Growth Of Phragmites Australis Research Articles

Role of Rhizophagus irregularis in alleviating cadmium toxicity via improving the growth, micro- and macroelements uptake in Phragmites australis.

Arbuscular mycorrhizal (AM) fungi have been used to alleviate heavy metal stress on plant growth and uptake of micro- and macroelements. A greenhouse pot experiment was conducted to verify the effects of AM fungus Rhizophagus irregularis on the growth, physiological characteristics, total Cd, and element uptake of Phragmites australis under different Cd stress (in the range of 0-20mgL-1). The results showed that the symbiosis could effectively alleviate Cd toxicity with greater root biomass, higher photosynthesis rate, and lower levels of malonaldehyde (MDA) and proline than non-mycorrhizal plants could. However, reduced transpiration rate (Tr) and stomatal conductance (g s) indicated R. irregularis protected host plants from Cd stress (≥5mgL-1) via the stomatal closure. Although micro- and macroelements displayed differently in the presence of Cd, higher concentrations were still detected in mycorrhizal plants in contrast to non-mycorrhizal plants. Moreover, step multiple regression significantly demonstrated Pnmax, stem diameter (Sd), and g s were the important factors with regard to total Cd uptake in the symbiosis, but Mn affected to non-mycorrhizal plants. These results suggested R. irregularis could alleviate the competition between Mn and Cd by altering plant physiology. This work clearly demonstrated that R. irregularis can be able to support P. australis growth better even though under high Cd stress (>1mgL-1), suggesting its good potential for practical use in high Cd-contaminated areas.

Title: Influences of reduced iron and magnesium on growth and photosynthetic performance of Phragmites australis subsp. americanus (North American common reed)

Studies of the North American native wetland plant Phragmites australis (Cav.) Trin. ex Steud. subsp. americanus Saltonst., P.M. Peterson & Soreng have been hindered by chlorosis – tissue yellowing due to reduced chlorophyll production – while grown in controlled conditions, resulting in reduced growth. This study tested the effects of reduced iron [Fe(II)] and magnesium [Mg(II)], both important nutrients for chlorophyll production, on photosynthetic performance and growth of North American Phragmites, a plant of interest for wetland restoration and management. Plants were exposed to five treatments in a 13-week greenhouse experiment. Four of the treatments consisted of a factorial arrangement of Fe(II) and Mg(II) treatments (0.0002M FeSO4, 0.0002M MgSO4, both, or none, in supplied water), supplemented with a slow-release fertilizer. A fifth treatment received no fertilizer, Fe(II), or Mg(II). Treatments that received added Fe(II) had significant increases in biomass, stem height, leaf and root production, chlorophyll B, and fluorescence parameters compared to non-Fe(II) treatments. Adding Mg(II) did not significantly improve plant health (growth, morphology, or resource capturing) compared to the fertilized control, and suppressed the stimulatory effect of Fe(II), possibly by interfering with root Fe(II) uptake. Under greenhouse conditions and normal fertilization practices, Fe(II) deficiency can sharply reduce growth and photosynthetic performance of Phragmites australis subsp. americanus. Supplementing plants with freshly prepared solutions of Fe(II) will alleviate limitation and facilitate experimental study and propagation under controlled conditions. The strong effect of iron limitation on native Phragmites suggests there could be a link between Fe(II) limitation and plant competitive interactions in some wetlands.

The potential for constructed wetlands to treat alkaline bauxite-residue leachate: Phragmites australis growth.

High alkalinity (pH>12) of bauxite-residue leachates presents challenges for the long-term storage and managements of the residue. Recent evidence has highlighted the potential for constructed wetlands to effectively buffer the alkalinity, but there is limited evidence on the potential for wetland plants to establish and grow in soils inundated with residue leachate. A pot-based trial was conducted to investigate the potential for Phragmites australis to establish and grow in substrate treated with residue leachate over a pH range of 8.6-11.1. The trial ran for 3months, after which plant growth and biomass were determined. Concentrations of soluble and exchangeable trace elements in the soil substrate and also in the aboveground and belowground biomass were determined. Residue leachate pH did not affect plant biomass or microbial biomass. With the exception of Na, there was no effect on exchangeable trace elements in the substrate; however, increases in soluble metals (As, Cd and Na) were observed with increasing leachate concentration. Furthermore, increases in Al, As and V were observed in belowground biomass and for Cd and Cr in aboveground biomass. Concentrations within the vegetation biomass were less than critical phytotoxic levels. Results demonstrate the ability for P. australis to grow in bauxite-residue leachate-inundated growth media without adverse effects.

