Polyaspartic acid assisted-phytoremediation of cadmium-contaminated farmland: Phytoextraction efficiency, soil quality, and rhizosphere microbial community

The effects of perfluoroalkyl substance pollution on microbial community and key metabolic pathways in the Pearl River Estuary

The extensive use of perfluoroalkyl substances (PFASs) has raised significant concerns regarding their adverse environmental implications. However, the understanding of their behaviors and biological effects in natural estuarine ecosystems remain limited. This study employed a multidisciplinary approach integrating chemical analysis, biological sequencing, and statistical modeling to comprehensively investigate the distribution of PFASs, as well as their intrinsic relationship with microbial community in the Pearl River Estuary (PRE), a rapidly urbanized area. Our findings demonstrate that the total PFAS concentrations ranged from 52-127 ng L-1 in water, and 2-70 μg kg-1 dry weight in sediment, with notably distinct compositions across habitats. Aquatic microbial communities exhibited higher sensitivity to environmental variables, including PFAS concentrations, attributed to increased stochasticity and reduced spatial turnover. Conversely, sediments harbored microbial communities with higher phylogenetic diversity, rendering them less susceptible to PFAS-induced stress. Furthermore, PFAS concentrations significantly affected microbial carbon, nitrogen, and phosphorus cycling, predominantly through indirect alterations in characteristic genus composition. Importantly, noteworthy variations in impacts were observed between perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs), which might contingent upon C-F bond dissociation energies. The findings shed light on PFAS ecological roles and interaction patterns with microbial communities in human-impacted estuarine environments.

Water-soluble carboxymethyl chitosan and rhamnolipids promote the remediation of Cd-contaminated soil by mediating the growth of Hylotelephium spectabile and regulating the rhizospheric ecological environment

The application of biodegradable chelating agents in phytoremediation is a promising approach. This study aimed to investigate the effects and roles of underlying mechanisms of water-soluble carboxymethyl chitosan (WSCC) and rhamnolipids (RLs) on the remediation of Cd-contaminated soil by Hylotelephium spectabile. WSCC and RLs mediated the growth of H. spectabile by increasing chlorophyll content and the activity of antioxidant enzymes as well as promoted the conversion of water-extractable Cd to HAc-extractable Cd in leaves. WSCC and RLs promoted the secretion of malic acid, acetic acid, and succinic acid by the roots; decreased soil pH; increased the number of functional groups, such as hydroxyl, amino, and carboxyl groups, in the soil; and changed the diversity and structure of bacterial communities in the soil, thereby improving the bioavailability of Cd in the soil and creating a good ecological environment of the rhizosphere. The combined application of WSCC and RLs had a better auxiliary effect than single application of either, especially under CR2 treatment (1.5 g·kg-1 WSCC + 0.2 g·kg-1 RLs), where the accumulation of Cd in plants significantly increased by 159.86 % compared with the control. These findings indicated that WSCC and RLs enhanced the remediation efficiency of H. spectabile by regulating both plant growth and the ecological environment of the rhizosphere.

Effects of naturally aged microplastics on arsenic and cadmium accumulation in lettuce: Insights into rhizosphere microecology

Naturally aged microplastics (NAMPs) are commonly found in farmland soils contaminated with heavy metals (HMs), such as arsenic (As) and cadmium (Cd); yet their combined effects on soil-plant ecosystems remain poorly understood. In this study, we investigated the toxic effects of NAMPs and As-Cd on lettuce, considering the influence of earthworm activity, and examined changes in As-Cd bioavailability in the rhizosphere. Four experimental systems were established: soil-only, soil-lettuce, soil-earthworms, and soil-lettuce-earthworms systems, with four NAMPs concentrations (0, 0.1, 0.5, 1 %). Our results showed that exposure to 0.1 % NAMPs reduced As accumulation in lettuce shoots (0.17-0.25 mg kg-1) and roots (1.13-1.72 mg kg-1), while increasing biomass and enhancing root growth by alleviating toxicity. In contrast, the combined stress of higher NAMPs concentration (0.5 %/1 %) and As-Cd caused a 28.4-58.4 % reduction in root activity, which stimulated low-molecular-weight organic acid (LMWOA) secretion in the rhizosphere, increasing the bioavailability of As and Cd and enhancing their absorption by lettuce. Partial least squares path modeling (PLS-PM) revealed that co-exposure altered LMWOA content, soil enzyme activity, and microbial community stability in the rhizosphere, ultimately influencing the bioavailability and uptake of As and Cd by lettuce.

