Two types nitrogen source supply adjusted interaction patterns of bacterial community to affect humifaction process of rice straw composting

Response of bacterial ecological and functional properties to anthropogenic interventions during maturation of mine sand soil

Soil formation is a complex process that starts from the biological development. The ecological principles and biological function in soil are of great importance, whereas their response to anthropogenic intervention has been poorly understood. In this study, a 150-day microcosmic experiment was conducted with the addition of sludge and/or fermented wood chips (FWC) to promote the soil maturation. The results showed that, compared to the control (natural development without anthropogenic intervention), sludge, FWC, and their combination increased the availability of carbon, nitrogen, and potassium, and promoted the soil aggregation. They also enhanced the cellulase activity, microbial biomass carbon (MBC) and bacterial diversity, indicating that anthropogenic interventions promoted the maturation of sand soil. Molecular ecology network and functional analyses indicated that soil maturation was accomplished with the enhancement of ecosystem functionality and stability. Specifically, sludge promoted a transition in bacterial community function from denitrification to nitrification, facilitated the degradation of easily degradable organic matter, and enhanced the autotrophic nutritional mode. FWC facilitated the transition of bacterial function from denitrification to ammonification, promoted the degradation of recalcitrant organic matter, and simultaneously enhanced both autotrophic and heterotrophic nutritional modes. Although both sludge and FWC promoted the soil functionality, they showed distinct mechanistic actions, with sludge enhancing the physical structure, and FWC altering chemical composition. It is also worth emphasizing that sludge and FWC exhibited a synergistic effect in promoting biological development and ecosystem stability, thereby providing an effective avenue for soil maturation.

Enhancing simultaneous nitrogen and phosphorus availability through biochar addition during Chinese medicinal herbal residues composting: Synergism of microbes and humus

The disposal of Chinese medicinal herbal residues (CMHRs) derived from Chinese medicine extraction poses a significant environmental challenge. Aerobic composting presents a sustainable treatment method, yet optimizing nutrient conversion remains a critical concern. This study investigated the effect and mechanism of biochar addition on nitrogen and phosphorus transformation to enhance the efficacy and quality of compost products. The findings reveal that incorporating biochar considerably enhanced the process of nutrient conversion. Specifically, biochar addition promoted the retention of bioavailable organic nitrogen and reduced nitrogen loss by 28.1 %. Meanwhile, adding biochar inhibited the conversion of available phosphorus to non-available phosphorus while enhancing its conversion to moderately available phosphorus, thereby preserving phosphorus availability post-composting. Furthermore, the inclusion of biochar altered microbial community structure and fostered organic matter retention and humus formation, ultimately affecting the modification of nitrogen and phosphorus forms. Structural equation modeling revealed that microbial community had a more pronounced impact on bioavailable organic nitrogen, while humic acid exerted a more significant effect on phosphorus availability. This research provides a viable approach and foundation for regulating the levels of nitrogen and phosphorus nutrients during composting, serving as a valuable reference for the development of sustainable utilization technologies pertaining to CMHRs.

Unraveling the ecological mechanisms of Aluminum on microbial community succession in epiphytic biofilms on Vallisneria natans leaves: Novel insights from microbial interactions

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans, elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems.

Phosphate additives promote humic acid carbon and nitrogen skeleton formation by regulating precursors and composting bacterial communities

This study aimed to compare the effect of different phosphate additives including superphosphate (CP) and MP [Mg(OH)2 + H3PO4] on nitrogen conversion, humus fractions formation and bacterial community in food waste compost. The results showed the ratio of humic acid nitrogen in total nitrogen (HA-N/TN) in CP increased by 49 %. Ammonium nitrogen accumulation was increased by 75 % (CP) and 44 % (MP). Spectroscopic techniques proved that phosphate addition facilitated the formation of complex structures in HA. CP enhanced the dominance of Saccharomonospora, while Thermobifida and Bacillus were improved in MP. Structural equation modeling and network analysis demonstrated that ammonium nitrogen can be converted to HA-N and has positive effects on bacterial composition, reducing sugars and amino acids, especially in CP with more clustered network and synergic bacterial interactions. Therefore, the addition of phosphate provides a new idea to regulate the retained nitrogen toward humification in composting.

The impact of microbial inoculants on large-scale composting of straw and manure under natural low-temperature conditions

Understanding large-scale composting under natural conditions is essential for improving waste management and promoting sustainable agriculture. In this study, corn straw (400 tons) and pig manure (200 tons) were composted with microbial inoculants. The thermophilic phase of composting lasted for fourteen weeks, resulting in an alkaline final product. Microbial systems with low-temperature initiation and high-temperature fermentation played a crucial role in enhancing lignocellulose degradation and humic substances (HS) formation. Adding microbes, including Rhodanobacter, Pseudomonas, and Planococcus, showed a positive correlation with degradation rates of cellulose, hemicellulose, and lignin. Bacillus, Planococcus, and Acinetobacter were positively correlated with HS formation. Microorganisms facilitated efficient hydrolysis of lignocelluloses, providing humic precursors to accelerate composting humification through phenolic protein and Maillard pathways. This study provides significant insights into large-scale composting under natural conditions, contributing to the advancement of waste management strategies and the promotion of sustainable agriculture.

Shifts in structure and dynamics of the soil microbiome in biofuel/fuel blend-affected areas triggered by different bioremediation treatments

The use of biofuels has grown in the last decades as a consequence of the direct environmental impacts of fossil fuel use. Elucidating structure, diversity, species interactions, and assembly mechanisms of microbiomes is crucial for understanding the influence of environmental disturbances. However, little is known about how contamination with biofuel/petrofuel blends alters the soil microbiome. Here, we studied the dynamics in the soil microbiome structure and composition of four field areas under long-term contamination with biofuel/fossil fuel blends (ethanol 10% and gasoline 90%-E10; ethanol 25% and gasoline 75%-E25; soybean biodiesel 20% and diesel 80%-B20) submitted to different bioremediation treatments along a temporal gradient. Soil microbiomes from biodiesel-polluted areas exhibited higher richness and diversity index values and more complex microbial communities than ethanol-polluted areas. Additionally, monitored natural attenuation B20-polluted areas were less affected by perturbations caused by bioremediation treatments. As a consequence, once biostimulation was applied, the degradation was slower compared with areas previously actively treated. In soils with low diversity and richness, the impact of bioremediation treatments on the microbiomes was greater, and as a result, the hydrocarbon degradation extent was higher. The network analysis showed that all abundant keystone taxa corresponded to well-known degraders, suggesting that the abundant species are core targets for biostimulation in soil remediation processes. Altogether, these findings showed that the knowledge gained through the study of microbiomes in contaminated areas may help design and conduct optimized bioremediation approaches, paving the way for future rationalized and efficient pollutant mitigation strategies.

