Effects of microplastics on functional genes related to CH4 and N2O metabolism in bacteriophages during manure composting and its planting applications

Hydrogen peroxide-aged biochar mitigating greenhouse gas emissions during co-composting of swine manure with rice bran

Compared to fresh biochar, aged biochar has a more significant effect on mitigating greenhouse gas (GHG) emissions in farmland soil. However, there is a relative scarcity of research addressing this effect in aerobic composting. In this study, a co-composting of swine manure and rice bran (NBC), with the addition of fresh biochar (FBC) and hydrogen peroxide-aged biochar (ABC), was conducted to investigate the dynamic changes in physicochemical properties, microbial communities, GHG emissions and related functional genes during different periods. In comparison to NBC, FBC led to a 32 % decrease in total GHG emissions (CO2-equiv), including a 29 % reduction in CO2 emissions, a 45 % reduction in CH4 emissions, and a 35 % decrease in N2O emissions. Furthermore, ABC resulted in a 14 % decrease in GHG emission (CO2-equiv), comprising a 47 % reduction in CH4 emissions and a 23 % decrease in N2O emissions compared to FBC. These findings indicated that the addition of aged biochar has a more significant impact on GHG reduction during composting. Network analyses, Mantel tests and redundancy analyses suggested that the mechanism behind the lowest GHG emissions in ABC is the reduction of the relative abundance of fungi associated with CH4 emissions, along with the nirS and nirK genes associated with denitrification. This reduction is associated with the decreasing anaerobic zones resulting from the increased pore volume in biochar after aging. Overall, this study demonstrates that hydrogen peroxide aging enhances the GHG-reducing efficiency in biochar, and provides new insights into the development of GHG-reducing technologies in composting.

Organic matter components rather than microbial enzymes and genes predominate CO2/CH4 emissions during composting amended with biochar at different stages

The composting process is accompanied by CO2 and CH4 emissions, leading to environmental pollution and lower fertilizer efficiency. Biochar has been widely applied to mitigate CO2 and CH4 emissions, while its effect when added at different composting stages is till unclear. Therefore, this study investigated the effects of biochar added on day 0, 10, or both days on CO2 and CH4 emissions during composting process, and explored the mechanisms from multiple aspects including physicochemcial properties of compost matrix, degradation of organic matter (OM) components, functional enzyme activities and genes abundances. The findings showed that biochar enhanced the activities of lignocellulolytic enzymes, thus facilitating the degradation of cellulose, hemicellulose and water-soluble organic carbon (WSOC). All biochar addition strategies resulted in higher CO2 emissions and C cycling genes abundances, while addition of 5 % or 10 % biochar on day 10 effectively reduced CH4 emissions by 17 % and 50 %, respectively. Mantel analysis and partial least squares path modeling revealed that OM components played the primary role in influencing CO2 emissions, with physicochemical properties, such as temperature, C/N and pH, playing a secondary role by influencing the degradation of OM and WSOC, while no significant factors were found to directly affected CH4 emissions. Moreover, the lignocellulolytic enzymes and C cycling genes did not show significant impacts on their emissions. This study provides important insights for improving the mitigation on CO2 and CH4 emissions by biochar.

Unlocking the potential differences and effects of the anode and cathode regions on N2O emissions during electric field-assisted aerobic composting

Electric field-assisted aerobic composting (EAC) is a novel strategy for effectively mitigating nitrous oxide (N2O) emissions, but its deeper effects require further exploration. In this study, the differences in N2O emissions between the anode regions (AR) and cathode regions (CR) during EAC were evaluated. The cumulative N2O emission from the compost in CR was 32.77% lower than in AR. Compared to AR, the physicochemical properties of CR contribute to the reduction of N2O emission. PLS-PM analysis suggested that differences in N2O emission are primarily regulated by N-cycling related functional genes and N-containing substances, with different regulatory effects. In AR, functional genes and N-containing substances are significantly positively correlated with N2O emissions, whereas in CR, they are significantly negatively correlated. This study highlights the differences and effects of electrode regions in EAC on N2O emissions, offering new perspectives for future optimization.

