Phytoextraction of Heavy Metals from Contaminated Soil by Co-CroppingSolanum nigrumL. with Ryegrass Associated with Endophytic Bacterium

Synergistic Effects of Earthworms and Plants on Chromium Removal from Acidic and Alkaline Soils: Biological Responses and Implications

Soil heavy metal pollution has become one of the major environmental issues of global concern and solving this problem is a major scientific and technological need for today's socio-economic development. Environmentally friendly bioremediation methods are currently the most commonly used for soil heavy metal pollution remediation. Via controlled experiments, the removal characteristics of chromium from contaminated soil were studied using earthworms (Eisenia fetida and Pheretima guillelmi) and plants (ryegrass and maize) at different chromium concentrations (15 mg/kg and 50 mg/kg) in acidic and alkaline soils. The effects of chromium contamination on biomass, chromium bioaccumulation, and earthworm gut microbial communities were also analyzed. The results showed that E. fetida had a relatively stronger ability to remove chromium from acidic and alkaline soil than P. guillelmi, and ryegrass had a significantly better ability to remove chromium from acidic and alkaline soil than maize. The combined use of E. fetida and ryegrass showed the best effect of removing chromium from contaminated soils, wih the highest removal rate (63.23%) in acidic soil at low Cr concentrations. After soil ingestion by earthworms, the content of stable chromium (residual and oxidizable forms) in the soil decreased significantly, while the content of active chromium (acid-extractable and reducible forms) increased significantly, thus promoting the enrichment of chromium in plants. The diversity in gut bacterial communities in earthworms decreased significantly following the ingestion of chromium-polluted soil, and their composition differences were significantly correlated with soil acidity and alkalinity. Bacillales, Chryseobacterium, and Citrobacter may have strong abilities to resist chromium and enhance chromium activity in acidic and alkaline soils. There was also a significant correlation between changes in enzyme activity in earthworms and their gut bacterial communities. The bacterial communities, including Pseudomonas and Verminephrobacter, were closely related to the bioavailability of chromium in soil and the degree of chromium stress in earthworms. This study provides insights into the differences in bioremediation for chromium-contaminated soils with different properties and its biological responses.

Garlic (Allium sativum) based interplanting alters the heavy metals absorption and bacterial diversity in neighboring plants

Heavy metals are naturally occurring elements that have a high atomic weight and let out in the environment by agriculture, industry, mining and therapeutic expertise and thrilling amassing of these elements pollutes the environment. In this study we have investigated the potential of garlic interplanting in promoting hyper accumulation and absorption of heavy metals to provide a basis for phytoremediation of polluted land. Monoculture and inter-plantation of garlic were conducted to investigate the absorption of cadmium and lead contamination in the land. A group of experiments with single planting (monoculture) of Lolium perenne, Conyza canadensis and Pteris vittata as accumulators were used. The results have shown that garlic has a potential as a hyper accumulate and absorb heavy metals. It was found that the accumulation of Cd and Pb was much higher with inter-planting. Garlic boosts up the absorption of heavy metals in Lolium perenne of Cd 66% and Pb 44% respectively. The Inter-planting of garlic with Pteris vittata promotes the Cd 26% and Pb 15%. While the maximum accumulation of Lead 87% and Cadmium 77% occurred in Conyza canadensis herb plant. The bacterial diversity in the soil was analyzed for each experimental soil and was found that the Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and Planctomycetes were commonly abundant in both single planting (monoculture) of ryegrass and interplanting ryegrass with garlic habitats. Variances were observed in the bacterial floral composition of single (monoculture) and intercropping (interplant) soils. Relative abundance of bacterial taxa revealed that the proportion of Proteobacteria, Acidobacteria, and Actinobacteria in the inter-planting group was slightly higher, while Firmicutes and Planctomycetes were low. This study provides the evidence to control the heavy metals contaminated soils with weed species. Growth promotion and heavy metal uptake of neighboring plants proved the specific plant-plant and plant-microbial associations with garlic plants. This inter-planting strategy can be used to improve heavy metal absorption.

Potential of rice straw biochar, sulfur and ryegrass (Lolium perenne L.) in remediating soil contaminated with nickel through irrigation with untreated wastewater

Background

Untreated wastewater carries substantial amount of heavy metals and causes potential ecological risks to the environment, food quality, soil health and sustainable agriculture.

Methodology

In order to reduce the incidence of nickel (Ni²⁺) contamination in soils, two separate experiments (incubation and greenhouse) were conducted to investigate the potentials of rice straw biochar and elemental sulfur in remediating Ni²⁺ polluted soil due to the irrigation with wastewater. Five incubation periods (1, 7, 14, 28 and 56 days), three biochar doses (0, 10 and 20 g kg⁻¹ of soil) and two doses of sulfur (0 and 5 g kg⁻¹ of soil) were used in the incubation experiment then the Ni²⁺ was extracted from the soil and analyzed, while ryegrass seeds Lolium perenne L. (Poales: Poaceae) and the same doses of biochar and sulfur were used in the greenhouse experiment then the plants Ni²⁺-uptake was determined.

