Intra-specific variability of root biomass production (RP) of six rooted macrophytes, i.e. Juncus effusus, Phragmites australis, Schoenoplectus lacustris, Typha latifolia, Phalaris arundinacea, and Iris pseudacorus grown from clones, in response to Cu exposure was investigated. Root biomass production varied widely for all these macrophytes in control conditions (0.08 μM) according to the sampling site. Root biomass production of T. latifolia and I. pseudacorus in the 2.5–25 μM Cu range depended on the sampling location but not on the Cu dose in the growth medium. For P. australis, J. effusus, S. lacustris, and P. arundinacea, an intra-specific variability of RP depending on both the sampling location and the Cu-dose was evidenced. This intra-specific variability of RP depending on the sampling location and of Cu-tolerance for these last four species suggests that Cu constitutive tolerance for all rooted macrophytes is not a species-wide trait but it exhibits variability for some species.

In order to select appropriate plant species for phytoremediation of explosive compounds, phytotoxicity, uptake proficiency, capability of the plant to degrade/transform the compounds, and several environmental factors need to be considered. The environmental factors comprise climatic attributes, soil type, the water environment, root penetration depth, contaminant kinetics, and bioavailability. Out of the plant species that have shown efficient TNT uptake, there are only a few that can do so in a variety of environments, which is imperative in case of contaminants that are widespread, such as TNT and RDX. The two most effective species for TNT uptake reported to date are Eurasian water milfoil, Myriophyllum spicatum and vetiver grass, Chrysopogon zizanioides. For RDX phytoremediation, reed canary grass, fox sedge, and rice have shown promise, although degradation of RDX in the plant tissue is limited. Over the past few decades, a considerable amount of information on phytotoxicity and metabolism of TNT and RDX in plants and microorganisms have been collected, which has led to the identification of potential plant species for use in TNT and RDX phytoremediation, as well as candidate genes for developing effective transgenic plants. Recent research has also revealed promising non-transgenic approaches, such as use of chaotropic agents for enhanced solubilization and uptake of TNT, which could prove to be practical and effective for military sites. Field trials of some of these promising new technologies are necessary for the development of effective, low-cost, and environmentally friendly phytoremediation of explosive-contaminated sites.

Secondary pollution resulting from shoot death is a difficult problem that complicated the application of wetland plants for water purification in northern wetlands. Phalaris arundinacea, a perennial herb with an obviously declining stage, or senescence, is a species that is often selected for water purification in Northern China; however, whether it reduces the secondary pollution risk via nitrogen (N) and phosphorus (P) accumulation during senescence or not remains unclear. To investigate this question, an experiment was conducted with containerized plants during the winter of 2016, after roughly half the leaves on the plants had withered. The experimental observations and analyses were conducted within 0, 2, 4, 6, and 8 weeks of the initiation of senescence. Results revealed that leaves continued to wither and shoot death occurred during weeks 4 to 6 and 8 to 10, respectively. However, no significant differences occurred in fresh biomass or in N and P accumulations of a single plant during senescence. The root biomass, root weight per volume, and total N content increased significantly, while total P content remained stable when leaves withered, respectively. H⁺-ATPase, a key enzyme for ion transportation, decreased after the leaves withered. However, root activity, evaluated by absorption surface per root volume, remained stable, and percentage of fine root length (diameter < 1 mm) increased significantly during senescence. In conclusion, the root activity and morphology enables P. arundinacea to accumulate N and P during senescence, which makes it a good choice for water purification in northern wetlands.

In this work, we evaluated the effect of harmful ecotoxins, 4,5,6-trichloroguaicol (4,5,6-TCG) and tetrachloroguaiacol (TeCG), on the oxidation of the fluorescent probe dihydrorhodamine 123, the content of free phenols and the level of the total, oxidized and reduced glutathione in the leaves of reed canary grass (Phalaris arudinacea). Furthermore, the effect on the activity of guaiacol peroxidase and glutathione S-transferase was investigated. Both 4,5,6-TCG and TeCG increased the activity of guaiacol peroxidase and glutathione S-transferase, they also elevated the content of free phenols and the level of the total glutathione. A stronger effect was exerted by tetrachloroguaiacol, which strongly increased the level of the total glutathione and the content of free phenols on the 3rd and 6th day of the experiment. The activity of glutathione S-transferase was more intensively induced by trichloroguaiacol. Both 4,5,6-TCG and TeCG oxidized dihydrorodamine 123 and the effect was stronger in the presence of magnesium ions.

