Analysis of ammonia-nitrogen removal kinetics by stage in pilot scale vertical flow wetlands treating landfill leachate in series.

This study explored the effect stage number and plant type have on ammonia-nitrogen (NH3-N) removal kinetics in a two-stage pilot-scale vertical flow constructed wetland (VFCW) system treating landfill leachate. Half of the VFCW columns were planted with Typha latifolia and the other half Scirpus californicus, and half of the columns were loaded with municipal solid waste landfill leachate (diluted to 1 part leachate to 2 parts total) with the effluent from these columns was collected in two separate barrels. The remaining columns were loaded with the effluent collected from the first columns, creating a two-stage VFCW system with four unique pairs to be tested. The leachate used here experienced no prior pre-treatment, and average influent concentrations of NH3-N for the first- and second-stage VFCWs were 508 and 321 mg L-1, respectively- much higher than many other VFCW treatment systems. Some reduction in chemical oxygen demand was observed, as well as generation of nitrate and nitrite, evidence of nitrification. No apparent correlation between aboveground biomass and removal of NH3-N was observed. Overall removal efficiency of NH3-N through two stages of VFCWs was 53.7% for columns planted with T. latifolia and 58.3% for those planted with S. Californicus. Average NH3-N removal efficiencies for the first stage VFCWs were 32.7% and 34.3%, while those in the second stage were 31.3% and 36.5%; no significant difference was observed between the first and second stage, suggesting that stage number does not have a significant effect on the removal efficiency of NH3-N in the primary treatment of landfill leachate via VFCWs. However, average mass removal rates of NH3-N in the first stage were 166 and 175 mg L-1 d-1; the second stage was significantly lower at 99.4 and 112 mg L-1 d-1, indicating that the first stage removed more pollutants overall.

Removal of high lead concentration by hydroponic cultures of normal and transformed plants of Scirpus americanus Pers.

Lead is a very toxic metal which affects human health. An alternative to remove it from contaminated water is the use of macrophytes, as Scirpus americanus Pers. This species is tolerant to salt and metals and has high biomass. The present research analyzed the capacity of hydroponic cultures of normal and transgenic plants (line T12) from S. americanus to remove high concentrations of lead. The antioxidant response of plants to metal exposure was also measured. The MINTEQ3.1 program was used to define the media composition in order to have the metal available to the plants. According to MINTEQ3.1 predictions, sulfate, phosphate, and molybdenum must be removed from the medium to avoid lead precipitation. Therefore, the plants were maintained in a modified Hoagland solution containing 100, 250, and 400 mg/L lead. The presence of metal did not affect the growth of roots and stems at all concentration tested. The normal and T12 plants accumulated 69,389 mg/kg and 45,297 mg/kg lead, respectively, and could be considered hyperaccumulators. Plant tolerance to lead mainly involved an increase in superoxide dismutase activity and glutathione accumulation. The bioconcentration factor indicated that S. americanus plants bioconcentrated between 192 and 300 times the metal; thus, S. americanus could be used for phytoremediation of water contaminated with a high concentration of lead.

Molecular characterization of oleosin genes in Cyperus esculentus, a Cyperaceae plant producing oil in underground tubers.

KEY MESSAGE: CeOLE genes exhibit a tuber-predominant expression pattern and their mRNA/protein abundances are positively correlated with oil accumulation during tuber development. Overexpression could significantly increase the oil content of tobacco leaves. Oleosins (OLEs) are abundant structural proteins of lipid droplets (LDs) that function in LD formation and stabilization in seeds of oil crops. However, little information is available on their roles in vegetative tissues. In this study, we present the first genome-wide characterization of the oleosin family in tigernut (Cyperus esculentus L., Cyperaceae), a rare example accumulating high amounts of oil in underground tubers. Six members identified represent three previously defined clades (i.e. U, SL and SH) or six out of seven orthogroups (i.e. U, SL1, SL2, and SH1-3) proposed in this study. Comparative genomics analysis reveals that lineage-specific expansion of Clades SL and SH was contributed by whole-genome duplication and dispersed duplication, respectively. Moreover, presence of SL2 and SH3 in Juncus effuses implies their appearance sometime before Cyperaceae-Juncaceae divergence, whereas SH2 appears to be Cyperaceae specific. Expression analysis showed that CeOLE genes exhibit a tuber-predominant expression pattern and transcript levels are considerably more abundant than homologs in the close relative Cyperus rotundus. Moreover, CeOLE mRNA and protein abundances were shown to positively correlate with oil accumulation during tuber development. Additionally, two dominant isoforms (i.e. CeOLE2 and -5) were shown to locate in LDs as well as the endoplasmic reticulum of tobacco (Nicotiana benthamiana) leaves, and are more likely to function in homo and heteromultimers. Furthermore, overexpression of CeOLE2 and -5 in tobacco leaves could significantly increase the oil content, supporting their roles in oil accumulation. These findings provide insights into lineage-specific family evolution and putative roles of CeOLE genes in oil accumulation of vegetative tissues, which facilitate further genetic improvement for tigernut.

Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution.

This study investigated the effects of radial oxygen loss (ROL) of three different plants on nitrobenzene (NB) wastewater treatment and bioelectricity generation performance in constructed wetland-microbial fuel cell (CW-MFC). ROL and root biomass from wetland plants showed positive effects on NB wastewater compared to unplanted CW-MFC. Scirpus validus exhibited higher tolerance to NB than Typha orientalis and Iris pseudacorus at 20-200 mg/L NB. As NB concentration reached 200 mg/L, the CW-MFC with Scirpus validus had relatively high DO (2.57 ±â€¯0.17 mg/L) and root biomass (16.42 ±â€¯0.18 g/m2), which resulted in the highest power density and voltage (19.5 mW/m2, 590 mV) as well as NB removal efficiency (93.9 %) among four reactors. High-throughput sequencing results suggested that electrochemically active bacteria (EAB) (e.g., Geobacter, Ferruginibacter) and dominant NB-degrading bacteria (e.g., Comamonas, Pseudomonas) could be enhanced by wetland plants, especially in CW-MFC with Scirpus validus. Therefore, Scirpus validus was a good option for simultaneously treating NB wastewater and producing bioelectricity.

The relief effects of organic acids on Scirpus triqueter L. under pyrene-lead stress.

During phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals, the phytoremediation plants are often stressed by pollutants, which would reduce the efficiency of phytoremediation. The addition of organic acids from root exudates could alleviate the stress. In this study, three organic acids (citric acid, succinic acid, glutaric acid) were added to investigate the effects of organic acids on the stress response of Scirpus triqueter L. at two pyrene-lead concentrations. The activities of reactive oxygen species, malondialdehyde, plasma membrane H+-ATPase, and vacuolar H+-ATPase and PPase activity, as well as the activities of antioxidant enzymes (SOD, POD, and CAT) in Scirpus triqueter L. were determined. The addition of organic acids could effectively reduce the activities of reactive oxygen species, malondialdehyde, plasma membrane H+-ATPase, and vacuolar H+-ATPase and PPase activities. Under higher pollution, the damage of plant plasma membrane is more serious, but the addition of citric acid can alleviate this situation and even more effective than the relief under low pollution. The effect of citric acid was more significant than that of succinic acid and glutaric acid. These results demonstrated that organic acids could attenuate the stress of pyrene and lead to Scirpus triqueter L.

Heterotrophic N2-fixation contributes to nitrogen economy of a common wetland sedge, Schoenoplectus californicus.

A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species' range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production.

Nitrogen uptake kinetics and saltmarsh plant responses to global change.

Coastal wetlands are important carbon sinks globally, but their ability to store carbon hinges on their nitrogen (N) supply and N uptake dynamics of dominant plant species. In terrestrial ecosystems, uptake of nitrate (NO3-) and ammonium (NH4+) through roots can strongly influence N acquisition rates and their responses to environmental factors such as rising atmospheric CO2 and eutrophication. We examined the 15N uptake kinetics of three dominant plant species in North American coastal wetlands (Spartina patens, C4 grass; Phragmites australis, C3 grass; Schoenoplectus americanus, C3 sedge) under ambient and elevated CO2 conditions. We further related our results to the productivity response of these species in two long-term field experiments. S. patens had the greatest uptake rates for NO3- and NH4+ under ambient conditions, suggesting that N uptake kinetics may underlie its strong productivity response to N in the field. Elevated CO2 increased NH4+ and NO3- uptake rates for S. patens, but had negative effects on NO3- uptake rates in P. australis and no effects on S. americanus. We suggest that N uptake kinetics may explain differences in plant community composition in coastal wetlands and that CO2-induced shifts, in combination with N proliferation, could alter ecosystem-scale productivity patterns of saltmarshes globally.