Influence of soil moisture and electrical conductivity on the growth of Phragmites australis (Cav.) in the Keriya oasis, China

In this study, we sought to explore the changes of soil moisture and soil electrical conductivity (EC), as well as to study the relationships between these soil properties and the vegetative indexes of plant coverage, height and crown density and diameter during the Phragmites australis (P. australis) growth period. By combining floristic and edaphic variables (soil moisture and EC), we found that at 0–10 cm depth, the soil moisture varied greatly, while the soil moisture at 10–50 cm depth, EC at 0–50 cm depth, and vegetation properties varied only moderately. A great amount of evaporation offered a possible reason for this moderate variability in soil moisture and EC. Geostatistical analyses revealed that the soil moisture at 0–50 cm depth, and the density of P. australis (Cav.) had a strong spatial autocorrelation, while the EC at 0–50 cm depth had only a weak spatial autocorrelation depending on the nugget effect. Furthermore, there was a positive correlation between the soil moisture and vegetation characteristics at the depth of 0–50 cm, but there was a negative correlation between EC and vegetation characteristics at the depth of 30–50 cm. Furthermore, an increase in soil moisture had a positive effect on P. australis (Cav.) growth, while an increase in EC had a negative effect.

Reed stands during different water level periods: physico-chemical properties of the sediment and growth of Phragmites australis of Lake Balaton

Water level fluctuations play a vital role in regulating macrophytes of shallow lakes. Morphology and growth dynamics of Phragmites australis, together with physico-chemical parameters of the sediment, were studied at stable (not degrading) and die-back (degrading) sites of Lake Balaton over an 8-year period that included low and average water levels. Lower water level increased plant density and green leaf number, positively affecting photosynthetically available leaf area. Nevertheless, rhizome carbohydrate content was not influenced by water level decrease. The physico-chemical parameters of the sediment did not vary greatly, although the nitrogen and phosphorus content and the midsummer redox potential of the sediment were higher at the low-water period. During the transition from average to low water levels, the sediment shifted from severely anoxic to poorly oxidised levels, with more favourable nutrient content, while the amount of ammonia and sulphides decreased, too. It was shown that lowering water levels could act on plants via increased redox potential of the sediment and could counteract the die-back of Phragmites, suggesting the effectiveness of water level decrease as a management practice to counter reed die-back.

Effects of annual harvesting on plants growth and nutrients removal in surface-flow constructed wetlands in northwestern China

Abstract The importance of harvest management for the growth and development of plants and nutrients removal in constructed wetlands (CWs) is highly controversial. This study evaluated the effects of annual harvesting on the growth and productivity of local Phragmites australis in northwestern China. Growth characteristics such as shoot density, biomass and height were studied using two pilot-scale surface-flow CWs over a two-year operation period. Plants were kept unharvested in one CW for comparative studies with the second CW, which was harvested at the end of the growing season. Each CW of 400 m2 was operated with a hydraulic loading of 34 m3/d for the treatment of water from an urban river polluted with municipal and industrial wastewater. The harvested CW recorded a higher shoot density (175 shoots/m2), biomass (1.4 kg/m2) and peak height (3.4 m) than the unharvested one (130 shoots/m2, 1.2 kg/m2 and 3.2 m). The overall nutrients removals were also slightly higher for the harvested CW (46.0% TN and 38.1% TP) than the unharvested CW (40.6% TN and 29.1% TP). Plants harvesting in the first year improved nutrients removal by plant uptake (41.9 g N/m2 and 3.7 g P/m2 versus 37.3 g N/m2 and 3.2 g P/m2) as well as in the substrate layer (216.9 g N/m2 and 8.0 g P/m2 versus 191.0 g N/m2 and 5.7 g P/m2) during the second year. Nonetheless, the increase in nutrients removal by harvesting was minimal.

