Naturally selected dominant weeds as heavy metal accumulators and excluders assisted by rhizosphere bacteria in a mining area

A new hyperaccumulator plant (Spergularia rubra) for the decontamination of mine tailings through electrokinetic-assisted phytoextraction

The screening of new effective metal hyperaccumulators is essential for the development of profitable phytoremediation projects in highly degraded environments such as mining areas. The goal of this research was to analyze the phytoextraction potential of the native plant Spergularia rubra to decontaminate and eventually recover metals (phytomining) from the mine tailings (belonging to an abandoned Pb/Zn Spanish mine) in which it grows spontaneously. To do so, the ability of this plant species to accumulate metals was evaluated both under natural conditions and through simple and electrokinetically assisted phytoextraction tests using alternating current and different combinations of voltage gradient (1/2 V cm-1) and application time (6/12 h per day). The complete duration of the greenhouse trial was 64 days, although alternating current was applied only during the last 14 days. The results obtained demonstrated the exceptional effectiveness of S. rubra for metal hyperaccumulation and growth without affecting toxicity in highly contaminated mining waste. Zn was the metal accumulated to a higher extent in the shoots, reaching concentrations up to 17,800 mg kg-1; Pb was mainly accumulated in the roots reaching a maximum concentration of 8709 mg kg-1. Cu and Cd were accumulated to a lesser extent but the bioconcentration factors were much >1. It has been proved that S. rubra is a hyperaccumulator species for Zn and Cd both in natural and greenhouse conditions and, very probably, Pb in wild conditions. The application of AC current did not significantly increase metal concentrations in plant tissues but it was able to increase the aerial biomass of S. rubra by 49.8 %. As a result, the phytoextraction yields of all metals were significantly improved as compared to wild conditions (up to 86 % for Zn). It could open new expectations about the economic viability of recovering high-value metals from mine tailings.

Phytoremediation strategies for heavy metal-contaminated soil by selecting native plants near mining areas in Inner Mongolia

Phytoremediation technology, as an eco-friendly and cost-effective approach, is widely used to restore soil contaminated by heavy metal(loid)s. However, the adaptability and absorption capacity of plants to multiple elements are the crucial factors affecting the application of phytoremediation in mining areas. In this study, dominant native plant species and their paired soils were collected near a lead-zinc mine in Inner Mongolia, to assess the ecological risk of heavy metal(loid)s and phytoremediation potential. The results showed that Cd and As were the dominant soil pollutants, with levels of 90.91% and 100%, respectively, exceeding the risk intervention values for soil contamination of agricultural land. The rates of Pb, Cu, and Zn exceeding the risk screening values were 69.70%, 60.61%, and 96.97%, respectively. Extremely high ecological risk of heavy metal(loid)s was observed in this area. The ability of native plants accumulating heavy metals varied among species. The bioconcentration factor (BCF) varied from 0.14 to 2.59 for Cd, 0.02 to 0.45 for As, 0.06 to 0.76 for Pb, 0.05 to 2.69 for Cr, 0.15 to 1.00 for Cu, and 0.22 to 4.10 for Zn. Chinese Cinquefoil Herb (Potentilla chinensis Ser.) showed the potential to accumulate multiple toxic elements based on the biomass, shoot content, translocation factor (TF), BCF, and metal extraction rate (MER), while, other species showed the potential to accumulate single toxic element: goosefoot (Chenopodium album L.), Lespedeza daurica (Laxm.) Schindl. and peashrubs (Caragana korshinskii Kom.), Herba Artemisiae Scopariae (Artemisia capillaris Thunb.), alfalfa (Medicago sativa L.), and Moldavian Dragonhead (Dracocephalum moldavica L.) for Cd, As, Cr, Cu, and Zn, respectively. Furthermore, wild leek (Allium ramosum L.), cogongrass (Imperata cylindrica (L.) Beauv.), fringed sagebrush (Artemisia frigida Willd.), and field bindweed (Convolvulus arvensis L.) were selected for phytostabilization of specific elements, considering the heavy metal contents in the roots and low TF values. This study provides a reference for selecting appropriate species for the remediation of heavy metal-contaminated soils in certain mining areas.

