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Combining microbial electrolytic cells with anaerobic digestion (MEC-AD) was considered as an important method for enhancing complex organic matter degradation. However, the magnetic biochar (MBC) addition would be an effective approach for enhancing biodegradation in MEC-AD. By designing orthogonal experiments, the optimal parameters of MBC-enhanced MEC-AD system for landfill leachate treatment were determined. The results indicated that the optimal conditions were identified as HRT of 72 h, electrode spacing of 2.5 cm, and applied voltage of 0.8 V. Under these conditions, the COD removal efficiency reached a maximum of 54.7 %. Additionally, the UV-vis, 3D-EEM, and GC-MS indicated the macromolecules 13-Docosenamide (Z), Bis(2-ethylhexyl) benzene-1,4-dicarboxylate and bis(2-ethylhexyl) phthalate were degraded. 13-Docosenamide (Z) was almost completely removed under the conditions of 0.8 V applied voltage, 2.5 cm electrode spacing and 24 h HRT, with a removal efficiency of 99.91 %. Significant differences were observed in the microbial core genera among the MEC-AD systems. The core genera in the anodic and cathodic biofilms were primarily fermentative and electroactive bacteria, including Soehngenia (2.2 % - 32.1 %, 3.2 % - 26.4 %) and Desulfomicrobium (1.1 % - 10.2 %, 2.0 % - 29.3 %). Fermentative bacteria, norank_f__Bacteroidetes_vadinHA17, established cooperative relationships with electroactive bacteria Acinetobacter. The enrichment of electrochemically active bacteria optimized microbial interactions, thereby synergistically enhancing the biotransformation of complex organic matter in landfill leachate.

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The phosphorus (P) concentration is increasing in parts of the Baltic Sea following the spring bloom. The fate of this excess P-pool is an open question, and here we investigate the role of microbial degradation processes in the excess P assimilation phase. During a 17-day-long mesocosm experiment in the southwest Finnish archipelago, we examined nitrogen, phosphorus, and carbon acquiring extracellular enzyme activities in three size fractions (<0.2, 0.2-3, and >3 µm), bacterial abundance, production, community composition, and its predicted metabolic functions. The mesocosms received carbon (C) and nitrogen (N) amendments individually and in combination (NC) to distinguish between heterotrophic and autotrophic processes. Alkaline phosphatase activity occurred mainly in the dissolved form and likely contributed to the excess phosphate conditions together with grazing. At the beginning of the experiment, peptidolytic and glycolytic enzymes were mostly produced by free-living bacteria. However, by the end of the experiment, the NC-treatment induced a shift in peptidolytic and glycolytic activities and degradation of phosphomonoesters toward the particle-associated fraction, likely as a consequence of higher substrate availability. This would potentially promote retention of nutrients in the surface as opposed to sedimentation, but direct sedimentation measurements are needed to verify this hypothesis.

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Anoxygenic phototrophic bacteria is a promising catalyst for constructing bioanode, but the mixed culture with non-photosynthetic bacteria is inevitable in an open environment application. In this study, a Rhodopseudomonas-dominated mixed culture with other electrogenic bacteria was investigated for deciphering the differentiated performance on electricity generation in light or dark conditions. The kinetic study showed that reaction rate of OM degradation was 9 times higher than that under dark condition, demonstrating that OM degradation was enhanced by photosynthesis. However, CE under light condition was lower. It indicated that part of OM was used to provide hydrogen donors for the fixation of CO2 or hydrogen production in photosynthesis, decreasing the OM used for electron transfer. In addition, higher COD concentration was not conducive to electricity generation. EIS analysis demonstrated that higher OM concentration would increase Rct to hinder the transfer of electrons from bacteria to the electrode. Indirect and direct electron transfer were revealed by CV analysis for light and dark biofilm, respectively, and nanowires were also observed by SEM graphs, further revealing the differentiate performance. Microbial community analysis demonstrated Rhodopseudomonas was dominated in light and decreased in dark, but Geobacter increased apparently from light to dark, resulting in different power generation performance. The findings revealed the differentiated performance on electricity generation and pollutant removal by mixed culture of phototrophic bacteria in light or dark, which will improve the power generation from photo-microbial fuel cells.

