Scirpus Triqueter Research Articles

Uptake of Silver-Containing Nanoparticles in an Estuarine Plant: Speciation and Bioaccumulation.

Understanding the bioaccumulation of silver-containing nanoparticles (Ag-NPs) with different species, concentrations, and sizes in estuarine plants is critical to their related environmental risk. Herein, the distribution of Ag-NPs in tidewater, sediments, and plants (Scirpus triqueter) of field-constructed mesocosm was investigated, where tidewater was exposed to Ag0-NPs and Ag+ at environmentally relevant concentrations. Particle number concentrations (PNCs) and sizes of Ag-NPs with various species were analyzed using a multistep selective dissolution method followed by the single-particle- inductively coupled plasma mass spectrometry technique. After 30 days of exposure, more than half of Ag0-NPs were dissolved to Ag+ and about 1/4 of Ag+ were transformed into Ag0-/AgCl-NPs in tidewater. Ag-NPs in stems exposed to Ag0-NPs were found to be dominated by metallic Ag, while Ag+ exposure led to more Ag2S-NPs in stems. In roots, 71% and 51% of Ag-NPs were found as Ag2S-NPs for Ag0-NPs and Ag+ treatment groups, respectively. Plant stems had a significantly higher enrichment of Ag-NPs than roots. Based on both random forests and structure equation models, it is suggested that salinity of tidewater can regulate Ag0-NPs in tidewater indirectly by influencing AgCl-NPs in tidewater and further affect the total PNCs of Ag-NPs in plant stems. Moreover, elevated sulfate-reducing bacteria (SRB) result in more Ag2S-NPs in rhizosphere sediments, thereby enhancing the bioaccumulation of Ag-NPs by roots.

Methanotrophs Contribute to Nitrogen Fixation in Emergent Macrophytes.

Root-associated aerobic methanotroph plays an important role in reducing methane emissions from wetlands. In this study, we examined the activity of methane-dependent nitrogen fixation and active nitrogen-fixing bacterial communities on the roots of Typha angustifolia and Scirpus triqueter using a 15N-N2 feeding experiment and a cDNA-based clone library sequence of the nifH gene, respectively. A 15N-N2 feeding experiment showed that the N2 fixation rate of S. triqueter (1.74 μmol h–1 g–1 dry weight) was significantly higther than that of T. angustifolia (0.48 μmol h–1 g–1 dry weight). The presence of CH4 significantly increased the incorporation of 15N-labeled N2 into the roots of both plants, and the rate of CH4-dependent N2 fixation of S. triqueter (5.6 μmol h–1 g–1 dry weight) was fivefold higher than that of T. angustifolia (0.94 μmol h–1 g–1 dry weight). The active root-associated diazotrophic communities differed between the plant species. Diazotrophic Methylosinus of the Methylocystaceae was dominant in S. triqueter, while Rhizobium of the Rhizobiaceae was dominant in T. angustifolia. However, there were no significant differences in the copy numbers of nifH between plant species. These results suggest that N2 fixation was enhanced by the oxidation of CH4 in the roots of macrophytes grown in natural wetlands and that root-associated Methylocystacea, including Methylosinus, contribute to CH4 oxidation-dependent N2 fixation.

Spartina alterniflora invasion has a greater impact than non-native species, Phragmites australis and Kandelia obovata, on the bacterial community assemblages in an estuarine wetland

The invasion of Spartina alterniflora poses a serious threat to the sustainability of native ecosystems worldwide. However, compared with other non-native plants (e.g., Phragmites australis and Kandelia obovata), how Spartina alterniflora invasion influences the community structure of bacteria and their assembly processes and functionality remains elusive. Here, we characterized the diversity, community structure, assembly processes and functional guilds of bacteria underneath five plant species and a bare tidal flat at three soil depths in an estuarine wetland. We found that plant species played a more important role than soil depth in mediating the bacterial community structure. Compared with bare tidal flats, the native species Cyperus malaccensis, rather than Scirpus triqueter, significantly changed the bacterial community structure. However, S. alterniflora invasion increased bacterial alpha diversity and significantly altered the bacterial community structure by enriching Chloroflexi, Bacteroidetes and Firmicutes while reducing Acidobacteria, Nitrospirae and Gemmatimonadetes. The invasion of P. australis and translocation of K. obovata had less pronounced effects on the bacterial community structure. Total carbon, total nitrogen and salinity were the key environmental factors mediating the bacterial community structure. Overall of all the non-native plant species, the invasion of S. alterniflora increased the relative importance of stochastic processes in the assembly of bacterial communities, and shifted the bacterial functional profiles by stimulating sulfur cycling groups and suppressing nitrogen cycling groups. Altogether, our results suggest that S. alterniflora invasion has a greater effect than P. australis invasion or K. obovata translocation on the profiles and assembly processes of the bacterial communities, with important implications for soil biogeochemical processes in coastal wetlands.

