Impacts of oxalic acid-activated phosphate rock and root-induced changes on Pb bioavailability in the rhizosphere and its distribution in mung bean plant

Zea mays cultivation, biochar, and arbuscular mycorrhizal fungal inoculation influenced lead immobilization

Plant cultivation can influence the immobilization of heavy metals in soil. However, the roles of soil amendments and microorganisms in crop-based phytoremediation require further exploration. In this study, we evaluated the impact of Zea mays L. cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation on soil lead (Pb) immobilization. Our results indicated that biochar addition resulted in a significant, 42.00%, reduction in AMF colonization. Plant cultivation, AMF inoculation, and biochar addition all contributed to enhanced Pb immobilization, as evidenced by decreased levels of diethylenetriaminepentaacetic acid- and CaCl2-extractable Pb in the soil. Furthermore, soil subjected to plant cultivation with AMF and biochar displayed reduced concentrations of bioavailable Pb. Biochar addition altered the distribution of Pb fractions in the soil, transforming the acid-soluble form into the relatively inert reducible and oxidizable forms. Additionally, biochar, AMF, and their combined use promoted maize growth parameters, including height, stem diameter, shoot and root biomass, and phosphorus uptake, while simultaneously reducing the shoot Pb concentration. These findings suggest a synergistic effect in Pb phytostabilization. In summary, despite the adverse impact of biochar on mycorrhizal growth, cultivating maize with the concurrent use of biochar and AMF emerges as a recommended and effective strategy for Pb phytoremediation.IMPORTANCEHeavy metal contamination in soil is a pressing environmental issue, and phytoremediation has emerged as a sustainable approach for mitigating this problem. This study sheds light on the potential of maize cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation to enhance the immobilization of Pb in contaminated soil. The findings demonstrate that the combined use of biochar and AMF during maize cultivation can significantly improve Pb immobilization and simultaneously enhance maize growth, offering a promising strategy for sustainable and effective Pb phytoremediation practices. This research contributes valuable insights into the field of phytoremediation and its potential to address heavy metal pollution in agricultural soils.

Combined Remediation Effects of Sewage Sludge and Phosphate Fertilizer on Pb-Polluted Soil from a Pb-Acid Battery Plant

Pb soil pollution poses a serious health risk to both the environment and humans. Immobilization is the most common strategy for remediation of heavy metal polluted soil. In this study, municipal sewage sludge was used as an amendment for rehabilitation of Pb-contaminated soils, for agricultural use, near a lead-acid battery factory. The passivation effect was further improved by the addition of phosphate fertilizer. It was found that the leachable Pb content in soils was decreased from 49.6 mg kg-1 to 16.1-36.6 mg kg-1 after remediation of sludge for 45 d at applied dosage of municipal sewage sludge of 4-16 wt%, and further decreased to 14.3-34.3 mg kg-1 upon extension of the remediation period to 180 d. The addition of phosphate fertilizer greatly enhanced the Pb immobilization, with leachable Pb content decreased to 2.0-23.6  mg kg-1 with increasing dosage of phosphate fertilizer in range of 0.8-16 wt% after 180 d remediation. Plant assays showed that the bioavailability of Pb was significantly reduced by the soil remediation, with the content of absorbed Pb in mung bean roots decreased by as much as 87.0%. The decrease in mobility and biotoxicity of the soil Pb is mainly attributed to the speciation transformation of carbonate, Fe-Mn oxides and organic matter bound Pb to residue Pb under the synergism of reduction effect of sludge and acid dissolution and precipitation effect of phosphate fertilizer. This study suggests a new method for remediation of Pb-contaminated soil and utilization of municipal sewage sludge resources.

A New Type of Quantum Fertilizer (Silicon Quantum Dots) Promotes the Growth and Enhances the Antioxidant Defense System in Rice Seedlings by Reprogramming the Nitrogen and Carbon Metabolism

To promote the growth and yield of crops, it is necessary to develop an effective silicon fertilizer. Herein, a new type of 2 nm silicon quantum dot (SiQD) was developed, and the phenotypic, biochemical, and metabolic responses of rice seedlings treated with SiQDs were investigated. The results indicated that the foliar application of SiQDs could significantly improve the growth of rice seedlings by increasing the uptake of nutrient elements and activating the antioxidative defense system. Furthermore, metabolomics revealed that the supply of SiQDs could significantly up-regulate several antioxidative metabolites (oxalic acid, maleic acid, glycine, lysine, and proline) by reprogramming the nitrogen- and carbon-related biological pathways. The findings provide a new strategy for developing an effective and promising quantum fertilizer in agriculture.

Microplastics reduced bioavailability and altered toxicity of phenanthrene to maize (Zea mays L.) through modulating rhizosphere microbial community and maize growth

Due to its large specific surface area and great hydrophobicity, microplastics can adsorb polycyclic aromatic hydrocarbons (PAHs), affecting the bioavailability and the toxicity of PAHs to plants. This study aimed to evaluate the effects of D550 and D250 (with diameters of 550 μm and 250 μm) microplastics on phenanthrene (PHE) removal from soil and PHE accumulation in maize (Zea mays L.). Moreover, the effects of microplastics on rhizosphere microbial community of maize grown in PHE-contaminated soil would also be determined. The results showed that D550 and D250 microplastics decreased the removal of PHE from soil by 6.5% and 2.7% and significantly reduced the accumulation of PHE in maize leaves by 64.9% and 88.5%. Interestingly, D550 microplastics promoted the growth of maize and enhanced the activities of soil protease and alkaline phosphatase, while D250 microplastics significantly inhibited the growth of maize and decreased the activities of soil invertase, alkaline phosphatase and catalase, in comparison with PHE treatment. In addition, microplastics changed the rhizosphere soil microbial community and reduced the relative abundance of PAHs degrading bacteria (Pseudomonas, Massilia, Proteobacteria), which might further inhibit the removal of PHE from soil. This study provided a new perspective for evaluating the role of microplastics on the bioavailability of PHE to plants and revealing the combined toxicity of microplastics and PHE to soil microcosm and plant growth.

Effect of simulated root exudates on the distribution, bioavailability, and fractionation of potentially toxic elements (PTEs) in various particle size fractions of zinc smelting slag: Implication of direct revegetation

Direct revegetation is a promising strategy for phytostabilization of metal smelting slag sites. Slag comes into direct contact with root exudates when slag sites undergo direct revegetation. The slag particle size fractions are considered the key factor influencing the geochemical behaviour of potentially toxic elements (PTEs). However, the effects of root exudates on the geochemical behaviours of PTEs in various slag particle size fractions remain unclear. Here, the effects of simulated root exudates of perennial ryegrass (Lolium perenne) directly revegetated at a zinc smelting slag site on the distribution, bioavailability, and fractionation of PTEs (Cu, Pb, Zn, and Cd) in various slag particle size fractions were investigated. The results showed that PTEs mainly occurred in the <1 mm slag particles; the mass loads of PTEs in the <1 mm slag particles were higher than those in the >1 mm slag particles. The bioavailability of Cu, Zn, and Cd rather than Pb in the slag increased as the particle size decreased. There was a decrease in the <0.25 and 1-2 mm slag particles and an increase in the 0.25-0.5, 0.5-1, and >2 mm slag particles in the presence of root exudates. Root exudates enhanced the transformation of acid-soluble PTEs into other more stable fractions in various slag particle size fractions. Root exudates enhanced the aggregation of slag particles associated with the migration of PTEs, causing differences in the geochemical behaviour of PTEs in various slag particle size fractions. These findings are beneficial for understanding the geochemical behaviour of PTEs in metal smelting slags undergoing direct revegetation and provide an important basis for the guidance of environmental risk management of the revegetated metal smelting slag sites.

Response of growth and Pb accumulation characteristics of plants with intercropping Arabis alpina-Zea mays to exogenous oxalic acid

In order to study the effects of oxalic acids on plant growth and Pb accumulation in different parts of the plants of intercropping Arabis alpina and Zea mays, pot experiment was conducted to investigate the changes of oxalic acid contents of the plants and Pb accumulation through exogenous oxalic acid addition (0, 5, 25 and 50 mmol kg-1). The results showed the root biomass of intercropped A. alpina and total biomass of Z. mays increased by 3.22 folds and 2.97 folds with 5 mmol kg-1 oxalic acid treatment. The oxalic acid contents of shoots and root secretions decreased by 86.5% and 44.3%, respectively. The BCF (bio-accumulation factor) and TF (translocation factor) of intercropping A. alpina reduced under 25 - 50 mmol kg-1 oxalic acid treatments. There were relationships between exogenous oxalic acid treatment concentrations and oxalic acid contents of A. alpina shoots, Z. mays root secretions. The Pb contents of shoots of A. alpina and Z. mays were related to exogenous oxalic acid additions and oxalic acid contents of shoots. In general, 5 mmol kg-1 oxalic acid treatment, that can improve plant growth of intercropped A. alpina and Z. mays, which Pb translocation and accumulation of A. alpina were promoted, whereas Pb accumulation of A. alpina was inhibited with 25 - 50 mmol kg-1 concentrations addition. This study will provide a basis for promoting the application of phytoremediation techniques and efficient crop production in heavy metal contaminated areas.