Foliar Application of Nanoparticles Reduced Cadmium Content in Wheat (Triticum aestivum L.) Grains via Long-Distance "Leaf-Root-Microorganism" Regulation

Foliar application of beneficial nanoparticles (NPs) exhibits potential in reducing cadmium (Cd) uptake in crops, necessitating a systematic understanding of their leaf-root-microorganism process for sustainable development of efficient nano-enabled agrochemicals. Herein, wheat grown in Cd-contaminated soil (5.23 mg/kg) was sprayed with different rates of four commonly used NPs, including nano selenium (SeNPs)/silica (SiO2NPs)/zinc oxide/manganese dioxide. SeNPs and SiO2NPs most effectively reduced the Cd concentration in wheat grains. Compared to the control, Cd concentration in grains was significantly decreased by 35.0 and 33.3% by applying 0.96 mg/plant SeNPs and 2.4 mg/plant SiO2NPs, and the grain yield was significantly increased by 33.9% with SeNPs application. Down-regulated gene expression of Cd transport proteins (TaNramp5 and TaLCT1) and up-regulated gene expression of vacuolar Cd fixation proteins (TaHMA3 and TaTM20) were observed with foliar SeNPs and SiO2NPs use. SeNPs increased the levels of leaf antioxidant metabolites. Additionally, foliar spray of SeNPs resulted in lower abundances of rhizosphere organic acids and reduced Cd bioavailability in rhizosphere soil, and soil microorganisms related to carbon and nitrogen (Solirubrobacter and Pedomicrobium) were promoted. Our findings underscore the potential of the foliar application of SeNPs and SiO2NPs as a plant and rhizosphere soil metabolism-regulating approach to reduce Cd accumulation in wheat grains.

Investigating fungal community characteristics in co-composted cotton stalk and various livestock manure products

Agricultural wastes, comprising cotton straw and livestock manure, can be effectively managed through aerobic co-composting. Nevertheless, the quality and microbial characteristics of co-composting products from different sources remain unclear. Therefore, this study utilized livestock manure from various sources in Xinjiang, China, including herbivorous sheep manure (G), omnivorous pigeon manure (Y), and pigeon-sheep mixture (GY) alongside cotton stalks, for a 40-day co-composting process. We monitored physicochemical changes, assessed compost characteristics, and investigated fungal community. The results indicate that all three composts met established composting criteria, with compost G exhibiting the fastest microbial growth and achieving the highest quality. Ascomycota emerged as the predominant taxon in three compost products. Remarkably, at the genus level, the biomarker species for G, Y, and GY are Petromyces and Cordyceps, Neurospora, and Neosartorya, respectively. Microorganisms play a pivotal role in organic matter degradation, impacting nutrient composition, demonstrating significant potential for the decomposition and transformation of compost components. Redundancy analysis indicates that potassium, total organic carbon, and C:N are key factors influencing fungal communities. This study elucidates organic matter degradation in co-composting straw and livestock manure diverse sources, optimizing treatment for efficient agricultural waste utilization and sustainable practices.

Revealing the response characteristics of periphyton biomass and community structure to sulfamethoxazole exposure in aquaculture water: The perspective of microbial network relationships

The widespread application of sulfonamide antibiotics in aquaculture has raised concerns about their adverse environmental impacts. Periphyton plays a crucial role in the aquatic ecosystem. In this study, we examined sulfamethoxazole (SMX) effects on the community structure and interactions of periphyton in simulated aquaculture water. Our findings indicated that the total biomass of periphyton decreased, while the biomass of periphytic algae and the secretion of extracellular polymeric substances (EPS) increased at 0.7 × 10-3 mg/L. Under higher SMX concentrations (5 mg/L and 10 mg/L), periphyton growth was severely inhibited, the microbial community structure of periphyton were sharply altered, characterized by the cyanobacteria growth suppression and decrease in the diversity index of community. Furthermore, elevated SMX concentrations (5 mg/L and 10 mg/L) increased the ratio of negative relationships from 45.4% to 49.4%, which suggested that high SMX concentrations promoted potential competition among microbes and disrupted the microbial food webs in periphyton. The absolute abundance of sul1 and sul2 genes in T2 and T3 groups were 2-3 orders of magnitude higher than those in control group after 30 days of SMX exposure, which elevated the risk of resistance gene enrichment and dissemination in the natural environment. The study contributes to our understanding of the detrimental effects of antibiotic pollution, which can induce changes in the structure and interaction relationship of microbial communities in aquaculture water.

Inoculating functional bacteria improved the humification process by regulating microbial networks and key genera in straw composting by adding different nitrogen sources

The aim of this study was to compare the effect of functional inoculant and different nitrogen sources on the relationship among lignocellulose, precursors, and humus as well as their interactions with bacterial genera in straw composting. Results showed that inoculation improved the heating process and retained more nitrate compared to control. Inoculation increased the degradation of lignocellulosic components by 26.9%-81.6% and the formation of humus by 15.7%-23.0%. Bioinformatics analysis showed that inoculation enriched key genera Chryseolinea in complex nitrogen source (pig manure) compost and Pusillimas, Luteimonas, and Flavobacteria in single nitrogen source (urea) compost, which were related to humus formation. Network analysis found that inoculation and urea addition improved the microbial synergistic effect and inoculation combined with pig manure had more complex modularity and interactions. Combining the functional bacterial inoculant with urea helped to enhance the degradation of lignocellulose and humification process during straw composting especially with single nitrogen source.

