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

Effects of different planting distances and fertilizer use on the remediation of farmland contaminated with Cd by intercropping Cucurbita moschata and Amaranthus hypochondriacus L

Selecting suitable agronomic measures can strengthen the application of intercropping in the remediation of cadmium (Cd)-contaminated soil. In this study, the effects of different planting densities and fertilizer applications on the crop growth and Cd absorption of a pumpkin (Cucurbita moschata)-Amaranthus hypochondriacus L. intercropping system was determined. The goal was to provide enhanced means and a scientific basis for the promotion and application of this intercropping system. The Cd content of pumpkin in different planting systems was lower than the national food safety standard (0.05 mg kg^-1). In the IN-1 (4 pumpkin plants intercropped with 200 A. hypochondriacus plants) and IN-2 (4 pumpkin plants intercropped with 400 A. hypochondriacus plants) intercropping systems, the bioconcentration amount (BCA) per plant of Cd in A. hypochondriacus increased by 32.43% and 25.25%, respectively, compared with that of the monocropping system (P < 0.05). The IN-2 system had the highest equivalent ratio of heavy metal removal (3.08), indicating that this model had a substantial advantage for removing Cd. The land equivalent ratio of IN-1 (2.89) and IN-2 (2.60) was significantly higher than that of other intercropping systems, indicating that these two models had obvious yield advantages. In our study, chicken manure was the best at promoting the growth and yield of the two plants and sludge treatment significantly enhance Cd absorption of A. hypochondriacus. In general, intercropping four pumpkin plants with 400 A. hypochondriacus plants and applying chicken manure fertilizer can strengthen the application of this intercropping system in Cd-contaminated soil.

Manganese-modified biochar promotes Cd accumulation in Sedum alfredii in an intercropping system

Intercropping of crops with hyperaccumulators is a sustainable method to remediate contaminated soil without impeding agro-production. However, the function of engineered biochar in intercropping systems and its possible influence on cadmium (Cd) accumulation in hyperaccumulators remain unknown. A root box experiment on celery and Sedum alfredii with and without root separation was conducted in this study. Pristine and KMnO₄-modified biochar (BC_Mn) were used to investigate the effects of different biochars on plant growth and Cd uptake in an intercropping system, as well as the influence of engineered biochar on Cd accumulation in hyperaccumulators. The results demonstrated that soil pH did not significantly vary with biochar application in the root separation treatment. However, BC_Mn significantly increased soil pH and thus reduced available Cd when the plant roots were not separated. Intercropping (no separation treatment) led to a 34% higher and 24% lower aboveground biomass of celery and S. alfredii, respectively, regardless of biochar addition. Compared with aboveground plant parts, plant roots exhibited more significant responses to biochar. Interestingly, intercropping may favour the phytoextraction of Cd by S. alfredii. In particular, the Cd uptake by S. alfredii roots substantially increased (118-187%), whereas that of celery roots decreased (51-71%) with BC_Mn addition, compared with other treatments. Moreover, after BC_Mn addition the accumulation of Cd in aboveground S. alfredii in the no separation treatment was 136% higher than that in the separation treatment. This was possibly related to the interaction of manganese (Mn) with Cd as well as the roots of S. alfredii. These findings provide new insights into the application of engineered biochar for phytoextraction, which is important for the efficient remediation of Cd-contaminated soils.

Phytoextraction potential of arsenic and cadmium and response of rhizosphere microbial community by intercropping with two types of hyperaccumulators

Intercropping with hyperaccumulators/accumulators is a promising alternative to enhance phytoextraction of heavy metal(loid)s in contaminated soil. In this research, a pot experiment was conducted to evaluate the influences of intercropping As hyperaccumulator Pteris vittata L. with Cd hyperaccumulator Sedum alfredii Hance or accumulator Hylotelephium spectabile (Boreau) H. Ohba on the plant growth, As and Cd phytoextraction, and rhizosphere bacterial microbiota. The results indicated that intercropping can promote the growth of plants. The total biomass of P. vittata, S. alfredii, and H. spectabile in intercropping systems was improved by 19.9-34.1%, 16.8%, and 11.5%, respectively, in comparison with corresponding plant monoculture. The As content in rhizoid and frond of P. vittata when intercropped with S. alfredii was significantly increased by 28.3% and 19.0% (P < 0.05), respectively, as compared with P. vittata monoculture, and this treatment acquired the maximum As and Cd accumulation with 2032 μg·pot^-1 and 397 μg·pot^-1, respectively. Intercropping enhanced the soil bacterial community diversity. The genera of Lysobacter in P. vittata rhizosphere and Massilia and Arthrobacter in S. alfredii rhizosphere had higher abundance in the intercropping system of P. vittata and S. alfredii. There were significantly positive correlation relationships between Massilia and Arthrobacter with plant Cd content and Lysobacter with plant As content, indicating that they may play important roles in As and Cd phytoextraction. The results suggested that intercropping P. vittata with S. alfredii could be a potential strategy for phytoextraction of As and Cd from co-contaminated soil.

