Portulaca grandiflora as green roof vegetation: Plant growth and phytoremediation experiments

Assessment of the Cu phytoremediation potential of Chrysanthemum indicum L. and Tagetes erecta L. using analysis of growth and physiological characteristics

In the current study, the Cu phytoremediation ability of two ornamental plants, Chrysanthemum indicum L. and Tagetes erecta L., was tracked concerning the growth and physiological responses. Plants were subjected to varying concentrations of Cu (0, 100, 200, and 400 mg/kg) under the pot experiment for 8 weeks. The results showed that the measured growth and physiological characteristics declined in T. erecta shoots and roots at all tested treatments compared with the control. However, in C. indicum at 100 mg/kg, shoot biomass, shoot total soluble protein, and leaves number remained equal to that of the control and then reduced by rising Cu concentrations, compared with the control. Also, results indicated that in C. indicum, after 56 days of exposure to Cu, the chlorophyll pigments content markedly increased and reached a maximum level at 100 mg/kg dose and gradually declined with enhancing Cu concentrations, compared with the control. Other measured growth and physiological parameters decreased in both tissues of C. indicum in response to Cu usage in the growth medium. The carotenoid content of T. erecta decreased in all studied Cu levels in comparison to the control, but in C. indicum remained unaffected up to 200 mg/kg Cu in comparison to the control and then enhanced with increasing Cu level. The augmentation of antioxidant enzyme activity in two species, especially in roots, reflected the incident of Cu stress as demonstrated by elevated MDA and ion leakage levels. Data concerning copper accumulation in tissues, TF, and BAF showed T. erecta is a weak Cu accumulator and seems not to be an appropriate candidate for Cu phytoremediation. However, the Cu content in shoots and roots of C. indicum increased significantly with an increment in applied Cu level. Also, C. indicum accumulated higher Cu concentrations in the roots than in shoots and exhibited TF < 1, 0.1 < BAF root < 1, and can be considered as a Cu excluder by the phytostabilization mechanism.

Bioaccumulation efficacy and physio-morphological adaptations in response to iron and aluminium contamination of Indian camphorweed (Pluchea indica L.) using different growth substrates

The aim of this study was to assess the removal capability of Fe/Al contamination of Indian camphorweed (Pluchea indica; hereafter, P. indica) using different growth substrates (100% sand, gardening soil, vermiculite, and zeolite). In addition, the study aimed at observing the physio-morphological adaptation strategies of P. indica under excess Fe/Al levels in a controlled greenhouse environment. After a 4-week treatment, P. indica plants under excess Fe in the 100% sand substrate exhibited signs of decay and eventually death. In contrast, the growth performances of P. indica under gardening soil substrate remained sustained even when exposed to Fe/Al stress. Under zeolite substrate, Fe in the root tissues was 23.1 and 34.7 mg g-1 DW after 1 and 4 weeks of incubation, respectively. In addition, Al in the root tissues also increased to 1.54 mg g-1 DW after 1 week and 1.59 mg g-1 DW after 4 weeks, when subjected to 20 mM Al treatment. Zeolite was observed to be a promising substrate to regulate the uptake of Fe (3.31 mg plant-1) and Al (0.51 mg plant-1) by the root tissues. The restriction of Fe and Al in the root and a low translocation to the leaf organ was indicated by a low translocation factor (< 1.0). High Fe concentrations in the root and leaf tissues negatively affected root elongation, and the net photosynthetic rate decreased by > 40% compared to positive control. Gas exchange parameters and leaf temperature were found the most sensitive to Fe/Al stress. Moreover, the limited transpiration rate under Fe/Al stress caused an increase of the leaf temperature and crop stress index. The findings suggest that P. indica grown using zeolite substrate may serve as a good model system for constructed wetlands, storing excess Al in the root tissues without any significant growth inhibition.

Cadmium removal potential of hyperaccumulator Solanum nigrum L. under two planting modes in three years continuous phytoremediation

Solanum nigrum L. is a Cd hyperaccumulator, but the potential for continuous remediation, or different planting methods have not been fully characterized. The potential for continuous phytoremediation of Cd-contaminated farmland soil (2.08 mg kg^-1 Cd) by 2 planting methods (flowering harvest twice a year and maturity harvest once a year) was studied in a 3-year pot experiment. The total Cd accumulation (ug plant^-1) of the 3-year flowering stage treatments was 26.3% higher than that of the maturity stage treatments, which was mainly due to that flowering harvest twice a year caused 65.5% increase of shoot biomass. Similarly, the Cd decreased concentration in soil and Cd removal rate in the flowering stage treatments were 29.2% and 27.9% higher than that in the maturity stage treatments, respectively. After 3 years of phytoremediation, the extractable Cd concentration in soil was reduced by 36.4% in the flowering stage treatments and by 27.6% in the maturity stage treatments, which also led to the same decreasing trend of Cd accumulation of S. nigrum. In conclusion, the study results have demonstrated that the planting mode of two harvests a year at the flowering stage seems to be a viable option to apply for continuous phytoremediation of Cd-contaminated farmland soil.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 2, Comparison between Two Growing Seasons

The positive impact on restoring soil functionality, decreasing toxic elements (TE) bioaccessibility, and enhancing soil physicochemical and biological parameters established a consensus on considering a Miscanthus × giganteus convenient species for phytomanaging wide TE contaminated areas. Nevertheless, information about the plant's mode of reaction to elevated soil multi-TE concentrations is still scarce. For the sake of investigating the miscanthus response to stressful TE concentrations, an ex-situ pot experiment was initiated for 18 months, with three miscanthus cultivars referred to as B, U, and A planted in soils with gradient Cd, Pb, and Zn concentrations. A non-contaminated control soil was introduced as well, and plants were cultivated within. Results revealed that the long exposure to increasing soil TE concentrations caused the number of tillers per plant to decline and the TE concentrations in the leaves to boost progressively with the soil contamination. The photosynthetic pigments (chlorophyll a, b, and carotenoids) were negatively affected as well. However, the phenolic compounds, flavonoids, tannins, and anthocyanins, along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase elevated progressively with the TE concentration and exposure duration. Conclusively, miscanthus plants demonstrated an intensified and synchronized antioxidative activity against the TE concentration.

Effect of panchakavya (organic formulation) on phytoremediation of lead and zinc using Zea mays

Chelate-assisted phytoextraction is proposed to be an effective approach for the removal of metals from contaminated soil. Organic chelators can improve this biological technique by increasing metal solubility. The aim of this study was to investigate the possibility of improving the phytoextraction of lead (Pb) and zinc (Zn) by the application of panchakavya, a traditional Indian organic formulation. Panchakavya was prepared by fermentation process in open environment using cow dunk, cow ghee, cow urine, cow milk, cow curd, tender coconut water, crude jaggery, and mashed bananas. Soil metal fraction studies indicate that the panchakavya treatment decreased (73%) water-soluble fraction of Pb. Plant growth analysis indicated the application of panchakavya to increase Zea mays fresh root weight, shoot biomass and superoxide dismutase level in Zn contaminated soil. Similarly, a significant increase in the Zn accumulation (12% in shoots and 9% in roots) was observed in panchakavya treated plants. However, when compared to control plants, panchakavya treatment significantly decreased (32% in shoots and 37% in roots) Pb accumulation in Z. mays. Obtained results point out that panchakavya could potentially increase the phytoremediation of Zn in Z. mays.