Continuous thermophilic composting of distilled grain waste improved organic matter stability and succession of bacterial community

Continuous thermophilic composting (CTC) is potentially helpful in shortening the composting cycle. However, its universal effectiveness and the microbiological mechanisms involved are unclear. Here, the physicochemical properties and bacterial community dynamics during composting of distilled grain waste in conventional and CTC models were compared. CTC accelerated the organic matter degradation rate (0.2 vs. 0.1 d-1) and shortened the composting cycle (24 vs. 65 d), mainly driven by the synergism of bacterial genera. Microbial analysis revealed that the abundance of Firmicutes was remarkably improved compared to that in conventional composting, and Firmicutes became the primary bacterial phylum (relative abundance >70 %) during the entire CTC process. Moreover, correlation analysis demonstrated that bacterial composition had a remarkable effect on the seed germination index. Therefore, controlling the composting process under continuous thermophilic conditions is beneficial for enhancing composting efficiency and strengthening the cooperation between bacterial genera.

Change of core microorganisms and nitrogen conversion pathways in chicken manure composts by different substrates to reduce nitrogen losses

Due to the rapid development of animal husbandry, the associated environmental problems cannot be ignored, with the management of livestock and poultry manure emerging as the most prominent issue. Composting technology has been widely used in livestock and poultry manure management. A deeper understanding of the nitrogen conversion process during composting offers a theoretical foundation for selecting compost substrates. In this study, the effects of sawdust (CK) and spent mushroom compost (T1) as auxiliary materials on nitrogen as well as microbial structure in the composting process when composted with chicken manure were investigated. At the end of composting, the nitrogen loss of T1 was reduced by 17.18% relative to CK. When used as a compost substrate, spent mushroom compost accelerates the succession of microbial communities within the compost pile and alters the core microbial communities within the microbial community. Bacterial genera capable of cellulose degradation (Fibrobacter, Herbinix) are new core microorganisms that influence the assimilation of nitrate reduction during compost maturation. Using spent mushroom compost as a composting substrate increased the enzyme activity of nitrogen assimilation while decreasing the enzyme activity of the denitrification pathway.

Accelerating the humification of mushroom waste by regulating nitrogen sources composition: Deciphering mechanism from bioavailability and molecular perspective

Regulating nitrogen source composition is efficient approach to accelerate the spent mushroom substrate (SMS) composting process. However, currently, most traditional composting study only focuses on total C/N ratio of initial composting material. Rarely research concerns the effect of carbon or nitrogen components at different degradable level and their corresponding decomposed-substances on humification process. This study deciphers and compares the mechanism of mixed manure-N sources on SMS humification from bioavailability and molecular perspective. Two different biodegradable manure-N sources, cattle manure (CM) and Hainan chicken manure (CH), were added into the SMS composting with the different CM:CH ratio of 1:0, 3:1, 1:1, 1:3, and 0:1, respectively. The physicochemical properties and humic substances were determined to evaluate the compost quality. Coupling analysis of spectroscopy, fluorescence, and humic intermediate precursors were conducted to characterizing molecular formation process of humic acid (HA). The results indicated that regulating the carbon-nitrogen nutrient biodegradability of composting material by adding mixed nitrogen sources is an effective strategy to accelerate the SMS humification process. The C1H3 (CM:CH ratio of 1:3) and CH treatments obtained great physicochemical properties and the highest growth rate of HA (31.96% and 27.02%, respectively). The rapid reaction of polysaccharide, ketone, quinone, and amide in DOM (LCP1) might be the key for the fast humification in C1H3 and CH. The polyphenol, reducing sugar and amino acid originated from the labile-carbon-proportion I (LCP1) and recalcitrant-carbon-proportion (RCP), labile-carbon-proportion II (LCP2) and RCP, and labile-nitrogen-proportion I (LNP1), respectively, were the main driving intermediate precursors for the formation of HA. This study deciphers the SMS humification mechanism at molecular level and provides a strategy in accelerating-regulating the composting process. which will be beneficial for enhancing the disposing efficiency of SMS, producing high-quality organic fertilizer, and even popularizing to the similar types of organic waste in practical field.

Soil microbial community composition and co-occurrence network responses to mild and severe disturbances in volcanic areas

Soil physicochemical properties and vegetation types are the main factors affecting soil microorganisms, but there are few studies on the effects of the disturbance following volcanic eruption. To make up for this lack of knowledge, we used Illumina Miseq high-throughput sequencing to study the characteristics of soil microorganisms on both shores of a volcanically disturbed lake. Soil microorganisms in the two sites were subjected to different degrees of volcanic disturbance and showed significant heterogeneity. Mild volcanic disturbance area had higher enrichment of prokaryotic community. Co-occurrence network analysis showed that a total of 12 keystone taxa (9 prokaryotes and 3 fungi) were identified, suggesting that soil prokaryote may play a more significant role than fungi in overall community structure and function. Compared with severe volcanic disturbance area, the soil microbial community in mild volcanic disturbance area had the higher modular network (0.327 vs 0.291). The competition was stronger (positive/negative link ratio, P/N: 1.422 vs 1.159). Random forest analysis showed that soil superoxide dismutase was the most significant variable associated with soil microbial community. Structural equation model (SEM) results showed that keystone had a directly positive effect on prokaryotic (λ = 0.867, P < 0.001) and fungal (λ = 0.990, P < 0.001) multifunctionality while had also a directly positive effect on fungal diversity (λ = 0.553, P < 0.001), suggesting that keystone taxa played a key role in maintaining ecosystem stability. These results were important for understanding the effects of different levels of volcanic disturbance on soil ecosystems.