Removal and ecological impact of sulfamethoxazole and N-acetyl sulfamethoxazole in mesocosmic wetlands dominated by submerged plants: Plant tolerance, microbial response, and nitrogen transformation

Sulfamethoxazole (SMX) and its human metabolite N-acetylsulfamethoxazole (N-SMX) are frequently detected in aquatic environments, posing potential threats to freshwater ecosystem health. Constructed wetlands are pivotal for wastewater treatment, with plant species serving as key determinants of pollutant removal efficiency. In this study, wetlands dominated by three submerged plants (Myriophyllum verticillatum, Vallisneria spiralis, Hydrilla verticillata) were respectively constructed to investigate the removal of SMX and N-SMX, and the impact on wetland ecology regarding plant tolerance, microbial response, and nitrogen transformation. Results showed that wetlands removed N-SMX (82.3-99.8 %) more effectively than SMX (54.3-80.2 %), with the wetland dominated by Myriophyllum verticillatum showing the highest removal efficiency. However, high concentrations (5 mg/L) of SMX and N-SMX significantly reduced NH4+-N and TN removal (p < 0.05), accompanied by shifts in microbial communities, especially a decreased abundance of Proteobacteria and key nitrogen-transforming genes. A total of 22 different ARGs (antibiotic resistance genes) were detected. SMX significantly increased the relative abundance of sulfonamide resistance genes (sul1, sul2) (p < 0.05), while major denitrifying genera, such as Thiobacillus, which were not the primary hosts of these genes, showed a significant negative correlation with sul1 and sul2 (p < 0.05). This study provides a reference for ecological remediation of wetlands in response to antibiotic contamination.

The Effect of Cysteine on the Removal of Cadmium in Paddy Soil by Combination with Bioremediation and the Response of the Soil Microbial Community

Bioremediation is widely recognized as a promising and efficient approach for the elimination of Cd from contaminated paddy soils. However, the Cd removal efficacy achieved through this method remains unsatisfactory and is accompanied by a marginally higher cost. Cysteine has the potential to improve the bioleaching efficiency of Cd from soils and decrease the use cost since it is green, acidic and has a high Cd affinity. In this study, different combination modes of cysteine and microbial inoculant were designed to analyze their effects on Cd removal and the soil microbial community through the sequence extraction of Cd fraction and high-throughput sequencing. The results demonstrate that the mixture of cysteine and the microbial inoculant was the best mode for increasing the Cd removal efficiency. And a ratio of cysteine to microbial inoculant of 5 mg:2 mL in a 300 mL volume was the most economically efficient matching. The Cd removal rate increased by 7.7-15.1% in comparison with the microbial inoculant treatment. This could be ascribed to the enhanced removal rate of the exchangeable and carbonate-bound Cd, which achieved 94.6% and 96.1%, respectively. After the treatment, the contents of ammonium nitrogen (NH3-N), total phosphorus (TP), available potassium (AK), and available phosphorus (AP) in the paddy soils were increased. The treatment of combinations of cysteine and microbial inoculant had an impact on the soil microbial diversity. The relative abundances of Alicyclobacillus, Metallibacterium, and Bacillus were increased in the paddy soils. The microbial metabolic functions, such as replication and repair and amino acid metabolism, were also increased after treatment, which benefitted the microbial survival and adaptation to the environment. The removal of Cd was attributed to the solubilizing, complexing, and ion-exchanging effects of the cysteine, the intra- and extracellular adsorption, and the production of organic acids of functional microorganisms. Moreover, cysteine, as a carbon, nitrogen, and sulfur source, promoted the growth and metabolism of microorganisms to achieve the effect of the synergistic promotion of microbial Cd removal. Therefore, this study underscored the potential of cysteine to enhance the bioremediation performance in Cd-contaminated paddy soils, offering valuable theoretical and technical insights for this field.

Synergistic effects of boron and cadmium on the metal enrichment and cell wall immobilization capacity of Cosmosbipinnatus

Cadmium (Cd), as a heavy metal pollutant, can seriously affect plant growth and development. Boron (B), as an indispensable nutrient element, plays an important role in plant growth and cell wall (CW) synthesis. However, the physiological effects of B and Cd on plant growth and the mechanism of Cd chelation by the CW remain unclear. Here, we investigate the effect of exogenous B on Cd accumulation in CW components of Cosmos bipinnatus roots and its mechanism of Cd mitigation. Under B deficiency and single Cd (30 μM) treatments, the growth of C. bipinnatus was significantly inhibited, but the addition of exogenous B significantly increased plant biomass, which increased the Cd content in the underground parts of C. bipinnatus by 20.18% and reduced the Cd translocation factor by 22.22%. Meanwhile, application of exogenous B affected the subcellular Cd content across various Cd forms and alleviated Cd-induced oxidative stress in C. bipinnatus. Additionally, exogenous B and Cd and their mixtures affected the functional groups of the root CW, the proportion of polysaccharide components, the Cd content of polysaccharides, and the polysaccharide uronic acid content of C. bipinnatus. However, B application increased 3-deoxy-oct-2-ulosonic acid content, pectin esterase activity, low esterified pectin content, and its Cd content by 149.52%, 55.69%, 206.38%, and 150.02%, respectively, compared to Cd treatment alone. Thus, our study showed that B mitigates the toxicity of Cd to plants, revealing the effect of B on the physiological aspects of Cd tolerance in plants.