A continuous flow filtration system was designed to identify and quantify the removal mechanisms of Cyanobacteria (Microcystis aeruginosa) by hydroponic biofilters of Phalaris arundinacea compared to synthetic filters. The filtration units were continuously fed under plug-flow conditions with Microcystis grown in photobioreactors. Microcystis cells decreased at the two flow rates studied (1.2 ± 0.2 and 54 ± 3 cm³ minˉ¹) and results suggested physical and chemical/biological removal mechanisms were involved. Physical interception and deposition was the main removal mechanism with packing density of the media driving the extent of cell removal at high flow, whilst physical and chemical/biological mechanisms were involved at low flow. At low flow, the biofilters decreased Microcystis cell numbers by 70% compared to the controls. The decrease in cell numbers in the biofilters was accompanied by a chlorotic process (loss of green colour), suggesting oxidative processes by the release of allelochemicals from the biofilters.

The impact of plants (Phalaris arundinacea L.) on the leakage of ammonium, cadmium, copper, nitrate, phosphate, and zinc from sulfidic mine tailings covered with wood fly ash and sewage sludge was investigated. Either ash or sludge was placed in contact with the tailings, and ash layers of either low or high compactness were used. It was revealed that an ash/sludge cover effectively decreased the metal leaching from the tailings regardless of the order in which the materials were applied. Plants decreased the amount of leachate and the concentrations of ammonium and phosphate. The presence of ash below the sludge decreased the plant uptake of copper and zinc and nitrate leakage. However, when the ash was added as a thin (1.5 cm) porous layer, roots and air reached the tailings and caused high metal leakage. The results support the use of a vegetated ash/sludge cover in the treatment of mine tailings, provided that the sealing layer is firm enough to prevent root penetration.

Phytoremediation is a promising alternative to conventional soil clean-up methods; however, up to date, there is still not enough information on plant species suitable for application in this field of science. Therefore, plant screening on contaminated sites can lead to the identification of further species of interest. In the present study, pedological and botanical characteristics of an industrialised area known for its metal contamination, in special with Zn—Esteiro de Estarreja, in Portugal—were examined in a 1-year screening. Twenty-seven species were found, with a higher occurrence and variability in the summer/spring season. Zinc levels in the tissues of the collected plant samples ranged from 34 mg kg−1 in shoots to 2,440 mg kg−1 in roots of different species. Species as Verbascum virgatum, Hypochoeris radicata, Phalaris arundinacea, Conyza bilbaoana, Paspalum urvillei and Aster squamatus have shown high Zn shoot accumulation and bioconcentration factors (BCFshoots > 1) and high metal translocation factors (TF > 1). Others, namely Spergularia capillacea, excluded Zn from the shoot tissues and stored the metal at the root zone (BCFroots > 1), behaving as tolerant plants. Plants were also screened for arbuscular mycorrhizal fungi colonisation, and only few species showed mycorrhizal presence, namely C. bilbaoana, Hirschfeldia incana, Epilobium tetragonum, Conyza sumatrensis, Pteridium aquilinum, P. urvillei and A. squamatus. The present work showed important indigenous species that can cope with installed harsh conditions and with potential for utilisation in phytoremediation strategies, either through metal removal to aerial parts or through its immobilisation in the root zone.