Quorum sensing in different subcommunities becomes the key factor affecting the humification of the aerobic composting system with sauerkraut fermentation wastewater

Aerobic composting is an effective and harmless method to treat Sauerkraut fermentation wastewater (SFW). Given the limited understanding of the effect of quorum sensing (QS) on humification in subcommunities under acidic environments, a large-scale analysis was conducted to identify features that impact the response of QS to humification in different subcommunities. The results showed that the addition of SFW directly affected humification in subcommunities A and C, and the abundances of functional genes related to carbon fixation and carbon degradation were significantly increased at 7 and 15 d, respectively. In addition, subcommunity B indirectly affected humus production but regulated carbon metabolic pathways such as glycolysis/gluconeogenesis and pentose phosphate by QS with subcommunities B. These findings provide a novel perspective for analysing the regulation of humification in aerobic composting and suggest that composting has potential applications in organic wastewater treatment.

Bacterial community dynamics and co-occurrence network patterns during different stages of biochar-driven composting

Bacterial communities were dynamically tracked at four stages of biochar-driven sheep manure pile composting, and the co-occurrence networks with keystone taxa were established. The succession of bacterial community obvious varied during the composting process, Proteobacteria predominant in initial stage (39%) then shifted into Firmicutes in thermophilic (41%) and mesophilic (27%) stages, finally the maturation stage dominant by Bacteroidota (26%). Visualizations of bacterial co-occurrence networks demonstrate more cooperative mutualism and complex interactions in the thermophilic and mesophilic phases. Noticeably, the 7.5 and 10% biochar amended composts shown highest connections (736 and 663 total links) and positive cooperation (97.37 and 97.13% positive link) as well as higher closeness centrality and betweenness centrality of keystone taxa. Overall, appropriate biochar addition alters bacterial community succession and strengthens connection between keystone taxa and other bacteria, with 7.5 and 10% biochar amended composts has intense mutualistic symbiosis among bacterial communities.

Microbial response to nitrogen removal driven by combined iron and biomass in subsurface flow constructed wetlands with plants of different ages

This study investigated the nitrogen removal enhanced by combined iron scraps and plant biomass, and its microbial response in the wetland with different plant ages and temperatures. The results showed that older plants benefitted the efficiency and stability of nitrogen removal, which could reach 1.97 ± 0.25 g m^-2 d^-1 in summer and 0.42 ± 0.12 g m^-2 d^-1 in winter. Plant age and temperature were the main factors determining the microbial community structure. Compared with temperature, plant ages affected more significantly on relative abundance of microorganisms such as Chloroflexi, Nitrospirae, Bacteroidetes and Cyanobacteria, and functional genera for nitrification (e.g., Nitrospira) and iron reduction (e.g., Geothrix). The absolute abundance of total bacterial 16S rRNA ranged from 5.22 × 10⁸ to 2.63 × 10⁹ copies g^-1 and presented extremely significant negative correlation to plant age, which would lead to a decline in microbial function on information storage and processing. The quantitative relationship further revealed that the ammonia removal was related to 16S rRNA and AOB amoA, while nitrate removal was controlled by 16S rRNA, narG, norB and AOA amoA jointly. These findings suggested that a mature wetland for nitrogen removal enhancement should focus on aging microbes caused by old plants and possible endogenous pollution.

A novel carbon-nitrogen coupled metabolic pathway promotes the recyclability of nitrogen in composting habitats

This study revealed a novel carbon-nitrogen coupled metabolic pathway. Results showed that the addition of inorganic carbon sources slowed down the decomposition of urea and conserved more nutrients in composting. Metagenomic analysis showed that the main bacteria involved in this new pathway were Actinobacteria, Proteobacteria and Firmicutes. During the late composting period, the dominant genus Microbacteium involved in denitrification accounted for 22.18% in control (CP) and only 0.12% in treatment group (T). Moreover, ureC, rocF, argF, argI, argG were key genes involved in urea cycle. The abundance of functional gene ureC and denitrification genes decreased in thermophilic and cooling phases, respectively. The genes hao, nosZ, ureA and nifH were more closely associated with Chloroflexi_bacterium and Bacillus_paralichenformis. In conclusion, composting habitats with additional inorganic carbon sources could not only weaken denitrification but also allow more nitrogen to be conserved through slow-release urea to improve resource utilization and decrease the environmental risk.

Changes in soil Cd contents and microbial communities following Cd-containing straw return

Contamination of soil with cadmium (Cd) threatens food safety and human health. In general, crop straws from contaminated soils could accumulate considerable amounts of Cd. The addition of Cd-containing rice straw can have negative effects on soil environment. In this study, straws varying in Cd concentration were added to soil at a rate of 5% (w/w) to investigate the effects of Cd-containing straw on soil Cd dynamics and soil microbial communities. Results showed that large amounts of Cd, especially bioavailable Cd, were released into soil during the decomposition of Cd-containing straws. The addition of straws with 10, 20 and 40 mg kg^-1 Cd increased total Cd in soils from 0.31 mg kg^-1 to 0.89, 1.39 and 2.09 mg kg^-1, respectively, exceeding the screening value of total Cd < 0.4 mg kg^-1 for paddy soils of pH 5.5-6.5 according to Chinese Soil Environmental Quality Standards. Moreover, the addition of Cd-containing straw decreased alpha-diversity of bacterial and fungal communities compared to the clean straw. Indeed, changes in soil factors including pH, Eh, dissolved organic C and Cd level jointly reconstructed soil microbial communities. The addition of Cd-containing straw increased the relative abundance of bacterial species Acidobacteria and Proteobacteria but decreased that of Firmicutes. Meanwhile, it increased the relative abundance of fungal species Basidiomycota and Fusarium which were considered Cd-tolerant. This study revealed the potential environmental risk and the variation of microbial communities caused by increasing soil Cd bioavailability after direct application of Cd-containing rice straw to the field.