Effects of intercropping on Se accumulation and growth of pakchoi, lettuce and radish

Selenium is one of the most basic trace elements in the human body. It is necessary to improve the selenium content in agricultural products through agricultural planting technology to ensure that human nutrition and health need selenium. Therefore, our research passed the effect of intercropping on the growth and selenium accumulation of pakchoi, lettuce and radish were studied through pot experiments to determine whether intercropping of the three crop species can improve their selenium accumulation ability. The results showed that intercropping increased the root and shoot biomass of pakchoi and radish compared with the monocultures, while the biomass of roots and shoots decreased in other intercropping combinations. Intercropping also affected the photosynthetic pigment content of the three crop species. Specifically, the photosynthetic pigments increased in pakchoi and decreased in radish after intercropping. Notably, intercropping the three crop species together increased the SOD (superoxide dismutase) activities of the three crops compared with the monocultures. Meanwhile, intercropping radish with lettuce significantly increased the activities of SOD and CAT (catalase) in radish. Intercropping also increased the soluble sugar content in pakchoi and soluble protein content of radish relative to the monocultures. Furthermore, intercropping decreased the selenium content and the bioconcentration factor of the roots of the three vegetable crops, but improved the shoot selenium content, the bioconcentration factor and the transport factor of Se in pakchoi and radish. In conclusion, intercropping combination of pakchoi and radish can improve selenium accumulation in the edible parts of the crops, which is significant for efficient production of selenium-enriched vegetables.

Intercropping of Euonymus japonicus with Photinia × fraseri Improves Phytoremediation Efficiency in Cd/Cu/Zn Contaminated Field

Intercropping plants for phytoremediation is a promising strategy in heavy metal-polluted soils. In this study, two typical greening plant species, Euonymus japonicus (E. japonicus) and Photinia × fraseri (P. × fraseri), were intercropped in a Cd/Cu/Zn-contaminated field. The phytoremediation efficiency was investigated by measuring the plant biomass, metal concentration, and mycorrhizal colonisation, as well as the effects on soil properties, including soil pH; soil total N; and available N, P, K, Cd, Cu, and Zn. The results showed that, compared with the monoculture system, intercropping significantly lowered the available Cd, Cu, and Zn contents, significantly improved the total and available N contents in rhizosphere soils of both plant species, and increased the hyphae colonisation rate of P. × fraseri. In both plants, intercropping significantly improved the total plant biomass. Furthermore, the concentrations Zn and Cd in the root of E. japonicus and Cu concentration in the root of P. × fraseri were enhanced by 58.16%, 107.74%, and 20.57%, respectively. Intercropping resulted in plants accumulating higher amounts of Cd, Cu, and Zn. This was particularly evident in the total amount of Cd in E. japonicus, which was 2.2 times greater than that in the monoculture system. Therefore, this study provides a feasible technique for improving phytoremediation efficiency using greening plants.

Effects of mutual intercropping on cadmium accumulation of Solanum photeinocarpum Nakamura et Odashima and its post-grafting generations