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Microbial activity and interaction are the important driving factors in the start-up phase of food waste composting at low temperature. The aim of this study was to explore the effect of inoculating Bacillus licheniformis on the degradation of organic components and the potential microbe-driven mechanism from the aspects of organic matter degradation, enzyme activity, microbial community interaction, and microbial metabolic function. The results showed that after inoculating B. licheniformis, temperature increased to 47.8°C on day 2, and the degradation of readily degraded carbohydrates (RDC) increased by 31.2%, and the bioheat production increased by 16.5%. There was an obvious enhancement of extracellular enzymes activities after inoculation, especially amylase activity, which increased by 7.68 times on day 4. The inoculated B. licheniformis colonized in composting as key genus in the start-up phase. Modular network analysis and Mantel test indicated that inoculation drove the cooperation between microbial network modules who were responsible for various organic components (RDC, lipid, protein, and lignocellulose) degradation in the start-up phase. Metabolic function prediction suggested that carbohydrate metabolisms including starch and sucrose metabolism, glycolysis / gluconeogenesis, pyruvate metabolism, etc., were improved by increasing the abundance of related functional genes after inoculation. In conclusion, inoculating B. licheniformis accelerated organic degradation by driving the cooperation between microbial network modules and enhancing microbial metabolism in the start-up phase of composting.

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Significant spatial variability of groundwater arsenic (As) concentrations in South/Southeast Asia is closely associated with sedimentogenesis and biogeochemical cycling processes. However, the role of fine-scale differences in biogeochemical processes under similar sedimentological environments in controlling the spatial heterogeneity of groundwater As concentrations is poorly understood. Within the central Yangtze Basin, dissolved organic matter (DOM) and microbial functional communities in the groundwater and solid-phase As-Fe speciation in Jianghan Plain (JHP) and Jiangbei Plain (JBP) were compared to reveal mechanisms related to the spatial heterogeneity of groundwater As concentration. The optical signatures of DOM showed that low molecular terrestrial fulvic-like with highly humified was predominant in the groundwater of JHP, while terrestrial humic-like and microbial humic-like with high molecular weight were predominant in the groundwater of JBP. The inorganic carbon isotope, microbial functional communities, and solid-phase As-Fe speciation suggest that the primary process controlling As accumulation in JHP groundwater system is the degradation of highly humified OM by methanogens, which drive the reductive dissolution of amorphous iron oxides. While in JBP groundwater systems, anaerobic methane-oxidizing microorganisms (AOM) coupled with fermentative bacteria, iron reduction bacteria (IRB), and sulfate reduction bacteria (SRB) utilize low molecular weight DOM degradation to drive biotic/abiotic reduction of Fe oxides, further facilitating the formation of carbonate associated Fe and crystalline Fe oxides, resulting in As release into groundwater. Different biogeochemical cycling processes determine the evolution of As-enriched aquifer systems, and the coupling of multiple processes involving organic matter transformation­iron cycling­sulfur cycling-methane cycling leads to heterogeneity in the spatial distribution of As concentrations in groundwater. These findings provide new perspectives to decipher the spatial variability of As concentrations in groundwater.

