Eichhornia crassipes

Cytokinin-like activity in extracts of leaf laminae, petioles, shoots, roots and flowers of young plants of the water hyacinth, Eichhornia crassipes S. was analyzed following Sephadex LH-20 column chromatography using the soybean callus bioassay. In all plant parts analyzed, two prominent peaks of cytokinin activity having elution volumes similar to zeatin and zeatin riboside were detected. Putative cytokinin gluco-side-like activity was detected only in leaves and flowers. The cytokinin complements of the leaves and the roots were qualitatively different. It would appear that cytokinins supplied by the roots are metabolized in the leaves or certain cytokinins are synthesized in the leaves themselves. The possible significance and distribution of cytokinins in different plant parts in relation to roots is discussed.     

基于富营养化水体修复的凤眼莲放养及采收条件研究

为实现富营养化水体的修复,对影响凤眼莲〔Eichhornia crassipes(Mart.)Sloms〕高产高效的放养及采收条件(包括初始放养日期、采收标准和采收比例)进行了研究,并对凤眼莲的生长曲线以及N、P和K的积累量进行了分析。实验结果表明:在总氮、总磷和钾含量分别为3.41~7.18、0.05~0.27和2.24~5.18 mg.L-1的水体中,在生长前期由于产生分蘖和植株个体生长,凤眼莲生物量快速增加;当植株生长至一定高度,生物量增幅减小;通过这一生长过程,凤眼莲的最高生物量可达28.28 kg.m-2。初始放养日期对凤眼莲的生长曲线和生物量均有明显影响,随初始放养日期的推迟生物量逐渐增大,在4月10日、4月17日、4月24日、5月1日和5月8日放养的凤眼莲经过63 d的放养,生物量均明显增加,其中,5月8日放养的凤眼莲总生物量最高,达到24.36 kg.m-2。采收标准和采收比例对凤眼莲的采收频率和累计采收量以及N、P和K积累量具有显著影响。按照10~15、15~20、20~25、25 kg.m-2以上及最高生物量的采收标准以及1/2和2/3的采收比例进行采收,凤眼莲的累计采收量均高于一次性采收(对照),且与其生物量呈抛物线型关系,但采收频率则与生物量成反比;采取不同的采收标准及采收比例,凤眼莲的干物质含量及N、P和K含量及总量均有一定的差异,但除干物质含量外,N、P和K含量及总量均明显高于一次性采收;总体上,采用20~25 kg.m-2的采收标准及2/3采收比例,凤眼莲的累计采收量最高、采收频率较少,对N、P和K的积累量最大。综合比较结果显示:在南京地区凤眼莲可于4月初开始放养,4月至5月分蘖,6月以后正常生长,并可按照20~25 kg.m-2的采收标准和2/3的采收比例进行采收。