Fungi drive soil multifunctionality in the coastal salt marsh ecosystem

Salt marshes are highly productive intertidal wetlands located in temperate climatic zones, in which marine-to-terrestrial transition significantly influences microbial life. Numerous studies revealed the important coupling relationship between microbial diversity and ecosystem functions in terrestrial ecosystems, however, the importance of microbial diversity in maintaining soil functions in coastal ecosystems remains poorly understood. Here, we studied the shifts of microbial communities and soil multifunctionality (SMF; nine functions related with C, N and P cycling) along a vegetation gradient in a salt marsh ecosystem and investigated the microbial diversity - ecosystem function relationship. The aboveground vegetation shifted from mud flat (MF) to Scirpus triqueter (SM) and then Phragmites australis (PA) with increasing distance away from the sea. Average approach showed that the SMF was much higher in halophytes covered zones including SM and PA than in MF. Structural equation model (SEM) analysis confirmed that vegetation was an important predictor on SMF besides moisture and organic carbon. Linear regression and multiple threshold methods showed that in MF and SM zones, fungal rather than bacterial richness was significantly and positively correlated with SMF, while in the PA zone microbial diversity did not relate with SMF. Random forest analysis identified several Ascomycota taxa with preference over marine environment as strong predictors of SMF. Taken together, our study lays the basis for a better understanding on the relationships between belowground microbial diversity and soil functions in coastal ecosystems.

Diversity of active anaerobic ammonium oxidation (ANAMMOX) and nirK-type denitrifying bacteria in macrophyte roots in a eutrophic wetland

Wetland eutrophication is a global ecological problem. Anaerobic oxidation of ammonium (ANAMMOX) and denitrification are the two major pathways of nitrogen removal in wetlands. However, little is known about the associated bacteria that are present around emergent macrophytes and their transcriptional activities. Here, we examine the transcriptional activity of bacteria that perform ANAMMOX and denitrification in the roots and vegetated sediments of three emergent macrophytes and in unvegetated sediment from a eutrophic wetland. Roots and vegetated sediments of three emergent macrophytes (Phragmites australis, Typha angustifolia, and Scirpus triqueter) and unvegetated sediment were collected from Wuliangsuhai wetland, China. The community structure and transcriptional activity of ANAMMOX and denitrifying bacteria were examined at the DNA and RNA levels. Additionally, the sediment physicochemical properties were determined. ANAMMOX (hzsB) and denitrifying bacteria (nirK, nirS, and nirSII) were detected in all sediments and roots at the DNA level. However, at the RNA level, root-associated ANAMMOX bacteria, including Candidatus Jettenia and Candidatus Brocadia, were detected only in the roots of P. australis. In contrast, nirK-carrying active denitrifiers, such as uncultured bacteria, Sinorhizobium, Rhizobiales, Mesorhizobium, Rhizobium, Devosia, and Bosea (all Rhizobiales), were detected in the roots of T. angustifolia and S. triqueter. The reduction of nitrogen concentration in the sediments of the vegetation zone was probably associated with active ANAMMOX bacteria and denitrifiers. Active root-associated ANAMMOX bacteria and nirK-type denitrifiers were influenced by plant species, and they likely contribute to nitrogen removal in eutrophic wetlands.

