Effects of thifluzamide on soil fungal microbial ecology

A salt-tolerant growth-promoting phyllosphere microbial combination from mangrove plants and its mechanism for promoting salt tolerance in rice

BACKGROUND

Mangrove plants growing in the high salt environment of coastal intertidal zones colonize a variety of microorganisms in the phyllosphere, which have potential salt-tolerant and growth-promoting effects. However, the characteristics of microbial communities in the phyllosphere of mangrove species with and without salt glands and the differences between them remain unknown, and the exploration and the agricultural utilization of functional microbial resources from the leaves of mangrove plants are insufficient.

RESULTS

In this study, we examined six typical mangrove species to unravel the differences in the diversity and structure of phyllosphere microbial communities between mangrove species with or without salt glands. Our results showed that a combination of salt-tolerant growth-promoting strains of Pantoea stewartii A and Bacillus marisflavi Y25 (A + Y25) was constructed from the phyllosphere of mangrove plants, which demonstrated an ability to modulate osmotic substances in rice and regulate the expression of salt-resistance-associated genes. Further metagenomic analysis revealed that exogenous inoculation with A + Y25 increased the rice rhizosphere's specific microbial taxon Chloroflexi, thereby elevating microbial community quorum sensing and ultimately enhancing ionic balance and overall microbial community function to aid salt resistance in rice.

CONCLUSIONS

This study advances our understanding of the mutualistic and symbiotic relationships between mangrove species and their phyllosphere microbial communities. It offers a paradigm for exploring agricultural beneficial microbial resources from mangrove leaves and providing the potential for applying the salt-tolerant bacterial consortium to enhance crop adaptability in saline-alkaline land. Video Abstract.

Fluxapyroxad induced toxicity of earthworms: Insights from multi-level experiments and molecular simulation studies

Fluxapyroxad, an emerging succinate dehydrogenase inhibitor fungicide, is widely used due to its excellent properties. Given its persistence in soil with a 50 % disappearance time of 183-1000 days, it is crucial to evaluate the long-term effects of low-dose fluxapyroxad on non-target soil organisms such as earthworms (Eisenia fetida). The present study investigated the impacts of fluxapyroxad (0.01, 0.1, and 1 mg kg-1) on Eisenia fetida over 56 days, focusing on oxidative stress, digestive and nervous system functions, and histopathological changes. We also explored the mechanisms of fluxapyroxad-enzyme interactions through molecular docking and dynamics simulations. Results demonstrated a significant dose-response relationship in the integrated biomarker response of 12 biochemical indices. Fluxapyroxad altered expression levels of functional genes and induced histopathological damage in earthworm epidermis and intestines. Molecular simulations revealed that fluxapyroxad is directly bound to active sites of critical enzymes, potentially disrupting their structure and function. Even at low doses, long-term fluxapyroxad exposure significantly impacted earthworm physiology, with effects becoming more pronounced over time. Our findings provide crucial insights into the chronic toxicity of fluxapyroxad and emphasize the importance of long-term, low-dose studies in pesticide risk assessment in soil. This research offers valuable guidance for the responsible management and application of fungicides.

Identification of emerging PFAS in industrial sludge from North China: Release risk assessment by the TOP assay

Per- and polyfluoroalkyl substances (PFAS) have been widely used across various industries, leading to their prevalent occurrence in sludges generated by wastewater treatment plants (WWTPs). Consequently, industrial sludges serve as typical reservoirs for PFAS. This study examined 46 target PFAS in sludge samples intended for brick production from nine WWTPs in North China, identifying emerging PFAS and categorizing their behaviors through high-resolution mass spectrometry (HRMS) screening and total oxidizable precursor (TOP) assay. Forty-one PFAS were detected, with trifluoroacetic acid (TFA), perfluorooctane sulfonic acid, and hexafluoropropylene oxide dimer acid being the most prevalent. Twenty-nine emerging PFAS were identified, and their behaviors were categorized using TOP assay. Notably, four CF3-containing PFAS were identified, all confirmed as precursors of TFA, with a molar yield of 16.4 %-25.6 % in Milli-Q water during TOP assay validation. These findings indicate that the transformation of these precursors during sludge recycling may substantially contribute to TFA release, underscoring potential risks associated with secondary PFAS release during sludge resource utilization.

