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.

Deciphering the carbon and nitrogen component conversion in humification process mediated by distinct microbial mechanisms in composting from different domestic organic wastes.

This study aimed to compare the process of maturity and humus fraction evolution as well as bacterial community dynamics in composting from different domestic organic wastes (food waste (FW), and vegetable waste (VW)) and decipher the key biotic influencing factors of humic acid formation through correlation analysis and ecological network. The results showed that organic carbon components in FW with high ratio of soluble organic carbon and hemicellulose were more easily to be degraded in composting compared to VW. After 30 days of composting, the content of HA-C generated by VW was 35.41%, higher than 29.01% of FW, and the growth rate of HA-C generated was 38.42% and 28.34%, respectively. PARAFAC analysis showed that the structure of HA generated in VW was more complex, and the proportion of humic acid-like components (C3 + C4) was 60.32%, while FW only accounted for 43.86%. However, the evolution growth rate of aromatic components in HA in FW was 26.88% in 30 days of compost, which was higher than 15.17% in VW. High-throughput sequencing indicated that Lactobacillus was the initial dominated genera in composting from different domestic wastes. Thermobifida, Thermovum, and Pusillimas as well as Aeribacillus were core bacterial genera that promoted the humification process in FW and VW, respectively. Network analysis showed that there was higher bacterial interacted connection degree and complexity in FW compared to VW. This study was of great significance for optimizing organics conversion and humification efficiency of household waste composting.

Co-inoculation of phosphate-solubilizing bacteria and phosphate accumulating bacteria in phosphorus-enriched composting regulates phosphorus transformation by facilitating polyphosphate formation.

This study aimed to explore the impact of co-inoculating phosphate-solubilizing bacteria (PSB) and phosphate accumulating bacteria (PAB) on phosphorus forms transformation, microbial biomass phosphorus (MBP) and polyphosphate (Poly-P) accumulation, bacterial community composition in composting, using high throughput sequencing, PICRUSt 2, network analysis, structural equation model (SEM) and random forest (RF) analysis. The results demonstrated PSB-PAB co-inoculation (T1) reduced Olsen-P content (1.4 g) but had higher levels of MBP (74.2 mg/kg) and Poly-P (419 A.U.) compared to PSB-only (T0). The mantel test revealed a significantly positive correlation between bacterial diversity and both bioavailable P and MBP. Halocella was identified as a key genus related to Poly-P synthesis by network analysis. SEM and RF analysis showed that pH and bacterial community had the most influence on Poly-P synthesis, and PICRUSt 2 analysis revealed inoculation of PAB increased ppk gene abundance in T1. Thus, PSB-PAB co-inoculation provides a new idea for phosphorus management.

Comparing bacterial dynamics for the conversion of organics and humus components during manure composting from different sources.

The study aimed to compare the differences in organic fractions transformation, humus components and bacterial community dynamics during manure composting from different sources, and to identify the key biotic and abiotic factors driving the humification process. Five types of manure [pig manure (PM), cow dung (CD), sheep manure (SM), chicken manure (CM), and duck manure (DM)] were used as raw materials for 30 days composting. The results showed the obvious difference of organic fractions decomposition with more cellulose degradation in CD and SM composting and more hemicellulose degradation in PM and CM composting. Composting of PM and CD contained significantly higher humus fractions than the other composts. Fluorescence spectra indicated that SM composting tended to form structurally stable humic acid fractions, while CM and DM tended to form structurally complex fulvic acid fractions. Pearson correlation analysis showed that humification process of composts in category A (PM, CD) with higher humification degree than category B (SM, CM, and DM) was positively correlated with lignin and hemicellulose degradation. Bioinformatics analysis found that Lysinibacillus promoted the degradation of hemicellulose and the conversion of fulvic to humic acid in the composts of category A, and in category B, Thermobifida, Lactobacillus, and Ureibacillus were key genera for humic acid formation. Network analysis indicated that bacterial interaction patterns had obvious differences in composting with different humus and humification levels.

Regulating pH and Phanerochaete chrysosporium inoculation improved the humification and succession of fungal community at the cooling stage of composting.

This study aimed to explore the effect of regulating pH and Phanerochaete chrysosporium inoculation at the cooling stage of composting on the lignocellulose degradation, humification process and related precursors as well as fungal community for secondary fermentation. Results showed that composting with P. chrysosporium inoculation and pH regulation (T4) had 58% cellulose decomposition, 73% lignin degradation and improved enzyme activities for lignin decomposition. There was 81.98% increase of humic substance content and more transformation of polyphenols and amino acids in T4 compared to control. Inoculating P. chrysosporium affected the fungal community diversity, and regulating pH helped to increase the colonization of P. chrysosporium. Network analysis showed that the network complexity and synergy between microorganisms was improved in T4. Correlation and Random Forest analysis suggested that enriched Phanerochaete and Thermomyces in the mature stage of T4 were key taxa for lignocellulose degradation, and humic acid formation by accumulating precursors.