Phytobeds with Fimbristylis dichotoma and Ammannia baccifera for treatment of real textile effluent: An in situ treatment, anatomical studies and toxicity evaluation.

Fimbristylis dichotoma, Ammannia baccifera and their co-plantation consortium FA independently degraded Methyl Orange, simulated dye mixture and real textile effluent. Wild plants of F. dichotoma and A. baccifera with equal biomass showed 91% and 89% decolorization of Methyl Orange within 60h at a concentration of 50ppm, while 95% dye removal was achieved by consortium FA within 48h. Floating phyto-beds with co-plantation (F. dichotoma and A. baccifera) for the treatment of real textile effluent in a constructed wetland was observed to be more efficient and achieved 79%, 72%, 77%, 66% and 56% reductions in ADMI color value, COD, BOD, TDS and TSS of textile effluent, respectively. HPTLC, GC-MS, FTIR, UV-vis spectroscopy and activated oxido-reductive enzyme activities confirmed the phytotrasformation of parent dye in to new metabolites. T-RFLP analysis of rhizospheric bacteria of F. dichotoma, A. baccifera and consortium FA revealed the presence of 88, 98 and 223 genera which could have been involved in dye removal. Toxicity evaluation of products formed after phytotransformation of Methyl Orange by consortium FA on bivalves Lamellidens marginalis revealed less damage of the gills architecture when analyzed histologically. Toxicity measurement by Random Amplification of Polymorphic DNA (RAPD) technique revealed bivalve DNA banding pattern in treated Methyl Orange sample suggesting less toxic nature of phytotransformed dye products.

Assessment of Pb and pyrene accumulation in Scirpus triqueter assisted by combined alkyl polyglucoside and nitrilotriacetic acid application.

To understand the accumulation and uptake of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by plants is an important part of the assessment of phytoremediation for PAHs and heavy metals co-contaminated soil. This study was an investigation of the accumulation and uptake of pyrene and lead (Pb) by Scirpus triqueter under the condition of alkyl polyglucoside (APG) and nitrilotriacetic acid (NTA) combined application. The results indicated that the accumulation of Pb by S. triqueter was significantly improved by NTA and APG addition into the soil. The pyrene accumulation in plant was also increased after application of APG when compared to the control treatment. However, the pyrene accumulation was decreased when APG was applied together with NTA. SEM and TEM images of root surface suggested that more Pb in the soil transferred to the plant by combined application of APG and NTA. More importantly, TEM images of xylem cells of S.triqueter root showed that permeability of cell membrane was improved by application of APG.

Differential distribution of amino acids in plants.

Plants are a rich source of amino acids and their individual abundance in plants is of great significance especially in terms of food. Therefore, it is of utmost necessity to create a database of the relative amino acid contents in plants as reported in literature. Since in most of the cases complete analysis of profiles of amino acids in plants was not reported, the units used and the methods applied and the plant parts used were different, amino acid contents were converted into relative units with respect to lysine for statistical analysis. The most abundant amino acids in plants are glutamic acid and aspartic acid. Pearson's correlation analysis among different amino acids showed that there were no negative correlations between the amino acids. Cluster analysis (CA) applied to relative amino acid contents of different families. Alismataceae, Cyperaceae, Capparaceae and Cactaceae families had close proximity with each other on the basis of their relative amino acid contents. First three components of principal component analysis (PCA) explained 79.5% of the total variance. Factor analysis (FA) explained four main underlying factors for amino acid analysis. Factor-1 accounted for 29.4% of the total variance and had maximum loadings on glycine, isoleucine, leucine, threonine and valine. Factor-2 explained 25.8% of the total variance and had maximum loadings on alanine, aspartic acid, serine and tyrosine. 14.2% of the total variance was explained by factor-3 and had maximum loadings on arginine and histidine. Factor-4 accounted 8.3% of the total variance and had maximum loading on the proline amino acid. The relative content of different amino acids presented in this paper is alanine (1.4), arginine (1.8), asparagine (0.7), aspartic acid (2.4), cysteine (0.5), glutamic acid (2.8), glutamine (0.6), glycine (1.0), histidine (0.5), isoleucine (0.9), leucine (1.7), lysine (1.0), methionine (0.4), phenylalanine (0.9), proline (1.1), serine (1.0), threonine (1.0), tryptophan (0.3), tyrosine (0.7) and valine (1.2).