Preliminary evidence of effects of Phragmites australis growth on N2O emissions by laboratory microcosms

Abstract Denitrification has been found to play a significant role in the nitrogen (N) biogeochemical cycle of riparian wetland systems; however, there is little understanding of the role of emergent macrophytes in sediment denitrification. In this study, laboratory culture experiments were conducted to examine how Phragmites australis growth affected N 2 O emissions. Additionally, preliminary investigations into the variability of carbon and available NO 3 − –N fractions were conducted. The N 2 O emission rate was quantified based on the high-resolution N 2 O microprofiles in acetylene-inhibited sediment cores. Seasonal-dependence of N 2 O emission was remarkable throughout incubation of both P. australis rooted sediments and control with no P. australis , and increased significantly with biomass steady accumulation (p 2 O m −2 day −1 at day 180 (in late autumn) in the P. australis rhizosphere . Simultaneously, N 2 O emissions were more highly influenced by fine-root biomass, belowground biomass and plant height than total biomass, root activity and relative growth rate in the Spearman rank correlation model. More specifically, based on the strong and significant (p 2 O emission flux, the rapid transformation indicated that changes in the HWC (ranging from 720 to 3564 mg kg −1 ) with plant growth could reflect a 14-fold variation in N 2 O emissions during the growth stage, and that N 2 O emissions were highly dependent on fine-root biomass and its delivery of organic carbon. The ion exchangeable form NO 3 -N (IEF-NO 3 -N) in sediments was found to be the predominant transferable form involved in denitrification, while the iron-manganese oxide form NO 3 -N (IMOF-NO 3 -N) can be considered as a potential source of nitrogen for denitrification. This study highlights that emergent macrophyte communities dominate riparian ecosystem denitrification and that the metabolic mechanisms of emergent macrophytes can have positive feedbacks on the HWC fraction and available NO 3 -N combined with sediment components in rhizosphere sediments.

Growth, photosynthesis and stress-inducible genes of Phragmites australis (Cav.) Trin. ex Steudel from different habitats

The present study investigates growth of Phragmites australis in relation to photosynthesis and stress-inducible genes in its natural habitats. P. australis was collected from fresh water (FW), brackish water (BW), mesophytic (M), salt marsh (SM) and sand dune (SD) habitats. These habitats were categorized according to their soil properties. FW and BW habitats are mainly characterized by flooded soil (hypoxia). SM and SD habitats are typical habitats for salt and drought conditions. Shoot growth parameters estimated in the present study would indicate that the optimum growth was in M habitat. The growth in other habitats was lower than that in M one and this reduction coincided with a reduction in photosynthetic rate (A). Internal CO2 concentration (Ci) did not show any significant reduction in all studied habitats except in M one. Starch, total soluble sugars and Rubisco contents could suggest that the growth reduction in FW habitat was a consequence of the reduction in photosynthetic rate while the reduction in growth was a cause of photosynthetic inhibition in BW habitat. Alcohol dehydrogenase (ADH) transcript level was constitutively expressed, and it was significantly increased in leaves collected from BW and SD habitats, suggesting its involvement in the fermentative metabolism. The expression of leaf plasma membrane Na+/H+ antiporter (SOS1) and high affinity potassium uptake (HKT) were stimulated in SM leaves assuming their roles in Na+ re-circulation and K+ uptake to maintain K+/Na+ ratio higher than one inside the leaf. Moreover, the reduced leaf water content could play a role in ion homeostasis inside this species. P. australis had the ability to maintain a stable water use efficiency (WUE) in all studied habitats assuming its ability in economizing water and maintaining the assimilation rate.

Decomposition of Phragmites australis rhizomes in artificial land-water transitional zones (ALWTZs) and management implications

Rhizomes are essential organs for growth and expansion of Phragmites australis. They function as an important source of organic matter and as a nutrient source, especially in the artificial land-water transitional zones (ALWTZs) of shallow lakes. In this study, decomposition experiments on 1- to 6-year-old P. australis rhizomes were conducted in the ALWTZ of Lake Baiyangdian to evaluate the contribution of the rhizomes to organic matter accumulation and nutrient release. Mass loss and changes in nutrient content were measured after 3, 7, 15, 30, 60, 90, 120, and 180 days. The decomposition process was modeled with a composite exponential model. The Pearson correlation analysis was used to analyze the relationships between mass loss and litter quality factors. A multiple stepwise regression model was utilized to determine the dominant factors that affect mass loss. Results showed that the decomposition rates in water were significantly higher than those in soil for 1- to 6-year-old rhizomes. However, the sequence of decomposition rates was identical in both water and soil. Significant relationships between mass loss and litter quality factors were observed at a later stage, and P-related factors proved to have a more significant impact than N-related factors on mass loss. According to multiple stepwise models, the C/P ratio was found to be the dominant factor affecting the mass loss in water, and the C/N and C/P ratios were the main factors affecting the mass loss in soil. The combined effects of harvesting, ditch broadening, and control of water depth should be considered for lake administrators.