Hydroponics culture generates large amounts of wastewater that are highly concentrated in nitrate and phosphorus but contains almost no organic carbon. Constructed wetlands (CWs) have been proposed to treat this type of effluent, but little is known about the performance of these systems in treating hydroponic wastewater. In addition, obtaining satisfactory winter performances from CWs operated in cold climates remains a challenge, as biological pathways are often slowed down or inhibited. The main objective of this study was to assess the effect of plant species (Typha sp., Phragmites australis, and Phalaris arundinacea) and the addition of organic carbon on nutrient removal in winter. The experimental setup consisted of 16 subsurface flow CW mesocosms (1 m², HRT of 3 days) fed with 30 L d¹ of synthetic hydroponics wastewater, with half of the mesocosms fed with an additional source of organic carbon (sucrose). Carbon addition had a significant impact on nitrate and phosphate removal, with removal means of 4.9 g m⁻² d⁻¹ of NO₃-N and 0.5 g m⁻² d⁻¹ of PO₄-P. Planted mesocosms were generally more efficient than unplanted controls. Furthermore, we found significant differences among plant treatments for NO₃-N (highest removal with P. arundinacea) and COD (highest removal with P. australis/Typha sp.). Overall, planted wetlands with added organic carbon represent the best combination to treat hydroponics wastewater during the winter.

As wastewater treatment systems that strengthen natural processes, constructed wetlands provide both ecosystem services and disservices. Manipulating both the physical and ecological structures of constructed wetlands has been the key to improve ecosystem services while reducing disservices. Herein, an experiment using simulated constructed wetlands was conducted to explore the effect of two different substrate sizes (fine sand or coarse sand), plant richness (1, 3, or 4 species), and plant species identity on ecosystem services. Results indicated that (1) only in microcosms with coarse sand, species richness enhanced nitrogen removal efficiency while reduced nitrous oxide emissions and that (2) the presence of Phalaris arundinacea increased nitrogen removal rate, and the presence of Rumex japonicus or Oenanthe javanica decreased nitrous oxide emissions; (3) however, the net ecosystem services (nitrogen removal, greenhouse gas emissions, biofuel production) of microcosms with fine sand were higher than those of microcosms with coarse sand, and (4) interestingly, there was no difference in net ecosystem services between microcosms with coarse sand (1033 yuan ha⁻¹ day⁻¹; 1 yuan ≈ 0.14 USD) and those with fine sand (1071 yuan ha⁻¹ day⁻¹) for the four-species mixtures. Hence, in practice, ensuring plant species richness with appropriate species in microcosms with coarse sand can improve ecosystem services to a level equal to that of microcosms with fine sand and help to prevent constructed wetlands from clogging.

Constructed wetlands (CWs) have been widely used for treating wastewater. CWs also are the sources of greenhouse gas (GHG) due to high pollutant load. It has been reported that plant species diversity can enhance nitrogen (N) removal efficiency in CWs for treating wastewater. However, the influence of plant species diversity on GHG emissions from CWs in habitats with high N levels still lack research. This study established four species richness levels (1, 2, 3, 4) and 15 species compositions by using 75 simulated vertical flow CWs microcosms to investigate the effects of plant species diversity on the GHG emissions and N removal efficiency of CWs with a high N level. Results showed plant species richness reduced nitrous oxide (N₂O) emission and N (NO₃ ⁻-N, NH₄ ⁺-N, and TIN) concentrations in wastewater, but had no effect on methane (CH₄) emission. Especially, among the 15 compositions of plant species, the four-species mixture emitted the lowest N₂O and had under-depletion of N (DₘᵢₙTIN < 0). The presence of Oenanthe javanica had a significantly negative effect on the N₂O emission but had no effect on N removal efficiency. The presence of Rumex japonicus significantly reduced the N (NO₃ ⁻-N and TIN) concentrations in wastewater but had no effect on the N₂O and CH₄ emissions. The N concentrations and GHG emissions in the community of R. japonicus × Phalaris arundinacea were as low as those in the four-species mixture. Assembling plant communities with relatively high species richness (four-species mixture) or particular composition (R. japonicus × P. arundinacea) could enhance the N removal efficiency and reduce the GHG emissions from CWs for treating wastewater with a high N level.