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The impoundment of rivers by dams has significantly modified sedimentation patterns and trophic structures. As a result, the algal-derived organic matter (OM), as opposed to terrestrial-derived OM, plays an increasingly important role along the river-reservoir gradient. This study utilized water-sediment microcosms to explore the impacts of allochthonous and autochthonous OM deposition on benthic nutrient dynamics mediated by microbial food webs. Our results revealed that OM addition led to increased fluxes of NH4+ and CO2, with the highest flux induced by cyanobacteria OM, followed by diatom and allochthonous OM. N2 release flux was promoted by allochthonous and diatom OM deposition but inhibited by cyanobacteria OM deposition. The amendment of autochthonous OM increased the activity of dehydrogenase and urease, while allochthonous OM with a higher C/N ratio enhanced the catalytic abilities of polyphenol oxidase and ß-glucosidase. Furthermore, OM deposition significantly reduced microbial community richness and diversity, except for eukaryotic richness, and induced pronounced changes in bacterial and eukaryotic community structures. Allochthonous OM deposition stimulated the utilization of bacteria and protozoan on native OM, resulting in a positive priming effect of 26.78 %. In contrast, diatom and cyanobacteria OM additions exerted negative priming effects of -44.53 % and -29.76 %, respectively. Bayesian stable isotope mixing models showed that diatom OM was primarily absorbed by protozoan and metazoan, while cyanobacteria OM was more easily decomposed by bacteria and transferred to higher trophic levels through microbial food webs. In addition, bacterial ammonification accounted for 74.5 % of NH4+ release in the allochthonous OM deposition treatment, whereas eukaryotic excretion contributed separately 83.3 % and 83.1 % to NH4+ release in the diatom and cyanobacteria OM addition treatments. These findings highlight the significance of accounting for the regulatory capacity of OM deposition when studying benthic metabolism within river-reservoir systems.

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Soil fungi belonging to different functional guilds, such as saprotrophs, pathogens, and mycorrhizal symbionts, play key roles in forest ecosystems. To date, no study has compared the actual gene expression of these guilds in different forest soils. We used metatranscriptomics to study the competition for organic resources by these fungal groups in boreal, temperate, and Mediterranean forest soils. Using a dedicated mRNA annotation pipeline combined with the JGI MycoCosm database, we compared the transcripts of these three fungal guilds, targeting enzymes involved in C- and N mobilization from plant and microbial cell walls. Genes encoding enzymes involved in the degradation of plant cell walls were expressed at a higher level in saprotrophic fungi than in ectomycorrhizal and pathogenic fungi. However, ectomycorrhizal and saprotrophic fungi showed similarly high expression levels of genes encoding enzymes involved in fungal cell wall degradation. Transcripts for N-related transporters were more highly expressed in ectomycorrhizal fungi than in other groups. We showed that ectomycorrhizal and saprotrophic fungi compete for N in soil organic matter, suggesting that their interactions could decelerate C cycling. Metatranscriptomics provides a unique tool to test controversial ecological hypotheses and to better understand the underlying ecological processes involved in soil functioning and carbon stabilization.

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BACKGROUND: Major advances over the past decade in molecular ecology are providing access to soil fungal diversity in forest ecosystems worldwide, but the diverse functions and metabolic capabilities of this microbial community remain largely elusive. We conducted a field survey in montane old-growth broadleaved and conifer forests, to investigate the relationship between soil fungal diversity and functional genetic traits. To assess the extent to which variation in community composition was associated with dominant tree species (oak, spruce, and fir) and environmental variations in the old-growth forests in the Jade Dragon Snow Mountain in Yunnan Province, we applied rDNA metabarcoding. We also assessed fungal gene expression in soil using mRNA sequencing and specifically assessed the expression of genes related to organic matter decomposition and nutrient acquisition in ectomycorrhizal and saprotrophic fungi. RESULTS: Our taxonomic profiling revealed striking shifts in the composition of the saprotrophic and ectomycorrhizal guilds among the oak-, fir-, and spruce-dominated forests. The core fungal microbiome comprised only ~ 20% of the total OTUs across all soil samples, although the overlap between conifer-associated communities was substantial. In contrast, seasonality and soil layer explained only a small proportion of the variation in community structure. However, despite their highly variable taxonomic composition, fungal guilds exhibited remarkably similar functional traits for growth-related and core metabolic pathways across forest associations, suggesting ecological redundancy. However, we found that the expression profiles of genes related to polysaccharide and protein degradation and nutrient transport notably varied between and within the fungal guilds, suggesting niche adaptation. CONCLUSIONS: Overall, our metatranscriptomic analyses revealed the functional potential of soil fungal communities in montane old-growth forests, including a suite of specialized genes and taxa involved in organic matter decomposition. By linking genes to ecological traits, this study provides insights into fungal adaptation strategies to biotic and environmental factors, and sheds light on the importance of understanding functional gene expression patterns in predicting ecosystem functioning. Video Abstract.