The cadmium (Cd) contaminated agricultural soil has become serious in recent years, but it will take long time for Cd-hyperaccumulator to remedy. To speed up the remediation of agricultural soil and achieve the safe agricultural production as soon as possible, the potential Cd-hyperaccumulator Solanum photeinocarpum Nakamura et Odashima was intercropped with its post-grafting generations in Cd-contaminated soil. Intercropping increased the biomass, Cd contents and Cd extractions of S. photeinocarpum and its post-grafting generations in the pot and field experiments. Both the whole plant or shoot biomass and the Cd extraction by whole plant or shoot in intercroppings had a linear regression relationship with that in monocultures. In the field experiment, intercropping increased the shoot Cd extraction of S. photeinocarpum by 9.86%-40.06% compared with the monoculture. Intercropping increased the content of chlorophyll, activity of superoxide dismutase, activity of catalase, and soluble protein content of S. photeinocarpum and its post-grafting generations but reduced their peroxidase activities in the pot experiment. Therefore, intercropping S. photeinocarpum with its post-grafting generations can improve their phytoremediation ability, and the best choice is S. photeinocarpum intercropped with its post-grafting generation of wild potato rootstock. Novelty statementIntercropping Solanum photeinocarpum Nakamura et Odashima with its post-grafting generations could mutually promote the Cd accumulation in the two types of plant species, and improve their phytoremediation ability for remedying the Cd-contaminated soil.

Positive effects of applying endophytic bacteria in eggplant-Sedum intercropping system on Cd phytoremediation and vegetable production in cadmium polluted greenhouse

The combination of intercropping and phytoremediation in the remediation of cadmium contaminated soil is an emerging model in recent years, but the results of previous studies are inconsistent. In the field experiment, eggplant was intercropped with hyperaccumulator Sedum alfredii Hance (inoculated or not inoculated with endophytic bacteria) to study the effects of intercropping on vegetable safety production, phytoremediation efficiency of hyperaccumulator and variation of soil available nutrients. The results showed that the intercropping treatment had a negative effect on the growth of eggplant and Sedum, but endophyte SaMR12 alleviated the inhibition of intercropping on plant growth. Intercropping treatment increases the Cd concentration in edible part of eggplant to 1.34 mg/kg compared with eggplant monoculture (1.19 mg/kg). While the application of SaMR12 reduces the Cd concentration of eggplant fruit to 0.95 mg/kg and significantly promotes the Cd uptake by Sedum. What's more surprising is that compared with eggplant monocropping, the content of soil available nitrogen, phosphorus and potassium in the treatment of intercropping with inoculated Sedum increased significantly. And according to the correlation analysis of various indexes of plants and soil, the Cd content of eggplant is negatively correlated with the available phosphorus and potassium in the soil, while the Cd content of Sedum is positively correlated with it, which suggested that the application of phosphorus and potassium fertilizers in this experimental site was beneficial to reduce Cd content in eggplant and improve Cd phytoextraction of Sedum. Therefore, in the daily production of moderately Cd-contaminated soil, intercropping eggplant with Sedum inoculated with endophytic bacteria is an excellent Phytoextraction Coupled with Agro-safe-production (PCA) pattern.

Stabilization of heavy metals in biochar derived from plants in antimony mining area and its environmental implications

Heavy metals pollution in mining soils seriously threatens the ecological environment and human health worldwide. Phytoremediation is considered to be an ideal method to reduce the toxicity, mobility, and bioavailability of heavy metals in the soils. However, the disposal of plant-enriched heavy metals has become a thorny problem. To estimate the effect of pyrolysis on the stabilization of heavy metals in post-phytoremediation plant residues, different biochars were prepared from Conyza canadensis (CC), Gahnia tristis (GT), and Betula luminifera (BL) at different pyrolysis temperatures (300, 450, and 600 °C). Results indicated that pyrolysis was effective in the stabilization of heavy metals (Cr, Ni, As, Sb, Hg, and Pb) in plants and significantly (P < 0.05) decreased the bioavailability of most heavy metals. Among them, GT₆₀₀ prepared by pyrolysis of GT at 600 °C has the best stabilization effect on Sb, which increases the residual fraction by 7.32 times, up to 82.05%. The results of environmental risk assessment show that pyrolysis of biomass at high temperature (600 °C) can effectively mitigate the environmental impact of As, Sb, and Hg. Additionally, the reutilization potential of biochar produced by post-phytoremediation plant residues as adsorbents was investigated. The results of adsorption experiments revealed that all biochars have an excellent performance to adsorb Pb(II), and the maximum adsorption capacity is 139.16 mg g^-1 for CC₄₅₀. The adsorption mechanism could be attributed to complexation, electrostatic attraction, and cation exchange. This study demonstrates that pyrolysis is an effective and environment-friendly alternative method to stabilize heavy metals in plants, and their pyrolysis products can be reused for heavy metal adsorption.