The tolerance of growth and clonal propagation of Phragmites australis (common reeds) subjected to lead contamination under elevated CO2conditions

Elevated CO2might improve growth and clonal propagation resistance to Pb contamination through increasing photosynthetic, phalanx growth and population expansion.

Effect of trenches on the habitat of aquatic organisms in a salt marsh in Saga, Japan

Trenches were constructed to control the growth of Phragmites australis on a riverbank in the Ushizu River in Saga, Japan. However, the effect of these trenches on the habitat of aquatic organisms is unclear. The purpose of this study is to clarify the effect that trenches have on aquatic organisms in the tidal river. The burrow density of a type of sand crab (Ilyoplax deschampsi) and the abundance of aquatic organisms (such as fish and shrimp) in our trenches were measured. The number of I. deschampsi burrows around trench D was similar to that observed before trench construction. However, mud sedimentation was accelerated in shallow trench D’, which created a suitable habitat for this species. Additionally, we found shrimp and gobies in all our trenches. This indicates that artificial trenches do provide habitat for shrimp and gobies in riverside marshes. Moreover, an endangered species and many aquatic insects were collected. Our results suggest that trenches provide important habitats for rare fishes and aquatic insects, similar to that of a lagoon.

塔里木盆地南缘旱生芦苇生态特征与水盐因子关系

In recent years,ecologists have experienced an increased awareness of the importance of plant-environment interactions. Studies have demonstrated that spatial ecosystem heterogeneity and availability of resources influence plant growth. Understanding the ecological response characteristics of plants and environmental laws influencing arid land vegetation in different water-salt environments should be quite valuable to scientists. To better understand the ecological characteristics of plants and factors that potentially control them such as water availability and salinity in arid regions,we conducted a study in Phragmites australis in dry habitats of the Yutian Oasis along the Keriya River,in the southern marginal zones of the Tarim Basin,Xinjiang,China. Using previously collected observational data related to water-salt distribution laws and the natural water-salt gradient caused by distance from the river,four sample regions were established parallel to the river from east to west,extending from the river to the desert. We analyzed the patterns and correlations of ecological characteristics of Phragmites australis and water-salt indicators in the field,using traditional statistics and redundancy analysis( RDA) in combination with CANOCO software( version 4.5). The statistical analysis revealed that plant ground cover was as low as less than 10%; the belowground biomass was greater than aboveground because of the way desert vegetation adapted to the arid environment. The sampled region was severely dry and salinated; soil moisture contentwas low,with a mean value of 7.22%. The average depth to ground water was 4.23m and soil salt content reached as high as18.24g /kg. Phragmites australis has a high tolerance to aridity and salt stress; the average plant height,coverage and aboveground biomass decreased gradually while the belowground biomass increased as distance from the river to the desert increased; there were also concurrent and expected gradient changes in water-salt indicators. Redundancy analysis showed that water was the key environmental factor influencing the growth of Phragmites australis. A significant correlation was found between ground water depth /soil moisture and the ecological characteristics of Phragmites australis including plant height,coverage,biomass; the sodium adsorption ratio( SAR) /total salt correlation with ecological characteristics was less significant while other indicators had no significant correlation with the plant's ecological characteristics. The importance of water-salt indicators to ecological characteristics of Phragmites australis could be arranged as ground water depth soil moisture SAR total salt HCO-3 pH Cl-/SO2-4. The results suggest that water has greater impact on Phragmites australis than salt,because water limits the plant's survival,growth and reproduction. When a plant is affected by an arid continental climate for long periods,the plant is usually influenced by both water and salt. Any study of Phragmites australis analyzing the effects of different water or soil salinity conditions independently would be fatally flawed; but must be considered together. Our study shows that redundancy analysis of ordination methods can be beneficially used in research into the relationship between plants and environmental factors; when combined with traditional statistics,the two methods can provide comprehensive information. The redundancy analysis can effectively reveal relationships between ecological characteristics of plants and water-salt indicators. The characteristics of Phragmites australis deserve more research,especially research related to the microscopic physiological effects of water-salt interaction.