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With the rapid development of aquaculture, the production of oyster shells has surged, posing a potential threat to the environment. While oyster shell powder is widely recognized for its inherent alkalinity and rich calcium carbonate content, making it a superior soil conditioner, its role in organic solid waste composting remains underexplored. To investigate the effects of varying concentrations of oyster shell powder on compost maturation and calcium activation, this study employed thermophilic co-composting with acidic sugar residue and bean pulp, incorporating 0% (control), 10% (T1), 20% (T2), 30% (T3), and 40% (T4) oyster shell powder. Findings revealed that appropriate proportions of oyster shell powder significantly enhance temperature stability during composting and elevate maturation levels, notably reducing ammonia emissions between 62.5% and 76.7%. Intriguingly, the calcium in the oyster shell powder was significantly activated during composting, with the 40% addition group achieving the highest calcium activation rate of 48.5%. In summation, the inclusion of oyster shell powder not only optimizes the composting process but also efficiently activates the calcium, resulting in an alkaline organic-inorganic composite soil conditioner with high exchangeable calcium content. This research holds significant implications for promoting the high-value utilization of oyster shells.

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The order Saprospirales, a group of bacteria involved in complex degradation pathways, comprises three officially described families: Saprospiraceae, Lewinellaceae, and Haliscomenobacteraceae. These collectively contain 17 genera and 31 species. The current knowledge on Saprospirales diversity is the product of traditional isolation methods, with the inherited limitations of culture-based approaches. This study utilized the extensive information available in public sequence repositories combined with recent analytical tools to evaluate the global evidence-based diversity of the Saprospirales order. Our analysis resulted in 1183 novel molecular families, 15,033 novel molecular genera, and 188 K novel molecular species. Of those, 7 novel families, 464 novel genera, and 1565 species appeared in abundances at ≥0.1%. Saprospirales were detected in various environments, such as saline water, freshwater, soil, various hosts, wastewater treatment plants, and other bioreactors. Overall, saline water was the environment showing the highest prevalence of Saprospirales, with bioreactors and wastewater treatment plants being the environments where they occurred with the highest abundance. Lewinellaceae was the family containing the majority of the most prevalent species detected, while Saprospiraceae was the family with the majority of the most abundant species found. This analysis should prime researchers to further explore, in a more targeted way, the Saprospirales proportion of microbial dark matter.

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Hyperthermophilic composting (HC) has been widely recognized for the advantage of high treatment efficiency for organic wastes. However, the humification process is still unclear. In this study, the humification process of HC was investigated, compared to conventional composting (CK). The results showed that the highest composting temperature, organic matter degradation rate, and humification index in HC were 92.62 °C, 23.98%, and 1.59, while those in CK were 70.23 °C, 14.49 %, and 1.04, indicating HC accelerated humification process. Moreover, the results of metagenomic and untargeted metabolomic showed that the genes and metabolisms related to carbohydrate, lipid, amino acid, fatty acid, and nucleotide were more abundant in HC. Consequently, the metabolic pathways regarding organic matter degradation and microbial reproduction were enhanced in the high temperature stage of HC, further accelerating the humification reaction in the low temperature stage. This work contributes to the comprehension of the humification mechanism in HC.