Improving peanut growth and cadmium phytoextraction capacity by inoculating Bacillus megaterium and Trichoderma harzianum

Arachis hypogaea L. (peanut) is an economic crop with abundant biomass and remarkable capacity for cadmium (Cd) uptake. In a two-year field experiment, the translocation and accumulation mechanisms of Cd in peanuts were investigated following inoculation of Bacillus megaterium (BM) and Trichoderma harzianum (TH). The results demonstrated that inoculating BM and TH enhanced both biomass and Cd concentration in peanut roots and shoots compared with those of the CK treatment. There was no statistically significant difference observed in kernel biomass between peanut plants inoculated with TH and the CK treatment. The inoculation of BM and TH increased the Cd concentration in the soluble fraction of peanut roots by 24.36% and 102.78%, thus promoting Cd translocation from roots to shoots. Additionally, inoculating BM and TH resulted in a 31.75% and 52.88% elevation in Cd concentration within the leaf cell walls, thereby facilitating the accumulation of Cd within the shoots. Simultaneously, inoculating BM and TH enhanced the concentration of highly bioavailable Cd forms in peanuts. The accumulation of Cd in shoots is the primary factor determining the phytoextraction capacity in peanut, and inoculation of TH resulted in a 16.35-54.54% increase in shoot biomass and an enhancement of 99.10-99.95% in shoot Cd concentration. Therefore, inoculating TH can enhance the phytoextraction capacity for Cd in peanuts, particularly the production of economically valuable components (kernels), without compromising production.

WRKY Transcription Factors in Response to Metal Stress in Plants: A Review

Heavy metals in soil can inflict direct damage on plants growing within it, adversely affecting their growth height, root development, leaf area, and other physiological traits. To counteract the toxic impacts of heavy metals on plant growth and development, plants mitigate heavy metal stress through mechanisms such as metal chelation, vacuolar compartmentalization, regulation of transporters, and enhancement of antioxidant functions. WRKY transcription factors (TFs) play a crucial role in plant growth and development as well as in responses to both biotic and abiotic stresses; notably, heavy metal stress is classified as an abiotic stressor. An increasing number of studies have highlighted the significant role of WRKY proteins in regulating heavy metal stress across various levels. Upon the entry of heavy metal ions into plant root cells, the production of reactive oxygen species (ROS) is triggered, leading to the phosphorylation and activation of WRKY TFs through MAPK cascade signaling. Activated WRKY TFs then modulate various physiological processes by upregulating or downregulating the expression of downstream genes to confer heavy metal tolerance to plants. This review provides an overview of the research advancements regarding WRKY TFs in regulating heavy metal ion stress-including cadmium (Cd), arsenic (As), copper (Cu)-and aluminum (Al) toxicity.

Investigating the role of poly-γ-glutamic acid in Pennisetum giganteum phytoextraction of mercury-contaminated soil

Farmland mercury (Hg) pollution poses a significant threat to human health, but there is a lack of highly efficient phytoextraction for its remediation at present. This study investigates the impact of poly-γ-glutamic acid (γ-PGA) on the phytoextraction capabilities of Pennisetum giganteum (P. giganteum) in Hg-contaminated soil. Our research indicates that amending γ-PGA to soil markedly enhances the assimilation of soil Hg by P. giganteum and transformation of Hg within itself, with observed increases in Hg concentrations in roots, stems, and leaves by 1.1, 4.3, and 18.9 times, respectively, compared to the control. This enhancement is attributed to that γ-PGA can facilitate the hydrophilic and bioavailable of soil Hg. Besides, γ-PGA can stimulate the abundance of Hg-resistance bacteria Proteobacteria in the rhizosphere of P. giganteum, thus increasing the mobility and uptake of soil Hg by P. giganteum roots. Moreover, the hydrophilic nature of Hg-γ-PGA complexes supports their transport via the apoplastic pathway, across the epidermis, and through the Casparian strip, eventually leading to immobilization in the mesophyll tissues. This study provides novel insights into the mechanisms of Hg phytoextraction, demonstrating that γ-PGA significantly enhances the effectiveness of P. giganteum in Hg uptake and translocation. The findings suggest a promising approach for the remediation of Hg-contaminated soil, offering a sustainable and efficient strategy for environmental management and health risk mitigation.

