Roots Of Wetland Plants Research Articles

Presence and persistence of wastewater pathogen Escherichia coli O157:H7 in hydroponic reactors of treatment wetland species.

Treatment wetlands (TWs) efficiently remove many pollutants including a several log order reduction of pathogens from influent to effluent; however, there is evidence to suggest that pathogen cells are sequestered in a subsurface wetland and may remain viable months after inoculation. Escherichia coli is a common pathogen in domestic and agricultural wastewater and the O157:H7 strain causes most environmental outbreaks in the United States. To assess attachment of E. coli to the TW rhizosphere, direct measurements of E. coli levels were taken. Experiments were performed in chemostats containing either Teflon nylon as an abiotic control or roots of Carex utriculata or Schoenoplectus acutus. Flow of simulated wastewater through the chemostat was set to maintain a 2 hour residence time. The influent was inoculated with E. coli O157:H7 containing DsRed fluorescent protein. Root samples were excised and analyzed via epifluorescent microscopy. E. coli O157:H7 was detected on the root surface at 2 hours after inoculation, and were visible as single cells. Microcolonies began forming at 24 hours post-inoculation and were detected for up to 1 week post-inoculation. Image analysis determined that the number of microcolonies with >100 cells increased 1 week post-inoculation, confirming that E. coli O157:H7 is capable of growth within biofilms surrounding wetland plant roots.

Lead sequestration in iron plaques developed on Phalaris arundinacea Linn. and Carex cinerascens Kukenth. from Poyang Lake (China)

Iron plaque often forms on the roots of wetland plants under anaerobic conditions, and it may play a role in the uptake and translocation of metals in wetland plants. A hydroponic experiment was conducted to investigate whether iron plaque could affect the uptake and translocation of lead by two dominant wetland plants, Carex cinerascens Kukenth. and Phalaris arundinacea Linn., growing in Poyang Lake, Jiangxi Province, China. After iron plaque on plant roots was induced by growing plants in solution containing 0, 30, 60, 100, 150, or 210mgL−1 Fe2+ for 7 days, plants were transferred to nutrient solution containing 10mgL−1 Pb2+ for 5 days. A significant positive correlation was observed between the content of iron plaque and Fe2+ concentration in the solution for both the species. The content of iron plaque formed on the root surfaces of C. cinerascens with higher root activity was slightly more than that of P. arundinacea with lower root activity. Iron plaque on the root surfaces of the two species could adsorb or co-precipitate with Pb and could immobilize Pb on the root surfaces. The Pb concentrations and percentage distribution in different organs were in the order iron plaque>root>shoot. The findings that the proportions of Pb in DCB extracts and roots (nearly 90% in the present study) were significantly higher than that in shoots had been observed. The results showed that iron plaque on the root surfaces could increase sequestration of Pb in the root and reduce the translocation Pb from root to shoot under hydroponic conditions.