Plant-soil feedback regulates the trade-off between phosphorus acquisition pathways in Pinus elliottii

Plant-soil feedback (PSF) is conventionally characterized by plant biomass growth, yet it remains unclear how PSF affects plant nutrient acquisition strategies (e.g., nutrient absorption and nutrient resorption) associated with plant growth, particularly under changing soil environments. A greenhouse experiment was performed with seedlings of Pinus elliottii Englem and conditioned soils of monoculture plantations (P. elliottii and Cunninghamia lanceolata Hook). Soil sterilization was designed to test plant phosphorus (P) acquisition strategy with and without native soil fungal communities. Soils from P. elliottii and C. lanceolata plantations were used to explore the specific soil legacy effects on two different P acquisition pathways (absorption and resorption). Phosphorus addition was also applied to examine the separate and combined effects of soil abiotic factors and soil fungal factors on P acquisition pathways. Due to diminished mycorrhizal symbiosis, PSF prompted plants to increasingly rely on P resorption under soil sterilization. In contrast, P absorption was employed preferentially in the heterospecific soil, where species-specific pathogenic fungi could not affect P absorption. Higher soil P availability diluted the effects of soil fungal factors on the trade-off between the two P acquisition pathways in terms of the absolute PSF. Moreover, P addition plays a limited role in terms of the relative PSF and does not affect the direction and strength of relative PSF. Our results reveal the role of PSF in regulating plant P acquisition pathways and highlight the interaction between mycorrhizal and pathogenic fungi as the underlying mechanism of PSF.

Health risk assessment and bioaccumulation of potentially toxic metals from water, soil, and forages near coal mines of district Chakwal, Punjab, Pakistan

Water, forages, and soil contamination with potentially toxic metals (PTMs) through anthropogenic activities has become a significant environmental concern. It is crucial to find out the level of PTMs in water, soil, and forages near industrial areas. The PTMs enter the body of living organisms through these sources and have become a potential risk for humans and animals. Therefore, the present study aims at the health risk assessment of PTMs and their accumulation in soil, water, and forages of three tehsils (Kallar Kahar, Choa Saidan Shah, and Chakwal) in district Chakwal. Samples of wastewater, soil, and forages were collected from various sites of district Chakwal. PTMs detected in the present study were cadmium (Cd), chromium (Cr), lead (Pb), zinc (Zn), cobalt (Co), copper (Cu), and nickel (Ni), and their levels were measured through atomic absorption spectrophotometer (AAs GF95 graphite furnace auto sampler). Pollution load index (PLI), bio concentration factor (BCF), soil enrichment factors (EF), daily intake value (DIM), and health risk index (HRI) in sheep, cow, and buffalo were also analyzed. The results revealed that the mean concentration (mg/L) of Cd (0.72-0.91 mg/L), Cr (1.84-2.23 mg/L), Pb (0.95-3.22 mg/L), Co (0.74-2.93 mg/L), Cu (0.84-1.96 mg/L), and Ni (1.39-4.39 mg/L) in wastewater samples was higher than permissible limits set by WHO, NEQS, WWF, USEPA, and Pakistan in all three tehsils of district Chakwal. Similarly, in soil samples, concentrations of Cd (1.21-1.95 mg/kg), Cr (38.1-56.4 mg/kg), and Ni (28.3-55.9 mg/kg) were higher than their respective threshold values. The mean concentration of PTMs in forage samples (Parthenium hysterophorus, Mentha spicata, Justicia adhatoda, Calotropis procera, Xanthium strumarium, Amaranthaceae sp.) showed that maximum values of Cd (5.35-7.55 mg/kg), Cr (5.47-7.51 mg/kg), Pb (30-36 mg/kg), and Ni (12.6-57.5 mg/kg) were beyond their safe limit set for forages. PLI, BCF, and EF were > 1.0 for almost all the PTMs. The DIM and HRI for sheep were less than < 1.0 but for cows and buffalo were > 1.0. The current study showed that soil, water, and forages near coal mines area are contaminated with PTMs which enter the food chain and pose significant harm to humans and animals. In order to prevent their dangerous concentration in the food chain, regular assessment of PTMs present in soil, forages, irrigating water, and food is recommended.

Assessment of potential ecological risk based on the vertical characteristics of potential toxic elements in sediments from a high-density cage culture reservoir in China

The pollution of sediments around Lu Ban Island is a serious environmental issue that is threatening human health. The concentration of As, Cd, Cu, Cr, Hg, Ni, Pb, and Zn at 73 layer points were investigated, vertical distribution characteristics, correlation among potential toxic elements and potential ecological risks of sediments at different depth were analyzed. The following results were obtained, (1) the hypothesis that there was a linear relationship between concentration of potential toxic elements and the reciprocal of deep was reasonable. Based on hypothesis, the ultimate value of concentration by making depth go to infinity was regarded as the background concentration. The background concentration of As, Cd, Cu, Cr, Hg, Ni, Pb, and Zn are respectively 4.94 mg/kg, 0.20 mg/kg, 15.48 mg/kg, 58.41 mg/kg, 0.062 mg/kg, 26.96 mg/kg, 20.29 mg/kg, and 53.31 mg/kg. (2) But correlation between Ni and As was relatively weak, high degree of correlation among other potential toxic elements were found. Based on their correlation, eight potential toxic elements were classified into three groups. First group included Ni and Cr, mainly releasing by coal burning; Cu, Pb, Zn, Hg, and Cd were grouped together, possibly due to their shared source of fish cage culture; Arsenic with relatively weak correlation with other potential toxic elements was classified as a separate class, which was usually one important mineral resource associated with phosphate. (3) Potential ecological risk index (PERI) of sediment above - 0.40 m belonged to moderate risk, the PERI of sediment in - 0.10 m, - 0.20 m, and - 0.40 m were 289.06, 254.33, and 201.44, respectively. Sediment below - 0.40 m belonged to low risk with average PERI value 112.82, with no significant changes in PERI values. The order of contribution to PERI was Hg > Cd > As > Cu > Pb > Ni > Cr > Zn. (4) According to result of cluster analysis and potential ecological risk, the potential ecological risk of sediment above - 0.40 m mainly contributed by potential toxic elements of Cu, Cd, Hg, Pb, and Zn sharing source of fish cage culture.

Rhizosphere effect on the relationship between dissolved organic matter and functional genes in contaminated soil

Arsenic contamination in a mining area is a potential threat to the local population. In the context of one-health, biological pollution in contaminated soil should be known and understandable. This study was conducted to clarify the effects of amendments on arsenic species and potential threat factors (e.g., arsenic-related genes (AMGs), antibiotic resistance genes (ARGs) and heavy-metal resistance genes (MRGs)). Ten groups (control (CK), T1, T2, T3, T4, T5, T6, T7, T8, and T9) were set up by adding different ratio of organic fertilizer, biochar, hydroxyapatite and plant ash. The maize crop was grown in each treatment. Compared with CK, the bioavailability of arsenic was reduced by 16.2%-71.8% in the rhizosphere soil treatments, and 22.4%-69.2% in the bulk soil treatments, except for T8. The component 2 (C2), component 3 (C3) and component 5 (C5) of dissolved organic matter (DOM) increased by 22.6%-72.6%, 16.8%-38.1%, 18.4%-37.1%, respectively, relative to CK in rhizosphere soil. A total of 17 AMGs, 713 AGRs and 492 MRGs were detected in remediated soil. The humidification of DOM might directly correlate with MRGs in both soils, while it was influenced directly on ARGs in bulk soil. This may be caused by the rhizosphere effect, which affects the interaction between microbial functional genes and DOM. These findings provide a theoretical basis for regulating soil ecosystem function from the perspective of arsenic contaminated soil.

Forecasting contamination in an ecosystem based on a network model

This paper aims to predict heavy metal pollution based on ecological factors with a new approach, using artificial neural networks (ANNs), by significantly removing typical obstacles like time-consuming laboratory procedures and high implementation costs. Pollution prediction is crucial for the safety of all living things, for sustainable development, and for policymakers to make the right decisions. This study focuses on predicting heavy metal contamination in an ecosystem at a significantly lower cost because pollution assessment still primarily relies on conventional methods, which are recognized to have disadvantages. To accomplish this, the data collected for 800 plant and soil materials have been utilized in the production of an ANN. This research is the first to use an ANN to predict pollution very accurately and has found the network models to be very suitable systemic tools for modelling in pollution data analysis. The findings appear are promising to be very illuminating and pioneering for scientists, conservationists, and governments to swiftly and optimally develop their appropriate work programs to leave a functioning ecosystem for all living things. It has been observed that the relative errors calculated for each of the polluting heavy metals for training, testing, and holdout data are significantly low.

