The effects of biochar aging on rhizosphere microbial communities in cadmium-contaminated acid soil

Foliar application of selenium and gibberellins reduce cadmium accumulation in soybean by regulating interplay among rhizosphere soil metabolites, bacteria community and cadmium speciation

Both selenium (Se) and gibberellins (GA3) can alleviate cadmium (Cd) toxicity in plants. However, the application of Se and GA3 as foliar spray to against Cd stress on soybean and its related mechanisms have been poorly explored. Herein, this experiment evaluated the effects of Se and GA3 alone and combined application on soybean rhizosphere microenvironment, Cd accumulation and growth of soybean seedlings. The results revealed that both Se and GA3 can effectively decrease the accumulation of Cd in soybean seedlings. Foliar application of Se, GA3 and their combination reduced Cd contents in soybean seedlings respectively by 21.70 %, 27.53 % and 45.07 % when compared with the control treatment, suggest a synergistic effect of Se and GA3 in decreasing Cd accumulation. Se and GA3 also significantly increased diversity and abundance of the metabolites in rhizosphere, which consequently played an important role in shaping rhizosphere bacteria community and improve rhizosphere soil physicochemical properties of Cd contaminated soil, as well as decreased the Cd available forms contents but enhance the immobilized form levels. Overall, this study affords a novel approach on mitigating Cd accumulation in soybean seedlings which is attributed to Se and GA3 regulated interplay among rhizosphere soil metabolites, bacteria community and cadmium speciation.

Microbial mediated remediation of heavy metals toxicity: mechanisms and future prospects

Heavy metal pollution has become a serious concern across the globe due to their persistent nature, higher toxicity, and recalcitrance. These toxic metals threaten the stability of the environment and the health of all living beings. Heavy metals also enter the human food chain by eating contaminated foods and cause toxic effects on human health. Thus, remediation of HMs polluted soils is mandatory and it needs to be addressed at higher priority. The use of microbes is considered as a promising approach to combat the adverse impacts of HMs. Microbes aided in the restoration of deteriorated environments to their natural condition, with long-term environmental effects. Microbial remediation prevents the leaching and mobilization of HMs and they also make the extraction of HMs simple. Therefore, in this context recent technological advancement allowed to use of bioremediation as an imperative approach to remediate polluted soils. Microbes use different mechanisms including bio-sorption, bioaccumulation, bioleaching, bio-transformation, bio-volatilization and bio-mineralization to mitigate toxic the effects of HMs. Thus, keeping in the view toxic HMs here in this review explores the role of bacteria, fungi and algae in bioremediation of polluted soils. This review also discusses the various approaches that can be used to improve the efficiency of microbes to remediate HMs polluted soils. It also highlights different research gaps that must be solved in future study programs to improve bioremediation efficency.

Alterations in the composition and metabolite profiles of the saline-alkali soil microbial community through biochar application

Saline-alkali soil poses significant chanllenges to sustainable development of agriculture. Although biochar is commonly used as a soil organic amendment, its microbial remediation mechanism on saline-alkali soil requires further confirmation. To address this, we conducted a pot experiment using cotton seedlings to explore the potential remediation mechanism of rice straw biochar (BC) at three different levels on saline-alkaline soil. The results showed that adding of 2% biochar greatly improved the quality of saline-alkaline soil by reducing pH levels, electrical conductivity (EC), and water-soluble ions. Moreover, biochar increased the soil organic matter (SOM), nutrient availability and extracellular enzyme activity. Interestingly, it also reduced soil salinity and salt content in various cotton plant tissues. Additionally, biochar had a notable impact on the composition of the microbial community, causing changes in soil metabolic pathways. Notably, the addition of biochar promoted the growth and metabolism of dominant salt-tolerant bacteria, such as Proteobacteria, Bacteroidota, Acidobacteriota, and Actinobacteriota. By enhancing the positive correlation between microorganisms and metabolites, biochar alleviated the inhibitory effect of salt ions on microorganisms. In conclusion, the incorporation of biochar significantly improves the soil microenvironment, reduces soil salinity, and shows promise in ameliorating saline-alkaline soil conditions.