Characteristics of growth and radial oxygen loss of eight wetland plants

湿地植物是人工湿地的核心部分,筛选优良的植物种类,将有利于充分发挥湿地植物的功能,提高人工湿地污水处理的能力.分析4种须根型植物香蒲(Typha orientalis)、美人蕉(Canna indica)、灯芯草(Juncus effusus)、纸莎草(Cyperus papyrus)和4种根茎型植物菖蒲(Acorus calamus)、再力花(Thalia dealbata)、芦竹(Arundo donax)、黄菖蒲(Iris pseudacorus)在厌氧、水培条件下的生长状况及根系泌氧特性;比较它们的根和茎叶生物量、相对生长速率(RGR)、根长、根孔隙度和泌氧量(率)等生理生态特性.结果表明,8种湿地植物在厌氧条件下生长状况良好;其中,须根型植物的生物量、RGR和泌氧能力均显著优于根茎型植物.在相同光照条件下,灯芯草的泌氧率最大,为192.62μmol O₂/(d·g (DW_root)),而黄菖蒲的根系泌氧率最小,仅为68.81μmol O₂/(d·g(DW_root)).各植物根系泌氧率大小为:灯芯草> 纸莎草> 香蒲> 美人蕉> 菖蒲> 再力花> 芦竹> 黄菖蒲.方差分析显示:植物根系泌氧率与根孔隙度呈极显著正相关,而植物泌氧量与RGR、各生物量呈极显著正相关,但与根茎比呈显著负相关.;Plant is the core component of constructed wetland. Selecting the superior varieties of wetland plants would make full use of their functions in constructed wetland, and then improve the efficiency of sewage water treatment. To investigate the growth characteristics and radial oxygen loss(ROL) from roots of wetland plants under extreme condition, 8 species of wetland plants which were cultured with synthetic water under anaerobic condition were collected for comparison. 8 wetland plants could divided into two groups, fibril-root plant(Typha orientalisl, Canna indica, Juncus effusus, Cyperus papyrus) and rhizomatic-root plant(Acorus calamus, Thalia dealbata, Arundo donax, Iris pseudacorus). The eco-physiological characteristics, such as biomass, relative growth rate(RGR) root length, root porosity, root ROL were compared. Results showed that 8 kinds of wetland plants all grown well under anaerobic conditions. Fibril-root plants had greater biomass, higher RGR and ROL than rhizomatic-root plant. Under the same illumination, Juncus effuses had the maximum ROL which reached 192.62μmol O₂/(d·g (DW_root)), while Iris pseudacorus had the minimum, which was only 68.81μmol O₂/(d·g (DW_root)). The ranking order of ROL of the 8 species wetland plants was: Juncus effuses> Cyperus papyrus> Typha orientalis> Canna indica> Acorus calamus> Thalia dealbata> Arundo donax> Iris pseudacorus. ANOVA analysis indicated that Rate of ROL was positively correlated with root porosity. The ROL was positively correlated with both of RGR and biomass,while negatively related to root/shoot ratio.

Biogeochemical processes at soil-root interface

Rhizosphere is a microsite where interactions among roots, microorganisms, soil constituents (minerals and organic matter), and soil solution take place. Biomolecules produced by plants and microorganisms and soil organic substances are involved in many biogeochemical processes at soil-root interface such as: a) weathering of clay minerals and release of Al and Fe, b) formation of nanoprecipitates and organo-mineral complexes, c) sorption/desorption of cations and anions on/from soil colloids and d) bioavailability of nutrients and pollutants. Many exudates form strong complexes with Fe and Al ions, retard or inhibit their hydrolytic reactions and promote the formation of noncrystalline or short-range ordered Al and Fe nanoprecipitates. The so-called iron plaques, present on many wetland plant roots, are Fe(III)-oxyhydroxides (mainly ferrihydrite). These precipitates may interact with biopolymers (proteins, polysaccharides, DNA, RNA and so on), phyllosilicates, soil organic substances as well as microorganisms forming organo-mineral complexes. Root exudates play a vital role on the sorption/desorption of nutrients and pollutants at soil-root interface. The processes, which affect the sorption of cations and anions on sorbents present in the rhizosphere are particularly complex, being sorption of cations quite different from that of anions. Root exudates usually inhibit the sorption of anions, but may promote or inhibit the sorption of cations. They may desorb, at least partially, nutrients and pollutants previously sorbed on soil components, promoting their bioavailability for plants and microorganisms. Finally, some plants release chelating organic ligands able to complex metals (e.g. Al) which become less toxic. Many factors control these processes, for example; pH, nature and concentration of the biomolecules present in the rhizosphere, nature of sorbent and sorbate, reaction time.