Effects of mowing on Pb accumulation and transport in Cynodon dactylon (L.) Pers

Bermudagrass is a perennial herb with the potential to remediate Pb pollution in soils, and it has mechanical resistance to shearing. However, the effects of mowing on Pb absorption and accumulation in bermudagrass are still unclear. In this study, we investigated the effects of different quantities (0, 1, 2, 4 applications) of mowing treatments under 200 mg L^-1 Pb application on Pb accumulation and transport in bermudagrass and explored the related mechanisms. Compared to the Pb treatment, all of the mowing treatments greatly decreased root Pb concentration/accumulation, significantly enhanced Pb concentrations/accumulations in stubble stems and stubble leaves, and ultimately promoted Pb enrichment and transport. Of the treatments in this study, two applications of mowing best promoted Pb enrichment, and four applications of mowing best promoted Pb transport efficiency. Furthermore, mowing mediated the microdistribution and physiological patterns of Pb in bermudagrass and affected the Pb transport by changing the subcellar distribution patterns and chemical forms of Pb in various tissues. Additionally, mowing promoted the transport of all mineral elements and showed a synergistic relationship with Pb absorption and transport. The change in mineral element metabolism patterns may be an important reason why mowing promoted Pb accumulation in bermudagrass. Our study provides the first comprehensive evidence regarding mowing facilitating the absorption, accumulation and transport of Pb in bermudagrass. Moderate mowing may be an effective strategy to assist in soil Pb remediation using bermudagrass.

Phosphorous fertilization alleviates shading stress by regulating leaf photosynthesis and the antioxidant system in mung bean (Vigna radiata L.)

Shading can limit photosynthesis and plant growth. Understanding how phosphorus (P) application mitigates the effects of shading stress on morphology and physiology of mung beans (Vigna radiata L.) is of great significance for the establishment of efficient planting structures and optimizing P-use management. The effects of various light environments (non-shading stress, S0; low light stress, S1; severe shading stress, S2) on the growth of two mung bean cultivars (Xilv1 and Yulv1) and the role of P application (0 kg ha^-1, P0; 90 kg ha^-1, P1; 150 kg ha^-1, P2) in such responses were investigated in a field experiment. Our results demonstrated that shading decreased the dry matter accumulation of mung bean markedly by limiting photosynthesis capacity and disrupting agronomic traits. For the leaf areas of the two cultivars, chlorophyll a+b, the net photosynthetic and electron transport rates were increased by 16.8%, 20.0%, 15.5%, and 12.5% under P1 treatment, and by 32.4%, 40.3%, 16.3% and 12.8% under P2 treatment, respectively, when compared to those for the non-fertilized plants under shading stress. These responses resulted in increased light capture and weak light utilization. Moreover, the activities of superoxide dismutase and peroxidase were enhanced by 20.9% and 43.7%, respectively; malondialdehyde and superoxide anion contents were reduced by 18.6% and 14.1%, respectively, under P application. These findings suggest that P application moderately mitigates the damage caused by shading stress and enhances tolerance by regulating mung bean growth. In addition, Xilv1 was more sensitive to P under shading stress than Yulv1.

Rhizosphere activity induced mobilization of heavy metals immobilized by combined amendments in a typical lead/zinc smelter-contaminated soil

The persistence of the stabilization effect of amendments on heavy metals (HMs) is of great concern when they are used for remediating HM-contaminated soil. Here, pot experiments were conducted to investigate the effects of two consecutive seasons of vegetable cultivation on the mobilization of HMs (Cu, Pb, Zn, and Cd) immobilized by different application ratios (0, 20, 40, and 80 g kg^-1, labelled C0, C2, C4, and C8) of a combined amendments (lime: sepiolite: biochar: humic acid = 2:2:1:1). The results showed that HM bioavailability decreased with increasing application ratios of the combined amendments in control (CK) treatments. The DOC contents, HM bioavailability, and HM contents in the leaves of vegetables increased, but the pH decreased during two consecutive seasons of vegetable cultivation; however, the HM bioavailability in the C2, C4, and C8 treatments was lower than that in the C0 treatments with vegetables. Catalase, urease, alkaline phosphatase, and dehydrogenase activities in the combined amendment treatments with and without vegetables were decreased compared to those in the C0 treatments. The relative abundances of the dominant bacterial phyla in the different treatments were Actinobacteria > Proteobacteria > Chloroflexi > Acidobacteria > Gemmatimonadetes > Bacteroidetes for the first season and Proteobacteria > Actinobacteria > Chloroflexi > Acidobacteria > Bacteroidetes > Gemmatimonadetes for the second season. Correlations showed that the pH and DOM properties during two consecutive seasons of vegetable cultivation were important factors influencing HM bioavailability, enzyme activity, and bacterial community composition. The bacterial community composition shift indirectly influenced the mobilization of HMs immobilized by the combined amendments. Thus, rhizosphere activity induced the mobilization of HMs immobilized by combined amendments during two consecutive seasons of vegetable cultivation.

Oxalate in Plants: Metabolism, Function, Regulation, and Application

Characterized by strong acidity, chelating ability, and reducing ability, oxalic acid, a low molecular weight dicarboxylic organic acid, plays important roles in the regulation of plant growth and development, the response to both biotic and abiotic stresses such as plant defense and heavy metals detoxification, and food quality. The metabolism of oxalic acid has been well-studied in microorganisms, fungi, and animals but remains less understood in plants. However, excessive accumulation of oxalic acid is detrimental to plants. Therefore, the level of oxalic acid has to be precisely controlled in plant tissues. In this review, we summarize the metabolism, function, and regulation of oxalic acid in plants, and we discuss solutions such as agricultural practices and plant biotechnology to manipulate oxalic acid metabolism to regulate plant responses to both external stimuli and internal developmental cues.

Phytoremediation potential, antioxidant response, photosynthetic behavior and rhizosphere bacterial community adaptation of tobacco (Nicotiana tabacum L.) in a bisphenol A-contaminated soil

Bisphenol A (BPA) is an emerging organic pollutant, widely distributed and frequently detected in soil in recent years. BPA toxicity is a problem that needs to be solved in terms of both human health and agricultural production. Up to now, the toxic effect of BPA and its mechanism of action on plants, as well as the possibility of using plants to remediate BPA-contaminated soil, remain to be explored. In this study, six treatment groups were set up to evaluate the effects of different concentrations of BPA on the germination and growth of tobacco (Nicotiana tabacum L.) by medium experiments. Furthermore, the representative indexes of photosynthetic and antioxidant system were determined. Meanwhile, tobacco seedlings were cultivated in soil to further explore the effects of BPA on rhizosphere soil enzyme activity and bacterial community structure with or without 100 mg/kg BPA exposure. The enhancement of BPA removal efficiency from soil by phytoremediation using tobacco plants would also be estimated. Our results showed that high doses of BPA in solid medium remarkably inhibited tobacco seedling growth, and its toxicology effect was positively correlated with BPA concentration, while lower BPA exposure (< 20 mg/L) had little limitation on tobacco growth and induced hormesis effect, which was reflected mainly in the increase of root length. In pot experiments, the reducing of chlorophyll content (36.4%) and net photosynthetic rate (41.2%) meant the inhibition of tobacco photosynthetic process due to high concentration of BPA exposure (100 mg/kg) in soil. The increase of H2O2 and O2- content suggested that BPA could destroy the balance of reactive oxygen species (ROS) in plants. However, tobacco plants still presented a high removal efficiency of BPA at the concentration of 100 mg/kg in soil, which could reach to 80% within 30 days. Furthermore, it was indicated that tobacco cultivation changed the structure of rhizosphere soil bacterial communities and the relative abundance of some valuable strains, including Proteobacteria, Acidobacteria and other strains, which might be participated in the BPA removal process. In addition, the tobacco-soil microbial system had the potential to reverse the negative effects caused by BPA through stimulating microorganism associated with soil nutrient cycling. In summary, tobacco is a competitive plant in phytoremediation of BPA-contaminated soil, though the growth of tobacco could be inhibited at high concentration of BPA. Moreover, tobacco might promote the removal efficiency of BPA by regulating the rhizosphere bacteria communities.