Performance of two small subsurface flow constructed wetlands treating domestic wastewaters in Italy

The performance of a vertical and a horizontal subsurface flow wetland (v-SSF and h-SSF), designed for treating domestic wastewater from a single family, was investigated by monitoring total nitrogen (TN), nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), total phosphorus (TP), chemical oxygen demand (COD) and the dissolved oxygen (DO) content of the influent and the effluent wastewater of each system during the first two years of operation. The growth of Phragmites australis in each system was recorded by measuring the height and observing their general conditions. The treated domestic wastewater presented similar chemical–physical characteristics in the two systems which operated in analogous environmental conditions. The median influent characteristics were: TN 81.9 mg L−1, NO3-N 0.19 mg L−1, NH4-N 33.5 mg L−1, TP 11.9 mg L−1 and COD 354.5 mg L−1. During the whole monitoring period median reductions in the v-SSF were TN 71%, NH4-N 94%, TP 27% and COD 92% whereas in the h-SSF they were TN 59%, NH4-N 21%, TP 52% and COD 70%. Internal production of NO3-N was observed, mainly in the v-SSF probably due to the difference in oxygen availability in the medium and the design of the system. DO concentration increased in the effluents in both years, with higher values measured in v-SSF than in h-SSF. The reduction performance increased in the second year, particularly in v-SSF, whereas no statistical differences were observed between spring–summer and autumn–winter periods. P. australis reached maximum development at the end of summer in both systems and maintained a stable height during autumn–winter. In h-SSF the vegetation located close to the influent showed lower growth than in the rest of the bed.

Growth and nutrient accumulation of Phragmites australis in relation to water level variation and nutrient loadings in a shallow lake

Shallow lake eutrophication is a global environmental issue. This study investigated the effects of water level variation and nutrient loadings on the growth and nutrient accumulation of Phragmites australis (reed) by field samplings in Baiyangdian Lake, the largest shallow lake of northern China. The field samplings were conducted in two sites of different nutrient loadings during the whole growth period of reeds, and three types of zones with different water depths were chosen for each site, including the terrestrial zone with water level below the ground, the ecotone zone with the water level varying from belowground to aboveground, and the submerged zone with water level above the ground. The result showed that reed growth was more limited by water level variation than nutrient loadings. The average stem lengths and diameters in terrestrial zones were about 26.3%–27.5% and 7.2%–12.0% higher than those in submerged zones, respectively. Similarly, the terrestrial status increased the aboveground biomass of reeds by 36.6%–51.8% compared with the submerged status. Both the nutrient concentrations and storages in the aboveground reeds were mainly influenced by the nutrient loadings in surface water and sediment rather than the water level variation of the reed growth environment, and the nutrient storages reached their maxima in late August or early September. It was observed that the maximum nitrogen storage occurred in the terrestrial zone with higher nutrient loadings, with the value of 74.5 g/m2. This study suggested that water level variation and nutrient loadings should be considered when using reeds to control and remediate eutrophication of shallow lakes.

Preliminary application of a novel and cost-effective in-site technology in compacted lakeshore sediments for wetland restoration

Sediment compaction is one of the major contributors to lakeshore wetland deterioration and shrinkage. A novel and relatively cost-effective in-site technology was implemented to alleviate the problem by loosening surface sediments. In the present study, the effect of a slight loosening method (cross-shaped tillage, CT), a heavy loosening method (plow-tillage, PT), and sand capping (SC) on sediment properties and Phragmites australis growth was investigated in mesocosm tanks. The results indicated that the loosening sediment methods, especially PT, increased the porosity and the water content and decreased the bulk density in the upper 0–5cm of sediments. O2 exchanges across the water–sediment interface were accelerated by 36 and 52% (from approximately 4.73 in CK (control treatment) to 7.21 in PT and 6.45mmol O2m−2d−1 in CT, respectively). The SC, PT and CT methods increased the O2 concentration in the bottom water and the O2 penetration depth (about a week at a quasi-steady state situation), ranging from 0.79±0.08mm in CK to 2.44±0.27, 1.45±0.09 and 2.38±0.28mm in SC, PT and CT, respectively). For comparison, a sharp increase in the P. australis relative growth rate was observed in SC, PT and CT of 9.2, 12.8 and 12.9mgg−1d−1, respectively, with an increase of 1.3- to 1.9-fold compared to the control. Based on our results, we recommend an appropriately loosening the compacted sediment method as an alternative for lakeshore wetland restoration.