Degradation kinetics of chlorinated aliphatic hydrocarbons by methane oxidizers naturally-associated with wetland plant roots

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants that can be removed from the environment by natural attenuation processes. CAH biodegradation can occur in wetland environments by reductive dechlorination as well as oxidation pathways. In particular, CAH oxidation may occur in vegetated wetlands, by microorganisms that are naturally associated with the roots of wetland plants. The main objective of this study was to evaluate the cometabolic degradation kinetics of the CAHs, cis-1,2-dichloroethene (cisDCE), trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1TCA), by methane-oxidizing bacteria associated with the roots of a typical wetland plant in soil-free system. Laboratory microcosms with washed live roots investigated aerobic, cometabolic degradation of CAHs by the root-associated methane-oxidizing bacteria at initial aqueous [CH4] ~1.9mgL−1, and initial aqueous [CAH] ~150μgL−1; cisDCE and TCE (in the presence of 1,1,1TCA) degraded significantly, with a removal efficiency of approximately 90% and 46%, respectively. 1,1,1TCA degradation was not observed in the presence of active methane oxidizers. The pseudo first-order degradation rate-constants of TCE and cisDCE were 0.12±0.01 and 0.59±0.07d−1, respectively, which are comparable to published values. However, their biomass-normalized degradation rate constants obtained in this study were significantly smaller than pure-culture studies, yet they were comparable to values reported for biofilm systems. The study suggests that CAH removal in wetland plant roots may be comparable to processes within biofilms. This has led us to speculate that the active biomass may be on the root surface as a biofilm. The cisDCE and TCE mass losses due to methane oxidizers in this study offer insight into the role of shallow, vegetated wetlands as an environmental sink for such xenobiotic compounds.

Natural attenuation potential of tricholoroethene in wetland plant roots: Role of native ammonium-oxidizing microorganisms

Bench-scale microcosms with wetland plant roots were investigated to characterize the microbial contributions to contaminant degradation of trichloroethene (TCE) with ammonium. The batch system microcosms consisted of a known mass of wetland plant roots in aerobic growth media where the roots provided both an inoculum of root-associated ammonium-oxidizing microorganisms and a microbial habitat. Aqueous growth media, ammonium, and TCE were replaced weekly in batch microcosms while retaining roots and root-associated biomass. Molecular biology results indicated that ammonium-oxidizing bacteria (AOB) were enriched from wetland plant roots while analysis of contaminant and oxygen concentrations showed that those microorganisms can degrade TCE by aerobic cometabolism. Cometabolism of TCE, at 29 and 46μgL−1, was sustainable over the course of 9weeks, with 20–30mgL−1 ammonium-N. However, at 69μgL−1 of TCE, ammonium oxidation and TCE cometabolism were completely deactivated in two weeks. This indicated that between 46 and 69μgL−1 TCE with 30mgL−1 ammonium-N there is a threshold [TCE] below which sustainable cometabolism can be maintained with ammonium as the primary substrate. However, cometabolism-induced microbial deactivation of ammonium oxidation and TCE degradation at 69μgL−1 TCE did not result in a lower abundance of the amoA gene in the microcosms, suggesting that the capacity to recover from TCE inhibition was still intact, given time and removal of stress. Our study indicates that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments, such as urban or treatment wetlands, and wetlands impacted by industrial solvents.

Uranium immobilization in an iron-rich rhizosphere of a native wetland plant from the Savannah River Site under reducing conditions.

The hypothesis of this study was that iron plaques formed on the roots of wetland plants and their rhizospheres create environmental conditions favorable for iron reducing bacteria that promote the in situ immobilization of uranium. Greenhouse microcosm studies were conducted using native plants (Sparganium americanum) from a wetland located on the Savannah River Site, Aiken, SC. After iron plaques were established during a 73-day period by using an anoxic Fe(II)-rich nutrient solution, a U(VI) amended nutrient solution was added to the system for an additional two months. Compared to plant-free control microcosms, microcosms containing iron plaques successfully stimulated the growth of targeted iron reducing bacteria, Geobacter spp. Their population continuously increased after the introduction of the U(VI) nutrient solution. The reduction of some of the U(VI) to U(IV) by iron reducing bacteria was deduced based on the observations that the aqueous Fe(II) concentrations increased while the U(VI) concentrations decreased. The Fe(II) produced by the iron reducing bacteria was assumed to be reoxidized by the oxygen released from the roots. Advanced spectroscopic analyses revealed that a significant fraction of the U(VI) had been reduced to U(IV) and they were commonly deposited in association with phosphorus on the iron plaque.