Spatiotemporal characterization of heavy metal and antibiotics in the Pearl River Basin and pollutants removal assessment using invasive species-derived biochars

Rivers play essential roles in human civilization, while anthropogenic activities have deteriorated their resilience and functionalities. Combating contamination is one of the priorities for building the river's resilience and providing safe water and habitats for livelihoods, wildlife preservation, and food production. We collected 174 water and sediment samples from the upstream to the estuary of the Pearl River (PR), characterized the heavy metal and antibiotics contamination levels, and analyzed the spatiotemporal distribution by compiling historical datasets extracted from published research papers and governmental documents. We also assessed the feasibility of removing PR water heavy metals and antibiotics using biochars derived from two invasive plants, Bidens pilosa L. and Lantana camara. According to our findings, heavy metals and antibiotics in water and sediment increased towards the downstream region of the Pearl River Delta (PRD). The water and sediment samples obtained from the Dongguan and Shenzhen regions exhibited the most elevated levels of heavy metals, whereas the samples from the Huizhou region demonstrated the highest levels of antibiotics. Compared with previously published PRD sediment heavy metals (1976-2011) and antibiotics contamination data (2006-2017), we found that some heavy metals and all measured antibiotics contents in sediment substantially reduced (80-100%). Cu, Zn, Cr, and As significantly polluted the sediment in PRD. Shenzhen had the highest Index of geo-accumulation (I_geo) for Cu, Zn, and Cr, while Zhaoqing had the highest I_geo for As. The dominant antibiotics were Ciprofloxacin, Doxycycline, Norfloxacin, Ofloxacin, Oxytetracycline, and Tetracycline. Invasive plant-derived biochars showed high antibiotic removal capacity but failed to reduce most PR water heavy metals since these invasive plants are potential heavy metal hyperaccumulators. The spatial distribution of heavy metal and antibiotics concentration/content in water and sediment samples is primarily affected by anthropogenic activities such as industrialization, aquaculture, pharmaceutical, and agricultural practice. Our study provides insights into the extensive freshwater watersheds' decontamination and green policymaking.

Potential use of saline resources for biofuel production using halophytes and marine algae: prospects and pitfalls

There exists a global challenge of feeding the growing human population of the world and supplying its energy needs without exhausting global resources. This challenge includes the competition for biomass between food and fuel production. The aim of this paper is to review to what extent the biomass of plants growing under hostile conditions and on marginal lands could ease that competition. Biomass from salt-tolerant algae and halophytes has shown potential for bioenergy production on salt-affected soils. Halophytes and algae could provide a bio-based source for lignoceelusic biomass and fatty acids or an alternative for edible biomass currently produced using fresh water and agricultural lands. The present paper provides an overview of the opportunities and challenges in the development of alternative fuels from halophytes and algae. Halophytes grown on marginal and degraded lands using saline water offer an additional material for commercial-scale biofuel production, especially bioethanol. At the same time, suitable strains of microalgae cultured under saline conditions can be a particularly good source of biodiesel, although the efficiency of their mass-scale biomass production is still a concern in relation to environmental protection. This review summaries the pitfalls and precautions for producing biomass in a way that limits environmental hazards and harms for coastal ecosystems. Some new algal and halophytic species with great potential as sources of bioenergy are highlighted.

New insights into the bioremediation of petroleum contaminants: A systematic review

Petroleum product is an essential resource for energy, that has been exploited by wide range of industries and regular life. A carbonaceous contamination of marine and terrestrial environments caused by errant runoffs of consequential petroleum-derived contaminants. Additionally, petroleum hydrocarbons can have adverse effects on human health and global ecosystems and also have negative demographic consequences in petroleum industries. Key contaminants of petroleum products, primarily includes aliphatic hydrocarbons, benzene, toluene, ethylbenzene, and xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), resins, and asphaltenes. On environmental interaction, these pollutants result in ecotoxicity as well as human toxicity. Oxidative stress, mitochondrial damage, DNA mutations, and protein dysfunction are a few key causative mechanisms behind the toxic impacts. Henceforth, it becomes very evident to have certain remedial strategies which could help on eliminating these xenobiotics from the environment. This brings the efficacious application of bioremediation to remove or degrade pollutants from the ecosystems. In the recent scenario, extensive research and experimentation have been implemented towards bio-benign remediation of these petroleum-based pollutants, aiming to reduce the load of these toxic molecules in the environment. This review gives a detailed overview of petroleum pollutants, and their toxicity. Methods used for degrading them in the environment using microbes, periphytes, phyto-microbial interactions, genetically modified organisms, and nano-microbial remediation. All of these methods could have a significant impact on environmental management.