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Sulfate-reducing bacteria (SRB) are essential functional microbial taxa for degrading organic matter (OM) in anoxic marine environments. However, there are little experimental data regarding how SRB regulates microbial communities. Here, we applied a top-down microbial community management approach by inhibiting SRB to elucidate their contributions to the microbial community during OM degradation. Based on the highly replicated microcosms (n = 20) of five different incubation stages, we found that many microbial community properties were influenced after inhibiting SRB, including the composition, structure, network, and community assembly processes. We also found a strong coexistence pattern between SRB and other abundant phylogenetic lineages via positive frequency-dependent selection. The relative abundances of the families Synergistaceae, Peptostreptococcaceae, Dethiosulfatibacteraceae, Prolixibacteraceae, Marinilabiliaceae, and Marinifilaceae were simultaneously suppressed after inhibiting SRB during OM degradation. A close association between SRB and the order Marinilabiliales among coexisting taxa was most prominent. They contributed to preserved modules during network successions, were keystone nodes mediating the networked community, and contributed to homogeneous ecological selection. The molybdate tolerance test of the isolated strains of Marinilabiliales showed that inhibited SRB (not the inhibitor of SRB itself) triggered a decrease in the relative abundance of Marinilabiliales. We also found that inhibiting SRB resulted in reduced pH, which is unsuitable for the growth of most Marinilabiliales strains, while the addition of pH buffer (HEPES) in SRB-inhibited treatment microcosms restored the pH and the relative abundances of these bacteria. These data supported that SRB could modify niches to affect species coexistence. IMPORTANCE Our model offers insight into the ecological properties of SRB and identifies a previously undocumented dimension of OM degradation. This targeted inhibition approach could provide a novel framework for illustrating how functional microbial taxa associate the composition and structure of the microbial community, molecular ecological network, and community assembly processes. These findings emphasize the importance of SRB during OM degradation. Our results proved the feasibility of the proposed study framework, inhibiting functional taxa at the community level, for illustrating when and to what extent functional taxa can contribute to ecosystem services.

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To alleviate excessive organic matter (OM) accumulation in sediments and reduce the risk of endogenous water pollution and eutrophication in aquaculture ponds, an 84-day experiment investigated the effect of the red swamp crayfish Procambarus clarkii on the OM degradation and bacterial communities in sediments. The experiment established two groups, P. clarkia treatment and control (represented as PG and CG, respectively), with three replicates for each group. At the end of experiment, the total, light fraction, and heavy fraction organic matter concentrations in the sediment of the PG group were significantly lower than those of the CG group. Significantly higher oxidation-reduction potential (ORP) and more extensively degraded OM, indicated by fatty acids, were observed in the PG group. Compared to the CG group, the average OM removal efficiency induced by crayfish in the PG group was 15.24%. Using 16S ribosomal RNA (rRNA) high-throughput sequencing, we investigated the differences in benthic bacterial communities between the PG and CG groups. Linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed that Nitrospirae, Nitrospira, Alphaproteobacteria, OLB14, Nitrospirales, Rhodobacterales, Rhizobiales, Micrococcales, Nitrospiraceae, Rhodobacteraceae, Nitrospira, Rhodobacter, Thermomonas, and Denitratisoma were significantly enriched in the PG group. Four significantly different functional groups related to OM degradation were determined between the PG and CG groups according to the functional annotation of procaryotic taxa (FAPROTAX) analysis. These four functional groups, aerobic chemoheterotrophy, manganese oxidation, dark iron oxidation, and dark sulfide oxidation, showed significantly higher relative abundances in the PG group. Overall, P. clarkia effectively increased the ORP values of sediments to provide favorable conditions for OM degradation and changed the composition and function of bacterial communities to improve bacterial abilities for OM decomposition, thereby promoting OM degradation in the sediment.

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Biodrying is a treatment to remove moisture using bio-heat generated during organic degradation. Organic matter degradation and microbial metabolism were studied during the whole kitchen waste biodrying, using metagenomic analysis. After the 25-day biodrying process, carbohydrate, protein and lipid contents decreased by 83.7%, 27.8% and 79.3%, respectively, and their degradation efficiencies increased after the thermophilic phase. Lipase activity exceeded 10 mmol d-1 g-1 throughout biodrying. Cellulase and lipase activities recovered by 2.21% and 5.77%, respectively, after the thermophilic phase, while the protease activity had a maximum increment of 347%. Metabolic analysis revealed that carbohydrate, amino acid and lipid metabolism was possibly inhibited by the high temperature, but the relative abundances of related predicted functions recovered by more than 0.9%, 7% and 11%, respectively, by the end of biodrying. Protein function prediction suggests that ß-oxidation, fatty acid biosynthesis, and the degradation of cellulose and chitin were possibly enhanced during the thermophilic phase. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that leucine, isoleucine and lysine could ultimately degraded to acetyl-CoA. Weissella, Aeribacillus and Bacillus were the genera with the most enriched functional genes during the whole biodrying process. These findings help elucidate the microbial degradation processes during biodrying, which provides further scientific support for improving the application of biodrying products.