Carbon-containing additives changes the phosphorus flow by affecting humification and bacterial community during composting.

Phosphorus recycling from organic wastes to prepare a fertilizer by composting is promising. The aim of this study was to compare the effect of diverse carbon-containing additives (T1, glucose; T2, biochar; T3, woody peat) on phosphorus (P) fractions transformations, humus formation and bacterial community succession in chicken manure composting. Results showed that orthophosphate monoester was significantly related to the humification process, and glucose or woody peat addition increased the P in humus. Lentibacillus was a key carbon cycle bacteria related to organics stabilization affected by carbon-containing additives. Redundancy analysis and variation partitioning indicated that phosphatase enzyme activity driven by bacterial community and humic substance had 59.7% contribution to P fractions dynamics. The findings highlight an efficient humus-regulation P stabilization way, notably in composting adding glucose to form humus with a better binding ability to labile P forms and phosphatase.

Insight into the dynamic microbial community and core bacteria in composting from different sources by advanced bioinformatics methods.

Microbial communities are important for high composting efficiency and good quality composts. This study was conducted to compare the changes of physicochemical and bacterial characteristics in composting from different raw materials, including chicken manure (CM), duck manure (DM), sheep manure (SM), food waste (FW), and vegetable waste (VW). The role and interactions of core bacteria and their contribution to maturity in diverse composts were analyzed by advanced bioinformatics methods combined sequencing with co-occurrence network and structural equation modeling (SEM). Results indicated that there were obviously different bacterial composition and diversity in composting from diverse sources. FW had a low pH and different physiochemical characteristics compared to other composts but they all achieved similar maturity products. Redundancy analysis suggested total organic carbon, phosphorus, and temperature governed the composition of microbial species but key factors were different in diverse composts. Network analysis showed completely different interactions of core bacterial community from diverse composts but Thermobifida was the ubiquitous core bacteria in composting bacterial network. Sphaerobacter and Lactobacillus as core genus were presented in the starting mesophilic and thermophilic phases of composting from manure (CM, DM, SM) and municipal solid waste (FW, VW), respectively. SEM indicated core bacteria had the positive, direct, and the biggest (> 80%) effects on composting maturity. Therefore, this study presents theoretical basis to identify and enhance the core bacteria for improving full-scale composting efficiency facing more and more organic wastes.

Humic acid and phosphorus fractions transformation regulated by carbon-based materials in composting steered its potential for phosphorus mobilization in soil.

This study investigated the effects of different carbon-based additives including biochar, woody peat, and glucose on humic acid, fulvic acid, and phosphorus fractions in chicken manure composting and its potential for phosphorus mobilization in soil. The results showed that the addition of glucose effectively increased the total humic substance content (90.2 mg/g) of composts, and the fulvic acid content was significantly higher than other groups (P < 0.05). The addition of biochar could effectively improve the content of available phosphorus by 59.9% in composting. The addition of carbon-based materials to the composting was beneficial for the production of more stable inorganic phosphorus in the phosphorus fraction. The highest proportion of soluble inorganic phosphorus components of sodium hydroxide was found in group with woody peat addition (8.7%) and the highest proportion of soluble inorganic phosphorus components of hydrochloric acid was found in group with glucose addition (35.2%). The compost products with the addition of biochar (humic acid decreased by 17.9%) and woody peat (fulvic acid decreased by 72.6%) significantly increased soil humic acid mineralization. The compost products with the addition of biochar was suitable as active phosphate fertilizer, while the compost products with the addition of glucose was suitable as slow-release phosphate fertilizer.

Impact of aeration rate on phosphorus conversion and bacterial community dynamics in phosphorus-enriched composting.

This study was to investigate the effects of different aeration rates on phosphorus (P) conversion and bacterial community dynamics in P-enriched composting by 16S rRNA gene sequencing, sequential P fractionation, network analysis and structural equation model (SEM). Results indicated that Olsen P content increased by 138 %, 150 %, 121 % after composting with aeration rate (L kg-1 DM min-1) at 0.2 (AR0.2), 0.4 (AR0.4) and 0.6 (AR0.6). AR0.4 was more conducive to enhance P solubilization efficacy and available P accumulation. Redundancy analysis indicated Lactobacillus, Spartobacteria and Pseudomonas were key bacteria associated with HCl-Pi especially in AR0.2 and AR0.4. Network analysis showed that increased aeration rate enhanced the connection and function homoplasy among modules and AR0.4 had more orderly community organization for key bacteria to solubilize P in directly and indirectly biotic way. SEM suggested indirectly biotic P-solubilization had more contribution than directly biotic way mainly by phosphate-solubilizing bacteria.

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.

Impact of inoculation and turning for full-scale composting on core bacterial community and their co-occurrence compared by network analysis.