Valorizing kitchen waste to produce value-added fertilizer by thermophilic semi-continuous composting followed by static stacking: Performance and bacterial community succession analysis

To explore an effective decentralized kitchen waste (KW) treatment system, the performance and bacterial community succession of thermophilic semi-continuous composting (TSC) of KW followed by static stacking (SS) was studied. A daily feeding ratio of 10% ensured stable performance of TSC using an integrated automatic reactor; the efficiencies of organic matter degradation and seed germination index (GI) reached 80.88% and 78.51%, respectively. SS for seven days further promoted the quality of the compost by improving the GI to 91.58%. Alpha- and beta-diversity analyses revealed significant differences between the bacterial communities of TSC and SS. Firmicutes, Actinobacteria, Chloroflexi, Gemmatimonadetes, and Myxococcota were dominant during the TSC of KW, whereas the members of Proteobacteria and Bacteroidetes responsible for product maturity rapidly proliferated during the subsequent SS and ultimately dominated the compost with Firmicutes and Actinobacteria. These results provide new perspectives for decentralized KW treatment using TSC for practical applications.

Insight into humification of mushroom residues under addition of Rich-N sources: Comparing key molecular evolution processes using EEM-PARAFAC and 2D-FTIR-COS analysis

Accelerating the humification of organic solid waste is one of the most important issues in composting. This present study aims to study and compare the humification process of different rich-N sources (chicken manure, cattle manure, and urea) addition during the composting of mushroom residues, from macro physicochemical properties to micro humic molecular structure evolution process. The physicochemical elements and humic components were determined for evaluating the compost quality and humification degree as composting proceed. The coupled analysis of excitation-emission matrix with parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation with Fourier transform infrared spectrum (2D-FTIR-COS) were used to characterize the functional molecular structure evolution of dissolved organic matter during humification process. The results indicated that the rank order for humification level were the treatments of chicken manure (HM), urea (UM), cattle manure (CM), and single mushroom residue treatment (CK), with their humification index of 22.18%, 22.05%, 18.47%, and 16.52%, respectively. Humic substance, humic acid, and fulvic acid were obtained the highest in HM treatment with contents of 35.41 ± 0.86%, 23.32 ± 1.57%, and 10.97 ± 0.52%, respectively. The rich-N source addition enhanced the degradation of protein-like and polysaccharides-like substances in dissolved organic matter, thus accelerating the humification process of mushroom residues. The key structure evolution of dissolved organic matter in the HM treatment, in which the CO and CC stretching of quinone, amide, or ketone, and the C-O stretching of polysaccharides may be responsible for the faster formation of humus compared to the other nitrogen treatments. In this study, redundancy analysis indicated that the total nitrogen (TN) and nitrate nitrogen (NO₃^--N) may be the potential indicators for determining the humification level as composting proceed. The result provides significant insight into the humification mechanism of mushroom residue under different types of nitrogen sources at the molecular level, and will be reference for improving the composting technique in practical field.

Evaluation of physicochemical properties, bacterial community, and product fertility during rice straw composting supplemented with different nitrogen-rich wastes

This study evaluated the compostability of rice straw as the main feedstock (75 % in dry weight), supplemented with three different nitrogen-rich wastes, namely food waste (FW), dairy manure (DM), and sewage sludge (SS). Organic matter (OM) degradation, maturity and fertility of the end-product, and bacterial community structure during the composting processes were compared. All composting processes generated mature end-product within 51 days. Notably, FW addition was more effective to accelerate rice straw OM degradation and significantly improved end-product fertility with a high yield of Chinese cabbage. The succession of the bacterial community was accelerated with FW supplementation. Genera Geobacillus, Chryseolinea, and Blastocatella were significantly enriched during the composting of rice straw with FW supplementation. Finally, temperature, total nitrogen, moisture, pH, and total carbon were the key factors affecting microorganisms. This study provides a promising alternative method to enhance the disposal of larger amounts of rice straw in a shorter time.

Community succession of microbial populations related to CNPS biological transformations regulates product maturity during cow-manure-driven composting

The main objective of present study was to understand the community succession of microbial populations related to carbon-nitrogen-phosphorus-sulfur (CNPS) biogeochemical cycles during cow-manure-driven composting and their correlation with product maturity. The abundance of microbial populations associated with C degradation, nitrification, cellular-P transport, inorganic-P dissolution, and organic-P mineralization decreased gradually with composting but increased at the maturation phase. The abundance of populations related to N-fixation, nitrate-reduction, and ammonification increased during the mesophilic stage and decreased during the thermophilic and maturation stages. The abundance of populations related to C fixation and denitrification increased with composting; however, the latter tended to decrease at the maturation stage. Populations related to organic-P mineralization were the key manipulators regulating compost maturity, followed by those related to denitrification and nitrification; those populations were mediated by inorganic N and available P content. This study highlighted the consequence of microbe-driven P mineralization in improving composting efficiency and product quality.

Role of fungal communities and their interaction with bacterial communities on carbon and nitrogen component transformation in composting with different phosphate additives

The aim of the study was to compare the succession of fungal community and their interaction with bacterial community during pig manure composting with different phosphate additives and further to identify microbial roles on the transformation of carbon and nitrogen (C&N) components and compost maturity. The results showed that the composition of fungal community was significantly affected by pH in composting and acidic phosphate might postpone the C&N degradation process. Network analysis showed that phosphate additives, especially acidic additives, could increase the interaction of microbial community but acidic phosphate decreased the core fungi:bacteria ratio. Redundancy analysis indicated that the interactions between bacterial and fungal communities played more roles than individual contribution of bacteria or fungi for C&N conversion of composting. Structural equation modeling suggested that bacterial community was positively directly correlated to C&N loss and the participation of fungal community significantly benefited the maturity of composting. pH exhibited a great intermediated role for driving C&N conversion, maturity, and safety of composts by regulating bacterial and fungal community in composting with phosphate addition, which suggested a fast-composting way based on pH regulation by additives.