Mapping Wetland Plant Communities Using Unmanned Aerial Vehicle Hyperspectral Imagery by Comparing Object/Pixel-Based Classifications Combining Multiple Machine-Learning Algorithms

Understanding the spatial patterns of plant communities is important for sustainable wetland ecosystem management and biodiversity conservation. With the rapid development of unmanned aerial vehicle (UAV) technology, UAV-borne hyperspectral data with high spatial resolution have become ideal for accurate classification of wetland plant communities. In this article, four dominant plant communities (Phragmites australis, Typha orientalis, Suaeda glauca, and Scirpus triqueter) and two unvegetated cover types (water and bare land) in the Momoge Ramsar wetland site were classified. This was achieved using UAV hyperspectral images and three object- and pixel-based machine-learning classification algorithms [random forest (RF), convolutional neural network (CNN), and support vector machine (SVM)]. First, spectral derivative analysis, logarithmic analysis, and continuum removal analysis identified the wavelength at which the greatest difference in reflectance occurs. Second, dimensionality reduction of hyperspectral images was conducted using principal component analysis. Subsequently, an optimal feature combination for community mapping was formed based on data transformation (spectral features, vegetation indices, and principal components). Image objects were obtained by segmenting the optimum object feature subsets. Finally, distribution maps of communities were produced by using three machine-learning classification algorithms. Our results reveal that object-based image analysis outperforms pixel-based methods, with overall accuracies (OAs) of 80.29-87.75%; RF has the highest OA of 87.75% (Kappa = 0.864), followed consecutively by CNN (OA = 83.31%, Kappa = 0.829) and SVM (OA = 80.29%, Kappa = 0.813). Phragmites australis dominates the plant community (55.9%) at the study area, followed by Typha orientalis (16.2%), Suaeda glauca (16.2%), and Scirpus triqueter (4.6%). The results highlight the importance of spectral transformation features in red-edge regions. The mapping results will help establish basic information for subsequent studies involving habitat suitability assessment at this study site.

Shifts of sediment bacterial community and respiration along a successional gradient in a typical karst plateau lake wetland (China)

Bacteria are important regulators of carbon cycling in lakes and are central to sediment ecosystem processes. However, the sediment microbial communities and their respiratory responses to the lake wetland succession are poorly understood. In this study, we collected sediment samples from four different succession points (the Potamogeton lucens zone, the Scirpus tabernaemontani zone, the Scirpus triqueter zone, and the Juncus effusus zone) in the Caohai Wetland of the Guizhou Plateau (China). The bacterial communities at these succession points were studied using a high-throughput sequencing approach. The sediment microbial respiration (SR) was measured using static chambers in the field and basal respiration (BR) was determined in the laboratory. The results show that the dominant bacterial taxa in the sediment was Proteobacteria (34.7%), Chloroflexi (17.8%), Bacteroidetes (7.3%), Acidobacteria (6.6%), and Cyanobacteria (6.1%). Principal coordinate analysis showed that the microbial community structure differs significantly at different sampling points along the successional gradient, indicating that the bacterial community structure is sensitive to the lake wetland succession. Different hydrological regimes and soil characteristics such as NH 4 + -N, Fe2+, Mn2+, and sediment organic carbon (SOC) content may be important factors responsible for the differences in the sediment microbial characteristics of the different successional stages in the Caohai wetland. Additionally, it was found that the SR increased significantly from the P. lucens zone to the J. effusus zone, but BR had the opposite response. The shifts in the bacterial community structure along the successional gradient may be the main reason for the observed differences in sediment respiration.

Diversity of active root-associated methanotrophs of\xa0three\xa0emergent\xa0plants in\xa0a eutrophic wetland in northern China

Root-associated aerobic methanotrophs play an important role in regulating methane emissions from the wetlands. However, the influences of the plant genotype on root-associated methanotrophic structures, especially on active flora, remain poorly understood. Transcription of the pmoA gene, encoding particulate methane monooxygenase in methanotrophs, was analyzed by reverse transcription PCR (RT-PCR) of mRNA isolated from root samples of three emergent macrophytes, including Phragmites australis, Typha angustifolia, and Schoenoplectus triqueter (syn. Scirpus triqueter L.) from a eutrophic wetland. High-throughput sequencing of pmoA based on DNA and cDNA was used to analyze the methanotrophic community. Sequencing of cDNA pmoA amplicons confirmed that the structure of active methanotrophic was not always consistent with DNA. A type I methanotroph, Methylomonas, was the most active group in P. australis, whereas Methylocystis, a type II methanotroph, was the dominant group in S. triqueter. In T. angustifolia, these two types of methanotroph existed in similar proportions. However, at the DNA level, Methylomonas was predominant in the roots of all three plants. In addition, vegetation type could have a profound impact on root-associated methanotrophic community at both DNA and cDNA levels. These results indicate that members of the genera Methylomonas (type I) and Methylocystis (type II) can significantly contribute to aerobic methane oxidation in a eutrophic wetland.

