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Combining biochar with irrigation management to alter the microbial community is a sustainable method for remediating soils contaminated by heavy metals. However, studies on how these treatments promote Cr(VI) reduction are limited, and the corresponding microbial mechanisms are unclear. Therefore, we conducted a pot experiment to explore the responses of soil microbial communities to combined biochar amendment and irrigation management strategies and their involvement in Cr transformation in paddy soils. Six treatments were established using varying concentrations of biochar (0, 1, and 2% [w/w]) combined with two irrigation management strategies (continuous flooding [CF] and dry–wet alternation [DWA]). The results showed that the combined biochar addition and irrigation management strategy significantly altered soil pH, redox potential, organic matter content, and Fe(II) and sulfide concentrations. In addition, the Cr(VI) concentration under CF irrigation management was conspicuously lower (48.2–54.4%) than that under DWA irrigation management. Biochar amendment also resulted in a substantial reduction (8.8–27.4%) in Cr(VI) concentration. Moreover, the changes in soil physicochemical properties remarkably affected the soil microbial community. The microbial diversity and abundance significantly increased with biochar amendment. Furthermore, the combined biochar amendment and CF strategy stimulated the growth of Geobacter - and Anaeromyxobacter-related Fe(III)-reducing bacteria, Gallionella-related Fe(II)-oxidizing bacteria, and Desulfovibro - and Clostridium -related sulfate-reducing bacteria, which simultaneously facilitated the generation of Fe(II) and sulfide, thereby enhancing Cr(VI) reduction. Consequently, our results suggest that the effectively increased abundance of Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria via combined CF irrigation management and biochar addition may be a key factor in reducing Cr(VI) in paddy soil. The keystone genera responsible for Cr(VI) reduction were Geobacter , Anaeromyxobacter , Gallionella , Desulfovibro, and Clostridium. This study provides novel insights into the coupling mechanism of the Fe/S/Cr transformation mediated by Fe-reducing/oxidizing bacteria and sulfate-reducing bacteria. [Display omitted] • Biochar and irrigation altered soil pH, Eh, OM, and Fe(II) and sulfide levels. • Biochar addition and continuous flooding markedly reduced Cr(VI) concentration. • Biochar and continuous flooding stimulated growth of Fe/S functional bacteria. • Fe-reducing/oxidizing and sulfate-reducing bacteria facilitated Cr(VI) reduction. • Keystone genera included Geobacter , Anaeromyxobacter , Gallionella, and Desulfovibro. [ABSTRACT FROM AUTHOR]

Abstract: An undisturbed heavy clay soil column experiment was conducted to examine the influence of the new nitrification inhibitor, 3,4- dimethylpyrazole phosphate (DMPP), on nitrogen and soil salt-ion leaching. Regular urea was selected as the nitrogen source in the soil. The results showed that the cumulative leaching losses of soil nitrate-N under the treatment of urea with DMPP were from 57.5% to 63.3% lower than those of the treatment of urea without DMPP. The use of nitrification inhibitors as nitrate leaching retardants may be a proposal in regulations to prevent groundwater contaminant. However, there were no great difference between urea and urea with DMPP treatments on ammonium-N leaching. Moreover, the soil salt-ion leaching losses of Ca2+,Mg2+,K+, and Na+ were reduced from 26.6% to 28.8%, 21.3% to 27.8%, 33.3% to 35.5%, and 21.7% to 32.1%, respectively. So, the leaching losses of soil salt-ion were declined for nitrification inhibitor DMPP addition, being beneficial to shallow groundwater protection and growth of crop. These results indicated the possibility of ammonium or ammonium producing compounds using nitrification inhibitor DMPP to control the nitrate and nutrient cation leaching losses, minimizing the risk of nitrate pollution in shallow groundwater. [Copyright &y& Elsevier]

• Magnetic biochars were successfully derived from the coagulation-flocculation sludge. • Zero valent Fe formed at relatively lower temperature. • pH of biochars was acidic except that of biochar pyrolysed at 700 °C under N 2 flow. • Heavy metals immobilization could be affected by iron-based phases and chlorination. • Pyrolysis can reduce the risk of heavy metals in coagulation-flocculation sludge. Coagulation-flocculation sludge (CFS) of swine wastewater was pyrolyzed at 400 °C – 700 °C to produce magnetic biochar (MBC) under anaerobic (MBCN) and hypoxic (MBCA) environments in order to investigate the characteristics and risks of heavy metals (HMs) in the MBC. Magnetite dominated the crystal phase of the MBCs obtained at 400 °C to 600 °C. Two forms of zero valent Fe were observed in the MBCs obtained at 700 °C, while γ -Fe was dominant in MBCA 700 and α -Fe was dominant in MBCN 700. Owing to the high concentration of chloride in the sludge, metal chlorides generated by chlorination lowered the pH of the MBCs compared to that of the CFS, except for MBCN 700 because of Fe-C micro-electrolysis. The unstable fractions of some HMs, such as Zn, Cu, Ni, and Mn, increased when the increasing temperature from 400 °C to 700 °C as metal chlorides formed. The percentages of the acid-soluble and exchangeable became zero in MBC 700 because HMs (except for Mn) could be adsorbed by ferric hydroxide colloid during the extraction. The lowest risk assessment code values were obtained in MBC 700 , except for the case of Mn. Compared with the CFS, the potential risk of HMs in the MBCs was significantly reduced, and MBCA 600 presented the lowest environmental risk. This work demonstrates that pyrolysis is a promising and cost-effective method for the safe disposal of HM-polluted CFS and production of MBCs. [ABSTRACT FROM AUTHOR]