Aspergillus niger-mediated release of phosphates from fish bone char reduces Pb phytoavailability in Pb-acid batteries polluted soil, and accumulation in fenugreek

Soil receiving discharges from Pb-acid batteries dismantling and restoring units (PBS) can have a high concentration of phytoavailable Pb. Reducing Pb phytoavailability in PBS can decline Pb uptake in food crops and minimize the risks to humans and the environment. This pot study aimed to reduce the concentration of phytoavailable Pb in PBS through Aspergillus niger (A. niger)-mediated release of PO₄^3- from fish bone [Apatite II (APII)] products. The PBS (Pb = 639 mg kg^-1 soil) was amended with APII powder (APII-P), APII char (APII-C), and A. niger inoculum as separate doses, and combining A. niger with APII-P (APII-P + A. niger) and APII-C (APII-C + A. niger). The effects of these treatments on reducing the phytoavailability of Pb in PBS and its uptake in fenugreek were examined. Additionally, enzymatic activities and microbial biomass carbon (MBC) in the PBS and the indices of plant physiology, nutrition, and antioxidant defense machinery were scoped. Results revealed that the APII-C + A. niger treatment was the most efficient one. Compared to the control, it significantly reduced the Pb phytoavailability (DTPA-extractable Pb fraction) in soil and its uptake in plant shoots, roots, and grain, up to 61%, 83%, 74%, and 92%. The grain produced under APII-C + A. niger were safe for human consumption as Pb concentration in grain was 4.01 mg kg^-1 DW, remaining within the permissible limit set by WHO/FAO (2007). The APII-C + A. niger treatment also improved soil pH, EC, CEC, MBC, available P content and enzymatic activities, and the fenugreek quality parameters. A. niger played a significant role in solubilizing PO₄^3- from APII-C, which reacted with Pb and formed insoluble Pb-phosphates, thereby reducing Pb phytoavailability in PBS and its uptake in plants. This study suggests APII-C + A. niger can remediate Pb-polluted soils via reducing Pb phytoavailability in them.

Microbial induced phosphate precipitation accelerate lead mineralization to alleviate nucleotide metabolism inhibition and alter Penicillium oxalicum's adaptive cellular machinery

Microbial-induced phosphate (P) precipitation (MIPP) based on P-solubilizing microorganisms (PSM) is regarded as a promising approach to bioimmobilize environmental lead (Pb). Nevertheless, the underlying changes of Pb²⁺ biotoxicity in PSM during MIPP process were rarely discussed. The current study explored the Pb²⁺ immobilization and metabolic changes in PSM Penicillium oxalicum postexposure to Pb²⁺ and/or tricalcium phosphate (TCP). TCP addition significantly increased soluble P concentrations, accelerated extracellular Pb mineralization, and improved antioxidative enzyme activities in P. oxalicum during MIPP process. Secondary Pb²⁺ biomineralization products were measured as hydroxypyromorphite [Pb₁₀(PO₄)₆(OH)₂]. Using untargeted metabolomic and transcriptomics, we found that Pb²⁺ exposure stimulated the membrane integrity deterioration and nucleotide metabolism obstruction of P. oxalicum. Correspondingly, P. oxalicum could produce higher levels of gamma-aminobutyric acid (GABA) to enhance the adaptive cellular machineries under Pb²⁺ stress. While the MIPP process improved extracellular Pb²⁺ mineralization, consequently alleviating the nucleotide metabolism inhibition and membrane deterioration. Multi-omics results suggested that GABA degradation pathway was stimulated for arginine biosynthesis and TCA cycle after Pb²⁺ mineralization. These results provided new biomolecular information underlying the Pb²⁺ exposure biotoxicities to microorganisms in MIPP before the application of this approach in environmental Pb²⁺ remediation.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Foliar uptake, accumulation, and distribution of cadmium in rice (Oryza sativa L.) at different stages in wet deposition conditions

Atmospheric deposition of cadmium (Cd) in rice (Oryza sativa L.) has become a major global concern. Foliar uptake allows vegetables to accumulate heavy metals from the atmosphere, but this has rarely been studied in rice. Therefore, this study investigated the Cd accumulation in rice growing at different exposure periods (the tillering, booting, heading, and maturity stages) under a wet deposition of CdCl₂·2.5H₂O solution through pot experiments. The Cd concentrations in leaves, roots, husk, brown rice, and leaf structures were analyzed to explore foliar uptake, accumulation, and distribution of Cd in rice tissues at different growth stages. The results showed that wet deposited Cd can be absorbed on the rice leaf surface and remains on the leaves for a long time. The sequence of Cd accumulation in rice tissues was: leaves > brown rice > husk > roots, with leaves accounting for greater than 71.78% of the total accumulation. The accumulation of wet deposited Cd in leaves, husk, and brown rice had large temporal variations between the four typical stages. There was no significant variations in Cd content in roots between different growth stages. Correspondingly, the foliar uptake of Cd was rarely transported from the leaves via the phloem to roots. Conversely, the foliar uptake of Cd was transported upwards to grains. The accumulation of Cd fluctuated with each growth stage, initially increasing and then decreasing at the heading stage and finally reaching a peak at the maturity stage. The highest total accumulation of Cd in both the high and low wet deposition conditions occurred at maturity, resulting in 15.53 and 11.23 μg plant^-1, respectively. These results provide theoretical support for further research into identifying efficient foliar control measures to reduce Cd accumulation and maintain food safety.

Inoculation with the pH Lowering Plant Growth Promoting Bacterium Bacillus sp. ZV6 Enhances Ni Phytoextraction by Salix alba from a Ni-Polluted Soil Receiving Effluents from Ni Electroplating Industry

Soil contamination with Ni poses serious ecological risks to the environment. Several members of the Salix genus have the ability to accumulate high concentrations of Ni in their aerial parts, and thus can be used for the remediation of Ni-contaminated soils. Interestingly, the efficacy of Ni phytoextraction by Salix may be improved by the acidification of rhizosphere with rhizosphere acidifying bacterial strains. Therefore, the aim of this study was to assess the efficacy of bacterial strain Bacillus sp. ZV6 in the presence of animal manure (AM) and leaf manure (LM) for enhancing the bioavailability of Ni in the rhizosphere of Salix alba via reducing the pH of rhizosphere and resultantly, enhanced phytoextraction of Ni. Inoculation of Ni-contaminated soil with strain ZV6 significantly increased plant growth as well as Ni uptake by alba. It was found that the addition of AM and LM resulted into a significant increase in plant growth and Ni uptake by alba in Ni-contaminated soil inoculated with ZV6 stain. However, the highest improvements in diethylene triamine penta-acetic acid (DTPA) extractable Ni (10%), Ni removal from soil (54%), Ni bioconcentration factor (26%) and Ni translocation factor (13%) were detected in the soil inoculated with ZV6 along with the addition of LM, compared to control. Similarly, the enhancements in microbial biomass (92%), bacterial count (348%), organic carbon (organic C) (57%) and various enzymatic activities such as urease (56%), dehydrogenase (32%), β-glucosidase (53%), peroxidase (26%) and acid phosphatase (38%) were also significantly higher in the soil inoculated with ZV6 along with the addition of LM. The findings of this study suggest that the inoculation of Ni-contaminated soils with rhizosphere acidifying bacteria can effectively improve Ni phytoextraction and, in parallel, enhance soil health.

Tobacco-associated with Methylophilus sp. FP-6 enhances phytoremediation of benzophenone-3 through regulating soil microbial community, increasing photosynthetic capacity and maintaining redox homeostasis of plant

Benzophenone-3 (BP-3) has attracted widespread attention due to its large accumulation in the environment and its potential toxicity effects to human. This study aimed to investigate the effects of the combined application of tobacco and Methylophilus sp. strain FP-6 with both plant growth promoting (PGP) traits and BP-3 degradation function on BP-3 remediation in soil. The results showed that about 79.18% of BP-3 was removed from the soil after 30 days of plant culture inoculated with the FP-6 strain, which was significantly higher than the plant-alone treatment. Simultaneously, inoculation with strain FP-6 significantly improved growth performance, biomass production, antioxidant levels, osmoregulation substance, photosynthetic capacity and chlorophyll accumulation in tobacco. Moreover, the application of FP-6 shifted the bacterial community, and enhanced the abundance of BP-3-degrading or soil nutrient cycling-affecting bacteria (e.g., Chloroflexi, Bryobacter, MND1 and Myxococcales), which might be valuable for the promotion of plant growth and degradation of BP-3 in the soil. The results from this study gave first insights into the enhancement of BP-3 removal efficiency from soil by phytoremediation assisted with bacteria possessing both PGP properties and BP-3 degradation function. The role of soil bacterial community in this remediation process was also discussed.