Plant Population Dynamics in a Degraded Coastal Wetland and Implications for the Carbon Cycle

Habitat destruction caused by human activities is threatening wetland plants. Based on Landsat 5 TM, Landsat 8 OLI, and Google Earth images, we analysed the spatiotemporal dynamics of plant populations in a degraded wetland in the Minjiang River Estuary from 2009 to 2019. Field survey records, tasselled cap transformation, and supervised classification were used for the image interpretation. The results indicate that the plant habitat area decreased by 42.1% over these 10 years. Consequently, the distribution area of each dominant species declined, and the proportion of total vegetated area in the habitat decreased from 53.1% to 32.6%. Moreover, the dominance relations of the species changed from Spartina alterniflora > Phragmites australis > Cyperus malaccensis > Scirpus triqueter to P. australis > S. alterniflora > C. malaccensis > S. triqueter. We predict that the vegetation landscape in the wetland will be composed exclusively of P. australis and S. alterniflora if habitat destruction continues. Finally, our research shows that the NPCS (net plant carbon sequestration) and PCS (plant carbon stock) in the wetland and the average values of methane flux, NPCS, PCS, and SOCS (sediment organic carbon stock) in the vegetated area have all decreased due to plant population declines.

Enrichment of Type I Methanotrophs with <i>nirS</i> Genes of Three Emergent Macrophytes in a Eutrophic Wetland in China

The pmoA gene, encoding particulate methane monooxygenase in methanotrophs, and nirS and nirK genes, encoding bacterial nitrite reductases, were examined in the root and rhizosphere sediment of three common emergent macrophytes (Phragmites australis, Typha angustifolia, and Scirpus triqueter) and unvegetated sediment from eutrophic Wuliangsuhai Lake in China. Sequencing analyses indicated that 334 out of 351 cloned pmoA sequences were phylogenetically the most closely related to type I methanotrophs (Gammaproteobacteria), and Methylomonas denitrificans-like organisms accounted for 44.4% of the total community. In addition, 244 out of 250 cloned nirS gene sequences belonged to type I methanotrophs, and 31.2% of nirS genes were the most closely related to paddy rice soil clone SP-2-12 in Methylomonas of the total community. Three genera of type I methanotrophs, Methylomonas, Methylobacter, and Methylovulum, were common in both pmoA and nirS clone libraries in each sample. A quantitative PCR (qPCR) analysis demonstrated that the copy numbers of the nirS and nirK genes were significantly higher in rhizosphere sediments than in unvegetated sediments in P. australis and T. angustifolia plants. In the same sample, the nirS gene copy number was significantly higher than that of nirK. Furthermore, type I methanotrophs were localized in the root tissues according to catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Thus, nirS-carrying type I methanotrophs were enriched in macrophyte root and rhizosphere sediment and are expected to play important roles in carbon/nitrogen cycles in a eutrophic wetland.

Ecological responses of three emergent aquatic plants to eutrophic water in Shanghai, P. R. China

Eutrophication is the main pollution in urban water in Shanghai. In this study, three emergent aquatic plant species (Scirpus triqueter, Phragmites australis, and Zizania latifolia) were grown in monoculture, as well as a three-species mixture, to compare their effectiveness in terms of nutrient removal in controlled indoor constructed wetland microcosms. The effect of different aeration treatments (above-aerated, sediment-water middle-aerated, below-aerated, non-aerated) and treatments combining aeration and wetland plants for total nitrate (TN) and total phosphate (TP) removal efficiency was also examined. The objective of this study was to test the following four scientific hypotheses: (1) Plant growth will be optimal in the below-aerated treatment; (2) Z. latifolia will have the highest removal efficiency of TN and TP; (3) Aeration will increase the efficiency of TN and TP removal, with below-aerated treatment having the best effect; (4) The activity of microorganisms will vary over time, and aeration and plant treatment together will be most effective. We found that P. australis was most effective at removing TN and TP from water. Below-aerated significantly promoted the growth of P. australis. Hypotheses 1, 2 and 4 were supported by our results. The combination of P. australis and sediment aeration removed TN from water most efficiently. Above-aerated also effectively reduced TP in water. Combined plant and below-aerated treatments had better removal efficiency of TP from above-aerated than below-aerated alone. These results provide new insights into the management of eutrophication.