莫莫格湿地芦苇对水盐变化的生理生态响应

Understanding the eco-physiological response characteristics of Phragmites australis to water-salt condition is the key of determining the threshold of wetland ecological water requirement,in order to supply a feasible method for calculating the wetland ecological water requirement and scientific base for wetland restoration.By field investigation of Phragmites australis in Momoge wetland,we analyzed the relationship between eco-physiological characteristics of Phragmites australis and water-salt gradient with method of redundancy analysis(RDA) by using CANOCO software in Version 4.5.The results showed that the combination of three environmental factors including water depth,Na+ and HCO-3,explained 54.7% of the variation of eco-physiological responses of Phragmites australis,suggesting that the three environmental factors led to great changes in eco-physiological responses of Phragmites australis.Water depth was the key environmental factor influencing the growth of Phragmites australis.There was a significant positive correlationship between water depth and the eco-physiological characteristics including plant height,biomass,chlorophyll content,maximum photosynthesis efficient(FV/FM) and maximum photosynthesis performance index(PIABS).There was no significant correlationship between Na+/HCO-3 and the characteristics of Phragmites australis.The results suggested that it is the key point in the process of wetland restoration in mild or moderate saline-alkaline wetland to consider the influence of water depth on the growth of Phragmites australis,and secondly consider the effect of Na+/HCO-3,and determining the ecological water depth and fulfilling the ecological water requirement.

Genotype and explant-type dependent morphogenesis and silicon response of common reed ( Phragmites australis) tissue cultures

The effects of silicon on the growth and development of Phragmites australis (Cav.) Trin. Ex Steud. (common reed) stem nodal and root embryogenic calli were investigated. Silicon is considered to be a beneficial or quasi-essential nutrient for several Gramineaceous plants, including reed. Seven callus lines of four geographical locations (genotypes 1–4) within Hungary were investigated. Callus lines 1A, 2A and 3A were produced from stem nodal explants, while lines 1B, 2B, 3B and 4 were produced from roots. For the assay of silicon-dependent growth of callus lines of identical genotype but originating from different explants, we measured the increase of fresh weight of lines 1A and 1B. The studied developmental parameters were the increase of the number of somatic embryos (for callus lines 1A and 1B) and plant or root production from somatic embryos (for all genotypes/callus lines). Silicon was added to the culture medium as sodium silicate. In control cultures, plant or root regeneration from embryogenic calli was strongly genotype- and explant type-dependent. Stem nodal explants developed plants on regeneration medium in case of callus lines 2A and 3A, while line 1A produced roots only. All root derived calli developed roots on regeneration medium. Silicon stimulated the growth of both stem nodal and root calli (callus lines 1A, B) however, the concentration optima were different. Somatic embryogenesis of root calli, but not of stem nodal calli, was stimulated by silicate at low concentrations. However, for both of these callus lines, root development was stimulated by silicon. It had genotype-dependent influences on plant regeneration: while stimulation was observed in case of callus line 2A, inhibition occurred for line 3A. Root morphogenesis on calli was significantly influenced by silicon and depended on the callus line studied. Root production was stimulated on callus lines 1A, B and 2B, while in case of callus line 3B, it was significantly inhibited. The morphogenetic effects of Si were similar for different explants of the same geographical origin, i.e. plant or root production was similarly stimulated or inhibited by this element. We can conclude that the effects of Si on plant or root development depend on reed genotype used for callus induction. Its effect on growth and somatic embryogenesis depends on the explant type used for callus production. This is the first detailed report on the role of silicon in plant vegetative development and morphogenesis of a Gramineaceous plant.