Effects of N, N-bis (carboxymethyl)-L-glutamic acid and polyaspartic acid on the phytoremediation of cadmium in contaminated soil at the presence of pyrene: Biochemical properties and transcriptome analysis

Chelator-assisted phytoremediation is an efficacious method for promoting the removal efficiency of heavy metals (HMs). The effects of N, N-bis(carboxymethyl)-L-glutamic acid (GLDA) and polyaspartic acid (PASP) on Cd uptake and pyrene removal by Solanum nigrum L. (S. nigrum) were compared in this study. Using GLDA or PASP, the removal efficiency of pyrene was over 98%. And PASP observably raised the accumulation and transport of Cd by S. nigrum compared with GLDA. Meanwhile, both GLDA and PASP markedly increased soil dehydrogenase activities (DHA) and microbial activities. DHA and microbial activities in the PASP treatment group were 1.05 and 1.06 folds of those in the GLDA treatment group, respectively. Transcriptome analysis revealed that 1206 and 1684 differentially expressed genes (DEGs) were recognized in the GLDA treatment group and PASP treatment group, respectively. Most of the DEGs found in the PASP treatment group were involved in the metabolism of carbohydrates, the biosynthesis of brassinosteroid and flavonoid, and they were up-regulated. The DEGs related to Cd transport were screened, and ABCG3, ABCC4, ABCG9 and Nramp5 were found to be relevant with the reduction of Cd stress in S. nigrum by PASP. Furthermore, with PASP treated, transcription factors (TFs) related to HMs such as WRKY, bHLH, AP2/ERF, MYB were down-regulated, while more MYB and bZIP TFs were up-regulated. These TFs associated with plant stress resistance would work together to induce oxidative stress. The above results indicated that PASP was more conducive for phytoremediation of Cd-pyrene co-contaminated soil than GLDA.

Rhizosphere microbiome of plants used in phytoremediation of mine tailing dams

Rhizospheric microbial communities improve the effectiveness of hyperaccumulators in the phytoremediation of heavy metals. However, limited access to tailing dams and inadequate assessment of plants' phytoremediation potential limit the characterization of native accumulators, hindering the effectiveness of local remediation efforts. This study evaluates the heavy metal sequestration potentials of Pennisetum purpureum, Leucaena leucocephala, and Pteris vittata and their associated rhizospheric microbial communities at the Marlu and Pompora tailing dams in Ghana. The results indicate shoot hyperaccumulation of Cd (334.5 ± 6.3 mg/kg) and Fe (10,647.0 ± 12.6 mg/kg) in P. purpureum and L. leucocephala, respectively. Analysis of rhizospheric bacterial communities revealed the impact of heavy metal contamination on bacterial community composition, associating Fe and Cd hyperaccumulation with Bacillus, Arthrobacter, and Sphingomonas species. This study reports the hyperaccumulation potentials of L. leucocephala and P. purpureum enhanced by associated rhizosphere bacterial communities, suggesting their potential application as an environmentally friendly remediation process of heavy metals contaminated lands.

Extraction of heavy metals from copper tailings by ryegrass (Lolium perenne L.) with the assistance of degradable chelating agents

Heavy metal contamination is an urgent ecological governance problem in mining areas. In order to seek for a green and environmentally friendly reagent with better plant restoration effect to solve the problem of low efficiency in plant restoration in heavy metal pollution soil. In this study, we evaluated the effects of three biodegradable chelating agents, namely citric acid (CA), fulvic acid (FA) and polyaspartic acid (PASP), on the physicochemical properties of copper tailings, growth of ryegrass (Lolium perenne L.) and heavy metal accumulation therein. The results showed that the chelating agent application improved the physicochemical properties of copper tailings, increased the biomass of ryegrass and enriched more Cu and Cd in copper tailings. In the control group, the main existing forms of Cu and Cd were oxidizable state, followed by residual, weak acid soluble and reducible states. After the CA, FA or PASP application, Cu and Cd were converted from the residual and oxidizable states to the reducible and weak acid soluble states, whose bioavailability in copper tailings were thus enhanced. Besides, the chelating agent incorporation improved the Cu and Cd extraction efficiencies of ryegrass from copper tailings, as manifested by increased root and stem contents of Cu and Cd by 30.29-103.42%, 11.43-74.29%, 2.98-110.98% and 11.11-111.11%, respectively, in comparison with the control group. In the presence of multiple heavy metals, CA, FA or PASP showed selectivity regarding the ryegrass extraction of heavy metals from copper tailings. PCA analysis revealed that the CA-4 and PASP-7 treatment had great remediation potentials against Cu and Cd in copper tailings, respectively, as manifested by increases in Cu and Cd contents in ryegrass by 90.98% and 74.29% compared to the CK group.