Study on the Effect of Moved Wastewater on Oxygen Release from Roots and Wastewater Treatment

Constructed wetlands (CW) have been gaining increasing international interest and application because of their unique purification and ecology. Numerous studies have reported that plants or hydraulics influence pollutants removal in CW but the reasons and the relationship between them remain poorly known. This study experimentally investigated the effect of moved wastewater on oxygen release from roots and pollutants removal. Experimental results have demonstrated that more oxygen was released from roots of wetland plants with higher hydraulic loading rate. substrate water DO levels and pollutants removal are accordingly followed by the same pattern as dischargeable oxygen release rate which exhibits diurnal fluctuations. Moved wastewater in CW will stimulate root oxygen release, and stimulate organics and nitrogen removal by increasing oxygen supply for the processes of aerobic degradation and nitrification.

Root porosity, radial oxygen loss and iron plaque on roots of wetland plants in relation to zinc tolerance and accumulation

Wetland plants have been widely used in constructed wetlands for the clean-up of metal-contaminated waters. This study investigated the relationship between rate of radial oxygen loss (ROL), root porosity, Zn uptake and tolerance, Fe plaque formation in wetland plants. A hydroponic experiment and a pot trial with Zn-contaminated soil were conducted to apply different Zn level treatments to various emergent wetland plants. Significant differences were found between plants in their root porosities, rates of ROL, Zn uptake and Zn tolerance indices in the hydroponic experiment, and concentrations of Fe and Mn on roots and in the rhizosphere in the pot trial. There were significant positive correlations between root porosities, ROL rates, Zn tolerance, Zn, Fe and Mn concentrations on roots and in the rhizosphere. Wetland plants with higher root porosities and ROL tended to have more Fe plaque, higher Zn concentrations on roots and in their rhizospheres, and were more tolerant of Zn toxicity. Our results suggest that ROL and root porosity play very important roles in Fe plaque formation, Zn uptake and tolerance, and are useful criteria for selecting wetland plants for the phytoremediation of Zn-contaminated waters and soils/sediments.

Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds

Thousands of existing wet retention ponds have been built across the United States, primarily for the mitigation of peak flow and removal of sediment. These systems struggle to mitigate soluble nutrient loads from urban watersheds. A simple retrofit for improvement of pond performance for nitrogen and phosphorus removal could become popular. Floating treatment wetlands (FTWs), one such retrofit, are a hydroponic system that provides a growing medium for hydrophytic vegetation, which obtain nutrients from the stormwater pond. Installation of FTWs does not require earth moving, eliminates the need for additional land to be dedicated to treatment, and does not detract from the required storage volume for wet ponds (because they float). To test whether FTWs reduce nutrients and sediment, two ponds in Durham, NC, were monitored pre- and post-FTW installation. At least 16 events were collected from each pond during both monitoring periods. The distinguishing characteristic between the two ponds post-retrofit was the fraction of pond surface covered by FTWs; the DOT pond and Museum ponds had 9% and 18%, respectively, of their surface area covered by FTWs. A very small fraction of N and P was taken up by wetland plants, with less than 2% and 0.2%, respectively, of plant biomass as N and P. Temperature measurements at three depths below FTWs and at the same depths in open water showed no significant difference in mean daily temperatures, suggesting little shading benefit from FTWs. The two ponds produced effluent temperatures that exceeded trout health thresholds. Both the pre- and post-FTW retrofit ponds performed well from a pollutant removal perspective. One pond had extremely low total nitrogen (TN) effluent concentrations (0.41mg/L and 0.43mg/L) during both pre- and post-FTW retrofit periods, respectively. Floating treatment wetlands tended to improve pollutant capture within both ponds, but not always significantly. Mean effluent concentrations of TN were reduced at the DOT pond from 1.05mg/L to 0.61mg/L from pre- to post-retrofit. Mean total phosphorus (TP) effluent concentrations were reduced at both wet ponds from pre- to post-retrofit [0.17mg/L to 0.12mg/L (DOT pond) and 0.11mg/L to 0.05mg/L (Museum pond)]. The post-retrofit effluent concentrations were similar to those observed for bioretention cells and constructed stormwater wetlands in North Carolina. The DOT pond showed no significant differences between pre- and post-retrofit effluent concentrations for all nine analytes. The Museum pond had a statistically significant improvement post-retrofit (when compared to the pre-retrofit period) for both TP and total suspended solids (TSS). Wetland plant root length was measured to be approximately 0.75m, which had the benefit of stilling water flow, thereby increasing sedimentation. Results suggested that greater percent coverage of FTWs produced improved pollutant removal.