Nature's patchwork: How water sources and soil salinity determine the distribution and structure of halophytic plant communities in arid environments of the Eastern Pamir.

The eastern part of the Pamir Mountains, located in Central Asia, is characterized by great climatic continentality and aridity. Wetlands developed in this hostile region are restricted to spring areas, terraces of shallow lakes or floodplains along rivers, and provide diversified ecosystem services e.g. as water reservoirs, refugia for rare species and pastures for domestic cattle. These ecosystems are particularly susceptible to climate changes, that in the Pamir Mountains result in increased temperatures, intense permafrost/glacial melt and alterations of precipitation patterns. Climatic changes affect pasture management in the mountains, causing overutilization of sites located at lower elevations. Thus, both climate and man-induced disturbances may violate the existing ecological equilibrium in high-mountain wetlands of the Eastern Pamir, posing a serious risk to their biodiversity and to food security of the local population. In this context, we sought to assess how environmental drivers (with special focus on soil features and potential water sources) shape the distribution and diversity of halophytic plant communities developed in valleys in the Eastern Pamir. This task was completed by means of a vegetation survey and comprehensive analyses of habitat conditions. The lake terraces and floodplains studied were covered by a repetitive mosaic of plant communities determined by differences in soil moisture and salinity. On lower, wetter sites, this patchwork was formed by Blysmus rufus dominated salt marshes, saline small sedge meadows and saline meadows with Kobresia royleana and Primula pamirica; and on drier, elevated sites, by endemic grasslands with Hordeum brevisubulatum and Puccinellia species and patches of xerohalophytic vegetation. Continuous instability of water sources and summer droughts occurring in the Pamir Mountains may lead to significant structural and functional transformations of described wetland ecosystems. Species more tolerant to decreased soil moisture and/or increased soil salinity will expand, leading to alterations of ecosystem services provided by the Pamirs' wetlands. The described research will help to assess the current state of the wetlands and to predict directions of their future changes.

Effect of the combined addition of Zn and Pb on partitioning in sediments and their accumulation by the emergent macrophyte Schoenoplectus californicus.

Wetlands usually provide a natural mechanism that diminishes the transport of toxic compounds to other compartments of the ecosystem by immobilization and accumulation in belowground tissues and/or soil. This study was conducted to assess the ability of Schoenoplectus californicus growing in natural marsh sediments, with zinc and lead addition, to tolerate and accumulate these metals, taking account of the metal distribution in the sediment fractions. The Zn and Pb were mainly found in available (exchangeable) and potentially available (bound to organic matter) forms, respectively. The absorption of Zn and Pb by plants increased in sediments with added metals. Both metals were largely retained in roots (translocation factor < 1). Lead rhizome concentrations only increased significantly in treatments with high doses of metal independently of added Zn. The addition of Zn increased its concentration in roots and shoots significantly, while its concentration in rhizomes only increased when both metals were added together. Zinc concentration in shoots did not reach the toxic level for plants. Zinc and Pb concentrations in roots were high, but they were not sufficient to reduce biomass growth.

Phytoremediation effect of Scirpus triqueter inoculated plant-growth-promoting bacteria (PGPB) on different fractions of pyrene and Ni in co-contaminated soils.

At present, few reveal the mechanism of inoculation plants with PGPB to remediate PAH-metal co-contaminated soil by analyzing the chemical speciations of contaminants. This study investigated the influence of inoculation plants with PGPB on different fractions of pyrene and Ni in rhizospheric and non-rhizospheric soil. The results demonstrated that the addition of PGPB brought the extensive increase of FDA activities in pyrene-Ni co-contaminated soil. PGPB increased the resistance of plants in nickel and pyrene-Ni contaminated soil, but decreased the plant biomass in single pyrene contaminated soil. The addition of PGPB efficiently decreased bioaccessible fractions of pyrene and increased the bioavailability of Ni in both rhizospheric and non-rhizospheric soil. Although inoculation plants with PGPB significantly increased the accumulation of Ni in single Ni and pyrene-Ni co-contaminated soil, the poor bioavailability of Ni in rhizospheric soil still restricted the phytoremediation of the heavy metal. The presence of pyrene hindered the inoculated plant from accumulating Ni to some extent. On the contrary, the presence of Ni significantly promoted the degradation of pyrene in both rhizospheric and non-rhizospheric soil after inoculation plants with PGPB.