Distribution by influence factors of pyrene removal in chemical enhancers assisted microbial phytoremediation of Scirpus triqueter in co-contaminated soils

The rehabilitation of soil co-contaminated by heavy metals and polycyclic aromatic hydrocarbons (PAHs) has become a serious global issue. Chemical enhancers and strains are often used to remove PAHs from contaminated soil. In this paper, the effects of chemical enhancers, strain HD-1, and Scirpus triqueter in removing pyrene from co-contaminated soil are studied. In the pot experiment, chemical enhancers and HD-1 were added to the co-contaminated soil. On the 60th day, the plants and soil were taken out for measurement. The result showed that the addition of chemical enhancers and microorganisms (Group PBC) alleviated the inhibition effect of plants on pollution. The accumulation of pyrene in plants of Group PC (chemical enhancers) and Group PBC (chemical enhancers and HD-1) were much higher than those in other groups. Plant enrichment was not the major way to remove pyrene from soil (less than 0.3%). Compared with the contributions of chemical enhancers, HD-1, and Scirpus triqueter, HD-1 had stronger effects on the removal of pyrene (17.23–22.80%). This study indicates that the combination of chemical enhancers, HD-1, and Scirpus triqueter constituted a beneficial composite system, in which the three elements interacted with each other and ultimately achieved the goal of removing pyrene from co-contaminated soil.

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.

Conservation of higher aquatic flora in the Kharkiv region

Based on the results of field research, inventory of CWU herbarium collections and study of scientific sources it was carried out the sozological assessment of rare plant species as a part of the higher aquatic flora of the Kharkiv region according to generally accepted criteria of rarity. It has been found that four species (Salvinia natans (L.) All., Trapa natans L., Utricularia intermedia Hayne, U. minor L.) are listed in the Red Book of Ukraine, the first two of which are in the Annex I of Bern Convention. The European Red List of Vascular Plants includes three species (Potamogeton acutifolius Link, P. rutilus Wolfg., Trapa natans), which have the conservation status “Near Threatened”. 27 plant species are in the Red List of Aquatic Macrophytes of Ukraine and 22 species are included in the Regional Red List of the Kharkiv region. It has been revealed that populations of six rare species (Batrachium aquatile (L.) Dumort., Potamogeton obtusifolius Mert. et Koch, P. rutilus Wolfg., Scirpus triqueter L., Vallisneria spiralis L., Wolffia arrhiza (L.) Horkel ex Wimmer) are on the border of the range. By the uniqueness for the region, one species (Salvinia natans) is considered as rare for Europe, 26 species are rare at the state level and 10 species are rare at the regional level. For 22 species there are known from one to five locations in the region. By the size of the habitat area, the most of cenopopulations of species occupy small areas (for 27 species it is less than 5 hectares). At present the location of 6 species has not been confirmed (Ceratophyllum tanaiticum Sapjeg., Potamogeton gramineus L., P. obtusifolius Mert.et W.D.J.Koch, P. praelongus Wulfen, P. sarmaticus Mäemets, Trapa natans). It has been established that populations of only 8 species are represented quite fully at the natural reserve areas of the region. On the basis of autphytosozological analysis we propose to include 22 species of vascular plants in the Regional Red List of the Kharkiv region and to exclude from it two species: Utricularia intermedia, which is in the Red Book of Ukraine and has the conservation status at the state level, and Vallisneria spiralis L., which is considered as adventive species.