Mechanisms of High Efficiency and Stabilization of Baffled Constructed Wetland in Treatment of Domestic Sewage

To solve the problem of short-circuit of individual current constructed wetland, a baffled constructed wetland was designed and applied to treat domestic sewage by our research group. The wetland plants were composed of Eichhormia crassipes, Oenanthe javanica, Cyperusalternifolius, Phragmites communis and Aquatic. The results of 18 month indicated that the optimal hydraulic load of baffled constructed wetland was 2.0~2.2 m3/(m2•d). At the hydraulic load of 2.0m3/(m2•d), the COD, TN and TP removal rates of baffled constructed wetland could be over 76.40%, 76.12%, 65.37%, respectively, at 24°C. When the temperature decreased to 12°C, the COD, TN, TP removal rates of system decreased to 67.56%、62.75% and 61.33%, respectively; The SS removal rate of the first 6 compartments was about 79.5% and that of system could maintain 87.18% during the operation of system. Based on the results of trial, the mechanisms of extending the baffled constructed wetland's operational life was owed to high efficient SS removal rate of the first 6 compartments which was used as constructed wetland and anaerobic baffled reactor (ABR). As a result, the long-term stable operation of system in treatment of domestic sewage was explained with extending about 5 times service life than that of individual current constructed wetland. The mechanisms of higher efficiency of baffled constructed wetland in treatment of domestic sewage were owed to the longer flow line of system and the up-down flow of domestic sewage makes pollutant more intimate contact with roots of wetland plants.

Microbiology of wetlands

Watersaturated soil and sediment ecosystems (i.e. wetlands) are ecologically as well as economically important systems due to their high productivity, their nutrient (re)cycling capacities and their prominent contribution to global greenhouse gas emissions. Being on the transition between terrestrial and – aquatic ecosystems, wetlands are buffers for terrestrial run off thereby preventing eutrophication of inland as well as coastal waters. The close proximity of oxic-anoxic conditions, often created by wetland plant roots, facilitates the simultaneous activity of aerobic as well as anaerobic microbial communities. Input of nutrients and fast recycling due to active aerobes and anaerobes makes these systems highly productive and therefore attractive for humans as well as many other organisms. Wetlands globally are under high pressure due to anthropogenic activities as well as climate change. Changes of land-use as well as altered hydrology due to climate change will lead to disturbance and loss of these habitats. However, the diversity and functioning of microbial communities in wetlands systems in highly underexplored in comparison to soils and aquatic ecosystems. Given the importance of wetlands and their immediate threats combined with the lack of knowledge on the microbiology of these systems is the basis for this special issue, focusing on the current microbiological knowledge and gaps therein to be assessed in future wetland research. Papers (research papers, reviews, perspectives, opinion papers) are welcomed that focus on all aspects that regulate the functioning and community composition of microbes (i.e. bacteria, archaea, protozoa, fungi) in wetland ecosystems (peat, coastal as well as freshwater marshes, flood plains, rice paddies, littoral zones of lakes etc) from all geographic regions. Welcomed topics are physiology, ecology, functioning, biodiversity, biogeography of microbes involved in nutrient cycling (C, N, P, Fe, Mn), green house gas emissions as well as plant-microbe interactions. These studies can be multidisciplinary and cover topics from the molecular to the community level.