Effect of dissimilatory iron and sulfate reduction on arsenic dynamics in the wetland rhizosphere and its bioaccumulation in wetland plants (Scirpus actus).

Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50µM ferrihydrite/g solid medium) and SO42- (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (Scirpus actus), probably because root exudates facilitate the microbial reduction of Fe(III), SO42-, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO42- rather than Fe levels. Compared to the low SO42- (0.1mM) treatment, high SO42- resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO42- than low SO42- levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO42- levels.

Different responses of alpine plants to nitrogen addition: effects on plant-plant interactions.

The different responses of plant species to resource stress are keys to understand the dynamics of plant community in a changing environment. To test the hypothesis that nitrogen (N) increase would benefit N competitive species, rather than N stress-tolerant species, to compete with neighbours, we conducted an experiment with neighbour removal, N addition and soil moisture as treatments in an alpine grassland on the southeastern Tibetan Plateau. Both growths and competitive-response abilities (CRA, the ability to tolerate the inhibitory effects of neighbors) of Kobresia macrantha, Polygonum viviparum and Potentilla anserine in wet site were facilitated by N addition, conversely, both growths and CRA of Taraxacum mongolicum and Ligularia virgaurea were suppressed by N addition, indicating that the responses of CRA of target species under N addition were consistent with the N utilization strategies of them. Moreover, the facilitative effects of N addition on competitive-response abilities of Kobresia macrantha and Polygonum viviparum were not found at the dry site, illustrating that soil moisture can alter the changes of neighbour effects caused by N addition. Life strategy of dominant species in plant community on the undisturbed southeastern Tibetan Plateau may shift from N stress-tolerant to N competitive, if the N increases continuously.

Bioaccumulation of copper, lead, and zinc in six macrophyte species grown in simulated stormwater bioretention systems.

Stormwater bioretention (BR) systems collect runoff containing heavy metals, which can concentrate in soil environments and potentially leach into groundwater. This greenhouse experiment evaluated differences among six plant species undergoing three varying hydraulic and pollutant loads in their bioaccumulation potential when subjected to continual application of low metal concentrations as a means of preventing copper, lead, and zinc accumulation in the BR soil. Results show that >92% of metal mass applied to the treatments via synthetic stormwater was removed from the exfiltrate within 27 cm of soil depth. Compacted soil conditions of unplanted controls retained significantly more Cu, Pb, and Zn than Carex praegracilis, and Carex microptera treatments. Differences in above and below ground plant tissue concentrations differed among species, resulting in significant differences in mass accumulation. In the above ground tissue, from highest to lowest, Phragmites australis accumulated 8 times more Cu than Scirpus acutus, and C. microptera accumulated 18 times more Pb, and 6 times more Zn than Scirpus validus. These results, and differences among species in mass distribution of the metals recovered at the end of the study, reveal various metal accumulation mechanisms.

A pilot study of a subsurface-flow constructed wetland treating membrane concentrate produced from reclaimed water.

A pilot study was conducted for 7 months for the City of Oxnard, California, on the use of constructed wetlands to treat concentrate produced by microfiltration and reverse osmosis (RO) of reclaimed wastewater. The treatment performance of a transportable subsurface-flow wetland was investigated by monitoring various forms of nitrogen, orthophosphate, oxygen demand, organic carbon, and selenium. Significant mass removal of constituents was measured under two hydraulic residence times (HRTs) (2.5 and 5 days). Inflow and outflow concentrations of nitrate-N and ammonia-N were significantly different for both HRTs, whereas nitrite-N and total organic carbon (TOC) were significantly different during HRT2. Mass removal by the constructed wetland averaged 61% of nitrate-N, 32% of nitrite-N, 42% of ammonia-N, 43% of biochemical oxygen demand, 19% of orthophosphate as P, 18% of TOC and 61% of selenium. Mass removal exceeded concentration reductions through water volume loss through evapotranspiration. Calibrated first-order area-based removal rates were consistent with literature ranges, and were greater during HRT1 consistent with greater mass loads, higher hydraulic loading and shorter HRTs. The rate constants may provide a basis for sizing a full-scale wetland receiving a similar quality of water. The results indicated that engineered wetlands can be useful in the management of RO membrane concentrate for reclaimed water reuse.