Response of soil fungi to textile dye contamination

This study examines the impact of textile dye contamination on the structure of soil fungal communities near a Shaoxing textile dye factory. We quantified the concentrations of various textile dyes, including anthraquinone azodye and phthalocyanine, which ranged from 20.20 to 140.62 mg kg^-1, 102.01-698.12 mg kg^-1, and 7.78-42.65 mg kg^-1, respectively, within a 1000 m radius of the factory. Our findings indicate that as dye concentration increases, the biodiversity of soil fungi, as measured by the Chao1 index, decreases significantly, highlighting the profound influence of dye contamination on fungal community structure. Additionally, microbial correlation network analysis revealed a reduction in fungal interactions correlating with increased dye concentrations. We also observed that textile dyes suppressed carbon and nitrogen metabolism in fungi while elevating the transcription levels of antioxidant-related genes. Enzymes such as lignin peroxidase (LiP), manganese peroxidase (MnP), laccase (Lac), dye-decolorizing peroxidases (DyPs), and versatile peroxidase (VP) were upregulated in contaminated soils, underscoring the critical role of fungi in dye degradation. These insights contribute to the foundational knowledge required for developing in situ bioremediation technologies for contaminated farmlands.

Evaluating the effects of mefenoxam on taxonomic and functional dynamics of nontarget fungal communities during carrot cultivation

Ridomil Gold SL (45.3% a.i. mefenoxam) is a widely used chemical fungicide for the control of oomycetes. However, its impact on fungal communities remains unexplored. Therefore, the goal of this study was to examine the effects of mefenoxam on the temporal dynamics of fungal taxonomic and functional diversities during carrot cultivation under four treatment groups: mefenoxam application with and without Pythium inoculation, and untreated control groups with and without Pythium inoculation. Our in vitro sensitivity assay showed that the maximum recommended concentration of mefenoxam, 0.24 ppm, did not suppress the mycelial growth of P. irregulare. At 100 ppm, mycelial growth was only reduced by 11.4%, indicating that the isolate was resistant to mefenoxam. MiSeq sequencing data revealed transient taxonomic variations among treatments 2 weeks post-treatment. Mortierella dominated the fungal community in the mefenoxam-Pythium combination treatment, as confirmed through PCR using our newly designed Mortierella-specific primers. Conversely, mefenoxam-Pythium combination had adverse effects on Penicillium, Trichoderma, and Fusarium, and decrease the overall alpha diversity. However, these compositional changes gradually reverted to those observed in the control by the 12th week. The predicted ecological functions of fungal communities in all Pythium and mefenoxam treatments shifted, leading to a decrease in symbiotrophs and plant pathogen functional groups. Moreover, the community-level physiological profiling approach, utilizing 96-well Biolog FF microplates, showed discernible variations in the utilization of 95 diverse carbon sources among the treatments. Notably, arbutin, L-arabinose, Tween 80, and succinamic acid demonstrated a strong positive association with Mortierella. Our findings demonstrate that a single application of mefenoxam at its recommended rate triggers substantial taxonomic and functional shifts in the soil fungal community. Considering this impact, the conventional agricultural practice of repeated mefenoxam application is likely to exert considerable shifts on the soil ecosystem that may affect agricultural sustainability.

Fate characteristics and risk identification of thifluzamide in buckwheat across China: Analytical method development, occurrence, and health assessment

Elaborating on the fate tendency of thifluzamide (thiazole-amide fungicide) in buckwheat based on nationwide application is vital for grain security and human health based on nationwide application. A rapid and sensitive analytical method was developed to trace thifluzamide in buckwheat matrices using an ultrahigh-performance liquid chromatography-tandem triple quadrupole mass spectrometer (UHPLC-MS/MS), with a retention time of 2.90 min and limit of quantitation (LOQ) of 0.001 mg/kg. Thifluzamide could be stably stored for 84 d in buckwheat matrices under -20 °C under dark condition. The occurrence, dissipation and terminal magnitudes of thifluzamide were reflected by the primary deposition of 0.02-0.55 mg/kg, half-lives of 12-14 d, and highest residues of 0.41 mg/kg. The long-term risks (ADI%) of thifluzamide were 37.268 %-131.658 % in registered crops, and the risks for the rural population were significantly higher than those of the urban population. The unacceptable dietary risks of thifluzamide should be continuously emphasized for children aged 2-7 with an ADI% values of 100.750 %-131.658 %. A probabilistic model was further introduced to evaluate the risk discrepancy of thifluzamide in buckwheat, showing the risks in Tartary buckwheat (Fagopyrum tararicum Gaerth) were 1.5-75.4 times than that in sweet buckwheat (Fagopyrum esculentum Moench). Despite the low risks for dietary buckwheat, the high-potential health hazards of thifluzamide should be pay more attention given the increasing applications and cumulative effects.