Heavy metal stabilization remediation in polluted soils with stabilizing materials: a review

The remediation of soil contaminated by heavy metals has long been a concern of academics. This is due to the fact that heavy metals discharged into the environment as a result of natural and anthropogenic activities may have detrimental consequences for human health, the ecological environment, the economy, and society. Metal stabilization has received considerable attention and has shown to be a promising soil remediation option among the several techniques for the remediation of heavy metal-contaminated soils. This review discusses various stabilizing materials, including inorganic materials like clay minerals, phosphorus-containing materials, calcium silicon materials, metals, and metal oxides, as well as organic materials like manure, municipal solid waste, and biochar, for the remediation of heavy metal-contaminated soils. Through diverse remediation processes such as adsorption, complexation, precipitation, and redox reactions, these additives efficiently limit the biological effectiveness of heavy metals in soils. It should also be emphasized that the effectiveness of metal stabilization is influenced by soil pH, organic matter content, amendment type and dosage, heavy metal species and contamination level, and plant variety. Furthermore, a comprehensive overview of the methods for evaluating the effectiveness of heavy metal stabilization based on soil physicochemical properties, heavy metal morphology, and bioactivity has also been provided. At the same time, it is critical to assess the stability and timeliness of the heavy metals' long-term remedial effect. Finally, the priority should be on developing novel, efficient, environmentally friendly, and economically feasible stabilizing agents, as well as establishing a systematic assessment method and criteria for analyzing their long-term effects.

Changing Rhizosphere Microbial Community and Metabolites with Developmental Stages of Coleus barbatus

Coleus barbatus is a medicinal herb belonging to Lamiaceae. It is the only living organism known to produce forskolin, which is a labdane diterpene and is reported to activate adenylate cyclase. Microbes associated with plants play an important role in maintaining plant health. Recently, the targeted application of beneficial plant-associated microbes and their combinations in abiotic and biotic stress tolerance has gained momentum. In this work, we carried out the rhizosphere metagenome sequencing of C. barbatus at different developmental stages to understand how rhizosphere microflora are affected by and affect the metabolite content in plants. We found that the Kaistobacter genus was abundantly present in the rhizosphere of C. barbatus and its accumulation pattern appears to correlate with the quantities of forskolin in the roots at different developmental stages. Members of the Phoma genus, known for several pathogenic species, were in lower numbers in the C. barbatus rhizosphere in comparison with C. blumei. To our knowledge, this is the first metagenomic study of the rhizospheric microbiome of C. barbatus, which may help to explore and exploit the culturable and non-culturable microbial diversity present in the rhizosphere.

Enrichment and distribution characteristics of heavy metal(loid)s in native plants of abandoned farmlands in sewage irrigation area

Soil samples and native plants were collected from abandoned farmlands with a long history of sewage irrigation along Dongdagou stream, Baiyin City. We investigated the concentrations of heavy metal(loid)s (HMMs) in soil-plant system to evaluate the accumulation and transportation ability of HMMs in native plants. Results indicated that soils in study area were severely polluted by Cd, Pb, and As. With the exception of Cd, the correlation between total HMM concentrations in soil and plant tissues was poor. Among all investigated plants, no one was close to the criteria for the HMM concentrations of hyperaccumulators. The concentrations of HMMs in most plants were reached the phytotoxic level and the abandoned farmlands could not be used as forages, which showed that native plants may possess resistance capabilities or high tolerance for As, Cu, Cd, Pb, and Zn. The FTIR (Fourier transform infrared spectrometer) results suggested that the detoxification of HMMs in plants may depend on the functional groups (-OH, C-H, C-O, and N-H) of some compounds. Bioaccumulation factor (BAF), bioconcentration factor (BCF), and biological transfer factor (BTF) were used to identify the accumulation and translocation characteristics of HMMs by native plants. S. glauca had the highest mean values of BTF for Cd (8.07) and Zn (4.75). C. virgata showed the highest mean BAFs for Cd (2.76) and Zn (9.43). P. harmala, A. tataricus, and A. anethifolia also presented high accumulation and translocation abilities for Cd and Zn. High HMMs (As, Cu, Cd, Pb, and Zn) accumulation in the aerial parts of plants may lead to increased accumulation of HMMs in the food chain; additional research is desperately required. This study demonstrated the HM enrichment characteristics of weeds and provided a basis for the management of abandoned farmlands.