Salt tolerant plants increase nitrogen removal from biofiltration systems affected by saline stormwater.

Biofiltration systems are used in urban areas to reduce the concentration and load of nutrient pollutants and heavy metals entering waterways through stormwater runoff. Biofilters can, however be exposed to salt water, through intrusion of seawater in coastal areas which could decrease their ability to intercept and retain pollutants. We measured the effect of adding saline stormwater on pollutant removal by six monocotyledonous species with different levels of salt-tolerance. Carex appressa, Carex bichenoviana, Ficinia nodosa, Gahnia filum, Juncus kraussii and Juncus usitatus were exposed to six concentrations of saline stormwater, equivalent to electrical conductivity readings of: 0.09, 2.3, 5.5, 10.4, 20.0 and 37.6 mS cm(-1). Salt-sensitive species: C. appressa, C. bichenoviana and J. usitatus did not survive ≥10.4 mS cm(-1), removing their ability to take up nitrogen (N). Salt-tolerant species, such as F. nodosa and J. kraussii, maintained N-removal even at the highest salt concentration. However, their levels of water stress and stomatal conductance suggest that N-removal would not be sustained at concentrations ≥10.4 mS cm(-1). Increasing salt concentration indirectly increased phosphorus (P) removal, by converting dissolved forms of P to particulate forms which were retained by filter media. Salt concentrations ≥10 mS cm(-1) also reduced removal efficiency of zinc, manganese and cadmium, but increased removal of iron and lead, regardless of plant species. Our results suggest that biofiltration systems exposed to saline stormwater ≤10 mS cm(-1) can only maintain N-removal when planted with salt-tolerant species, while P removal and immobilisation of heavy metals is less affected by species selection.

Phytoremediation of cadmium by the facultative halophyte plant Bolboschoenus maritimus (L.) Palla, at different salinities.

The cadmium phytoremediation capacity of the halophyte plant Bolboschoenus maritimus (L.) Palla and the influence of water salinity were assessed in a greenhouse experiment, in order to better understand the bioremediation capacity of this plant. Three concentrations of cadmium (0, 50 and 100 µg l(-1)) and four salinity conditions (0, 5, 10 and 20) were chosen to evaluate the cadmium accumulation, in order to test these plants as a potential phytoremediation tool in brackish environments. The cadmium content in water and plants (underground organs, stems and leaves) was analysed with graphite furnace atomic absorption spectrometry. All the plants submitted to salinity 20 and in the three cadmium treatments died. The plants' survival was highest in the lowest salinities, where highest growth and biomasses were also obtained. The plants presented more cadmium content in the rhizomes, followed by stems and even less in leaves. The salt stress of the plants interfered with their cadmium accumulation capacity. The highest cadmium accumulation in the rhizomes occurred at salinity 0, while the salinities 0 and 5 were the most adequate for stems and leaves. The experiment pointed out that B. maritimus represents a good possible intervenient for cadmium bioremediation in freshwater and low salinity brackish water environments, but its use is limited in the habitats of higher salinity.

Cd accumulation and subcellular distribution in two ecotypes of Kyllinga brevifolia Rottb as affected by Cd treatments.

The Cadmium (Cd) accumulation capacity and subcellular distribution in the mining ecotype (ME) and non-mining ecotype (NME) of Kyllinga brevifolia Rottb were investigated in pot experiments. The results showed that average Cd contents in shoots of the two ecotypes of K. brevifolia were higher than those in roots, whereas Cd concentrations in roots were greater than those in shoots. Also, shoot Cd contents in NME of K. brevifolia were 1.65-45.45 times greater than those in ME when the plants were grown at 5, 25, 50, and 100 mg Cd kg(-1) soil. Moreover, Cd contents in the roots in NME were 1.75-45.45 times higher than those in ME. Subcellular distribution of Cd demonstrated that the majority of Cd in the two ecotypes of K. brevifolia was distributed in the cell walls and soluble fraction, and a small percentage of Cd existed in organelle fraction. In addition, proportions of Cd distributed in shoots and roots cell walls of NME were greater than those in ME. It could be assumed that compared with ME, NME of K. brevifolia has better Cd accumulation capacity, and the subcellular distribution of Cd might be one of the mechanisms to explain such phenomena.