The Synergistic Effect of Biochar-Combined Activated Phosphate Rock Treatments in Typical Vegetables in Tropical Sandy Soil: Results from Nutrition Supply and the Immobilization of Toxic Metals

Sandy soils in tropical areas are more vulnerable to potential toxic elements as a result of their low nutrition. The composite addition of biochar and phosphate material is considered a promising method of immobilizing toxic metals in sandy soils, but the synergistic effects of this process still need to be further explored, especially in typical tropical vegetables. In this study, a pot experiment was conducted to evaluate the agronomic and toxic metal-immobilization effects of single amendments (phosphate rock, activated phosphate rock, and biochar) and combined amendments, including biochar mixed with phosphate rock (BCPR) and biochar mixed with activated phosphate rock (BCAPR), on vegetables grown in tropical sandy soil. Among these amendments, the composite amendment BCAPR was the most effective for increasing Ca, Mg, and P uptake based on water spinach (Ipomoea aquatica L.) and pepper (Capsicum annuum L.), showing increased ratios of 22.5%, 146.0%, and 136.0%, respectively. The SEM-EDS and FTIR analysis verified that the activation process induced by humic acid resulted in the complexation and chelation of the elements P, Ca, and Mg into bioavailable forms. Furthermore, the retention of available nutrition elements was enhanced due to the strong adsorption capacity of the biochar. In terms of cadmium (Cd) and lead (Pb) passivation, the formation of insoluble mineral precipitates reduced the mobility of these metals within the BCAPR treatments, with the maximum level of extractable Cd (86.6%) and Pb (39.2%) reduction being observed in the tropical sandy soil. These results explore the use of sustainable novel cost-effective and highly efficient bi-functional mineral-based soil amendments for metal passivation and plant protection.

Migration and Transformation of Multiple Heavy Metals in the Soil–Plant System of E-Waste Dismantling Site

E-waste generation has become a major environmental issue worldwide. Heavy metals (HMs) in e-waste can be released during inappropriate recycling processes. While their pollution characteristics have been studied, the migration and transformation of different multi-metal fractions in soil–plant system of e-waste dismantling sites is still unclear. In this study, pot experiments were conducted to investigate the migration and transformation of different multi-metal fractions (Cu, Pb, Zn and Al) in the soil–plant system using two Chinese cabbage cultivars (heavy metals low-accumulated variety of Z1 and non-low-accumulated Z2) treated with or without biochar. The result showed that the acid-soluble fraction of Cu, Pb, Zn and Al in soil decreased by 5.5%, 55.7%, 7.8% and 21.3%, but the residual fraction (ResF) of them increased by 48.5%, 1.8%, 30.9% and 43.1%, respectively, when treated with biochar and plants, compared to that of the blank soil (CK). In addition, Pb mainly existed as a reducible fraction, whereas Cu existed as an oxidisable fraction. Biochar combined with plants significantly increased the ResF of multi-metals, which reduced the migration ability of Pb among all other metals. The relative amount of labelled ¹³C in the soil of Z1 was higher than that of Z2 (25.4 fold); among them, the Gram-negative bacteria (18-1ω9c, 18-1ω7c) and fungi (18-2ω6c) were significantly labelled in the Z1-treated soil, and have high correlation with HM migration and transformation. In addition, Gemmatimonadete were significantly positive in the acid-soluble fraction of HMs, whereas Ascomycota mostly contributed to the immobilisation of HMs. Therefore, the distribution of fractions rather than the heavy metal type plays an important role in the HM migration in the soil–plant system of e-waste dismantling sites.

Enhanced Lead (Pb) immobilization in red soil by phosphate solubilizing fungi associated with tricalcium phosphate influencing microbial community composition and Pb translocation in Lactuca sativa L

Phosphate (P) minerals and phosphate solubilizing fungi (PSF) play essential roles in lead (Pb) immobilization, but their roles in driving Pb bioavailability and ecological risks in red soil remains poorly understood. In this study, the inoculation of P. oxalicum and TCP successfully enhanced available P (AP) and urease concentrations in artificially Pb contaminated red soil. Combined P. oxalicum and TCP inoculation significantly reduced Pb bioavailability, bioaccessibility, leachability and mobility by increasing soil AP concentration and forming stable Pb-P compounds during the 21-day experiment. Soil AP and Pb bioavailability play an important role in shifting soil microbial communities induced by co-occurrence of P. oxalicum and TCP. Combined P. oxalicum and TCP could notably promote the relative abundances of predominant soil genus to enhance microbial resistance to soil Pb. Likewise, coexistence of P. oxalicum and TCP showed the highest biomass and better branch root development of Pb-stressed in lettuces (Lactuca sativa L.) in pot experiment, and significantly reduced up to 88.1% of Pb translocation from soil to root over control. The reductions of Pb translocation and accumulation in root in P. oxalicum + TCP treatment could enhance the oxidase activities and alleviate the oxidative damages of H2O2 and O2.- in shoot tissues. Our study provided strong evidence to use PSF associated with P materials for the stable and eco-friendly soil Pb remediation.

Effect of different direct revegetation strategies on the mobility of heavy metals in artificial zinc smelting waste slag: Implications for phytoremediation

The establishment of vegetation cover is an important strategy to reduce wind and water erosion at metal smelting waste slag sites. However, the mobility of heavy metals in waste slag-vegetation-leachate systems after the application of revegetation strategies is still unclear. Large microcosm experiments were conducted for revegetation of waste slag for 98 d using combined amendments, i.e., phosphate rock and an organic waste coming from the anaerobic digestion of pig manure (named as biogas residue), and by single- and co-planted perennial ryegrass (Lolium perenne L.) and Trifolium repens (T. repens). The results showed that the application of biogas residue slightly increased the concentrations of Zn and Cd in the leachates; however, the establishment of plants could avoid the excessive leaching of heavy metals coming from the biogas residue. The bioavailability of Cu, Zn, and Cd slightly increased, but Pb bioavailability significantly decreased regardless of single- or co-planting patterns. Additionally, the bioavailability of Cu, Zn, and Cd in the waste slag revegetated with perennial ryegrass was lower than that in T. repens under the single-planting pattern. The change in the heavy metals bioavailability under different revegetation strategies was mainly due to the root-induced change in the pH and speciation of heavy metals in the waste slag. The application of biogas residue and phosphate rock tends to the immobilization of Pb. Heavy metals mainly accumulated in the underground parts of the two herbs, and the heavy metal contents in the underground parts of perennial ryegrass were higher than those in T. repens regardless of single- or co-planting patterns. The heavy metals accumulated in T. repens were lower than those in perennial ryegrass in the single-planting pattern. The bioaccumulation and transportation factors of the two herbs were extremely low. Thus, the two herbs are potential candidates for phytostabilization of zinc smelting waste slag sites.

Calcite in combination with olive pulp biochar reduces Ni mobility in soil and its distribution in chili plant

The presence of Ni above the permissible limit in agriculture soils poses negative effects on soil health, crop quality, and crop productivity. Surprisingly, the usage of various organic and inorganic amendments can reduce Ni mobility in the soil and its distribution in the crops. A pot experiment was conducted to elucidate the effects of olive pulp biochar (BR), calcite (CAL), and wheat straw (WS), as sole amendments and their mixtures of 50:50 ratio, added to Ni polluted soil on Ni mobility in the soil, Ni immobilization index (Ni - IMi), soil enzymatic activities, Ni distribution in parts of chili plant, Ni translocation factor and bioaccumulation factor in fruit, plant growth parameters and oxidative stress encountered by the plants. Outcomes of this pot experiment revealed that amendments raised soil pH, improved soil enzymatic activities, values of Ni - IMi, while significantly reduced bioavailable Ni fraction in the post-harvest soil. However, the highest activities of acid phosphatase, urease, catalase, and dehydrogenase by 50, 70, 239, and 111%, respectively, improvement in Ni - IMi up to 60% while 60% reduction in the bioavailable Ni fraction was observed in BR + CAL treatment, compared to control was noted. Among all amendments, the top most reduction in Ni concentrations in shoots, roots, fruit, Translocation Factor (TF), and Bioaccumulation Factor (BAF) values of fruit by 72%, 36%, 86%, 72%, and 86%, in BR + CAL treatment, compared to control. Moreover, the plants growing on BR + CAL amended Ni contaminated soil showed the topmost improvement in plant phonological parameters while encountered the least oxidative stress. Such findings refer to the prospective usage of BR + CAL at 50:50 ratio than BR, CAL, WS alone, and BR + WS as well as WS + CAL for reducing Ni mobility in the soil, improving Ni - IMi, soil enzymatic activities, plant phonological and oxidative stress while reducing Ni distribution in plant parts. Novelty statementIn this experiment, it was hypothesized that amending Ni polluted soil with olive pulp biochar (BR), CAL, and WS as alone soil amendments and their combinations at 50:50 ratios can reduce Ni bioavailability in soil, Ni distribution in chili plant and oxidative stress encountered by the plants. Moreover, these amendments may improve, soil enzymatic activities, Ni immobilization index, plant phenological traits. Therefore, it was aimed to undertake useful scientific planning and research, to restore and rehabilitate the dwellings, biological resources and to minimize the sufferings of the peoples in nutrient-poor Ni contaminated soils, by improving soil health and chili productivity.