Melatonin alleviates arsenite toxicity by decreasing the arsenic accumulation in cell protoplasts and increasing the antioxidant capacity in rice

Arsenic (As) is a common environmental pollutant that seriously interferes with the normal growth of organisms. There is an urgent need to take environment-safe and efficient strategies to mitigate As toxicity. Melatonin (MT) is a pleiotropic molecule that regulates plant growth and organ development and alleviates heavy metal stresses. The experiment aims to explore the mechanism of MT in reducing arsenite toxicity by hydroponic rice seedlings. The results showed that MT application reduced the As content in rice roots and shoots by 26.4% and 37.5%, respectively, and mainly decreased As content in the soluble fractions of the rice root cell. MT application also increased the As content of chelated-soluble pectin and alkali-soluble pectin in the cell wall by 14.7% and 74.4%, respectively. It promoted the generation of the functional group of the root cell walls by the FTIR analysis, indicating that MT may promote the fixation of As on the cell wall. Meanwhile, MT contributed to scavenging excess H₂O₂, reducing MDA content, and maintaining normal morphology of root cells by stimulating SOD, POD and CAT activities and increasing the level of GSH. The research deepens our understanding of how MT participates in maintaining redox homeostasis in rice cells, reducing As toxicity, and decreasing As concentration in rice seedlings, thereby providing more possibilities for reducing As accumulation in rice.

An Alliance of Trifolium repens—Rhizobium leguminosarum bv. trifolii—Mycorrhizal Fungi From an Old Zn-Pb-Cd Rich Waste Heap as a Promising Tripartite System for Phytostabilization of Metal Polluted Soils

The Bolesław waste heap in South Poland, with total soil Zn concentrations higher than 50,000 mg kg^–1, 5,000 mg Pb kg^–1, and 500 mg Cd kg^–1, is a unique habitat for metallicolous plants, such as Trifolium repens L. The purpose of this study was to characterize the association between T. repens and its microbial symbionts, i.e., Rhizobium leguminosarum bv. trifolii and mycorrhizal fungi and to evaluate its applicability for phytostabilization of metal-polluted soils. Rhizobia originating from the nutrient-poor waste heap area showed to be efficient in plant nodulation and nitrogen fixation. They demonstrated not only potential plant growth promotion traits in vitro, but they also improved the growth of T. repens plants to a similar extent as strains from a non-polluted reference area. Our results revealed that the adaptations of T. repens to high Zn-Pb-Cd concentrations are related to the storage of metals predominantly in the roots (excluder strategy) due to nodule apoplast modifications (i.e., thickening and suberization of cell walls, vacuolar storage), and symbiosis with arbuscular mycorrhizal fungi of a substantial genetic diversity. As a result, the rhizobia-mycorrhizal fungi-T. repens association appears to be a promising tool for phytostabilization of Zn-Pb-Cd-polluted soils.

Root-associated microbiota drive phytoremediation strategies to lead of Sonchus Asper (L.) Hill as revealed by intercropping-induced modifications of the rhizosphere microbiome

Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a 'root-to-shoot' transition of lead sequestration and improved phytoremediation capacities of S. asper. These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant-microbe-plant interactions shapes the phytoremediation potential of S. asper. Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

Phytochemicals mitigation of Brassica napus by IAA grown under Cd and Pb toxicity and its impact on growth responses of Anagallis arvensis

Beginning of industrialization accelerates the heavy metal pollution in the biosphere. Plant being the immovable entity utilizes different mechanisms to flee from unfavourable conditions. To alleviate toxic impact of metals like cadmium (Cd) and lead (Pb), phytohormones such as indole acetic acid (IAA) has been applied exogenously. This manuscript aims to evaluate the significant change occurring in biochemical parameters of Indian mustard (Brassica napus) grown under individual and combined treatments of IAA with Cd and Pb. Herbicidal potential of treated Brassica extracts were evaluated on growth and development of Anagallis arvensis. Quantum yield parameters were more sensitive to Cd than Pb stress resulted in reduced photosynthetic pigments. However, exogenously applied IAA together with Cd and Pb considerably improved the level of photosynthetic attributes along with reduced accumulation of Cd and Pb in Brassica plant. Cd and Pb enhanced the activities of reactive oxygen species (ROS) and antioxidant machinery. However, addition of IAA with Cd and Pb mitigated the effect of heavy metals on antioxidant system. Moreover, activity of the phenylalanine ammonia lyase enzyme and the defensive metabolites (phenolic, flavonoid and anthocyanin compounds) were boosted under individual treatments of Cd and Pb responsible for increasing herbicidal potential of Brassica plant. Our results exhibited essentiality of IAA in mitigating Cd and Pb stress in Brassica through up-regulated mechanisms of the antioxidant system for balancing ROS related injuries. Increased metabolites enhancing herbicidal potential of Brassica napus against Anagallis weed were also observed.