Results

The results of the incubation experiment revealed a dose-dependent reduction of DTPA-extractable Ni²⁺ in soils treated with biochar. Increasing the biochar dose from 0 g kg⁻¹ (control) to 10 or 20 g kg⁻¹ (treatments) decreased the DTPA-extractable Ni²⁺ from the soil by 24.6% and 39.4%, respectively. The application of sulfur increased the Ni²⁺-uptake by ryegrass plant which was used as hyper-accumulator of heavy metals in the green house experiment. However, the biochar decreased the Ni²⁺-uptake by the plant therefore it can be used as animal feed.

Conclusions

These results indicate that the biochar and sulfur could be applied separately to remediate the Ni²⁺-contaminated soils either through adsorbing the Ni²⁺ by biochar or increasing the Ni²⁺ availability by sulfur to be easily uptaken by the hyper-accumulator plant, and hence promote a sustainable agriculture.

Effects of intercropping with floricultural accumulator plants on cadmium accumulation in grapevine

Grapevine (Vitis vinifera L.) intercropping with floricultural cadmium (Cd) accumulator plants (Helianthus annuus L., Cosmos sulphureus Cav., Cosmos bipinnata Cav., and Impatiens balsamina L.) in Cd-contaminated soils (5 mg/kg) was conducted in pot experiment to screen the floricultural Cd-accumulator plants that can effectively reduce Cd uptake in grapevine. Intercropping with H. annuus, C. sulphureus, and I. balsamina decreased the biomass of grape plants compared with that of the grape monoculture, whereas intercropping with C. bipinnata did not show differences in grape plant biomass both as compared to monoculture in Cd-contaminated soils and to control plants, grown in the same soil without Cd spiking. The superoxide dismutase and catalase activities, as well as soluble protein content, were increased by intercropping with C. bipinnata compared with the grape monoculture, but were decreased by the other intercropping treatments. In general, intercropping with the four floricultural Cd-accumulator plants decreased the Cd content in grape plants compared with the monoculture, and the Cd content in grapevine for the different treatments was as follows: monoculture > intercropped with I. balsamina > intercropped with C. bipinnata > intercropped with H. annuus > intercropped with C. sulphureus. As for the amount of Cd accumulated by shoots of the floricultural plants, the ranking was as follows: I. balsamina > C. sulphureus > H. annuus > C. bipinnata. Therefore, intercropping with floricultural Cd-accumulator plants could effectively decrease Cd accumulation in grape plants, and intercropping with C. sulphureus gave the best results in this study.

Remediation of heavy metal contaminated soils by using Solanum nigrum: A review

Heavy metals are among the major environmental pollutants and the accumulation of these metals in soils is of great concern in agricultural production due to the toxic effects on crop growth and food quality. Phytoremediation is a promising technique which is being considered as an alternative and low-cost technology for the remediation of metal-contaminated soils. Solanum nigrum is widely studied for the remediation of heavy metal-contaminated soils owing to its ability for metal uptake and tolerance. S. nigrum can tolerate excess amount of certain metals through different mechanism including enhancing the activities of antioxidant enzymes and metal deposition in non-active parts of the plant. An overview of heavy metal uptake and tolerance in S. nigrum is given. Both endophytic and soil microorganisms can play a role in enhancing metal tolerance in S. nigrum. Additionally, optimization of soil management practices and exogenous application of amendments can also be used to enhance metal uptake and tolerance in this plant. The main objective of the present review is to highlight and discuss the recent progresses in using S. nigrum for remediation of metal contaminated soils.

Mixed planting with a leguminous plant outperforms bacteria in promoting growth of a metal remediating plant through histidine synthesis

The effectiveness of plant growth promoting bacteria (PGPB) in improving metal phytoremediation is still limited by stunted plant growth under high soil metal concentrations. Meanwhile, mixed planting with leguminous plants is known to improve yield in nutrient deficient soils but the use of a metal tolerant legume to enhance metal tolerance of a phytoremediator has not been explored. We compared the use of Pseudomonas brassicacearum, Rhizobium leguminosarum, and the metal tolerant leguminous plant Vicia sativa to promote the growth of Brassica juncea in soil contaminated with 400 mg Zn kg(-1), and used synchrotron based microfocus X-ray absorption spectroscopy to probe Zn speciation in plant roots. B. juncea grew better when planted with V. sativa than when inoculated with PGPB. By combining PGPB with mixed planting, B. juncea recovered full growth while also achieving soil remediation efficiency of >75%, the maximum ever demonstrated for B. juncea. μXANES analysis of V. sativa suggested possible root exudation of the Zn chelates histidine and cysteine were responsible for reducing Zn toxicity. We propose the exploration of a legume-assisted-phytoremediation system as a more effective alternative to PGPB for Zn bioremediation.