Effect of Bacillus subtilis and NTA-APG on pyrene dissipation in phytoremediation of nickel co-contaminated wetlands by Scirpus triqueter

A complex mix of organic pollutants and heavy metal made the remediation of contaminated wetlands more difficult. Few research focus on the remediation for pyrene enhanced by chemical reagents and pyrene degrading bacteria in the nickel co-contaminated soil. In this paper, the effect of chemical reagents (nitrilotriacetic acid and alkyl polyglucoside) and Bacillus subtilis on pyrene dissipation in phytoremediation of nickel co-contaminated soil by Scirpus triqueter was investigated. Similar seedlings of Scirpus triqueter were moved to uncontaminated soil and pyrene-nickel co-contaminated soil. The pots (14.8 cm diameter and 8.8 cm height) were set up in greenhouse and treated in different ways. After 60 days, plant biomass, radial oxygen loss (ROL), soil dehydrogenase activity (DHA) and pyrene concentration in soil were determined. Results showed that ROL rate and DHA in different groups was positively correlated with pyrene dissipation from soil. In the process of remediation, chemical reagents might have an indirect slight effect on pyrene dissipation (pyrene dissipation increased 21%) by affecting DHA firstly and redistributing pyrene fractions in the presence of pyrene degrading bacteria. Pyrene degrading bacteria were likely to affect pyrene dissipation by impacting ROL rate and DHA and played a more vital role in contributing to pyrene dissipation (pyrene dissipation increased 45%) from wetland. This study demonstrated that phytoremediation for pyrene in nickel co-contaminated soil by Scirpus triqueter can be enhanced by the application of NTA-APG and pyrene degrading bacteria and they could be reasonably restore the ecological environment of PAH-contaminated wetlands.

Evapotranspiration partitioning using a simple isotope‐based model in a semiarid marsh wetland in northeastern China

AbstractPartitioning evapotranspiration (ET) into evaporation (E) and transpiration (T) in wetlands is important for understanding the hydrological processes in wetlands and the contribution of wetland ET to local and regional water cycling and for designing effective wetland management strategies. Stable water isotopes are useful in the application of ET partitioning through the evaluation of the isotopic compositions of E (δE), T (δT), and ET (δET) obtained from observation or modelling methods. However, this approach still suffers from potentially large uncertainties in terms of estimating the isotopic endmembers. In this study, we modified the traditional isotope‐based ET partitioning methods to include leaf‐level biological constraints to separately estimate the relative contributions of T from Scirpus triqueter and Phragmites australis and the relative contributions of E from the standing surface water in a semiarid marsh wetland in northeastern China.The results showed that although the δT values of S. triqueter and P. australis were rather similar, the mean δT values of the 2 species were different from the values of δE, making it possible to distinguish the relative contributions of E and T through the use of isotopes. The simulation of leaf water using a non‐steady‐state model indicated obvious deviations in leaf water enrichment (δLb) from isotopic steady states for both species, especially during early mornings and evenings when relative humidity was highest. The isotopic mass balance showed that E accounted for approximately 60% of ET, and T from S. triqueter and P. australis each contributed approximately 20% to ET; this implied that the transpiration of one reed was equivalent to that of 5.25 individuals of S. triqueter. Using the estimated ratio of T to ET and the measured leaf transpiration, the total ET was estimated to be approximately 10 mm day−1. Using the NSS‐Tr method, the estimated ET was higher than the water loss calculated from the water level gauge. This indicated that the river water and surrounding groundwater were the sources of the marsh wetland, with a supply rate of 8.3 mm day−1.

CONTRASTIVE SOIL PROPERTIES, MICROBIAL STRUCTURE AND SOIL ENZYMES IN THE RHIZOSPHERE OF Scirpus triqueter AND BULK SOIL IN PETROLEUM-CONTAMINATED WETLAND