Are Grasses Really Useful for the Phytoremediation of Potentially Toxic Trace Elements? A Review

The pollution of soil, water, and air by potentially toxic trace elements poses risks to environmental and human health. For this reason, many chemical, physical, and biological processes of remediation have been developed to reduce the (available) trace element concentrations in the environment. Among those technologies, phytoremediation is an environmentally friendly in situ and cost-effective approach to remediate sites with low-to-moderate pollution with trace elements. However, not all species have the potential to be used for phytoremediation of trace element-polluted sites due to their morpho-physiological characteristics and low tolerance to toxicity induced by the trace elements. Grasses are prospective candidates due to their high biomass yields, fast growth, adaptations to infertile soils, and successive shoot regrowth after harvest. A large number of studies evaluating the processes related to the uptake, transport, accumulation, and toxicity of trace elements in grasses assessed for phytoremediation have been conducted. The aim of this review is (i) to synthesize the available information on the mechanisms involved in uptake, transport, accumulation, toxicity, and tolerance to trace elements in grasses; (ii) to identify suitable grasses for trace element phytoextraction, phytostabilization, and phytofiltration; (iii) to describe the main strategies used to improve trace element phytoremediation efficiency by grasses; and (iv) to point out the advantages, disadvantages, and perspectives for the use of grasses for phytoremediation of trace element-polluted soils.

Do New-Generation Recycled Phosphorus Fertilizers Increase the Content of Potentially Toxic Elements in Soil and Plants?

Phosphorus (P)-rich secondary raw materials can provide a valuable base for modern mineral fertilizers, provided that the new formulations do not load the soil–plant system with potentially toxic elements. Fertilizers from sewage sludge ash (SSA) and/or animal bones, activated by phosphorus-solubilizing bacteria (Bacillus megaterium or Acidithiobacillus ferrooxidans), were tested in field experiments in north-eastern Poland. The reference provided treatments with superphosphate and treatment without phosphorus fertilization. In one experiment, all P-fertilizers were applied at a P dose of 21 kg·ha−1, and in the other three experiments, three P doses were adopted: 17.6, 26.4, and 35.2 kg·ha−1. The effect of recycled fertilizers on the content of arsenic (As), chromium (Cr), nickel (Ni), copper (Cu), and zinc (Zn) in the soil, in wheat grain and straw (test plant), weeds, and post-harvest residues was investigated. The application of recycled fertilizers in P amounts up to 35.2 kg·ha−1 did not change the As, Cr, Ni, Cu, or Zn contents in the soil and plant biomass. The contents of these elements in soil were below the permissible levels for arable land in Poland. Their concentrations in wheat grain and straw did not exceed the permissible or suggested limits for plant material to be used for food and feed, while in the weed and post-harvest residue biomass, they usually fell within the biological plant variability ranges.

Organic amendment improves rhizosphere environment and shapes soil bacterial community in black and red soil under lead stress

Heavy metal pollution is a worldwide problem affecting the quality of agricultural production and human health. In this study, spent mushroom substrate (SMS) and its compost (CSMS) were used to remedy black soil and red soil with simulated Pb contamination, aiming to discover their role in the improving rhizosphere environment and structuring rhizosphere bacterial community under lead stress. We designed an ultra-small-scale plot experiment to separate the rhizosphere from non-rhizosphere soil when planting water spinach (Ipomoea aquatica Forsk). The results showed that under 600 mg/kg of lead pollution, CSMS and SMS had no significant effect on the rhizosphere bacterial diversity in the black soil, but CSMS significantly increased the rhizosphere bacterial diversity in the red soil. The amendments significantly increased the percentage of Proteobacteria and Bacteroidetes in rhizosphere soil, and the relative abundance of some beneficial genera, such as Pseudoxanthomonas, Rhizomicrobium, Lysobacter etc., which subsequently restructured the bacterial community. The compositions of bacterial community of the red soil remediated by both amendments evolved to those of the black soil.

