The Response of Purslane (Portulaca oleracea) to Soil-Added Pb: Is It Suitable as a Potential Phytoremediation Species?

Soils with high lead (Pb) levels can be decontaminated with the use of tolerant plants. Their effectiveness may be increased with added soil N due to boosted plant vigor, but such an agronomic practice has not been widely reported so far. In this work, purslane (Portulaca oleracea) was tested in a pot experiment as a potential phytoremediation species using soil spiked with Pb at doses of 0, 150, 300, 600, and 900 mg kg-1 (referred to as Pb(0), Pb(150), Pb(300), Pb(600), and Pb(900), respectively) with added N (referred to as N(1); at 300 kg N ha-1) and without added N (N(0)). We found that added Pb did not cause any adverse effects on plant growth (height, and aerial and root dry biomass) and physiological parameters, which were boosted with added N. Lead plant concentration and uptake significantly increased with added N, a finding that confirms our hypothesis. The number of necessary harvests of purslane in order to reduce soil Pb to half its initial concentration was also calculated and found to decrease with added N, being 131 at Pb(900)N(1). Although results indicate the potential of purslane as a phytoremediation species, further research is needed under real field conditions.

Phytotoxicity level and accumulation ability of pot marigold (Calendula officinalis L.) to zinc.

The study aims to reveal the effects of different Zn levels on pot marigold. We determined some germination and young seedling properties in the first experiment, and morphological, stomatal, and physiological parameters besides uptake profiles of both Zn and other plant nutrients in the second one. We supplied the water requirement of the seeds with Zn solutions (0, 250, 500, 750, and 1,000 mg l-1) in the first experiment, and We added the same zinc doses as mg kg-1 to the soil of the pots where the plants would grow in the second one. As a result, the inhibitory effects were more prominent in the early seedling stage (especially at 1,000 mg l-1 Zn) than in the germination one. We determined plant growth retardation, decreases in leaf water contents, and increases in membrane damages with higher Zn (≥500 mg kg-1) in the experiment conducted by potting soil. We detected decreases in chlorophyll parameters parallel with the increases in Zn. The alterations in plant zinc contents revealed the accumulation capacity of pot marigold in potting conditions. That TF value >1 in Zn treatments up to 500 mg kg-1 points to the efficiency limit of pot marigold as a Zn-accumulator plant.

To reveal the zinc tolerance of the plant through experiments carried out in two different plant growth stages, germination-young seedling and adult plant is an innovative approach. Besides, it is the first study to evaluate detailed morphological, physiological, stomatal and nutrient contents of pot marigold under heavy metal stress conditions. Thus, this study displayed both tolerance level and accumulation potential in potting conditions of pot-marigold to zinc.

The impact of nanoparticles zero-valent iron (nZVI) and rhizosphere microorganisms on the phytoremediation ability of white willow and its response.

Soil contaminated with heavy metals (HMs) is a serious problem throughout the world that threatens all living organisms in the soil. Therefore, large-scale remediation is necessary. This study investigated a new combination of remediation techniques on heavy metal contaminated soil, phytoremediation, and soil amendment with nano-sized zero-valent iron (nZVI) and rhizosphere microorganisms. White willow (Salix alba L.) was grown for 160 days in pots containing Pb, Cu, and Cd and amended with 0, 150, and 300 (mg kg-1) of nZVI and rhizosphere microorganisms, including the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis, and the plant growth promoting rhizobacteria (PGPR), Pseudomonas fluorescens. The results showed that inoculation with PGPR and AMF, particularly dual inoculation, improved plant growth as well as the physiological and biochemical parameters of white willow, and increased the bioconcentration factor (BCF) of Pb, Cu, and Cd. The low dose of nZVI significantly increased the root length and the leaf area of the seedlings and increased the BCF of Cd. In contrast, the high dose of nZVI had negative effects on the seedlings growth and the BCF of Pb and Cu, about - 32% and - 63%, respectively. Our results demonstrate that nZVI at low doses can improve plant performance in a phytoremediation context and that the use of beneficial rhizosphere microorganisms can minimize nZVI stress in plants and make them less susceptible to stress even under high dose conditions.

Effects of mutual intercropping on cadmium accumulation by the accumulator plants Conyza canadensis, Cardamine hirsuta, and Cerastium glomeratum.