Plant Species Diversity of Plant Communities and Heavy Metal Accumulation in Buffer Zone of Momianhe Stream Along a Long-Term Mine Wastes Area, China

The species composition of eight shrub communities were investigated in order to understand the species diversity of plant communities in buffer zone and wetland of Momianhe stream along a long-term mine waste area, Lanping county, Yunnan province, China. Dominant plant species and soil samples were collected to analysis heavy metal (Cu, Zn, Pb and Cd) accumulation characteristics. The results showed that 100% samples for Zn, Pb, Cd, and 87.5% samples for Cu in the investigated area exceeded the Yunnan geochemical background value of the heavy metals in the soil. There were 36 plants species in communities, among which Epilobium pyrricholophum, Elsholtzia argyi, Artemisia vestita, Tripogon chinensis were the dominant species. Plant species, the number of individuals, Ecological Dominance (Do), Shannon-Wiener index (H'), Simpson diversity index (Dsi) and Pielou evenness index (Epi) were affected by Cd and Cu contents of the soil and sediment. Therefore, the results indicate that Cu and Cd contents and ecological risk in the process of long-term vegetation restoration of small catchment in lead-zinc mine waste area should pay more attention.

Evaluation of trace metal accumulation in six vegetable crops intercropped with phytostabilizing plant species, in a French urban wasteland

The extensive development of agriculture in urban and peri-urban wastelands polluted with several trace elements (TE) poses risks to human health through contaminated food products. The objective was to explore the accumulation of TE in the various parts of vegetable crop plants (tomato, French bean, radish, potato, spinach, and leek) intercropped with phytostabilizing plant species (ryegrass and white clover, respectively). Field studies were conducted in a multicontaminated French urban wasteland with Cd, Cu, Pb and Zn, and an alkaline soil pH. Analyses of the respective non-edible parts of monocultured vegetable crops showed accumulation of all TE, mostly Zn, then Pb and Cu, and finally Cd. The corresponding TE accumulation factors (soil to plant) were all below 0.25. In the edible parts, average concentrations for TE were above the limit values, according to European and Chinese standards. TE contents in the phytostabilizing species chosen were in the same orders of magnitude and the same ranking as described for vegetable crops and most accumulation was in the roots. Unexpectedly, the presence of the phytostabilizing plants had a very strong positive impact on the soil to plant accumulation factor. Moreover, the edible plant parts were poorly impacted by the co-cropping with phytostabilizing plants.

Effects of intercropping with Solanum photeinocarpum and its post-grafting generations on cadmium accumulation in loquat (Eriobotrya japonica)

Cadmium (Cd) contamination of orchard soils is a global problem that has been increasing. To decrease the Cd accumulation in fruits, intercropping the orchard crops with hyperaccumulator plants has been used for soil remediation. A pot and a field experiment were conducted to study the effects of intercropping the potential Cd-hyperaccumulator Solanum photeinocarpum and its post-grafting generations with loquat (Eriobotrya japonica) on the growth and Cd uptake of these two plant species. In the pot experiment, intercropping improved the biomass, Cd content, Cd extraction, and root-to-shoot Cd translocation in both species. Intercropping increased the DNA methylation levels, antioxidant enzyme activity, and soluble protein content of loquat seedlings. These results indicate that intercropping could improve the phytoremediation of S. photeinocarpum and its post-grafting generations and increase the Cd uptake in loquat seedlings. In the field experiment, intercropping increased the Cd contents in the old branches, while it decreased that in the young branches and fruits of loquat. These findings indicate that intercropping could increase the Cd uptake in old tissues but reduce the Cd uptake in young tissues and fruits of loquat. So, intercropping loquat with S. photeinocarpum and its post-grafting generations could be used in Cd-contaminated orchards.