Comprehensive evaluation of spent mushroom substrate-chicken manure co-composting by garden waste improvement: physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter

The performance of garden waste on spent mushroom substrate (SMS) and chicken manure (CM) co-composting efficiency and humification is unclear. Therefore, this study investigated the impact of garden waste addition on SMS-CM co-composting physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter (DOM). The results showed that garden waste improved the physicochemical properties of SMS-CM co-compost, the thermophilic period was advanced 2 days, the seed germination index increased by 30.2%, and the total organic carbon and total nitrogen content increased by 8.80% and 15.0%, respectively. In addition, garden waste increased humic substances (HS) and humic acid (HA) contents by 10.62% and 34.52%, respectively; the HI, PHA and DP increased by 31.53%, 43.19% and 55.53%, respectively; and the SUVA₂₅₄ and SUVA₂₈₀ of DOM also increased by 6.39% and 4.39%, respectively. In particular, HA content and DOM humification increase rapidly in the first 10 days. The increase of HA accounted for 52% of the total increase during composting. Fourier-transform infrared and two-dimensional correlation analysis further confirmed that garden waste could facilitate the degradation of organic molecules, including amino acids, polysaccharides, carboxyl groups, phenols, and alcohol, and contributed to the preferential utilization of carboxyl groups and polysaccharides and thus enhanced humification.

Humification improvement by optimizing particle size of bulking agent and relevant mechanisms during swine manure composting

For purpose of clarifying the impact on particle size of bulking agents on humification and relevant mechanisms, different length (<2 cm, 2 cm, 5 cm, 10 cm) of branch and straw were blended with swine manure individually for 100 days aerobic composting. Results demonstrated that, 2 cm and 5 cm of branch and straw promoted the highest degradation of DOC by 41.49 % and 58.42 %, and increased the humic substances by 23.81 % and 55.82 % in maturity stage, respectively, compared with other treatments. As shown in microbial consequence, the maximum relative abundance of humus funguses increased by 99.55 % and 99.92 % at phylum, and 98.95 % and 99.24 % at genus in 2 cm and 5 cm of branch and straw treatment, thus verifying the result in variation of humus content. In a word, particle size could result in obvious impact on humification, and the optimized size were about 2 cm and 5 cm of branch and straw.

Phytotoxicity of farm livestock manures in facultative heap composting using the seed germination index as indicator

Static facultative heap composting of animal manure is widely used in China, but there is almost no systematic research on the phytotoxicity of the produced compost. Here, we evaluated the phytotoxic variation in compost produced by facultative heap composting of four types of animal manure (chicken manure, pig manure, sheep manure, and cattle manure) using different plant seeds (cucumber, radish, Chinese cabbage, and oilseed rape) to determine germination index (GI). The key factors that affected GI values were identified, including the dynamics of the phytotoxicity and microbial community during heap composting. Sensitivity to toxicity differed depending on the type of plant seed used. Phytotoxicity during facultative heap composting, evaluated by the GI, was in the order: chicken manure (0-6.6 %) < pig manure (14.4-90.5 %) < sheep manure (46.0-93.0 %) < cattle manure (50.2-105.8 %). Network analysis showed that the volatile fatty acid (VFA) concentration was positively correlated with Firmicutes abundance, and NH₄⁺-N was correlated with Actinobacteria, Proteobacteria, and Bacteroidetes. More bacteria were stimulated to participate in conversions of dissolved organic carbon, dissolved nitrogen, VFA, and ammonia-nitrogen (NH₄⁺-N) in sheep manure heap composting than that in other manure. The GI was most affected by VFA in chicken manure and cattle manure heap composting, while NH₄⁺-N was the main factor affecting the GI in pig manure and sheep manure compost. The dissolved carbon and nitrogen content and composition, as well as the core and proprietary microbial communities, were the primary factors that affected the succession of phytotoxic substances in facultative heap composting, which in turn affected GI values. In this study, the key pathways of livestock manure composting that affected GI and phytotoxicity were found and evaluated, which provided new insights and theoretical support for the safe use of organic fertilizer.

Thermophilic semi-continuous composting of kitchen waste: Performance evaluation and microbial community characteristics

This study evaluated the feasibility, system stability, and microbial community succession of thermophilic semi-continuous composting of kitchen waste (KW). The results revealed that treatment performance was stable at a 10 % feeding ratio, with an organic matter (OM) degradation efficiency of 81.5 % and seed germination index (GI) of 50.0 %. Moreover, the OM degradation efficiency and GI were improved to 83.4 % and 70.0 %, respectively, by maintaining an optimal compost moisture content (50-60 %). However, feeding ratios of ≥ 20 % caused deterioration of the composter system owing to OM overloading. Microbial community analysis revealed that Firmicutes, Actinobacteria, Chloroflexi, Proteobacteria, and Gemmatimonadetes were dominant. Additionally, moisture regulation significantly increased the Proteobacteria abundance by 57.1 % and reduced the Actinobacteria abundance by 57.8 %. Moreover, network analysis indicated that the bacterial community stability and positive interactions between genera were enhanced by moisture regulation. This information provides a useful reference for practical KW composting treatment in the semi-continuous mode.

Influence of carbon-to-phosphorus ratios on phosphorus fractions transformation and bacterial community succession in phosphorus-enriched composting

This study aims to assess the effect of different carbon-to-phosphorus (C:P) ratios on phosphorus (P) fractions transformation, bacterial community succession and microbial P-solubilizing function in kitchen waste composting with rock phosphate (RP) amendment and phosphate-solubilizing bacteria (PSB) inoculation. Results indicated that initial C:P ratio at 50 enhanced organic carbon degradation, available P (AP) accumulation, the amount of PSB and pqqC gene abundance in composting but higher C:P ratio increased microbial biomass phosphorus (MBP) content. Redundancy analysis showed C:P ratios, PSB amount and pqqC gene abundance greatly affected bacterial community diversity and composition. Network analysis indicated that lower C:P ratio enhanced the interaction frequency in core bacterial network for AP transformation. Variance partitioning analysis abiotic factors contributed more to MBP and AP conversion. The study revealed that C:P ratio could directly drive PSB to regulate P fractions and the accumulation of MBP or AP in P-enriched composting.