The application of nitrogen fertilizers leads to various ecological problems such as nitrate leaching. The use of nitrification inhibitors (NI) as nitrate leaching retardants is a proposal that has been suggested for inclusion in regulations in many countries. In this study, the efficacy of the new NI, 3,4-dimethyl pyrazole phosphate (DMPP), was tested under simulated high-risk leaching situations in two types of undisturbed soil columns. The results showed that the accumulative leaching losses of soil nitrate under treatment of urea with 1. 0% DMPP, from columns of silt loam soil and heavy clay soil, were 66. 8% and 69. 5% lower than those soil columns tested with regular urea application within the 60 days observation, respectively. However, the losses of ammonium leaching were reversely increased 9. 7% and 6. 7% under the former treatment than the latter one. Application of regular urea with 1. 0% DMPP addition can reduce about 59. 3%–63. 1% of total losses of inorganic nitrogen via leaching. The application of DMPP to urea had stimulated the inhibition effects of DMPP on the ammonium nitrification process in the soil up to 60 days. It is proposed that the DMPP could be used as an effective NI to control inorganic N leaching losses, minimizing the risk of nitrate pollution in shallow groundwater. [Copyright &y& Elsevier]

Cr(VI) contamination is widely recognized as one of the major environmental hazards. To address the problem of remediation of soil Cr(VI) contamination and utilization of waste peanut shells, this study comprehensively investigated the effects of peanut shell-derived biochar loaded with root exudates of hyperaccumulator Leersia hexandra Swartz on Cr(VI) reduction and microbial community succession in soil. This study confirmed that root exudate-loaded peanut shell biochar reduced soil pH while simultaneously increasing DOC, sulfide, and Fe(II) concentrations, thereby facilitating the reduction of Cr(VI), achieving a reduction efficiency of 81.8%. Based on XPS and SEM elemental mapping analyses, Cr(VI) reduction occurred concurrently with the Fe and S redox cycles. Furthermore, the microbial diversity, abundance of the functional genera (Geobacter , Arthrobacter , and Desulfococcus) and the metabolic functions associated with Cr(VI) reduction were enhanced by root exudate-loaded biochar. Root exudate-loaded biochar can promote both direct Cr(VI) reduction mediated by the Cr(VI)-reducing bacteria Arthrobacter , and indirect Cr(VI) reduction through Cr/S/Fe co-transformation mediated by the sulfate-reducing bacteria Desulfococcus and Fe(III)-reducing bacteria Geobacter. This study demonstrates the effectiveness of peanut shell biochar loaded with root exudates of hyperaccumulator Leersia hexandra Swartz to promote soil Cr(VI) reduction, reveals the mechanism how root exudate-loaded biochar shapes functional microbial communities to facilitate Cr(VI) reduction, and proposes a viable strategy for Cr(VI) remediation and utilization of peanut shell. [Display omitted] • Peanut shell biochar loaded with root exudates of L. hexandra facilitated Cr(VI) reduction. • Root exudate-loaded biochar enhanced Cr(VI) reduction by shaping microbial communities. • Cr(VI) reduction occurred concurrently with Fe and S redox cycles. • Root exudate-loaded biochar promoted indirect Cr(VI) reduction through Cr/S/Fe co-transformation. • Geobacter , Arthrobacter , and Desulfococcus are involved in Cr(VI) reduction. [ABSTRACT FROM AUTHOR]

Although Cd accumulation varies among rice varieties is recognized, the underlying mechanisms are not well clarified. In this study, comparative transcriptome analysis were performed by hydroponic culture system with two rice varieties, Y1540 (high Cd accumulator) and Y15 (low Cd accumulator) under 20 μM Cd stress. Results revealed 17,320 differentially expressed genes (DEGs) in roots of Y15 (7,655 upregulated and 9,665 downregulated) and 17,386 DEGs in roots of Y1540 (8,823 upregulated and 8,563 downregulated) expose to 20 μM Cd stress. Gene ontology (GO) analysis enriched 24 and 26 terms in Y15 and Y1540 respectively, including 23 common terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed 27 and 28 significant pathways in Y15 and Y1540 respectively, with 19 common pathways. Different responses to Cd stress between cultivars were not only reflected in differently enriched GO terms and KEGG pathways but also in different DEGs of 23 common GO terms and significant sequences represented by p-values of 19 common KEGG pathways. Both cultivars resist Cd through common processes with different weights; hence glutathione metabolism, mineral absorption, biosynthesis of secondary metabolites, and degradation of aromatic compounds could be playing a more important role in Y1540, whereas ribosome biogenesis in eukaryotes, mismatch repair, aminoacyl-tRNA biosynthesis, and the cell cycle maybe playing a more important role in Y15. Weighted gene co-expression network analysis (WGCNA) showed that five and three modules were clustered in Y15 and Y1540, respectively, with yellow and brown modules in Y15 and brown modules in Y1540 being significantly related to Cd stress. Further analysis showed that most of hub genes in Y15 were related to signal transduction or transcription factors, while most of hub genes in Y1540 were related to binding, metabolic, and secondary metabolic processes, which demonstrated their different response patterns at transcriptomic level to Cd stress. [Display omitted] • Y1540 accumulated more Cd than that of Y15 in root. • Cd stress induced more up- and less down-regulated genes in Y1540 than Y15. • Both cultivars resist Cd through common pathways with different weights. • Y15 has transcription factor/signal transduction as core process in Cd resistance. • Y1540 use chelation/metabolic/compartmentalization as core process to resist Cd. [ABSTRACT FROM AUTHOR]