About plant species potentially promising for phytoextraction of large amounts of toxic trace elements

There is no information yet about plant species capable of accumulating many different metals/metalloids. The plants feasible for phytoremediation aims must grow fast, have high biomass, deep roots, and should accumulate and tolerate a range of toxicants in their aerial parts. In our research, greenhouse and field experiments have been performed to investigate accumulation and tolerance of not well-studied trace elements such as Br, Eu, Sc, Th (and also U) in couch grass and wheat. We compared bioaccumulation abilities of the plants with those of some other plant species grown under the same conditions. Additionally, we tested the effects of inoculation of seeds with Cellulomonas bacteria on phytoextraction of the trace elements from contaminated soils. For determination of elements, we used neutron activation analysis and ICP-MS. It was found that couch grass and wheat can grow in heavily contaminated soils and accumulate different toxic trace elements to levels that exceed physiological requirements typical for most plant species. Infection of seeds with bacteria resulted in a significant increase in the uptake of various trace elements and their translocation to upper plant parts. The use of couch grass and/or wheat, either alone or in combination with microorganisms, is a promising way to phytoextract metals/metalloids from contaminated soils.

Characterization and utilization of biochars derived from five invasive plant species Bidens pilosa L., Praxelis clematidea, Ipomoea cairica, Mikania micrantha and Lantana camara L. for Cd2+ and Cu2+ removal

Exotic invasive plants endanger the integrity of agricultural and natural systems throughout the world. Thus, the development of cost-effective and economic application of invasive plants is warranted. Here, we characterized fifteen biochars derived from five invasive plants at different temperatures (300, 500, and 700 °C) by determining their yield, ash content, pH, CEC, surface area, elementary composition, functional groups, and mineral composition. We conducted batch adsorption experiments to investigate the adsorption capacity and efficiency for Cd²⁺ and Cu²⁺ in wastewater. Our results suggest that all invasive plants are appropriate for biochar production, temperature and plant species had interacting effects on biochar properties, and the biochars pyrolyzed at 500 and 700 °C exhibited high metal adsorption capacity in neutral (pH = 7) solutions. The adsorption kinetics can be explained adequately by a pseudo-second-order model. BBC500 (Bidens pilosa L. derived biochar at 500 °C) and MBC500 (Mikania micrantha) exhibited higher metal equilibrium adsorption capacities (38.10 and 38.02 mg g^-1 for Cd²⁺, 20.01 and 20.10 mg g^-1 for Cu²⁺) and buffer abilities to pH than other biochars pyrolyzed at 500 °C. The Langmuir model was a better fit for IBC500 (Ipomoea cairica), MBC500, and LBC500 (Lantana camara L.) compared to the Freundlich model, whereas the opposite was true for BBC500 and PBC500 (Praxelis clematidea). These results suggest that the adsorption of metals by IBC500, MBC500, and LBC500 was mainly monolayer adsorption, while that by BBC500 and PBC500 was mainly chemical adsorption. Our results are important for the utilization and control of invasive plants as well as the decontamination of aqueous pollution.

Rice intercropping with alligator flag (Thalia dealbata): A novel model to produce safe cereal grains while remediating cadmium contaminated paddy soil

Phytoremediation has been employed as a cost-effective technique to remove the cadmium (Cd) from soil and water in several ecosystems. However, little is known about whether intercropping the remediating plants with rice (Oryza sativa) crop could reduce Cd accumulation in rice grains. We conducted greenhouse pot and concrete pond trials to explore the effects of intercropping alligator flag (Thalia dealbata, Marantaceae) on soil Cd remediation, paddy soil and microbial properties, and rice production. Our results suggest that intercropping with alligator flag significantly decreased Cd absorption, transportation, and accumulation from the soil to the rice grains (under 0.2 mg kg^-1 at a soil Cd content below 2.50 mg kg^-1). This decrease was due to the lowered Cd availability and higher soil pH in the rice-alligator flag intercropping system. Although planting alligator flag resulted in the reduction of soil NH₄-N and NO₃-N, Cd content in the rhizosphere was the main factor restricting microbial biomass, species, and community composition. Alligator flag could tolerate higher Cd contamination, and accumulate and stabilize more Cd in its tissues than rice. Our study suggests that alligator flag intercropped with rice has potential as a phytostabilization plant to produce rice safely for human consumption in moderately Cd-contaminated soils.