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To investigate the effect of intermittent aeration on oxygen dynamics, organic matter degradation and main gas emissions, a lab-scale pig manure composting experiment was conducted with intermittent aeration (I_A, 30-min on and 30-min off) and continuous aeration (C_A). Although aeration volume and oxygen supply of I_A was only half of C_A, I_A could obviously enhance the oxygen utilization efficiency by 96.67 % and reduce energy dissipation for aeration by 50.87 %. Based on the comprehensive analysis of total organic matter, total carbon, total nitrogen, cellulose, hemicellulose and lignin contents, there was no significant difference in organic matter degradation between I_A and C_A (p > 0.05). Moreover, a reduction of 21.71 %, 38.93 %, 44.40 % and 62.19 % of CH4, N2O and the total GHG emission equivalent as well as NH3 emissions was realized, respectively, in I_A compared with C_A. Therefore, adopting intermittent aeration was a useful strategy and choice for high-efficiency, high-quality and environment-friendly composting.

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This study aimed to establish anaerobic biosystems which could tolerate high ammonia, and investigate the microbial community structure in these reactors. High-ammonia anaerobic biosystems that could tolerate 3600 mg L-1 total ammonia nitrogen (TAN) and 1000 mg L-1 free ammonia nitrogen (FAN) were successfully established. The removal efficiencies of COD and total volatile fatty acids (TVFAs) in R1 with dewatered sludge as inoculum were 68.8% and 69.2%, respectively. The maximum methane production rate reached 71.7 ± 1.0 mL CH4 L-1 d-1 at a TAN concentration of 3600 mg L-1. The three-dimension excitation-emission matrix analysis indicated that both easily degradable organics and refractory organics were removed from ADFE in R1 and R2. Functional microorganisms which could bear high ammonia were gradually enriched as TAN stress was elevated. Lysinibacillus, Coprothermobacter and Sporosarcina dominated the final bacterial community. Archaeal community transformed to hydrogenotrophic methanogen. The synergy of Coprothermobacter and Methanothermobacter undertook the organic matter degradation, and was enhanced by increasing TAN stress. This study offers new insights into anaerobic bioremediation of ammonia-rich wastewater.

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Bottom water oxygen depletion is a central concern in estuaries and coastal oceans worldwide. However, a mechanistic understanding and quantitative diagnosis of different oxygen-consuming processes are less clear. In this study, a multi-stable isotope approach is developed to delineate the role of oxygen respiration and nitrification contributing to total oxygen consumption in the Pearl River Estuary (PRE), a large eutrophic estuary in south China. The approach highly couples with analysis of the carbon isotope composition of dissolved inorganic carbon (δ13C-DIC) and with stable nitrogen isotope analysis in ammonium (δ15N-NH4+) and nitrate (δ15N-NO3-). In all seasons, relatively low DO concentrations were observed in the upper reach and, to some extent, in the outer estuary during summer, while high concentrations of DO were found in the transition zone between the inner and outer estuary. On the basis of isotopic differentiation, our data reveal that much more depleted δ13C-DIC is coincident with DIC additions and low oxygen in the upper reach and inner estuary during most seasons. This is most likely a consequence of organic carbon (OC) degradation via aerobic respiration. Based on the carbon isotopic mass balance of DIC and the stoichiometry ratio of -ΔDO/ΔDIC, we found that the OC degradation dominates the total oxygen consumption in the upper reach, as well as in the inner estuary during summer (48.3%-93.5%). In addition, nitrification is another key process in contributing to total oxygen loss in the upper reach, as supported by the well-coupled variations of δ15N of NH4+ and NO3- and apparent oxygen utilization (AOU). Using the formerly determined N isotopic fractionation and observed δ15N variation, we estimated that nitrification could account for 35.3%-44.1% and 28.5%-31.6% of the total oxygen consumption in the upper reach during winter and summer, respectively, while its contribution to total oxygen loss is minor in the inner and outer estuary. Overall, this study demonstrates the potential of the multi-stable isotopic approach to assess oxygen sink partitioning in large human-perturbed estuaries.