In this study, three cadmium (Cd) accumulator species (Conyza canadensis, Cardamine hirsuta, and Cerastium glomeratum) were co-cultured in Cd-contaminated soil in pots to study the effects of intercropping on co-remediation. Only C. canadensis intercropped with C. glomeratum, C. hirsuta intercropped with C. glomeratum, and three-species intercropping increased plant biomass compared with their respective monocultures. The treatments of C. canadensis intercropped with C. glomeratum and three-species intercropping increased the Cd contents in roots and shoots of C. canadensis, whereas the other intercropping treatments decreased or had no significant impact on Cd contents. As for Cd accumulation, the treatments of C. canadensis intercropped with C. glomeratum, C. hirsuta intercropped with C. glomeratum, and three-species intercropping increased Cd accumulation in a single plant compared with that of their respective monocultures, whereas other intercropping treatments decreased Cd accumulation in individual plants. Only the treatments of C. canadensis intercropped with C. glomeratum and C. hirsuta intercropped with C. glomeratum increased Cd accumulation in shoots of a single pot compared with that of their respective monocultures. Therefore, C. canadensis intercropped with C. glomeratum and C. hirsuta intercropped with C. glomeratum may improve the phytoremediation efficiency for Cd-contaminated soil.

Effects of indole-3-butytric acid on lead and zinc accumulations in Pseudostellaria maximowicziana.

Plant hormones can improve the phytoremediation capabilities of heavy metal hyperaccumulator plants. In this study, different doses of indole-3-butytric acid (IBA) were sprayed on the leaves of the lead (Pb) and zinc (Zn) accumulator plant Pseudostellaria maximowicziana, which was planted in Pb-Zn contaminated soil, and the effects of IBA on Pb and Zn accumulation levels in P. maximowicziana were studied. Spraying 25- and 50-mg/L IBA doses increased the stem, leaf and shoot biomasses of P. maximowicziana compared with the control, while 75- and 100-mg/L IBA doses decreased them. The 50-mg/L IBA dose increased the P. maximowicziana contents of chlorophyll a, total chlorophyll and carotenoid of compared with the control, and other doses had no significant effects or decreased these values. Spraying IBA reduced the superoxide dismutase activity of P. maximowicziana compared with the control, but improved the peroxidase and catalase activities. The 50-, 75-, and 100-mg/L IBA doses increased the Pb and Zn contents in P. maximowicziana compared with the control and also increased the amounts of Pb and Zn extracted by P. maximowicziana. Thus, 50 mg/L of IBA could promote the growth and the Pb and Zn phytoremediation capabilities of P. maximowicziana.

Effects of mutual intercropping on the cadmium accumulation in accumulator plants Stellaria media, Malachium aquaticum, and Galium aparine.

Intercropping affects heavy-metal uptake in plants. In this study, three cadmium (Cd)-accumulator species (Stellaria media, Malachium aquaticum, and Galium aparine) were intercropped together in Cd-contaminated soil to study the effects of intercropping on co-remediation. Mutual intercropping significantly increased the biomasses of S. media, M. aquaticum, and G. aparine compared with their respective monocultures. The photosynthetic pigment contents of three species were not significantly affected by mutual intercropping. Mutual intercropping did not increase the Cd contents in roots and shoots of G. aparine, but it increased the Cd contents in roots of S. media and M. aquaticum. It also decreased the Cd contents in shoots of S. media and M. aquaticum. Only G. aparine intercropped with M. aquaticum and three-species intercropping increased Cd-accumulation levels in whole plants of each species. Only S. media intercropped with M. aquaticum and three-species intercropping increased the Cd accumulation at the whole plant level in every plant in a single pot, with S. media intercropped with M. aquaticum showing the greatest increase. Therefore, S. media intercropped with M. aquaticum and three-species intercropping may improve the efficiency of phytoremediation of Cd-contaminated soil, with S. media intercropped with M. aquaticum representing the best combination.

Uniconazole (S-3307) strengthens the growth and cadmium accumulation of accumulator plant Malachium aquaticum.

The effects of uniconazole (S-3307) application on the growth and cadmium (Cd) accumulation of accumulator plant Malachium aquaticum (L.) Fries. were studied through a pot experiment. The application of S-3307 increased the biomass and photosynthetic pigment content of M. aquaticum in Cd-contaminated soil, and also improved the superoxide dismutase (SOD) and peroxidase (POD) activities in M. aquaticum. Application of S-3307 increased Cd content in shoots and decreased Cd content in roots of M. aquaticum, but the translocation factor (TF) of M. aquaticum increased with the increase of S-3307 concentration. For phytoextraction, the application of S-3307 increased Cd extractions by roots, shoots and whole plants of M. aquaticum, and the maxima were obtained at 75 mg L-1 S-3307, which increased by 22.07%, 37.79% and 29.07%, respectively, compared with their respective controls. Therefore, S-3307 can be used for enhancing the Cd extraction ability of M. aquaticum, and 75 mg L-1 S-3307 was the optimal dose.

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

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