Roots of the wetland plants Typha latifolia and Phragmites australis are inhabited by methanotrophic bacteria in biofilms

Wetland plants create partly aerobic conditions in the rhizosphere by releasing oxygen to the waterlogged substrate. The present study was conducted to characterise the arrangement of rhizobacteria, especially those active in methane oxidation, in root-associated biofilms of wetland plants. Root cross sections sampled from Typha latifolia L. (broadleafed cattail) and Phragmites australis (Cav.) Trin. ex Steud. (common reed) were scanned using light and electron microscopy. Methane-oxidising bacteria were identified and quantified by immunological labelling of the α-subunit of the methanol dehydrogenase (α-MDH; encoded in mxaF). On roots of both species there was a diverse subset of bacteria arranged in a microbial biofilm around the roots’ exodermis. Similar bacterial densities in the root-associated biofilm were detected in more basal regions and closer to the root tip. Many microbes carried notable internal membrane systems that are characteristic of methanotrophic bacteria. This morpho-anatomical characterisation was confirmed by immunogold labelling with α-MDH antibodies. Quantification of labelled bacteria revealed that 34–43% of the biofilm bacteria were potentially capable of methane turnover. These findings confirm the presence of methane-oxidising bacteria in the root-associated biofilms of the two common macrophytes T. latifolia and P. australis. This implies that the methanotrophs participate essentially in the microbial processes related to oxygen-releasing roots of wetland plants.

Current standard assays using artificial substrates overestimate phosphodiesterase activity

Phosphodiesterases (PDE) are important enzymes in environments with significant proportion of phosphodiesters. The breakdown of phosphodiesters is a two step process, initiated by PDE hydrolyzing an ester-P bond on the diester molecule, breaking it into an organic moiety and a phosphomonoester. In the second step, the phosphomonoester is further hydrolyzed by phosphomonoesterase (PME) into the second organic moiety and free phosphate, Pi. The methods to assess extracellular PDE activities commonly use the substrate analogues bis-(p-nitrophenyl) phosphate (bis-pNPP) or bis-(4-methylumbelliferyl) phosphate (bis-MUFP), measure the resulting concentration of p-nitrophenol (pNP) or 4-methylumbelliferon (MUF), and assume the contribution from phosphomonoester hydrolysis by PME to be insignificant. To verify this, we measured concentrations of MUF and Pi at the end of the 30- and 60-min incubation of wetland plant root segments with a phosphodiester substrate. We found that the hydrolysis was complete (MUF:Pi ratio ∼ 2) confirming the importance of step 2. We suggest that a correction for additional hydrolysis by PME should be employed in samples where this is possible, such as plant roots or microbial cultures. Here, the MUF:Pi should be verified for each new sample type tested for its PDE activity, and values obtained from the PDE assay should be lowered accordingly. We do not recommend using the standard artificial substrates for PDE activity measurements in more heterogeneous samples, for example soils, where these assays have low reliability and can produce erroneous results.

New distribution information for Coquillettidia perturbans (Walker) (Diptera, Culicidae) in northern British Columbia, Canada