Effect of attapulgite on heavy metals passivation and microbial community during co-composting of river sediment with agricultural wastes

This paper investigated the effects of attapulgite addition on the physicochemical processes, heavy metal transformation, and microbial community during the composting of agricultural wastes and sediment. In addition, the correlation between environmental factors, heavy metals (HMs), and microbial community was also assessed by redundancy analysis (RDA). The results showed that pile B with attapulgite addition entered the thermophilic phase earlier and lasted longer than pile A as the control group. The reduction in the bioavailability of HMs (Cr, Cd, and Zn) was also greater in pile B, and the passivation of HMs was ranked as Cd > Zn > Cr. The relative abundance of phylum Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria was the highest throughout the composting process. Furthermore, the RDA showed that the bacterial community composition was significantly correlated with temperature and C/N ratio in pile A, while significantly correlated with organic matter and pH in pile B. And the addition of attapulgite facilitated the conversion of HMs into more stable fractions by Pseudomonas. The study would provide a reference for the application of attapulgite to remediate the river sediment polluted by HMs.

Impact of biochar, calcium magnesium phosphate fertilizer and spent mushroom substrate on humification and heavy metal passivation during composting

The effects of exogenous additives (biochar, calcium magnesium phosphate fertilizer, and spent mushroom substrate) on humification process and heavy metal passivation during pig manure composting were investigated. The aerobic composting trial were carried out in 60 L reactors for 49 d. The calcium magnesium phosphate fertilizer, biochar, and spent mushroom substrate amendment treatments all accelerated the organic matter degradation and increased the temperature, decreased the volatile fatty acid content by 45%-49.0% and promoted humification of the compost (increasing the humic acid content and humus index). The biochar passivated Cu best, calcium magnesium phosphate fertilizer passivated Zn best (passivation rate 13.85%), and spent mushroom substrate passivated Cd, Cr, and Pb best (passivation rates 25.47%-47.91%). The additives amendment improved Cu, Zn, Cd, Cr, and Pb passivation performance by promoting composting humification process.

Insights into the effect of iron-carbon particle amendment on food waste composting: Physicochemical properties and the microbial community

The effects of iron-carbon (Fe-C) particle amendment on organic matter degradation, product quality and functional microbial community in food waste composting were investigated. Fe-C particles (10%) were added to the material and composted for 32 days in a lab-scale composting system. The results suggested that Fe-C particle enhanced organic matter degradation by 12.3%, particularly lignocellulose, leading to a greater humification process (increased by 15.5%). In addition, NO₃^--N generation was enhanced (15.9%) by nitrification with more active ammonia monooxygenase and nitrite oxidoreductase activities in the cooling and maturity periods. Fe-C particles not only significantly increased the relative abundances of Bacillus and Aspergillus for organic matter decomposition, but also decreased the relative abundances of acid-producing bacteria. RDA analysis demonstrated that the bacterial community was significantly influenced by dissolved organic matter, C/N, NO₃^--N, humic acid, volatile fatty acids and pH, while electrical conductivity was the key factor affecting the fungal community.

Aerobic composting of chicken manure with penicillin G: Community classification and quorum sensing mediating its contribution to humification

Chicken manure containing antibiotics is a hazardous biological waste. The purpose of our study was to investigate how different concentrations of penicillin G alter the bacterial community to affect humification during aerobic composting of chicken manure. The effect of quorum sensing on the bacterial community was also evaluated. Penicillin G mainly affects low fold changes (within 4) for low-abundance (within 200) microbial genera. We found that the bacterial community cooperated to regulate humus and humic acid synthesis. The microbial genera that make up the bacterial community are different, but each bacterial community may have the same ecological function. Quorum sensing affects humic acid synthesis by regulating carbohydrate metabolism and amino acid metabolism in bacterial communities through mechanisms such as the pentose phosphate pathway and the shikimate pathway. This work presents an understanding of the impact of quorum sensing on the collaboration between bacterial communities during composting.

Effects of digestion duration on energy efficiency, compost quality, and carbon flow during solid state anaerobic digestion and composting hybrid process

This study investigated the effects of anaerobic digestion duration on methane yield, net energy production, and humification of compost during solid state anaerobic digestion (SSAD) and composting hybrid process for food waste treatment. Carbon flow and balance were used to evaluate organic methanation and humification inclination of carbon in the whole SSAD and aerobic composting system. Results showed that SSAD for 15 (AD-15) and 21 days (AD-21) could increase net energy production and degraded organic matter contained in the mixtures to achieve high biological stability. The cumulative net energy production between the AD-15 and AD-21 treatments was not significantly different, which was 8.3% higher than that in SSAD for 30 days (AD-30). Furthermore, digestate (AD-15 and AD-21) composting for 3 days reached maturity and absence of phytotoxic substances. Carbon fixed into humus of the AD-21 treatment (11.6%) was not significantly different from that of AD-15 (12.0%). However, the total amount of carbon fixed into compost in AD-15 was 6.6% higher than that in AD-21. Moreover, the CO₂ -C loss of the AD-15 treatment (22.9%) was slightly higher than that of AD-21 (20.6%). Thus, AD-21 treatment achieved the most effective use of carbon during SSAD and composting hybrid process for food waste treatment. These results could provide valuable insights for the effective management of food waste in practice.

Effect of distillery sewage sludge addition on performance and bacterial community dynamics during distilled grain waste composting

This study evaluated the dynamics of physicochemical characteristics and bacterial communities during the co-composting of distilled grain waste (DGW) and distillery sewage sludge (SS), with DGW mono-composting as a control. Results showed that co-composting with SS significantly improved DGW degradation efficiency (61.38% vs. 54.13%) and end-product quality (seed germination index: 129.82% vs. 113.61%; N + P₂O₅ + K₂O: 9.08% vs. 5.28%), compared to DGW mono-composting. Microbial community analysis revealed that co-composting accelerated the bacterial community succession rate and enhanced the abundance of the phyla Proteobacteria, Firmicutes, Chloroflexi, and Deinococcota by 45.86%, 4.38%, 37.49%, and 15.29%, respectively. Network analysis showed that DGW-SS co-composting altered the interactions among the bacterial genera and improved bacterial community stability. Spearman correlation analysis indicated that the correlation between bacterial genera and environmental factors was more significant in DGW-SS co-composting. Therefore, co-composting of DGW and SS is a suitable strategy for the treatment of solid byproducts from spirit distilleries.