Effects of naturally aged microplastics on the distribution and bioavailability of arsenic in soil aggregates and its accumulation in lettuce

Naturally aged microplastics (NAMPs) and arsenic (As) have been reported to coexist in and threaten potentially to soil-plant ecosystem. The research explored the combined toxic effects of NAMPs and As to lettuce (Lactuca sativa L.) growth, and the distribution, accumulation and bioavailability of As in soil aggregates. The As contaminated soil with low, medium and high concentrations (L-As, M-As, H-As) were treated with or without NAMPs, and a total of six treatments. The results displayed that, in comparison to separate treatments of L-As and M-As, the presence of NAMPs increased the total biomass of lettuce grown at these two As concentrations by 68.9 % and 55.4 %, respectively. Simultaneous exposure of NAMPs and L-As or M-As led to a decrease in As content in shoot (0.45-2.17 mg kg-1) and root (5.68-14.66 mg kg-1) of lettuce, indicating an antagonistic effect between them. In contrast, co-exposure to H-As and NAMPs showed synergistic toxicity, and the leaf chlorophyll and nutritional quality of lettuce were also reduced. NAMPs altered the ratio of different soil aggregate fractions and the distribution of bioavailable As within them, which influenced the absorption of As by lettuce. In conclusion, these direct observations assist us in enhancing the comprehend of the As migration and enrichment characteristics in soil-plant system under the influence of NAMPs.

Farmland phytoremediation in bibliometric analysis

Phytoremediation is an environmentally friendly, economical, and sustainable technique for restoring farmland. It can remove heavy metals and organic pollutants from the soil through the implementation of hyperaccumulator plants. In recent years, it has garnered significant interest from academic and industrial sectors. This article screened 368 research papers from the Web of Science core collection database related to farmland phytoremediation and conducted a bibliometric analysis of the domain based on CiteSpace. The paper intuitively demonstrates the most influential countries, the most productive institutions, the most contributing groups of authors, and the primary sources of farmland phytoremediation research domain. The findings additionally indicate that the research hotspots include: (1) mechanisms and principles of phytoremediation, (2) the improvement of restoration efficiency, (3) the economic, ecological, and sustainable development of phytoremediation. The exploration of plants with potential to accumulate heavy metals and produce large amounts of biomass is the research frontier within the field of farmland phytoremediation. Additionally, this bibliometric analysis can help scholars willing to work in this research field by concisely understanding the overall research field and frontiers. With the continuous improvement of phytoremediation and its combination with other remediation technologies, the future of farmland remediation will have a promising prospect.

Combination of Biochar and Trichoderma harzianum Can Improve the Phytoremediation Efficiency of Brassica juncea and the Rhizosphere Micro-Ecology in Cadmium and Arsenic Contaminated Soil

Phytoremediation is an environment-friendly method for toxic elements remediation. The aim of this study was to improve the phytoremediation efficiency of Brassica juncea and the rhizosphere soil micro-ecology in cadmium (Cd) and arsenic (As) contaminated soil. A field experiment was conducted with six treatments, including a control treatment (CK), two treatments with two contents of Trichoderma harzianum (T1: 4.5 g m-2; T2: 9 g m-2), one biochar treatment (B: 750 g m-2), and two combined treatments of T1B and T2B. The results showed Trichoderma harzianum promoted the total chlorophyll and translocation factor of Brassica juncea, while biochar promoted plant biomass compared to CK. T2B treatment showed the best results, which significantly increased Cd accumulation by 187.49-308.92%, and As accumulation by 125.74-221.43%. As a result, the soil's total Cd content was reduced by 19.04% to 49.64% and total As contents by 38.76% to 53.77%. The combined amendment increased the contents of soil available potassium, phosphorus, nitrogen, and organic matter. Meanwhile, both the activity of glutathione and peroxidase enzymes in plants, together with urease and sucrase enzymes in soil, were increased. Firmicutes (dominant bacterial phylum) and Ascomycota (dominant fungal phylum) showed positive and close correlation with soil nutrients and plant potentially toxic elements contents. This study demonstrated that phytoremediation assisted by biochar and Trichoderma harzianum is an effective method of soil remediation and provides a new strategy for enhancing plant remediation efficiency.