Shifts in bacterial diversity, interactions and microbial elemental cycling genes under cadmium contamination in paddy soil: Implications for altered ecological function

Cadmium (Cd) contamination has become an emergent environmental issue in agroecosystems worldwide. The impacts of Cd on microbial community and their ecological functional remain unrevealed. This study investigated the response of bacterial community and microbial ecological functions to Cd contamination in paddy soil of East China. Bacterial diversity and community structure significantly changed under Cd contamination. Proteobacteria and Acidobacteria were identified as biomarkers to indicate Cd contamination. The overall elemental cycling genes abundance was negatively correlated to soil Cd content. Acetyl-CoA synthesis, organic N mineralization, N fixation and nitrous reduction genes were especially sensitive to elevated Cd stress, resulting in loss of microbial derived soil C and N pool and increase in N2O emission potential. Bacteria interactions were sparser yet more competitive under Cd contamination. Cd resistant genera Massilia, Burkholderia, Streptomyces and Methylobacterium were essential to bacterial interactions via building connections with non-resistant species. Microbial Cd immobilization potential by urea hydrolysis was enhanced under Cd contamination, with Massilia being the keystone functional taxa involved in this process. Our study elucidated the ecological risks of altered microbial functions under Cd contamination in paddy soil, as well as the significance of Cd resistant bacteria to microbial community and ecological functionality.

Keystone taxa of phoD-harboring bacteria mediate alkaline phosphatase activity during biochar remediation of Cd-contaminated soil

Phosphorus (P)-modified biochar can efficiently remediate cadmium (Cd)-contaminated soil. However, the mechanisms of responses of alkaline phosphatase (ALP) and phoD-harboring microorganisms, which are notably sensitive to Cd and P, are not clear during the remediation process. In this study, apple (Malus domestica) tree branches were co-pyrolyzed with tripotassium phosphate (K3PO4) to prepare P-modified biochar, which was used to remediate Cd-soil contaminated soil collected near a mine site. The effect of P-modified biochar on the composition of the phoD-harboring microbial community and its mechanism of interacting with ALP were analyzed. The results showed that the application of P-modified biochar to Cd-contaminated soil promoted the co-precipitation of Cd and phosphate and reduced the content of bioavailable Cd by 69.77 %. P-modified biochar improved the complexity and stability of the soil phoD-harboring microbial community. Furthermore, this study clarified that ALP activity was not completely regulated by the abundance of phoD, but Priestia and Massilia that contain phoD genes dominated the activity of ALP in rhizosphere and bulk soils, respectively. It is notable that bioavailable Cd significantly stimulated Priestia, Massilia, and ALP activity. These findings provide a theoretical basis for the application of P-modified biochar to the remediation of soil contaminated with Cd with respect to P functional microorganisms.

Risk assessment of toxic and hazardous metals in paddy agroecosystem by biochar-for bio-membrane applications

Toxic and carcinogenic metal (loid)s, such arsenic (As) and cadmium (Cd), found in contaminated paddy soils pose a serious danger to environmental sustainability. Their geochemical activities are complex, making it difficult to manage their contamination. Rice grown in Cd and As-polluted soils ends up in people's bellies, where it can cause cancer, anemia, and the deadly itai sickness. Solving this issue calls for research into eco-friendly and cost-effective remediation technology to lower rice's As and Cd levels. This research delves deeply into the origins of As and Cd in paddy soils, as well as their mobility, bioavailability, and uptake mechanisms by rice plants. It also examines the current methods and reactors used to lower As and Cd contamination in rice. Iron-modified biochar (Fe-BC) is a promising technology for reducing As and Cd toxicity in rice, improving soil health, and boosting rice's nutritional value. Biochar's physiochemical characteristics are enhanced by the addition of iron, making it a potent adsorbent for As and Cd ions. In conclusion, Fe-BC's biomembrane properties make them an attractive option for remediating As- and Cd-contaminated paddy soils. More efficient mitigation measures, including the use of biomembrane technology, can be developed when sustainable agriculture practices are combined with these technologies.