Key factors affecting seed germination in phytotoxicity tests during sheep manure composting with carbon additives

The germination index (GI) was widely applied to evaluate the phytotoxicity of compost. This study investigated the key phytotoxicity factors affecting seed germination in compost by using aqueous extracts in seed germination tests. The relationship between water-soluble substances in compost and seed germination, and their association with the microbial community were identified. In this study, sheep manure (SM) composted along or with three carbon additives (mushroom substrate, MS; cornstalks, CS; garden substrate, GS) for 49 days and, during this time, changes in multiple physical-chemical parameters, carbon and nitrogen matters, germination indexes (GI) and the compost microbiome were monitored. The results showed that all additives decreased water-soluble total nitrogen (TN), ammonium nitrogen (NH₄⁺-N) and low molecular weight organic acids, and significantly improved the seed germination indexes (seed germination rate, radical length and GI). The GI was correlated with water-soluble carbon degradation products (TOC, butyric acid, humic acid) and certain bacteria (Planifilum, Oceanobacillus, Ruminococcaceae_UCG_005 and Saccharomonospora). A structural equation model revealed that the main factors affecting seed germination were TOC (SM compost), acetic acid (SM+MS compost), humic acid (SM+CS compost), and pH (SM+GS compost). Low TOC and low molecular weight organic acids contents and higher humic acid content promoted GI. The research results could provide theoretical basis and measures for directional regulation of compost maturity.

Temporal changes of microbial community structure and nitrogen cycling processes during the aerobic degradation of phenanthrene

Phenanthrene (PHE) is frequently detected in worldwide soils. But it is still not clear that how the microbial community succession happens and the nitrogen-cycling processes alter during PHE degradation. In this study, the temporal changes of soil microbial community composition and nitrogen-cycling processes during the biodegradation of PHE (12 μg g^-1) were explored. The results showed that the biodegradation of PHE followed the second-order kinetics with a half-life of 7 days. QPCR results demonstrated that the bacteria numbers increased by 67.1%-194.7% with PHE degradation, whereas, no significant change was observed in fungi numbers. Thus, high-throughput sequencing based on 16 S rRNA was conducted and showed that the abundances of Methylotenera, Comamonadaceae, and Nocardioides involved in PHE degradation and denitrification were significantly increased, while those of nitrogen-metabolism-related genera such as Nitrososphaeraceae, Nitrospira, Gemmatimonadacea were decreased in PHE-treated soil. Co-occurrence network analysis suggested that more complex interrelations were constructed, and Proteobacteria instead of Acidobacteriota formed intimate associations with other microbes in responding to PHE exposure. Additionally, the abundances of nifH and narG were significantly up-regulated in PHE-treated soil, while that of amoA especially AOAamoA was down-regulated. Finally, correlation analysis found several potential microbes (Methylotenera, Comamonadaceae, and Agromyces) that could couple PHE degradation and nitrogen transformation. This study confirmed that PHE could alter microbial community structure, change the native bacterial network, and disturb nitrogen-cycling processes.

Give priority to abiotic factor of phosphate additives for pig manure composting to reduce heavy metal risk rather than bacterial contribution

Phosphate additives especially superphosphate can reduce nitrogen loss, and increase phosphorus availability in composting. This study investigated the changes of different heavy metals fractions and their relationship with bacterial community and abiotic factors during pig manure composting with adding equimolar H₃PO₄, H₂SO₄ and K₂HPO₄. Results showed that both acidic and alkaline labile phosphate increased the potential ecological risk of heavy metals compared to control, but K₂HPO₄ decreased the accumulation of exchangeable Zn and Mn by 12% and 15% than that with H₃PO₄ and H₂SO₄ addition. Network analysis showed that K₂HPO₄ enhanced the proportion of negative links in bacterial species with heavy metals, but H₃PO₄ decreased the stability of bacterial network. Redundancy analysis demonstrated that pH was the key factor on metal speciation and risk with phosphate additives than bacterial role. The study presented theoretical basis for additive selection in controlling composting nitrogen fixation and environmental risk.

Inoculation of phosphate-solubilizing bacteria (Bacillus) regulates microbial interaction to improve phosphorus fractions mobilization during kitchen waste composting

Bacillus presents in most composts as core microbial taxa and is widely used as inoculant in composting. However, the role of Bacillus as phosphate-solubilizing bacteria (PSB) inoculant in composting and the response of indigenous bacterial community are unclear. This study used redundancy analysis (RDA), network analysis and structural equation model (SEM) to investigate the dynamics of phosphorus (P) fractions, bacterial community, and microbial interaction in composting with PSB (Bacillus sp. P6) inoculation. Results indicated that Bacillus inoculation increased Olsen P content, organic matter degradation, and bacterial diversity, benefiting P fractions mobilization during composting. RDA showed that pH was the main factor influencing P fractions transformation and bacterial taxa. Network analysis and SEM revealed that Bacillus indirectly improved the contribution of bacterial community on P mobilization by enhancing microbial interactions. Therefore, Bacillus with P solubilizing function may be a potential inoculant to regulate the biotic process of P transformation.

Phosphorus excess changes rock phosphate solubilization level and bacterial community mediating phosphorus fractions mobilization during composting

This study investigated the changes of phosphorus (P) fractions, bacterial community and their response to available P or carbon (C):P during composting with different rock phosphate (RP) addition levels. Results showed that adding RP at 10% or 15% promoted the rise of temperature, maturity and Olsen P accumulation in composting, which had a higher amount of RP solubilization than other groups. Available P changed bacterial composition and decreased diversity in composts. RP solubilization efficiency was negatively correlated to C:P ratio and the highest (22.7%) when 10% RP was added, in which bacterial community changed from "function redundancy" to "intensive P-solubilization". Low C:P ratio (〈300) increased the RP solubilization ratio especially within 135-160. Therefore, this study proposed that adding P-rich substrates to decrease C:P ratio could regulate P-solubilizers' activity for increasing RP solubilization efficiency during composting.