Influence of Planting Density on the Phytoremediation Efficiency of Festuca arundinacea in cd-Polluted Soil

Planting density can influence the biomass generation and element uptake capacity of various plants, which are two critical factors that determine the phytoremediation efficiency of plants. A series of 70 d experiments was performed to evaluate the influence of the planting density (10, 15, 20, 25, and 30 g seeds·m^- 2, namely D10, D15, D20, D25, and D30, respectively) of Festuca arundinacea on the decontamination of Cd-polluted soils. The variations in the biomass yield, falling tissue (senescent and dead leaf tissues) proportion, and Cd extraction capacity of the species under different cultivation strategies were determined. The results showed that the biomass generation of the species per square meter increased as the planting density increased, reached a peak at D20, and then decreased significantly. In addition, planting density can change the proportions of different leaf types, and the highest amount of senescent and dead leaves which accumulated significantly more Cd compared with the emerging and mature leaf tissues was observed at D20. A suitable planting density can also drive the species to secrete more dissolved organic matter (DOM), especially hydrophilic fractionations in to the soil, activating more Cd. Therefore, the phytoremediation efficiency of the species was determined by the dry weight of the falling tissues, which contained more than 75% of the leaf Cd. A suitable planting density can enhance the Cd decontamination capacity of F. arundinacea, and the adjustment of the planting density is a practicable and economical method that can be performed in real fields.

Influence of elevated atmospheric CO2 levels on phytoremediation effect of Festuca arundinacea intercropped with Echinochloa caudata

Atmospheric CO₂ levels have been increasing with increasing industrialization. Studies have shown the growth response of various plant species to climate change and increasing CO₂ levels, but variations in phytoremediation caused by elevated CO₂ levels, especially in intercropping systems, have rarely been reported. The current study therefore revealed variations in the phytoremediation effect of Festuca arundinacea intercropped with Echinochloa caudata, a pernicious annual weed, exposed to various CO₂ levels (280, 400, and 550 ppm). The biomass yield and Cd uptake capacity of monocultured F. arundinacea were found to increase with increasing atmospheric CO₂ level, highlighting the promoted phytoremediation efficiency of this species under elevated CO₂ levels. Elevated CO₂ levels also significantly increased the dry weight of monocultured E. caudata but did not change the Cd content in various parts of the plant. However, the intercropping system decreased the biomass yield of belowground and aerial parts of F. arundinacea under all treatments, since E. caudata competed with it for water and nutrients. The weight reduction of F. arundinacea in the intercropping system increased with increasing CO₂ level, because elevated CO₂ significantly increased the competitiveness of the weed. Therefore, the Cd phytoremediation efficiency of F. arundinacea intercropped with E. caudata exposed to 280, 400, and 550 ppm CO₂ decreased by 46.1%, 81.5%, and 215.0%, respectively, as evidenced by the decreased dry weight of F. arundinacea. Therefore, elevated CO₂ levels could decrease the phytoremediation effect of F. arundinacea in fields where weed growth is unavoidable.

Upland rice intercropping with Solanum nigrum inoculated with arbuscular mycorrhizal fungi reduces grain Cd while promoting phytoremediation of Cd-contaminated soil

Intercropping of hyperaccumulators with crops is a promising measure to enhance phytoremediation without impeding agricultural production. A Cd-hyperaccumulator, Solanum nigrum L. (S. nigrum), was intercropped with upland rice in a pot and rhizo-box experiment with Cd-contaminated soil to evaluate the combined effects of intercropping and arbuscular mycorrhizal fungi on plant growth and Cd accumulation. The results showed that, compared with monoculture, the combined treatments markedly decreased Cd concentration in rice parts, with the lowest Cd concentration in brown rice (reducing by 64.5%). The spatial distribution of root surface area and DTPA-Cd in the rhizo-box indicated competitive Cd uptake by neighbouring S. nigrum. Moreover, the combined treatments reduced Nramp5 expression but increased HMA3 levels in rice roots, leading to lower bioaccumulation and transfer coefficients. Additionally, fewer secreted organic acids and a higher rhizosphere pH were observed in rice. Conversely, the combined treatments promoted biomass, root length, root surface area, and decreased the rhizosphere pH in S. nigrum, thus increasing the Cd accumulation. Although the intercropping system with AMF inoculation notably reduced rice yield, the land-use efficiency was higher. These results provided insights into the role of AMF in the upland rice/S. nigrum system and demonstrated an alternative system for Cd phytoremediation.