Though Scirpus triqueter plays an important role in protecting the ecological functions of Yangtze River estuary wetland which is frequently contaminated by petroleum, knowledge is limited about the mechanisms involved. In this study, comparative analysis of soil properties, microbial community structure and soil enzymes in the rhizosphere of S. triqueter and bulk soil was conducted throughout one year to provide an insight into the phytoremediation mechanism in the field. The total petroleum hydrocarbon content and soil pH in the rhizosphere were averagely 0.06 g kg -1 and 0.1 lower, respectively, than in the bulk soil. Analysis of phospholipid fatty acids shew the microbial community structure was quite different from that in the bulk soil with much higher activity and diversity. The relative abundance of Gram-positive to Gram-negative bacteria was 0.12 lower in the rhizosphere, while the relative abundance of aerobes to anaerobes was 0.74 higher, than in the bulk soil. Positively correlated with the relative abundance of fungi to bacteria and microbial diversity, the activities of dehydrogenase, catalase, polyphenol oxidase were significantly lower (P < 0.05) in the bulk soil than in the rhizosphere. Redundancy analysis and Pearson correlation shew that soil organic matter, total nitrogen, total phosphorus, as well as temperature were crucial factors influencing soil microbial communities and enzymes which were responsible for the degradation of petroleum hydrocarbons. These results would improve our understanding of the phytoremediation processes in fragile contaminated wetland and supply valuable information for its application in the restoration of damaged ecosystems.

Increased accumulation of Pb and Cd from contaminated soil with Scirpus triqueter by the combined application of NTA and APG

Phytoremediation of heavy metals contaminated soils shows many advantages and it can be improved by adding chelating agents and surfactants. In this study, pot culture experiments were set up to explore the effect of alone application of nitrilotriacetic acid (NTA) and combined application of NTA and alkyl polyglucoside (APG) on changes in absorption and adsorption of heavy metals by root of Scirpus triqueter and bioaccumulation of metals in single or co-contamination. Different additives were added into the soils artificially after 10 d and heavy metals extracted from different plant tissues were analyzed after 60 d. Results showed that more cadmium (Cd) was adsorbed on the root surface while more lead (Pb) was absorbed in root interior with the combined application of NTA and APG during phytoremediation of single contaminated soil. In co-contaminated soils, such a combined application not only strengthened the plant growth, but also promoted accumulation of Pb and Cd by Scirpus triqueter. NTA improved absorption amounts of Pb (9.7-fold) and Cd (1.0-fold) in root interior significantly. APG induced more metals to gather on the root surface in the presence of NTA and the adsorption amounts of Pb and Cd ranged from 26.2 and 17.7 mg kg−1 to 412 and 46.0 mg kg−1 respectively. Besides, the coexistence metal increased bioaccumulation of another metal under combined application of NTA and APG in co-contamination of Pb and Cd. In conclusion, the combined application of NTA and APG would be beneficial to accumulate Pb and Cd from contaminated soils by Scirpus triqueter.

The Contribution of Pyrene Degrading Bacteria and Chemical Reagents to Scirpus triqueter Phytoremediation of Pyrene and Ni Co-contaminated Soil

Phytoremediation of organic pollutant and heavy metal (HM) co-contaminated soils shows many advantages and can be improved by adding chemical reagents or inoculating with degrading bacteria. In this study, pot culture experiments were performed to explore the effects of chemical reagents (nitrilotriacetic acid and alkyl polyglucoside), pyrene degrading bacteria HD-1, and their combination on phytoremediation efficiency for pyrene and nickel (Ni) co-contaminated soil by Scirpus triqueter. After a 60-day culture, plant biomass, pyrene dissipation from soil, Ni accumulation in plant, and Ni accessibility in co-contaminated soil were determined. Results showed that although the application of chemical reagents alone had no apparent effect on plant growth, their combination with the introduced HD-1 alleviated the inhibition effects on plant growth in co-contaminated soil. The dissipation of pyrene in the soil with plant (P), soil with bacteria (NPB), soil with chemical reagents (NPC) and soil with both of them (PBC) were 35.49, 51.36, 42.89, and 59.78%, respectively, and were higher than NP (19.52%) with neither of them. The Ni concentration in Scirpus triqueter of group with bacteria (PB), group with chemical reagents (PC) and group PBC increased to 100.40, 80.97 and 87.77 mg kg−1 respectively when compared with that of group P (46.04 mg kg−1) without bacteria or chemical reagents. Besides, inoculation with HD-1 or/and adding chemical reagents caused Ni to shift from less bioavailable forms to more bioavailable forms. This study suggested the contribution of pyrene degrading bacteria and chemical reagents to Scirpus triqueter phytoremediation of pyrene and Ni co-contaminated soil.

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.