Microplastics in agricultural soil: Unveiling their role in shaping soil properties and driving greenhouse gas emissions

Microplastics (MPs) contamination is pervasive in agricultural soils, significantly influencing carbon and nitrogen biogeochemical cycles and altering greenhouse gas (GHG) fluxes. This review examines the sources, status, mechanisms, and ecological consequences of MPs pollution in agricultural soils, with a focus on how MPs modified soil physicochemical properties and microbial gene expression, ultimately impacting GHG emissions. MPs were found to reduce soil water retention, decreasing soil respiration and increasing emissions of CO2, CH₄, and N2O. They also enhanced soil aggregate stability and influenced soil organic carbon (SOC) sequestration, contributing further to GHG emissions. MPs-induced increases in soil pH were associated with suppressed CH₄ and N2O emissions, whereas the abundance of genes encoding enzymes for cellulose and lignin decomposition (e.g., abfA and mnp) stimulated enzyme activity, intensifying N2O release. Additionally, a reduced soil C/N ratio promoted denitrification processes. Changes in microbial communities, including increases in Actinomycetes and Proteobacteria, were observed, with a rise in genes associated with carbon cycling (abfA, manB, xylA) and nitrification-denitrification (nifH, amoA, nirS, nirK), further exacerbating CO2 and N2O emissions. This review provides valuable insights into the complex roles of MPs in GHG dynamics in agricultural soils, offering perspectives for improving environmental management strategies.

A critical review of microplastic pollution in breeding industry: Sources, distribution, impacts, and characterization techniques, mitigation strategies and future research directions

Microplastic (MP) pollution has garnered significant attention due to its detrimental effects on ecosystems and human health. If MPs contaminate farmed animals, they are more likely to enter the human body through the food chain, thereby impacting human health. Exploring MPs in breeding industry can provide a theoretical basis for breeding industry to prevent MP pollution. However, there is currently a lack of comprehensive summaries and overviews of MPs research in the industry as a whole. The core focus of the review is to improve our understanding of MPs in the breeding industry and provide valuable references and support for the development of mitigation strategies and policies. The review found that there are more studies related to MP pollution in the breeding industry, but there is inadequate information on the prevention and control technology. This review proposes strategies for prevention and control and discusses future research directions.

Micro/nanoplastics pollution poses a potential threat to soil health

Micro/nanoplastic (MNP) pollution in soil ecosystems has become a growing environmental concern globally. However, the comprehensive impacts of MNPs on soil health have not yet been explored. We conducted a hierarchical meta-analysis of over 5000 observations from 228 articles to assess the broad impacts of MNPs on soil health parameters (represented by 20 indicators relevant to crop growth, animal health, greenhouse gas emissions, microbial diversity, and pollutant transfer) and whether the impacts depended on MNP properties. We found that MNP exposure significantly inhibited crop biomass and germination, and reduced earthworm growth and survival rate. Under MNP exposure, the emissions of soil greenhouse gases (CO2, N2O, and CH4) were significantly increased. MNP exposure caused a decrease in soil bacteria diversity. Importantly, the magnitude of impact of the soil-based parameters was dependent on MNP dose and size; however, there is no significant difference in MNP type (biodegradable and conventional MNPs). Moreover, MNPs significantly reduced As uptake by plants, but promoted plant Cd accumulation. Using an analytical hierarchy process, we quantified the negative impacts of MNP exposure on soil health as a mean value of -10.2% (-17.5% to -2.57%). Overall, this analysis provides new insights for assessing potential risks of MNP pollution to soil ecosystem functions.

Microbial necromass facilitated the humification process through amino sugar reactions during the co-composting of cow manure plus sawdust

Humus (HS) reservoirs can embed microbial necromass (including cell wall components that are intact or with varying degrees of fragmentation) in small pores, raising widespread concerns about the potential for C/N interception and stability in composting systems. In this study, fresh cow manure and sawdust were used for microbial solid fermentation, and the significance of microbial residues in promoting humification was elucidated by measuring their physicochemical properties and analyzing their microbial informatics. These results showed that the stimulation of external carbon sources (NaHCO3) led to an increase in the accumulation of bacterial necromass C/N from 6.19 and 0.91 µg/mg to 21.57 and 3.20 µg/mg, respectively. Additionally, fungal necromass C/N values were about 3 times higher than the initial values. This contributed to the increase in HS content and the increased condensation of polysaccharides and nitrogen-containing compounds during maturation. The formation of cellular debris mainly depends on the enrichment of Actinobacteria, Proteobacteria, Ascomycota, and Chytridiomycota. Furthermore, Euryarchaeota was the core functional microorganism secreting cell wall lytic enzymes (including AA3, AA7, GH23, and GH15). In conclusion, this study comprehensively analyzed the transformation mechanisms of cellular residuals at different profile scales, providing new insights into C/N cycles and sequestration.