Intercropping with post-grafting generation of Solanum photeinocarpum decreases cadmium accumulation in soybean (Glycine max)

A pot experiment was designed to explore the effects of different post-grafting generations of Solanum photeinocarpum Nakamura et Odashima intercropping on growth and cadmium (Cd) accumulation in soybeans (varieties: "Zaodou" and "Liaoxian"). Post generation of S. photeinocarpum (ungrafted, grafted on eggplant, potato, and tomato, respectively) were utilized to intercrop with two varieties of soybean in Cd-contaminated soil. Soybean monoculture was employed as a control. Consequently, intercropping with different post-grafting S. photeinocarpum generation, except for tomato rootstock grafts post-generation, could reduce soybean biomass and photosynthetic pigment content. Additionally, all S. photeinocarpum post-grafting generations had the capacity to reduce Cd content in soybean when intercropping, while tomato rootstock grafts post-generation exhibited an adequate ability to accumulate Cd in S. photeinocarpum compared to the ungrafted treatment. In particular, tomato rootstock grafts post-generation could effectively decrease Cd content in soybean organs by 14.09-62.13%, relative to soybean monoculture, but increased shoot Cd content and shoot Cd extraction of S. photeinocarpum by 10.33-13.49% and 10.38-12.03%, respectively, compared to the ungrafted treatment. Thus, tomato rootstock grafting may enhance the ability of post-grafting generation of S. photeinocarpum to remediate Cd-contaminated soil, and this grafting was able to reduce Cd accumulation in soybean.

How intercropping and mixed systems reduce cadmium concentration in rice grains and improve grain yields

Ecological theories can be applied to improve agricultural sustainability. In our study, a core hypothesis behind this claim is that "selfish behaviour" of rice cultivars results in "aversion" to a toxic substance in a multi-cropping system. We studied Changliangyou 772, a low-cadmium rice cultivar, cultivated with 11 different rice cultivars in intercropping and mixed systems. Rice cultivars with medium grain yield, ranging from 25 to 45 g plant^-1, had distinctly higher yields in mixtures. Rice varieties with lower grain cadmium concentrations in monocultures had greater reductions in grain cadmium in the mixtures. In the intercropping systems, the yields of Changliangyou 772 were positively correlated with those of the neighbouring rice cultivars, while the grain cadmium showed a negative correlation with the grain cadmium of intercrops in the monocultures. The neighbouring cultivars with low grain cadmium concentrations in the intercropping showed higher cadmium concentrations in the monocultures. The intercropping and mixtures reduced the grain cadmium in two ways: 1) they increased the soil pH, resulting in lower cadmium bioavailability; and 2) they enhanced the iron plaque (Ip). However, a high Ip or cadmium concentration that was too high in the Ip weakened the Ip to block cadmium uptake by the roots.

Role of passivators for Cd alleviation in rice-water spinach intercropping system

Soil pollution with cadmium (Cd) has posed a threat to our food safety. And rice consumption is the main source of Cd intake in China. Rice intercropping with water spinach is an efficient way for crop production and phytoremediation in Cd-contaminated soil. However, few people work on the Cd remediation by a combination of the passivation and intercropping. In this study, two passivators (the Si-Ca-Mg ameliorant and the Fe-modified biochar with microbial inoculants) were used in the monoculture and intercropping systems to evaluate the potential of co-effect of passivators and cropping systems on the plant growth and Cd phytoremediation. Results showed that the highest rice biomass and rice yield were presented in the intercropping system with the passivator additions, however, relatively lower biomass was showed in water spinach due to the competition with rice. And more Cd accumulated in water spinach while lower Cd in that of different rice parts. The intercropping system with the addition of the Si-Ca-Mg ameliorant and the microbial Fe-modified biochar significantly reduced the Cd contents in brown rice by 58.86% and 63.83%, while notably enhanced the Cd accumulation of water spinach by 32.0% and 22.0%, compared with the monoculture without passivation, respectively. This probably due to the increased pH, the lowered Cd availability in soil, and the reduced TF and BCF values in rice plants with passivator applications. Collectively, this study indicated that rice-water spinach intercropping, especially with the passivator additions, may function as an effective way for Cd remediation and guarantee rice grain safety.