Gibberellic acid and urease inhibitor optimize nitrogen uptake and yield of maize at varying nitrogen levels under changing climate

Worldwide, nitrogen (N) deficiency is the main yield limiting factor owing to its losses via leaching and volatilization. Urease inhibitors slow down urea hydrolysis in soil by inhibiting urease enzyme activities whereas gibberellic acid is growth regulator. That is why, we evaluated the role of urease inhibitor [N-(n-butyl)thiophosphorictriamide (NBPT)] and gibberellic acid (GA₃) in improving nitrogen uptake and yield of maize under different N levels (120 and 150 kg ha^-1) along with control. Both N levels alone and in combination with GA₃ and NBPT significantly increased yield and yield components of maize over control. In addition, 150 kg N ha^-1 + NBPT + GA₃ produced highest biological, grain, and stover yields, 1000 grain weight, plant height, and N uptake exhibiting 33.15%, 56.46%, 27.56%, 19.56%, 23.24%, and 78% increase over 150 kg N ha^-1, respectively. The sole use of gibberellic acid or NBPT with each level of N also improved the yield and yield components of maize compared to sole N application and control. Furthermore, application of 120 kg N ha^-1 along with NBPT and GA₃ performed at par to 150 kg N ha^-1 + NBPT + GA₃ but it was superior than sole applied 150 kg N ha^-1 for all the studied traits. These results imply that application of GA₃ and/or NBPT can reduce dependence on urea and improve the yield and N uptake in maize by slowing urea hydrolysis in calcareous soils and shall be practiced.

Understanding the microstructure, mineralogical and adsorption characteristics of guar gum blended soil as a liner material

Guar gum blended soil (GGBS) offers potentially advantageous engineering characteristics of hydraulic conductivity and strength for a soil to be used as a liner material. Characterization techniques such as X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy and scanning electron microscope were used to examine the mineral composition, functional groups and morphological changes in the unblended soil (UBS) and GGBS. These characterization approaches are used to understand adsorption-associated mechanisms of Pb(II) removal. Batch adsorption tests were performed to evaluate the adsorption capacity of UBS and the GGBS with various proportions (0.5%, 1.0%, 1.5% and 2.0%) of guar gum (GG) towards the removal of Pb(II) ions. Batch adsorption experiments were conducted by varying the pH, dosage of adsorbent, concentration of metal ions and contact time. The experimental results showed that the optimum removal of Pb(II) ions was high at a pH of 3.0 for all blends, and adsorption tests beyond 3.0 pH demonstrated a decline in adsorption performance. The maximum Pb(II) removal efficiency of 95% was obtained using the 2.0% GGBS. The isotherm model assessment for adsorption experimental data of Pb(II) showed the best fit for the Langmuir model on using GG. The present research demonstrated that the guar gum-treated blends exhibited potential Pb(II) ion adsorption properties and therefore can be used as sustainable liner material in sanitary landfills.

Effects of iron-modified biochar with S-rich and Si-rich feedstocks on Cd immobilization in the soil-rice system

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Mapping groundwater-dependent ecosystems in arid Central Asia: Implications for controlling regional land degradation

Groundwater-dependent ecosystems (GDEs) exist all over the world, especially in water-limited regions. To achieve better water management, it is necessary to map and identify GDEs. Central Asia (CA) is one of the most arid regions in the mid-latitudes and one of the major regions with shallow groundwater tables. However, the role of groundwater in the impacts of climate change and regional anthropogenic activities on environmental risks, especially regional desertification, is inadequately understood due to the limited available research on GDEs. In the present study, a remote sensing-based method was used for mapping GDEs in regional CA, and three means-overlay analysis, correlation analysis, and the water balance method-were adopted to validate the accuracy of the mapping outcomes. Our results indicated that: 1) GDEs were concentrated around large lakes and in central Kazakhstan (between 46°N and 50°N latitudes), and areas "Very Likely" and "Likely" to be GDEs accounted for 36.89%, and 28.85% of the total natural vegetation areas, respectively; 2) at the watershed scale, the Sarysu Basin had the largest proportion (94.02% of the area) of potential GDEs while the Ysyk-Kol Basin had the lowest proportion (17.84%); 3) all the three validation methods indicated a good performance for our GDE mapping results. We concluded that the remote sensing-based GDE identification method can be considered a potential approach for mapping GDEs regionally. Better recognition of relationships among groundwater availability, ecosystem health and groundwater management policies should be developed by conducting further studies, to protect GDEs and to prevent regional land degradation.

Hydrologic gradient changes of soil respiration in typical steppes of Eurasia

Soil respiration (R_S) is affected by many factors and shows significant diurnal and seasonal changes at different spatial and temporal scales. However, in a semi-arid steppe, the mechanism of the dynamic influence of environmental factors on R_S is not clear, and the effect of subtle changes of soil water on R_S under drought stress is yet to be explored. Therefore, Xilin River Basin, was the study area and a hydrological gradient on the four ecosystems for R_S and hydrometeorological monitoring was selected. We proposed the use of dynamic sunrise and sunset time to distinguish day from night and determine related statistics. Additionally, we analyzed the temporal variation of R_S and its response process and mechanism for hydrometeorological factors during the growing season and at daily scales. Further, we quantitatively simulated the R_S of 594 scenarios in different growing season stages, ecosystems, and precipitation patterns. Results showed that: (1) in the hydrological gradient belt, different ecosystems exhibited the same trend but different characteristics of R_S regulation. From May to November 2020, R_S was 2.34-3.89, 1.89-5.97, 1.90-5.27 and 2.29-3.45 gC m^-2 day^-1 for the four ecosystems. (2) The use of dynamic sunrise and sunset time to distinguish day and night can more accurately describe the statistical value of each variable, which exhibits remarkable feasibility in daily scale research. (3) The changes in R_S were adequately explained by temperature at various time scales, and the photosynthetically active radiation was positively correlated with R_S at the daily scale. The special soil water content (M_S) condition in the study area was not sufficient to explain R_S. (4) Precipitation can affect R_S by changing soil and air; however, only when precipitation exceeds the effective precipitation threshold of 0.6 ± 0.3 mm, it significantly affects R_S.

Effect of fertilization on nitrogen losses through surface runoffs in Chinese farmlands: A meta-analysis

Surface runoff is the main cause of farmland nitrogen (N) losses in plain areas, which adversely affect water quality. The impact of fertilization on N runoff loss often varies. A meta-analysis was performed using 245 observations from 31 studies in China, to estimate the response of N loss in both paddy and upland fields subjected to different fertilization strategies, and investigate the link between N runoffs, soil properties, as well as precipitation in the planting season. The results showed that compared to the control (without fertilization), N losses subjected to fertilization increased from 3.31 kg/ha to 10.03 kg/ha and from 3.00 kg/ha to 11.24 kg/ha in paddy and upland fields respectively. Importantly, paddy N loss was significantly correlated with fertilizer type and N application rate (predictors); in upland fields N application rate and seasonal precipitation were the main driving factors. For the N application rate, N loss increased with increase in rates for both paddies and upland fields. Moreover, the N loss from upland fields increased with the precipitation during planting season. Between the three fertilizers used in paddies, the increase in loss of CRF (controlled release fertilizer) or OF (organic fertilizer) was lower than that of CF (inorganic chemical fertilizer) with the lowest value in CRF. Subset analysis showed that the effect of CRF and OF in paddies was not affected by the predictors, revealing the steadily controlling property of CRF and OF in paddies. Also, all the predictors had an insignificant impact to N loss risk in paddies during the high application rate. Overall, the results confirm the importance of N dosage in N runoff loss from farmland. Fertilizer type is a key consideration for N loss control in paddies, while the seasonal precipitation should not be ignored in upland fields.

Solid state anaerobic digestion of food waste and sewage sludge: Impact of mixing ratios and temperature on microbial diversity, reactor stability and methane yield

Food waste (FW) and sewage sludge (SS) were anaerobically co digested under solid state conditions (Total solids >15%) and observed that mixing ratio of 3:1 and 2:1 is optimum for mesophilic and thermophilic conditions respectively. The VS reduction and methane yield at optimized ratio was 76% and 0.35 L CH₄/(g VS reduced) respectively at mesophilic temperature whereas it was 88% and 0.42 L CH₄/(g VS reduced) at thermophilic temperature. The metagenomic analysis for these cases were done and high throughput DNA sequencing revealed that diversified bacterial groups that participate in the different metabolisms (hydrolysis, acidogenesis and acetogenesis) were mainly dominated by the phylum Firmicutes and Bacteriodetes. Genus Methanothrix is found to be dominant which is capable of generating methane by any methanogenic pathway among all the archaeal communities in the reactors followed by Methanolinea and Methanoculleus. However, it was understood through metagenomic studies that acetotrophic pathway is observed to be the major metabolic pathway in the reactors.