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Lake eutrophication remains a serious environmental problem of global significance, and phosphorus (P) plays a key role in lake eutrophication. Internal P loading, as a result of P release from sediments, is gathering more and more recognition as an important source governing the P availability in these ecosystems. Anoxic condition can promote the release of P associated with Fe oxides, which has already been a consensus. However, it is still unknown whether the anoxic conditions induced by eutrophication act to intensify or weaken the regeneration of organic P (Porg) in sediments. We selected the Hongfeng Reservoir, a typical sub-deep lake, to study the regeneration behaviours of C and P in the sediments buried before and after eutrophication. The results showed that Porg did not significantly increase with the rapid increase in organic C (Corg) since eutrophication occurred. Furthermore, the organic C/P ratio was much higher in sediments buried after eutrophication than in those buried before, which indicated that Porg regeneration had been significantly enhanced since eutrophication occurred. Based on C/P ratios, our estimation suggested that the Porg regeneration and P release from sediment to water approximately enhanced 45.2% ± 8.7% and 34.5% ± 9.8%, respectively. Elevated primary productivity (algae) and the corresponding hypoxic/anoxic condition, both caused by eutrophication, promoted P biogeochemical cycle in the sub-deep reservoir. This study further verifies the significant contribution of regenerated Porg to the internal P load, and highlights the importance of controlling P release from sediments in order to restore clear water ecosystems in sub-deep lakes or reservoirs.

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The effectiveness of newly isolated ammonia-oxidizing bacteria (AOBs; T-AOB-2, M-AOB-4 and MT-AOB-2-4) in promoting organic matter degradation and humification of cattle manure compost was explored. The results show that, compared with the control, the inoculation of AOBs (5%, v/w) promoted the humification process, particularly in the MT-AOB-2-4, which showed the lowest total organic carbon (19.13%) and dissolved organic carbon (2.61%), whereby humic substances (CEX) and humic acid (CHA) increased to 89.84 g/kg and 85.20 g/kg, and fulvic acid (CFA) decreased to 4.63 g/kg. The high-throughput sequencing and quantitative PCR showed that the abundance of Bacillaceae, amoA and nirS had a significant correlation with humification factors. Among the treatments, the inoculation of MT-AOB-2-4 provided the driving force for the composting process by enhancing the bacterial activity and had the most significant effect on the formation of humic substances and the efficiency of organic matter decomposition.

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While both bacteria and fungi are important for the degradation and humification of organic matter during composting, it is unclear to what extent their roles are associated with abiotic compost properties. This study evaluated changes in abiotic compost properties and the succession of bacterial and fungal communities during pig manure composting for 90 days. The compost rapidly reached thermophilic phase (>58 ℃), which lasted for 15 days. Both bacterial and fungal community compositions changed drastically during composting and while bacterial diversity increased, the fungal diversity decreased during the thermophilic phase of composting. Two taxa dominated both bacterial (Bacillales and Clostridiales) and fungal (Eurotiales and Glomerellales) communities and these showed alternating abundance fluctuations following different phases of composting. The abundance fluctuations of most dominant bacterial and fungal taxa could be further associated with decreases in the concentrations of fulvic acid, cellulose, hemicellulose and overall biodegradation potential in the compost. Moreover, bacterial predicted metabolic gene abundances dominated the first three phases of composting, while predicted fungal saprotrophic functional genes increased consistently, reaching highest abundances towards the end of composting. Finally, redundancy analysis (RDA) showed that changes in abiotic compost properties correlated with the bacterial community diversity and carbohydrate metabolism and fungal wood saprotrophic function. Together these results suggests that bacterial and fungal community succession was associated with temporal changes in abiotic compost properties, potentially explaining alternating taxa abundance patterns during pig manure composting.

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