Physiological response of Conyza Canadensis to cadmium stress monitored by Fourier transform infrared spectroscopy and cadmium accumulation

The cadmium(Cd) pollution of soil causes serious environmental problems. Cd is a high toxic and high water soluble element without biological function, and it is easily taken in by plants owing to its high bioavailability. Thus it easily entered the food chain and threaten people's health. Here，different concentrations of Cd solutions were used to study the physiological response and Cd accumulation characteristics of Conyza Canadensis (L.) Cronq. The physiological response was characterized by Fourier Transform Infrared (FTIR) spectroscopy, and Cd accumulation in plant and distribution were tested by Atomic absorption spectroscopy (AAS) under different concentrations Cd stress. When Cd concentrations toxicity <3 mg·L^-1, the C. Canadensis (L.) Cronq. could grow normally without any symptoms, and the Cd concentrations increased to 7 mg·L^-1, the C. Canadensis (L.) Cronq. had a little lower biomass, but there was no significant difference in the biomass among treatment concentrations. The peak shape of each component remained unchanged before and after Cd treatment. Only the absorption peak of some functional groups involved in Cd adsorption shifted with different degrees, such as hydroxy groups (3417-3429 cm^-1), carboxyl groups (1380-1386 cm^-1), and acid amide groups (1631-1637 cm ^-1). The characteristic peak absorption intensity of root, stem and leaf was different with the increase of heavy metal concentration. The absorbance of the roots with high Cd concentration was higher than that with medium-low Cd concentration. This shows that high concentration of Cd could induce C. Canadensis (L.) Cronq. seedlings to produce a large number of protein, amino acid and other substances, and through osmotic regulation to enhance stress resistance, provide nitrogen source, reduce heavy metal toxicity, and stabilize the internal environment. After Cd treatment, the characteristic peaks of stem and leaf were higher than or close to the control. This is due to the high tolerance of C. Canadensis (L.) Cronq. seedlings to heavy metals. The Cd accumulation in the shoots (stems and leaves) of C. Canadensis (L.) Cronq. was obviously lower than that in roots and the Cd content in the shoots usually increased with increasing Cd concentration. The maximum accumulation of Cd in shoots was 1898.07 mg·kg^-1 after 11 days grown in the water spiked with 7 mg·L^-1 Cd concentration. The study suggests that C. Canadensis (L.) Cronq. has some remediation effect and endurance ability against heavy metal polluted contaminated soil and has potential utilization value in the technical field of phytoremediation of Cd polluted soil.

A novel phytoremediation method assisted by magnetized water to decontaminate soil Cd based on harvesting senescent and dead leaves of Festuca arundinacea

It is more economical and feasible to harvest above-ground plant tissues, especially leaves, than to uproot the entire plant during phytoremediation. The major goal of this study is to estimate the promoting effect of an external magnetic field on soil Cadmium (Cd) remediation efficiency by harvesting the leaves of Festuca arundinacea, irrigated by normal and magnetized water. Changes in the amount of emerging, mature, senescent, and dead leaves, as well as Cd concentrations in the corresponding tissues were compared. It was found that F. arundinacea irrigated by either kind of water accumulated significantly more Cd in senescent and dead leaves than in other tissues. After irrigation with magnetized water, the biomass of senescent and dead leaves increased from 15.7 and 6.4% to 17.2 and 11.6%, respectively, and a significantly higher amount of Cd (˜23.6%) was redistributed into dead leaves compared with the control. Thus, significantly more Cd was removed by harvesting the senescent and dead leaves of F. arundinacea. These results indicate that magnetic fields can increase the phytoremediation efficiency of F. arundinacea for Cd, and simultaneously reduce the cost of harvested residue disposal.

Distribution characteristics of Cd in different types of leaves of Festuca arundinacea intercropped with Cicer arietinum L.: A new strategy to remove pollutants by harvesting senescent and dead leaves

Although cost-effective, phytoremediation is too expensive when considering the large-scale pollution. Relative to harvesting the whole plant, it is more practicable to remove and dispose of senescent and dead leaves after phytoremediation. The phytoremediation efficiency of Festuca arundinacea for Cd was evaluated in this study, because over about 7% of the land area in China was contaminated with Cd. The accumulation, redistribution, and extraction of Cd were evaluated in different leaves of F. arundinacea intercropped with N-fixing species at different densities (Cicer arietinum L). The results showed that coordinate and malposed intercropping systems increased the dry weight of the senescent and dead leaves of F. arundinacea by 30-41% and 103-168% compared to the monoculture system, respectively. More Cd was redistributed to the senescent and dead leaves of F. arundinacea under both intercropping systems. Occupying only 22-30% of the total leaf biomass, senescent and dead leaves accumulated 74-88% of leaf Cd under different cultivation conditions. Relative to the monoculture system, intercropping decreased the amount of time needed to reduce soil Cd by 44-53%. The biomass production and Cd accumulation of F. arundinacea were higher in the malposed intercropping system, and it had higher remediation efficiency than the coordinate intercropping system. This study demonstrated that intercropping, especially malposed intercropping of F. arundinacea and C. arietinum L., is a practicable technology for leaf harvesting phytoremediation.