The detection of West Nile virus (WNV) in North America in 1999 (Jia et al. 1999) prompted an increased interest in the biology of mosquito species throughout Canada, including the province of British Columbia. Increased funding for research was further fueled by the presence of WNV in neighboring provinces and states. Recent surveys of mosquito diversity have been carried out primarily to determine the geographic distributions of potential WNV vectors and, therefore, to help estimate the risk of WNV infection in human and other populations in various regions of the province (Stephen et al. 2006). While WNV has been the arbovirus emphasized in recent years, improved understanding of mosquito distributions and biology may prove invaluable if other pathogens become threats in the future. In BC, prior to 2003, surveys of mosquito species had been largely restricted to the southern half of the province (Hearle 1927, Belton and Belton 1981). Early results from surveys conducted by the British Columbia Centre for Disease Control (BCCDC) suggested that the estimated geographic ranges for several species in BC were in need of revision. In particular, Coquillettidia (=Mansonia) perturbans, has been described by most authors as having a southerly distribution (Hearle 1927, Wood et al. 1979, Belton and Belton 1981, Belton 1983). This species was trapped as far north as Prince George (53.9°N, 122.8°W) in 2004 (BCCDC 2005). The larvae attach their siphons to the roots of wetland plants, such as cattails (Typha latifolia L.) and obtain oxygen from the root aerenchyma; this habit makes the larvae difficult to catch, monitor or manage (Belton 1983). The cattail marsh habitat type is common throughout British Columbia, especially at low elevations in areas with warm summers (Mackenzie and Moran 2004), suggesting that Cq. perturbans may be far more widely distributed than previously thought. In 2005, 2007, and 2010, surveys were conducted in northern British Columbia (Figure 1) with CDC (Center for Disease Control) miniature light traps fitted with incandescent light bulbs and using dry ice as a source of carbon dioxide for the primary attractant. Traps were placed

A novel sediment microbial fuel cell with a biocathode in the rice rhizosphere

Wetland plants possess the unique ability to release oxygen as well as organic matter into the rhizosphere. It is understood that microbial fuel cells (MFCs) can use organic matter from plants as key electron donors, but the effect of root excreted oxygen on MFCs is presently unknown. In this study, a novel biocathode was buried in the rice rhizosphere and found to be capable of delivering electrons to root excreted oxygen for oxygen reduction reactions. The voltages between electrodes in the rhizosphere and bulk soil were found to increase initially, but dissipate after approximately 1month. Results from the MFC and oxygen microelectrode experiments indicated that the oxygen efflux rate from rice roots was dependent on the root maturity. Furthermore, the excreted oxygen from wetland plant roots could be used for the construction of highly efficient biocathodes.

Flooding greatly affects the diversity of arbuscular mycorrhizal fungi communities in the roots of wetland plants.

The communities of arbuscular mycorrhizal fungi (AMF) colonizing the roots of three mangrove species were characterized along a tidal gradient in a mangrove swamp. A fragment, designated SSU-ITS-LSU, including part of the small subunit (SSU), the entire internal transcribed spacer (ITS) and part of the large subunit (LSU) of rDNA from samples of AMF-colonized roots was amplified, cloned and sequenced using AMF-specific primers. Similar levels of AMF diversity to those observed in terrestrial ecosystems were detected in the roots, indicating that the communities of AMF in wetland ecosystems are not necessarily low in diversity. In total, 761 Glomeromycota sequences were obtained, which grouped, according to phylogenetic analysis using the SSU-ITS-LSU fragment, into 23 phylotypes, 22 of which belonged to Glomeraceae and one to Acaulosporaceae. The results indicate that flooding plays an important role in AMF diversity, and its effects appear to depend on the degree (duration) of flooding. Both host species and tide level affected community structure of AMF, indicating the presence of habitat and host species preferences.