Cadmium exposure dysregulates purine metabolism and homeostasis across the gut-liver axis in a mouse model

Cadmium (Cd) exposure has been associated with the development of enterohepatic circulation disorders and hyperuricemia, but the possible contribution of chronic low-dose Cd exposure to disease progression is still need to be explored. A mouse model of wild-type mice (WT) and Uox-knockout mice (Uox-KO) to find out the toxic effects of chronic low-dose Cd exposure on liver purine metabolism by liquid chromatography-mass spectrometry (LC-MS) platform and associated intestinal flora. High throughput omics analysis including metabolomics and transcriptomics showed that Cd exposure can cause disruption of purine metabolism and energy metabolism. Cd changes several metabolites associated with purine metabolism (xanthine, hypoxanthine, adenosine, uridine, inosine) and related genes, which are associated with elevated urate levels. Microbiome analysis showed that Cd exposure altered the disturbance of homeostasis in the gut. Uox-KO mice were more susceptible to Cd than WT mice. Our findings extend the understanding of potential toxicological interactions between liver and gut microbiota and shed light on the progression of metabolic diseases caused by Cd exposure.

Insight into functional mechanisms of percarbamide and nitrification inhibitors in degrading fungicide residues and shaping microbial communities in soil-plant systems

Fungicides and nitrogen (N) fertilizers are essential to maintain plant yield in current intensive agriculture. Percarbamide is a novel type of N fertilizer with strong oxidizing property, and the nitrification inhibitor is widely used in agricultural production. It may be feasible to apply percarbamide and nitrification inhibitor as N management to promote fungicide dissipations in soil-plant system. This study quantified the effects of percarbamide and nitrification inhibitor dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP) on carbendazim residues, and microbial communities of soil-plant systems, and relationships among carbendazim residues, soil and endophytic microbial communities and plant yields were also comprehensively quantified. Compared with the control, the percarbamide significantly reduced soil carbendazim residues by 29.4% but enhanced the lettuce yield by 28.0%. Soil carbendazim residues were significantly and negatively correlated with the soil total N and NO3--N contents. Soil microbial community structures and co-occurrence networks were more sensitive to N management than their endophytic counterparts. In comparison to the percarbamide alone, the DCD significantly increased the nodes of soil fungal community co-occurrence network which were positively correlated with the plant yield. The DCD outweighed DMPP in increasing the lettuce yield and soil fungal community stability and reshaping soil bacterial community structure. Our study suggested that soil microbial communities were more sensitive to percarbamide and nitrification inhibitor applications than their endophytic counterparts under fungicide pressure and that the DCD outweighed DMPP in reshaping microbial communities. The integrated applications of percarbamide and nitrification inhibitors were promising soil N management strategies to promote fungicide removal and stimulate microbial community in the soil-plant systems.

Cadmium-resistant phosphate-solubilizing bacteria immobilized on phosphoric acid-ball milling modified biochar enhances soil cadmium passivation and phosphorus bioavailability

Cadmium (Cd) can accumulate in agriculture soil from the regular application of phosphorus (P) fertilizer. Microbiological method is considered as a potentially effective strategy that can not only remediate the Cd-contaminated soil but also provide the phosphorus needed for crop growth. However, the toxicity of Cd may affect the activity of microorganisms. To solve this problem, Klebsiella variicola with excellent phosphate solubilization ability (155.30 mg L^-1 at 48 h) and Cd adsorption rate (90.84 % with 10 mg L^-1 Cd initial concentration) was firstly isolated and identified in this study. Then, a phosphoric acid and ball milling co-modified biochar (PBC) was selected as the carrier to promote the activities of K. variicola under Cd pollution. Surface characterization revealed that the promotion of K. variicola by PBC was mainly attributed to the large specific surface area and diverse functional groups. Compared to contaminated soil, microbial PBC (MPBC) significantly increased the pakchoi biomass and phosphorus (P) content, while the Cd content in leave and root of pakchoi (Brassica chinensis L.) decreased by 25.90-43.46 % (P < 0.05). The combined application also favored the transformation of the resistant P fractions to bioavailable P, and facilitated the immobilization of 20.12 % exchangeable Cd to reducible, oxidizable, and residual Cd in the treated soil. High-throughput sequencing revealed that the response of the soil microbial community to the MPBC was more beneficial than K. variicola or PBC alone. Therefore, the application of MPBC has the potential to act as an efficient, stable, and environmentally friendly sustainable product for Cd remediation and enhanced P bioavailability in agricultural production.