Enhanced phytoremediation of uranium contaminated soil by artificially constructed plant community plots

In order to develop an artificially constructed plant community plot for the enhanced phytoremediation of uranium contaminated soils, three uranium accumulators including Bamboo-willow (Salix sp.), Paspalum scrobiculatum linn and Macleaya cordata were used to construct four artificial plant community plots, and greenhouse experiments were conducted to investigate the bioaccumulation of uranium by the plants and the organic acid content, enzyme activity, and the change of microbial community structure in their rhizosphere soils. The transfer factor (TF) and the total bioaccumulation amount (TBA) of uranium were used to describe remediation efficiencies in this paper. It was found that their remediation efficiencies were in the order Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata > Bamboo-willow (Salix sp.)-Macleaya cordata > Paspalum scrobiculatum linn-Macleaya cordata > Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn. The bioaccumulation amount of uranium by each plant in the Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata community plot was significantly (P < 0.05) higher than that by its single population, the bioaccumulation amounts of uranium by Bamboo-willow (Salix sp.), Paspalum scrobiculatum linn and Macleaya cordata were 0.29, 0.32 and 2.19 mg/plant, respectively, and they were increased by 31.82%, 77.78% and 146.07%, respectively, and the transfer efficiencies by the plants were increased by 150%, 110% and 52.17%, respectively. The interaction between the plants' roots and the microorganisms in the rhizosphere soil of the Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata community plot resulted in the high content of organic acids such as oxalic acid in the rhizosphere soil of the plant community plot, which was significantly (P < 0.05) higher than that of its single population. The chelation of the organic acids with uranium led to an increase in the proportion of exchangeable uranium in soil solution. In addition, Burkholderia, which is an iron-producing carrier bacterium and can increase the uptake and accumulation of uranium by plants, and Leptolyngbya, which is a plant growth promoting rhizobacteria and can increase the biomass of plants, emerged in the rhizosphere soil of the plant community plot. These may be the mechanisms by which the phytoremediation of the uranium contaminated soils was enhanced by the plant community plot.

Phytoextraction potential of Pteris vittata L. co-planted with woody species for As, Cd, Pb and Zn in contaminated soil

The objective of this study was to determine the phytoextraction potential of a hyperaccumulator co-planted with a large biomass of woody plant in metal(loid)-contaminated soil. A pot experiment was conducted for 270 days (d) to study the growth, physiological responses, and metal(loid)s accumulation characteristics of plants, which included a shade-requiring, As-hyperaccumulator perennial herb, Pteris vittata L., co-planted with a woody tree, namely Morus alba L. or Broussonetia papyrifera L., for soil contaminated with arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn). The results showed that the biomass, photosynthetic pigment contents, antioxidant enzyme activity, and uptake of As in P. vittata L. were significantly enhanced by co-planting with M. alba L. or B. papyrifera L. Especially, the uptake of As by P. vittata L. was significantly (p < 0.05) increased by 80.0% and 64.2% when it was co-planted with M. alba L. or B. papyrifera L., respectively, while the As, Cd, Pb, and Zn contents of both M. alba L. and B. papyrifera L. were not significantly promoted by the co-planting. The comprehensive phytoextraction of metal(loid)s could be optimized by the co-planting of P. vittata L. with M. alba L. or B. papyrifera L. The total amount of As in the shoots from co-planting species was significantly (p < 0.05) higher than that of the monoculture with M. alba L. or B. papyrifera L., and that of Cd and Zn in the shoots was significantly (p < 0.05) higher than that of the monoculture with P. vittata L. The results showed that the co-planting of P. vittata L. with M. alba L. or B. papyrifera L. can alleviate the toxic effects of metal(loid)s on plant growth and improve the comprehensive phytoextraction amounts of metal(loid)s, and is a promising strategy for remediation of metal(loid)-contaminated soil.