Root features related to plant growth and nutrient removal of 35 wetland plants

Morphological, structural, and eco-physiological features of roots, nutrient removal, and correlation between the indices were comparatively studied for 35 emergent wetland plants in small-scale wetlands for further investigation into the hypothesis of two types of wetland plant roots ( Chen et al., 2004). Significant differences in root morphological, structural, and eco-physiological features were found among the 35 species. They were divided into two types: fibrous-root plants and thick-root plants. The fibrous-root plants had most or all roots of diameter ( D) ≤ 1 mm. Roots of D > 1 mm also had many fine and long lateral roots of D ≤ 1 mm. The roots of these plants were long and had a thin epidermis and a low degree of lignification. The roots of the thick-root plants were almost all thicker than 1 mm, and generally had no further fine lateral roots. The roots were short, smooth, and fleshy, and had a thick epidermis. Root porosity of the fibrous-root plants was higher than that of the thick-root plants ( p = 0.001). The aerenchyma of the fibrous-root plants was composed of large cavities which were formed from many small cavities, and distributed radially between the exodermis and vascular tissues. The aerenchyma of the thick-root plants had a large number of small cavities which were distributed in the mediopellis. The fibrous-root plants had a significantly larger root biomass of D ≤ 1 mm, of 1 mm < D < 3 mm, above-ground biomass, total biomass, and longer root system, but shorter root longevity than those of the thick-root plants ( p = 0.003, 0.018, 0.020, 0.032, 0.042, 0.001). The fibrous-root plants also had significantly higher radial oxygen loss (ROL), root activity, photosynthetic rate, transpiration rate, and removal rates of total nitrogen and total phosphorus than the thick-root plants ( p = 0.001, 0.008, 0.010, 0.004, 0.020, 0.002). The results indicate that significantly different root morphological and structural features existed among different wetland plants, and these features had a close relationship to nutrient removal capacity.

Biodegradation of Trichloroethene by Methane Oxidizers Naturally Associated with Wetland Plant Roots

Trichloroethene (TCE) can undergo natural attenuation within wetland environments, particularly by oxidative processes that occur in the vegetated subsurface. The goal of this study was to evaluate TCE degradation potential through aerobic cometabolism by methane-oxidizing microorganisms associated with the roots of wetland plant species, Carex comosa and Scirpus atrovirens. The degradation experiments were conducted in 2.4 L Teflon microcosms with 15 g of washed, soil-free roots and amended with methane (2.1 mg/L), oxygen (8 mg/L), and TCE (three enrichment cycles without TCE and four cycles at 150 μg/L, one cycle at 600 μg/L, and one cycle at 900 μg/L of TCE). Our results indicated that methane-oxidizing activity and TCE degradation potential were comparable for the plant species investigated. The initial rates of methane degradation with TCE amendments varied between 0.21 and 0.30 mg L–1 d–1 for Carex comosa, and between 0.14 and 0.25 mg L–1 d–1 for Scirpus atrovirens. The average TCE mass removal per cycle varied between 24 and 32%, and the overall transformation yield was 0.0004 mmol TCE/mmol CH4 for both plant species. This study suggests that wetland plants can play an important role in the natural attenuation of TCE in contaminated aquatic environments.

A comparative study on the potential of oxygen release by roots of selected wetland plants

The capacity of root oxygen release by selected wetland plants pre-grown under both nutrient solution and artificial wastewater conditions were determined. The results indicated that the significant differences of root oxygen release by the tested wetland plants existed, and the biochemical process was the main source of root oxygen release as oxygen released by Vetiveria zizanioides L. Nash roots through biochemical process was contributed to 77% and 74% of total root oxygen release under nutrient solution conditions and artificial wastewater conditions, respectively, and that was 72% and 71% of total root oxygen release for Cyperus alternifolius L. It was found that the formation of root plaque with iron oxide was a function of root oxygen release as iron oxide concentration in root plaque was positively correlated to the potential of oxygen released by wetland plant roots with the regression coefficients as 0.874 *( p < 0.05) under nutrient solution conditions and 0.944 **( p < 0.01) under artificial wastewater conditions, which could be regarded as an important mechanism of wetland plants being tolerant to anoxia during wastewater treatment. It was suggested that the potential of root oxygen release could be used as a parameter for selecting wetland plants that can increase oxygen supply to soil or substrate of constructed wetlands and enhance nutrient transformation and removal, and V. zizanioides L. Nash with the highest potential of root oxygen release and higher tolerance to wastewater could be recommended to establish vegetated wetlands for treating nutrient-rich wastewater such as domestic wastewater.