Effect of heavy metal stress on emerging plants community constructions in wetland

In this paper, we report the effects of heavy metals (HMs) (cadmium and mercury) on seed germination and seedling growth of Phragmites australis and Triarrhena sacchariflora, which are the two main typical emerging plants in Hongze Lake wetland. The results showed that there was a reduction in germination percentage, germination index and seedling length as HM concentration in the growing media increased for both treatments. The effect of HMs toxicity on seed germination and seedling growth of T. sacchariflora was more obvious than of P. australis. At the stage of seed germination, P. australis and T. sacchariflora were sensitive to Hg(2 + ) and Cd(2 + ), respectively, and Hg(2 + ) was more toxic than Cd(2 + ) at the stage of seedling growth. The effect of HMs toxicity is not invariable during plant growth. Compared to the stage of seedling growth, P. australis and T. sacchariflora are more susceptible to HMs at the stage of seed germination. In addition, we calculated the ecological thresholds of P. australis to Cd and Hg are 19.32 and 1.08 mg kg(-1), and that of T. sacchariflora to Cd is 4.62 mg kg(-1) based on the lab simulation. The results also indicated that the species of P. australis is more tolerant than T. sacchariflora to the HMs and is a better candidate for restoration in Hongze Lake wetland ecosystem.

Advantages of NH4 + on growth, nitrogen uptake and root respiration of Phragmites australis

We investigated growth, N nutrition, and root respiration in Phragmites australis (Cav.) Trin. ex Steud. grown under conditions with different N sources, and evaluated the advantages of NH4 + nutrition in relation to adaptation to anaerobic soil conditions. Hydroponics culture was carried out for 2 months under two treatment conditions with different N sources, NH4 + and NO3 −. The relative growth rate (RGR) of the roots, shoot and whole plant, net N uptake rate (NNUR), and root respiration rate were examined. Shoot RGR, shoot to root (S/R) ratio, and NNUR were obviously higher with the NH4 + treatment. High S/R ratio of plants grown in the NH4 + treatment contributed to repression of whole-root oxygen consumption. In consequence, NNUR per root respiration rate was higher with the NH4 + treatment, which clearly suggested efficient oxygen consumption in the roots. In conclusion, higher S/R ratio due to higher NNUR enable to efficiently use oxygen for N nutrition through the repression of whole-root oxygen consumption, which is consequently achieved by NH4 + nutrition. Therefore, we suggest that NH4 + nutrition is indispensable for hydrophytic species growing in anaerobic soil because it enables both sufficient N nutrition and efficient oxygen consumption.

Effects of Phragmites australis growth on nitrogen retention in a temporal stream

En los ultimos anos, en el SE iberico con el incremento de la superficie de regadio, se ha producido un crecimiento masivo de las poblaciones de Phragmites australis que terminan invadiendo por completo las ramblas y en general los cauces de aguas superficiales. Esta situacion lleva consigo la transformacion fisica de los cauces, modificando muchas caracteristicas implicadas en los procesos bioticos y abioticos de retencion de N. En este estudio testamos la hipotesis de que la ocupacion de los cauces por Phragmites australis afecta negativamente a la retencion de N. Asi comparamos las tasas de retencion (%R) de N - NO-3 y N - NH+4 en diferentes subtramos de una misma rambla: un subtramo no vegetado (238 m2) y dos subtramos vegetados que diferian en superficie (480 m2 y 910 m2). Los resultados demostraron que las eficacias de retencion (%R) para ambos solutos fueron superiores en el tramo no vegetado. Aunque no existen resultados concluyentes parece intuirse que estas diferencias fueron mas acusadas fuera del periodo vegetativo del helofito, mientras que en los meses de primavera y verano pudiera ocurrir un incremento de las tasas de retencion en los tramos vegetados. Asi mismo, la capacidad de los subtramos para la retencion de N-nitrato, mostro una clara dependencia de los aportes de nitrogeno, disminuyendo conforme la carga de nitrogeno aumenta. Sin embargo, el tramo no vegetado mostro una mayor capacidad de carga que el tramo vegetado de mayor superficie y este que el tramo vegetado de menor superficie. Este estudio pone de manifiesto que la ocupacion de los cauces por Phragmites australis, fenomeno generalizado en muchas partes del mundo, no solo puede suponer cambios en la estructura de la vegetacion y la fauna de las ramblas sino que tambien afectar a su funcionamiento y muy especialmente a un proceso clave implicado en la calidad de las aguas como es la eliminacion del nitrogeno.