Redesign of urban biowaste sustainable management system based on industrial ecology concept: A case study in China

Urban biowaste, which refers to the organic fraction of municipal solid waste (MSW), is a predominant type of waste in low- and middle-income countries. Therefore, the sustainable management of urban biowaste is a key problem in solid waste management (SWM). However, treatment technologies usually come with secondary pollution and by-products that need further treatment, which would limit the economic and environmental benefits of the waste management system. The concept of industrial ecology has the potential to be introduced into the waste management field to solve this problem. Based on a practical case study of a city in eastern China, this paper conducted a complete urban biowaste treatment system planning exercise using concepts in industrial ecology. The establishment of the new system has significant economic, environmental and social benefits. The total output value of the project would reach 342 million yuan in 2025, corresponding to 945,000 tons of solid wastes consumed every year, which would significantly reduce the environmental pollution caused by solid waste. More than 700 jobs could also be created. In addition, the establishment of an urban biowaste sustainable management system requires the joint effort of enterprise, government and the public, which in turn requires innovation in business models and management policies. Therefore, a special management committee should be established to promote collaboration among stakeholders, and an online platform that enables end-to-end process supervision covering the entire system, including emergency management mechanisms, needs to be established to ensure the long-term stable operation of various treatment facilities. The results of this paper show that synergies among technologies should be promoted to provide systemic benefit, and that the infrastructure for pollution control should be shared to ensure high utilization.

Rhizosphere dissolved organic matter and iron plaque modified by organic amendments and its relations to cadmium bioavailability and accumulation in rice

Organic amendments can modify rhizosphere dissolved organic matter (DOM) properties and Fe-plaque quantity, thereby affecting cadmium (Cd) bioavailability and uptake by rice. Pot experiments were conducted to investigate effects of biochar (BC) and vermicompost (VC) at different rates (0, 1%, and 5%) on rhizosphere DOM characteristics and Fe-plaque quantity, and their impacts on Cd bioavailability and accumulation in high and low Cd-accumulation rice cultivars (HAC and LAC). Soil DOM was characterized by ultraviolet-visible (UV-Vis) and fluorescence excitation-emission matrix (EEM) spectrum analyses. Hydroponic experiments were conducted to investigate effects of BC- or VC-derived DOM combined Fe-plaque on Cd uptake by rice. Results showed that increasing rates of organic amendments increased DOM concentration while decreased Cd availability in rhizosphere and bulk soils and Cd contents in rice tissues. The Cd reduction in LAC grains (31.9%-72.7%) was better than that in HAC grains (6.3%-25.4%) after organic amendment addition. Soil DOM properties were modified by organic amendments towards higher aromaticity, molecular weight, and stability. VC resulted in a greater increase of humic-like fractions but reduced protein-like proportions in rhizosphere DOM over BC. Negative correlations were observed between humic-like fractions and available Cd in the rhizosphere. Likewise, VC (especially 5%VC) promoted the formation of Fe-plaque and limited Cd soil-to-root transport, while BC groups showed a reverse trend. The results of hydroponic experiments confirmed BC- and VC-derived DOM and Fe-plaque further inhibited Cd uptake by rice via the complexation with Cd and the sequestration of Cd, respectively. Hence, VC application combined with low Cd-accumulation rice could be an effective strategy for the safe utilization of Cd-contamination soils.

A novel glucose-based highly selective phosphate adsorbent

Industrial wastewater discharge leads to serious eutrophication of water bodies, but most of the adsorbents are difficult to selectively remove phosphorus and are difficult to use multiple times, therefore, developing an efficient and reusable material for removal phosphate is extremely necessary. In this work, a kind of highly selective phosphate adsorbent, microporous carbon material (MCM), based on glucose was synthesized by hydrothermal and activation method. The MCM were characterized by SEM, XPS, BET, element analysis, et al. The phosphate adsorption mechanism of MCM were investigated by batch adsorption experiment and model calculation. Results showed that MCM had a high adsorption capacity for phosphate in a wide range of pH (1.5-10). Langmuir model and pseudo-second-order kinetic revealed that the process was endothermic and involved both physical and chemical adsorption. The main phosphate adsorption mechanisms of MCM are electrostatic attraction, ion complexation, hydrogen bonding, and physical adsorption. The ions competition simulation experiment indicated that the MCM was highly selective for phosphate removal. Furthermore, the phosphate adsorption tests were carried out on five kinds of water, and the removal rates were all above 99.98%. The 20 regenerative cycles experiment revealed that the MCM had high reusability. Therefore, this kind of novel glucose-based highly selective phosphate adsorbent with multi-cycle phosphorus removal performance can improve the eutrophication of water. This study provides a new idea for phosphate removal and expands the application range of glucose-based carbon materials.

Heavy metals concentrations and naturally occurring radionuclides in soils affected by and around a solid waste dumpsite in Osogbo metropolis, Nigeria

The presence of heavy metals and naturally occurring radioactive materials (NORMs) in high concentrations in soils can be hazardous to exposed humans. This study is aimed at measuring the concentrations of heavy metals (Cu, Pb, Ni, Zn, Cd, Co, and Cr) and activity concentration of ²³²Th, ²³⁸U, and ⁴⁰K in soils affected by and around a solid waste dumpsite in Osogbo metropolis, Nigeria. Atomic absorption spectrometry and gamma-ray spectrometric techniques were used to determine the concentrations of metals and NORMs, respectively. Possible environmental impact of the heavy metal content and the probable radiological hazard by the NORMs to the general public were assessed. The calculated pollution indices reported in this work for Co, Cr, Pb, and Ni show low pollution status. Geoaccumulation indices for Cu, Zn, and Cd indicated that the area under study is strongly contaminated by these metals. Evaluated ecological risk index narrowed down Cd as the poisonous metal with high concentration. The measured radionuclides' mean activity concentrations and the evaluated mean of radium equivalent and absorbed dose rate values are higher than the recommended safe limit, an indication of possible radiological hazard. The principal factor analysis results explained 76% of the collection of data and described chips of galvanized/chrome metals, scrap metals, waste from electronics, Cr, and Cd-containing waste as sources of the heavy metals. The practice of land cultivation around the dumpsite should be deterred to prevent the transportation of these vicious heavy metals into the food chain.

Progress in the catalytic glycolysis of polyethylene terephthalate

This paper briefly reviews the development history of polyethylene terephthalate (PET) and the recycling of PET. As one of the most promising way to degrade PET into oligomers and monomers that can be used for the production of high-quality PET, catalytic glycolysis is highlighted in this review. The developments on metal salt, metal oxide and ionic solvent catalysts for glycolysis of PET are systematically summarized, besides, the proposed catalytic mechanisms of ionic liquids (ILs) and deep eutectic solvents (DESs) are presented. The metallic catalysts show high catalytic performance but causing serious environmental pollution and high waste treatment costs, thereby it is proposed that metal-free catalysts, especially ILs and DESs can be the "greener" alternatives to address the PET waste problem. Additionally, the studies related to the glycolysis kinetics are discussed in this review, showing the results that PET glycolysis process consists of heterogeneous and homogeneous depolymerization, and different models should be used to investigate different depolymerization stages in order to obtain a more realistic picture.

Response surface optimization, combustion characteristics and kinetic analysis of mixed fuels of Fenton/CaO conditioned municipal sewage sludge and rice husk

The co-combustion characteristics and kinetics of Fenton/CaO conditioned MSS, and biomass rice husk (RH) are studied by thermogravimetry, and the condition optimization was carried out by response surface methodology (RSM). The results show that the mixed fuel with RH is helpful to decrease T_i and T_b values and increase combustion characteristic index (CCI). The CCI of MSS after conditioning is 0.59-0.88 times lower than that of the pure MSS. In addition, the total E_m of S2, MSS/RH mixed combustion after Fenton/CaO conditioning is lower, the combustion reactivity is stronger. According to RSM, the optimum conditions are considered to be: RH mixing ratio 56%, Fenton/CaO conditioner dosage 147 mg g^-1 dry solids, heating rate 30 K min^-1, the maximum CCI 25.3305 × 10^-7%² °C^-3 min^-2, and the minimum E_m 10.6403 kJ min^-1. This study supplies new insights into combustion technology of sludge.

Using stable isotope probing and fluorescence spectroscopy to examine the roles of substrate and soluble microbial products in extracellular polymeric substance formation in activated sludge process

In this study, we used stable isotope-labeled soluble microbial products (SMP) and substrates to explore their assimilation into the formation of new biological products (i.e., extracellular polymeric substances and biomass) in two adjacent sequencing batch reactors. The isotope labeling approach along with fluorescence spectroscopy allowed us to distinguish between refractory and labile portions of SMP constituents as well as their roles in the formation of extracellular polymeric substances (EPS). Comparison of SMP fluorescence and the specific UV absorbance values between the two reactors revealed the presence of humic-like aromatic substances in the non-consumable part of SMP, which can be ultimately released as effluent organic matter. Parallel factor analysis modeling of fluorescence spectra showed that the hydrolysis of EPS contents mostly resulted in humic-like components in SMP rather than protein-like components, which were initially abundant in EPS (>80%). From variations in carbon and nitrogen isotopic contents in EPS and biomass, it was found that carbon-containing substrates were enriched faster than their nitrogenous counterparts. The contributions to new EPS formation reached 87.5% for carbon and 60.5% for nitrogen. Meanwhile, the isotopic tracking of the labeled SMP revealed that only 11.0% and 11.9% of carbon and 13.3% and 11.6% of nitrogen from the influent SMP were finally assimilated into EPS and biomass, respectively. In contrast, the isotopic enrichment in SMP was higher (~50%) than that of EPS and biomass, indicating the low bioavailability and refractory nature of the feed SMP. This study proposed a promising approach for estimating the relative contributions of different forms of labile substrate and SMP to the formation of EPS in activated sludge processes. This approach could be suggested as a versatile method for establishing the kinetics, substrate element flow, mass balance on organic substrates and nutrients, as well as for tracking the consumption and uptake pathways of hazardous materials.