Earthworms enhance the bioremediation of tris(2-butoxyethyl) phosphate-contaminated soil by releasing degrading microbes

The escalating awareness of the environmental risks posed by organophosphorus flame retardants (OPFRs), e.g., tris(2-butoxyethyl) phosphate (TBOEP), necessitates the development of effective approaches to mitigate their adverse ecological effects. However, research on the remediation of OPFR-contaminated soil remains limited. In this study, a strategy is proposed to enhance the microbial remediation of TBOEP-contaminated soil through the introduction of exotic earthworms (Eisenia fetida). The presence of earthworms led to a substantial increase in the 28-d removal rates of TBOEP at concentrations of 0.05, 0.5, and 5 mg/kg, with improvements of 32.3 ± 2.0%, 33.2 ± 1.3%, and 33.0 ± 5.6% compared to rates in the absence of earthworms, respectively. The underlying mechanisms for this enhancement include the earthworm-mediated enrichment of TBOEP-degrading bacteria, particularly Rhodococcus, Flavobacterium, and Pseudomonas, and the transfer of Rhodococcus from the earthworm gut to the soil, resulting in an increased relative abundance within the soil. Concurrently, the earthworms stimulated soil peroxidase activity, facilitating the oxidative degradation of TBOEP. Furthermore, the rise in dissolved organic matter content following earthworm treatment fostered the growth of degrading bacteria in the soil. Rhodococcus emerged as a dominant contributor to soil TBOEP removal, consuming humic-like compounds in dissolved organic matter. This investigation underscores the significance of gut microbes and offers valuable insights for the application of earthworm-based remediation strategies in OPFR-contaminated soil.

Extreme environmental doses of diisobutyl phthalate exposure induce oxidative stress and DNA damage in earthworms (Eisenia fetida): Evidence at the biochemical and molecular levels

Diisobutyl phthalate (DIBP), as a plasticizer, is widely used and has caused many extreme soil contamination scenarios, posing potential risks to soil fauna. However, the toxic effects and mechanisms of DIBP on soil fauna remain unclear. In this study, earthworms (Eisenia fetida) were used as model animals to explore the subchronic toxicity of extreme DIBP soil exposure (300, 600, and 1200 mg/kg) for 28 days. The results showed that the level of reactive oxygen species (ROS) and the contents of malondialdehyde (MDA) and 8-hydroxydeoxyguanosine (8-OHdG) in E. fetida were significantly increased during continuous DIBP exposure. In addition, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were significantly inhibited while glutathione S-transferase (GST) activity was activated during continuous exposure. Integrated biological response (IBR) analysis showed that DIBP had positive dose-dependent toxicity and negative time-dependent toxicity to E. fetida, and SOD/CAT were selected as sensitive biomarkers. The molecular docking study found that DIBP could stably bind to SOD/CAT through hydrogen bonding, which further proved its sensitivity. This study provides primary data for ecological and environmental risk assessment of extreme dose DIBP soil pollution.

Effects of micro-positive pressure environment on nitrogen conservation and humification enhancement during functional membrane-covered aerobic composting

Aerobic composting is a humification process accompanied by nitrogen loss. This study is the first research systematically investigating and elucidating the mechanism by which functional membrane-covered aerobic composting (FMCAC) reduces nitrogen loss and enhances humification. The variations in bioavailable organic nitrogen (BON) and humic substances (HSs) in different composting systems were quantitatively studied, and the functional succession patterns of fungal groups were determined by high-throughput sequencing and FUNGuild. The FMCAC improved oxygen utilization and pile temperature, increased BON by 29.95 %, reduced nitrogen loss by 34.00 %, and enhanced humification by 26.09 %. Meanwhile, the FMCAC increased the competitive advantage of undefined saprotroph and significantly reduced potential pathogenic fungi (<0.10 %). Structural equation modeling indicated that undefined saprotroph facilitated the humification process by increasing the production of BON and storing BON in stable humic acid. Overall, the FMCAC increased the safety, stability, and quality of the final compost product.

Chemical fumigants control apple replant disease: Microbial community structure-mediated inhibition of Fusarium and degradation of phenolic acids

Fusarium and phenolic acids in apple replant soil have deleterious effects on soil, which affects the growth of young replanted apple trees. Here, we studied the effects of different chemical fumigants (metham sodium, dazomet, calcium cyanamide, 1,3-dichloropropene, and methyl bromide) on Fusarium and phenolic acids in soil. The chemical fumigants disturbed the apple replant soil microbial community to different degrees in the order from highest to the lowest as methyl bromide > 1,3-dichloropropene > dazomet > metham sodium > calcium cyanamide. Compared with the control, the total numbers of Operational Taxonomic Unit (OTU) were 104.63 % and 9.38 % lower in the methyl bromide and calcium cyanamide treatments, respectively while the average contents of Fusarium were 88.04 % and 59.18% lower in these treatments, respectively. Higher disturbance degrees resulted in a slower recovery rate of the soil microbial community, which facilitated the transformation of the soil into a disease-suppressing state. During the recovery process, the roots recruited Streptomyces OTU2796 and Bacillus OTU2243, which alleviated Fusarium-induced stress via the synthesis of polyketones and macrolides. The roots also recruited Sphingomonas OTU3488, OTU5572, and OTU8147, which alleviated phenolic acid-induced stress through the degradation of benzoate and polycyclic aromatic hydrocarbons.