Window composting with inoculation or frequent turning is a superior way to improve traditional composting efficiency. However, the relationship between the innocent treatment in composting with inoculation or turning and microbial dynamics is unclear. Here, the impact of inoculation and turning for full scale composting on core bacterial community and their co-occurrence network as well as harmless level were compared by network analysis. Results showed that composts with both inoculation and turning had 46% increase of total organic carbon degradation compared to traditional composting and decreased the abundance of potential pathogens. The relative abundance of thermophilic bacteria and Galbibacter, Methylocaldum, Steroidobacter, etc. increased during composting with turning and inoculation. Luteimonas, Sphaerobacter, Turicibacter and Flavobacterium as core bacteria had significant difference between control and composting with enhanced innocent treatment efficiency. Network analysis suggested that turning increased the number of indigenous core bacteria and inoculation enhanced the interaction among key bacterial network.

Tomato microbiome under long-term organic and conventional farming.

The compartment niche is the main reason behind the shifts in endophytic bacterial communities. Long-term organic greenhouse exerted limited influence on the variations of endophytic bacterial communities. Organic greenhouse and root had more complex co-occurrence networks than conventional greenhouse and stem, respectively. Cultivable method results found that Protecbacteria, Bacteriodes, and Actinobacteria are the dominant phyla in the endophytes.

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.

Recycling of nutrients from organic waste by advanced compost technology- A case study.

Composting is widely used as an easily operated and economical method to manage organic wastes. However, the long residence time of composting impedes the recycling nutrients from large amounts of organic wastes produced every day. In this study, the intelligent biodrying + continuous dynamic trough (IB + CDT) was created and used in China's first urban and rural organic waste treatment and utilization demonstration center in Suzhou city. Results showed that IB + CDT composting had higher temperature, more reduction of moisture than windrow composting, enhancing 40% of composting efficiency. Primary fermentation of the IB + CDT composting in the indoor conditions could achieve the harmless treatment (GI > 80%) of compost within 12 days. The IB + CDT composting product enhanced 17% soil organic matter and 11% available nitrogen. The IB + CDT composting mode could earn 57.6 USD/ton by recycling organic waste and producing organic fertilizer, leading to a sustainable and profitable mode.

Insight into the mechanisms of insoluble phosphate transformation driven by the interactions of compound microbes during composting.

Phosphate-solubilizing (PS) microbes are important to improve phosphorus availability and transformation of insoluble phosphate, e.g., rock phosphate (RP). The use of phosphate solubilizing bacteria (PSB) as inoculants have been proposed as an alternative to increase phosphate availability in RP and composting fertilizers. In this study, the effect of compound PSB coinoculation and single-strain inoculation on the transformation of insoluble phosphate were compared in a liquid medium incubation and RP-enriched composting. The goal of this study was to understand the possible mechanisms of insoluble phosphate transformation driven by the interactions of compound PS microbes during composting. The correlations between organic acids production, P-solubilization capacity and bacterial community with PSB inoculation were investigated in the RP-enriched composting by redundancy analysis (RDA) and structural equation models (SEM). Results showed that both single-strain and compound PSB inoculants had a high P-solubilization capacity in medium, but the proportion of Olsen P to total P in composts with inoculating compound PS microbes was 7% higher than that with single strain. PS inoculants could secrete different organic acids and lactic was the most abundant. However, RDA and SEM suggested that oxalic might play an important role on PS activity, inducing RP solubilization by changing pH during composting. Interaction between compound microbes could intensify the acidolysis process for insoluble P transformation compared to the single strain. Our findings help to understand the roles of complex microbial inoculants and regulate P availability of insoluble phosphate for the agricultural purposes.

Composting with biochar or woody peat addition reduces phosphorus bioavailability.

Biochar and woody peat have been recognized as an additive to reduce carbon and nitrogen loss during composting. Yet little is known about their influences on the transformation of phosphorus (P) fractions in composting. This study investigated the quantitative and qualitative changes in different P forms during composting with adding biochar or woody peat using sequential extraction and P K-edge X-ray absorption near-edge structure (XANES). The results showed that compost products from the treatment with adding woody peat had a higher HA/FA (the ratio of humic acid to fulvic acid) compared to biochar treatment and the control, suggesting that the addition of woody peat might benefit the humification process of composting. Sequential extraction and XANES illustrated that adding biochar or woody peat limited the P availability. Biochar increased the proportion of Pi and woody peat decreased the conversion from Po to Pi compared to the control. Structural equation modeling and redundancy analysis suggested that biochar improved the refractory P based on the indirect effects of NH4+-N by regulating microbial community, while woody peat was beneficial for Po accumulation by affecting humic acid. Taken together, this research provides basis for regulating the nutrient level of carbon, nitrogen, and phosphorus in composts and reducing environmental risks.