Chitin and crawfish shell biochar composite decreased heavy metal bioavailability and shifted rhizosphere bacterial community in an arsenic/lead co-contaminated soil

Sustainable management of ever-increasing organic biowaste and arable soil contamination by potentially toxic elements are of concern from both environmental and agricultural perspectives. To tackle the waste issue of crawfish shells and simultaneously minimize the threat of arsenic (As) and lead (Pb) to human health, a pot trial was conducted using chitin (CT), crawfish shell biochar (CSB), crawfish shell powder (CSP), and CT-CSB composite to compare their remediation efficiencies in As/Pb co-contaminated soil. Results demonstrated that addition of all amendments decreased Pb bioavailability, with the greatest effect observed for the CT-CSB treatment. Application of CSP and CSB increased the soil available As concentration, while significant decreases were observed in the CT and CT-CSB treatments. Meanwhile, CT addition was the most effective in enhancing the soil enzyme activities including acid phosphatase, α-glucosidase, N-acetyl-β-glucosaminidase, and cellobiohydrolase, whereas CSB-containing treatments suppressed the activities of most enzymes. The amendments altered the bacterial abundance and composition in soil. For instance, compared to the control, all treatments increased Chitinophagaceae abundance by 2.6-4.7%. The relative abundance of Comamonadaceae decreased by 1.6% in the CSB treatment, while 2.1% increase of Comamonadaceae was noted in the CT-CSB treatment. Redundancy and correlation analyses (at the family level) indicated that the changes in bacterial community structure were linked to bulk density, water content, and As/Pb availability of soils. Partial least squares path modeling further indicated that soil chemical property (i.e., pH, dissolved organic carbon, and cation exchange capacity) was the strongest predictor of As/Pb availability in soils following amendment application. Overall, CT-CSB could be a potentially effective amendment for simultaneously immobilizing As and Pb and restoring soil ecological functions in contaminated arable soils.

Microbiological mechanism for "production while remediating" in Cd-contaminated paddy fields: A field experiment

Security utilization measures (SUMs) for "production while remediating" in moderate and mild Cd-polluted paddy fields had been widely used. To investigate how SUMs drove rhizosphere soil microbial communities and reduced soil Cd bioavailability, a field experiment was conducted using soil biochemical analysis and 16S rRNA high-throughput sequencing. Results showed that SUMs improved rice yield by increasing the number of effective panicles and filled grains, while also inhibiting soil acidification and enhancing disease resistance by improving soil enzyme activities. SUMs also reduced the accumulation of harmful Cd in rice grains and transformed it into FeMn oxidized Cd, organic-bound Cd, and residual Cd in rhizosphere soil. This was partly due to the higher degree of soil DOM aromatization, which helped complex the Cd with DOM. Additionally, the study also found that microbial activity was the primary source of soil DOM, and that SUMs increased the diversity of soil microbes and recruited many beneficial microbes (Arthrobacter, Candidatus_Solibacter, Bryobacter, Bradyrhizobium, and Flavisolibacter) associated with organic matter decomposition, plant growth promotion, and pathogen inhibition. Besides, special taxa (Bradyyrhizobium and Thermodesulfovibrio) involved in sulfate/sulfur ion generation and nitrate/nitrite reduction pathway were observably enriched, which effectively reduced the soil Cd bioavailability through adsorption and co-precipitation. Therefore, SUMs not only changed the soil physicochemical properties (e.g., pH), but also drove rhizosphere microbes to participate in the chemical species transformation of soil Cd, thus reducing Cd accumulation in rice grains.