Enhanced lignin biodegradation by consortium of white rot fungi: microbial synergistic effects and product mapping

BACKGROUND

As one of the major components of lignocellulosic biomass, lignin has been considered as the most abundant renewable aromatic feedstock in the world. Comparing with thermal or catalytic strategies for lignin degradation, biological conversion is a promising approach featuring with mild conditions and diversity, and has received great attention nowadays.

RESULTS

In this study, a consortium of white rot fungi composed of Lenzites betulina and Trametes versicolor was employed to enhance the ligninolytic enzyme activity of laccase (Lac) and manganese peroxidase (MnP) under microbial synergism. The maximum enzymatic activity of Lac and MnP was individually 18.06 U mL^-1 and 13.58 U mL^-1 along with a lignin degradation rate of 50% (wt/wt), which were achieved from batch cultivation of the consortium. The activities of Lac and MnP obtained from the consortium were both improved more than 40%, as compared with monocultures of L. betulina or T. versicolor under the same culture condition. The enhanced biodegradation performance was in accordance with the results observed from scanning electron microscope (SEM) of lignin samples before and after biodegradation, and secondary-ion mass spectrometry (SIMS). Finally, the analysis of heteronuclear single quantum coherence (HSQC) NMR and gas chromatography-mass spectrometry (GC-MS) provided a comprehensive product mapping of the lignin biodegradation, suggesting that the lignin has undergone depolymerization of the macromolecules, side-chain cleavage, and aromatic ring-opening reactions.

CONCLUSIONS

Our results revealed a considerable escalation on the enzymatic activity obtained in a short period from the cultivation of the L. betulina or T. versicolor due to the enhanced microbial synergistic effects, providing a potential bioconversion route for lignin utilization.

Recycling of Blast Furnace and Coal Slags in Aided Phytostabilisation of Soils Highly Polluted with Heavy Metals

(1) Background: The growing demand for developing new methods of degraded land remediation is linked to the need to improve the soil environment, including post-industrial soils. Biological methods such as the aided phytostabilisation technique are the most common methods applied to achieve effective remediation. This study aimed to determine the technical potential of methods using novel or yet not used soil amendments, such as blast furnace slag (BFS) and coal slag (CS), with Dactylis glomerata L. as a test plant. (2) Methods: The experiment was conducted on post-industrial area soil with high concentrations of Cu (761 mg/kg), Cd (23.9 mg/kg), Pb (13,539 mg/kg) and Zn (8683 mg/kg). The heavy metal content in roots and the above-ground parts of plants and soil was determined by flame atomic absorption spectrometry. (3) Results: The addition of BFS to the soil was the most effective in increasing Dactylis glomerata L. biomass yield. The Cu, Cd, Pb, and Zn concentrations were higher in the roots than in the above-ground parts of the plants. BFS and CS induced a considerable increase in soil pH, compared to the control treatment. The addition of BFS also produced the greatest significant decrease in the Pb content in soil following the phytostabilisation process. (4) Conclusions: In view of the above, the use of BFS in the aided phytostabilisation in soils contaminated with high levels of Cu, Cd, Pb, and Zn can be recommended for larger-scale in situ projects.

A hybrid Pythagorean fuzzy AHP - CoCoSo framework to rank the performance outcomes of circular supply chain due to adoption of its enablers

In the last few years, the Circular Supply Chain (CSC) has gained considerable attention among researchers, practitioners, and policymakers. It offers immense opportunities to embrace supply chain operations in three dimensions of sustainability. This study aims to identify and rank the performance outcomes (POs) realized due to CSC enablers (CSCEs) adoption. The study proposes a hybrid framework of the Pythagorean fuzzy analytic hierarchy process (PF-AHP) and Pythagorean fuzzy combined compromised solution (PF-CoCoSo) to achieve the objectives of this research. PF-AHP is used to obtain the CSCEs relative weights while PF-CoCoSo is used to ranks the POs concerning the CSCEs. An empirical case study is conducted for an Indian manufacturing organization to demonstrate the proposed framework's applicability. The result reveals that 'global climate pressure and ecological scarcity of resources' is the most significant CSCE to achieve the sustainability in the supply chain, followed by 'government rules, legislations and directives for CSC adoption', 'environment management certifications and systems', whereas, 'reduces waste and promotes green development' is the most critical PO realized due to adoption of CSCEs in CSC implementation process. The proposed framework is a systematic, more comprehensive, accurate, and structured approach to the business organization to improve its POs in a step-wise manner by implementing CSCEs. Sensitivity analysis is performed to check the effectiveness of the proposed framework. This research provides substantial contributions to sustainable development in the society as well as in the industry, and it will help researchers, practitioners, and policymakers working in the domain of CSC.

Modeling and identification of suitable motivational mechanism in the collection system of municipal solid waste supply chain

Many studies have identified that incentive, subsidy, and reward-penalty mechanisms improve the collection rate of recyclables and end of life products. But there is a lack of studies mathematical models and analysis of these mechanisms in the context of municipal solid waste supply chain. Therefore, in this study, models have been formulated for municipal solid waste supply chain (profit) considering government and collectors' profit under incentive, subsidy, and reward-penalty mechanisms. The study has analysed the models against the non-separation and separation scenario of waste. A numerical analysis is performed and observed that: (i) separation of waste at source along with incentive, subsidy, and reward-penalty mechanisms scenario improve the collection rate by 17%, 23%, 30%, and 45% compared to non-separated MSW. (ii) Incentive, subsidy, and reward-penalty mechanisms increases the total supply chain profit by around 9%, -36% and 18%. (iii) reward-penalty mechanism performs better than incentive and subsidy mechanism by providing the high supply chain profit (18% and 85%) and collection rate (22% and 15%) comparatively. Further, sensitivity analysis carried out to understand the behaviour of the models against the key parameters. The study also develops interesting propositions and proved for a better understanding of the models. From results, some key managerial insights have been drawn and a few future scopes of the study are presented.

Intercropping of Peanut-Tea Enhances Soil Enzymatic Activity and Soil Nutrient Status at Different Soil Profiles in Subtropical Southern China

Intercropping is one of the most widely used agroforestry techniques, reducing the harmful impacts of external inputs such as fertilizers. It also controls soil erosion, increases soil nutrients availability, and reduces weed growth. In this study, the intercropping of peanut (Arachishypogaea L.) was done with tea plants (Camellia oleifera), and it was compared with the mono-cropping of tea and peanut. Soil health and fertility were examined by analyzing the variability in soil enzymatic activity and soil nutrients availability at different soil depths (0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm). Results showed that the peanut-tea intercropping considerably impacted the soil organic carbon (SOC), soil nutrient availability, and soil enzymatic responses at different soil depths. The activity of protease, sucrase, and acid phosphatase was higher in intercropping, while the activity of urease and catalase was higher in peanut monoculture. In intercropping, total phosphorus (TP) was 14.2%, 34.2%, 77.7%, 61.9%; total potassium (TK) was 13.4%, 20%, 27.4%, 20%; available phosphorus (AP) was 52.9%, 26.56%, 61.1%; 146.15% and available potassium (AK) was 11.1%, 43.06%, 46.79% higher than the mono-cropping of tea in respective soil layers. Additionally, available nitrogen (AN) was 51.78%, 5.92%, and 15.32% lower in the 10-20 cm, 20-30 cm, and 30-40 cm layers of the intercropping system than in the mono-cropping system of peanut. Moreover, the soil enzymatic activity was significantly correlated with SOC and total nitrogen (TN) content across all soil depths and cropping systems. The depth and path analysis effect revealed that SOC directly affected sucrase, protease, urease, and catalase enzymes in an intercropping system. It was concluded that an increase in the soil enzymatic activity in the intercropping pattern improved the reaction rate at which organic matter decomposed and released nutrients into the soil environment. Enzyme activity in the decomposition process plays a vital role in forest soil morphology and function. For efficient land use in the cropping system, it is necessary to develop coherent agroforestry practices. The results in this study revealed that intercropping certainly enhance soil nutrients status and positively impacts soil conservation.