Insight into N2O emission and denitrifier communities under different aeration intensities in composting of cattle manure from perspective of multi-factor interaction analysis

Nitrous oxide (N2O) emission from composting is a significant contributor to greenhouse effect and ozone depletion, which poses a threat to environment. To address the challenge of mitigating N2O emission during composting, this study investigated the response of N2O emission and denitrifier communities (detected by metagenome sequencing) to aeration intensities of 6 L/min (C6), 12 L/min (C12), and 18 L/min (C18) in cattle manure composting using multi-factor interaction analysis. Results showed that N2O emission occurred mainly at mesophilic phase. Cumulative N2O emission (QN2O, 9.79 mg·kg-1 DW) and total nitrogen loss (TN loss, 16.40 %) in C12 composting treatment were significantly lower than those in the other two treatments. The lower activity of denitrifying enzymes and the more complex and balanced network of denitrifiers and environmental factors might be responsible for the lower N2O emission. Denitrification was confirmed to be the major pathway for N2O production. Moisture content (MC) and Luteimonas were the key factors affecting N2O emission, and nosZ-carrying denitrifier played a significant role in reducing N2O emission. Although relative abundance of nirS was lower than that of nirK significantly (P < 0.05), nirS was the key gene influencing N2O emission. Community composition of denitrifier varied significantly with different aeration treatments (R2 = 0.931, P = 0.001), and Achromobacter was unique to C12 at mesophilic phase. Physicochemical factors had higher effect on QN2O, whereas denitrifying genes, enzymes and NOX- had lower effect on QN2O in C12. The complex relationship between N2O emission and the related factors could be explained by multi-factor interaction analysis more comprehensively. This study provided a novel understanding of mechanism of N2O emission regulated by aeration intensity in composting.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.

Semi-permeable membrane-covered high-temperature aerobic composting: A review

Semi-permeable membrane-covered high-temperature aerobic composting (SMHC) is a suitable technology for the safe treatment and disposal of organic solid waste as well as for improving the quality of the final compost. This paper presents a comprehensive summary of the impact of semi-permeable membranes centered on expanded polytetrafluoroethylene (e-PTFE) on compost physicochemical properties, carbon and nitrogen transformations, greenhouse gas emission reduction, microbial community succession, antibiotic removal, and antibiotic resistance genes migration. It is worth noting that the semi-permeable membrane can form a micro-positive pressure environment under the membrane, promote the uniform distribution of air in the heap, reduce the proportion of anaerobic area in the heap, improve the decomposition rate of organic matter, accelerate the decomposition of compost and improve the quality of compost. In addition, this paper presents several recommendations for future research areas in the SMHC. This investigation aims to guide for implementation of semi-permeable membranes in high-temperature aerobic fermentation processes by systematically compiling the latest research progress on SMHC.

Incorporating microbial inoculants to reduce nitrogen loss during sludge composting by suppressing denitrification and promoting ammonia assimilation

To address the challenge of increasing nitrogen retention in compost, this study investigated the effects of microbial communities on denitrification and ammonia assimilation during sludge composting by inoculating microbial inoculants. The results showed that the retention rates of total Kjeldahl nitrogen (TKN) and humic acid (HA) in MIs group (with microbial inoculants) were 4.94 % and 18.52 % higher than those in the control group (CK), respectively. Metagenomic analysis showed that Actinobacteria and Proteobacteria were identified as main microorganisms contributing to denitrification and ammonia assimilation. The addition of microbial agents altered the structure of the microbial community, which in turn stimulated the expression of functional genes. During cooling period, the ammonia assimilation genes glnA, gltB and gltD in MIs were 15.98 %, 24.84 % and 32.88 % higher than those in CK, respectively. Canonical correspondence analysis revealed a positive correlation between the dominant bacterial genera from the cooling stage to the maturity stage and the levels of NO3--N, NH4+-N, HA, and TKN contents. NH4+-N was positively correlated with HA, indicating NH4+-N might be incorporated into HA. Heat map and network analyses revealed NH4+-N as a key factor affecting functional genes of denitrification and ammonia assimilation, with Nitrospira identified as the core bacteria in the microbial network. Therefore, the addition of microbial agents could increase nitrogen retention and improve compost product quality.