Effect of aged biochar after microbial fermentation on antibiotics removal: Key roles of microplastics and environmentally persistent free radicals

For the first time, biochar was prepared by changing the polystyrene (PS) content in sludge, and the efficiency of antibiotics removal by biochar was evaluated after fermentation aging. Fermentation aging affects the efficiency of antibiotics removal by reducing the specific surface area and active sites of biochar. The antibiotics removal efficiency of different types of biochar after aging decreased by 5.95%-13.59%. Owing to the biotoxicity of biochar, the relative abundance of most communities decreased during fermentation, whereas Anaerolineae still increased (14.29% to 33.05% or 33.02%). However, controlled experiments confirmed that biochar was much less toxic to Scenedesmus obliquus than to antibiotics, with concentrations of 11.09 × 10⁵ cells/mL and 0.188 × 10⁵ cells/mL, respectively. With the positive effect of environmentally persistent free radicals (EPFRs) considered, increasing the PS content in sludge facilitated the removal of antibiotics by biochar. This study assesses the stability of biochar in removing antibiotics after long-term microbial aging.

Enhancing the effect of biochar ageing on reducing cadmium accumulation in Medicago sativa L

Biochar (BC) application to farmland soil can reduce the mobility and bioavailability of Cd. Nevertheless, BC is prone to natural ageing in soil, which alters its structure, physicochemical properties, thereby affecting the immobilisation of Cd. We used dry-wet and freeze-thaw cycles to mimic the natural ageing of BC, and used adsorption experiments to explore the changes of Cd adsorption capacity of BC and aged BC (ABC). We conducted a pot experiment to investigate the effects of BC and ABC on soil biotic and abiotic factors, alfalfa growth, and Cd accumulation in agricultural soils with high and low Cd concentrations. The increase of specific surface area, pore size, oxygen containing functional groups and mineral composition leads to better adsorption capacity of ABC. The adsorption of Cd(II) by BC and ABC is mainly by monolayer adsorption and chemical adsorption. Applying BC and ABC to Cd-contaminated soil significantly increased the aboveground biomass and decreased the Cd accumulation by reducing the Cd bioconcentration factor in alfalfa. At high Cd levels, adding BC and ABC reduced the Cd content in alfalfa shoots by 32.8 % and 35.1 %, respectively; the fixing effect of ABC was better than that of BC. Adding BC and ABC significantly increased the microbial biomass and geometric mean of enzymes. BC addition increased soil pH by 0.32-0.36 units and cation exchange capacity (CEC) by 15.5 %. Adding BC and ABC significantly increased soil organic matter (SOM) by 5.7 % and 6.2 %, respectively. Random forest analysis showed that SOM, total organic carbon, and fluorescein diacetate hydrolase were important variables for Cd content in alfalfa shoots. Structural equation modelling showed that BC indirectly affected the Cd content in alfalfa shoots by affecting soil pH, CEC, SOM, microbial biomass, and microbial metabolic activity. BC has a long-term effect on alleviating Cd pollution in farmland.

Pollution Profiles, Source Identification and Health Risk Assessment of Heavy Metals in Soil near a Non-Ferrous Metal Smelting Plant

Heavy metal pollution related to non-ferrous metal smelting may pose a significant threat to human health. This study analyzed 58 surface soils collected from a representative non-ferrous metal smelting area to screen potentially hazardous heavy metals and evaluate their health risk in the studied area. The findings demonstrated that human activity had contributed to the pollution degrees of Cu, Cd, As, Zn, and Pb in the surrounding area of a non-ferrous metal smelting plant (NMSP). Cu, Cd, As, Zn, Pb, Ni, and Co pollution within the NMSP was serious. Combining the spatial distribution and Spearman correlations with principal component analysis (PCA), the primary sources of Cd, As, Pb, and Zn in surrounding areas were related to non-ferrous metal smelting and transportation activities. High non-cancer (THI = 4.76) and cancer risks (TCR = 2.99 × 10^-4) were found for adults in the NMSP. Moreover, heavy metals in the surrounding areas posed a potential cancer risk to children (TCR = 3.62 × 10^-6) and adults (TCR = 1.27 × 10^-5). The significant contributions of As, Pb, and Cd to health risks requires special attention. The construction of a heavy metal pollution management system will benefit from the current study for the non-ferrous metal smelting industry.