Body size mediates the functional potential of soil organisms by diversity and community assembly across soil aggregates.

Body size is an important life-history trait that affects organism niche occupancy and ecological interactions. However, it is still unclear to what extent the assembly process of organisms with different body sizes affects soil biogeochemical cycling processes at the aggregate level. Here, we examined the diversity and community assembly of soil microorganisms (bacteria, fungi, and protists) and microfauna (nematodes) with varying body sizes. The microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism within three soil aggregate sizes (large macroaggregates, > 2 mm; small macroaggregates, 0.25-2 mm; and microaggregates, < 0.25 mm) were determined by metagenomics. We found that the smallest microbes (bacteria) had higher α-diversity and lower ß-diversity and were mostly structured by stochastic processes, while all larger organisms (fungi, protists, and nematodes) had lower α-diversity and were relatively more influenced by deterministic processes. Structural equation modeling indicated that the microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism was mainly influenced by the bacterial and protist diversity in microaggregates. In contrast, the microbial functional potential was primarily mediated by the assembly processes of four organism groups, especially the nematode community in macroaggregates. This study reveals the important roles of soil organisms with different body sizes in the functional potential related to nutrient cycling, and provides new insights into the ecological processes structuring the diversity and community assembly of organisms of different body sizes at the soil aggregate level, with implications for soil nutrient cycling dynamics.

Community assembly of organisms regulates soil microbial functional potential through dual mechanisms.

Unraveling the influence of community assembly processes on soil ecosystem functioning presents a major challenge in the field of theoretical ecology, as it has received limited attention. Here, we used a series of long-term experiments spanning over 25 years to explore the assembly processes of bacterial, fungal, protist, and nematode communities using high-throughput sequencing. We characterized the soil microbial functional potential by the abundance of microbial genes associated with carbon, nitrogen, phosphorus, and sulfur cycling using GeoChip-based functional gene profiling, and determined how the assembly processes of organism groups regulate soil microbial functional potential through community diversity and network stability. Our results indicated that balanced fertilization (NPK) treatment improved the stochastic assembly of bacterial, fungal, and protist communities compared to phosphorus-deficient fertilization (NK) treatment. However, there was a nonsignificant increase in the normalized stochasticity ratio of the nematode community in response to fertilization across sites. Our findings emphasized that soil environmental factors influenced the assembly processes of the biotic community, which regulated soil microbial functional potential through dual mechanisms. One mechanism indicated that the high phosphorus levels and low soil nutrient stoichiometry may increase the stochasticity of bacterial, fungal, and protist communities and the determinism of the nematode community under NPK treatment, ultimately enhancing soil microbial functional potential by reinforcing the network stability of the biotic community. The other mechanism indicated that the low phosphorus levels and high soil nutrient stoichiometry may increase the stochastic process of the bacterial community and the determinism of the fungal, protist, and nematode communities under NK treatment, thereby enhancing soil microbial functional potential by improving the ß-diversity of the biotic community. Taken together, these results provide valuable insights into the mechanisms underlying the assembly processes of the biotic community that regulate ecosystem functioning.

Black soldier fly pretreatment promotes humification and phosphorus activation during food waste composting.

Black soldier fly (BSF) and thermophilic composting (TC) treatments are commonly adopted to manage food waste. In this study, 30 days of TC of food waste following seven days BSF pretreatment (BC) was compared to 37 days of TC of food waste (TC, the control). Fluorescence spectrum and 16S rRNA high-throughput sequencing analysis were used to compare the BC and TC treatments. Results showed that BC could decrease protein-like substances and increase humus substances more quickly, and that the humification index of compost products was 106.8% higher than that of TC, suggesting that the humification process was accelerated by BSF pretreatment resulting in a 21.6% shorter maturity time. Meanwhile, the concentrations of total and available phosphorus rose from 7.2 and 3.3 g kg-1 to 44.2 and 5.5 g kg-1, respectively, which were 90.5% and 118.8% higher in compost products from BC as compared to those in TC. Furthermore, BC had higher richness and diversity of humus synthesis and phosphate-solubilizing bacteria (PSB), with Nocardiopsis (53.8%) and Pseudomonas (47.0%) being the dominant PSB. Correlation analysis demonstrated that the introduction of BSF gut bacteria contributed to the effectiveness of related functional bacteria, resulting in a rapid humification process and phosphorus activation. Our findings advance understanding of the humification process and provide novel perspectives on food waste management.

Enhanced degradation of microplastics during sludge composting via microbially-driven Fenton reaction.

It has been increasingly documented that the hydroxyl radical (•OH) can promote the transformation of organic contaminants such as microplastics (MPs) in various environments. However, few studies have sought to identify an ideal strategy for accelerating in situ MPs degradation through boosting the process of •OH production in practical applications. In this work, iron-mineral-supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing in situ degradation of sludge-based MPs through strengthening •OH generation. The results show that the reduction efficiency of sludge-based MPs abundance was about 35.93% in imTC after treatment for 36 days, which was 38.99% higher than that of ordinary thermophilic composting (oTC). Further investigation on polyethylene-microplastics (PE-MPs) suggested that higher abundance of •OH (the maximum value was 408.1 µmol·kg-1) could be detected on the MPs isolated from imTC through microbially-mediated redox transformation of iron oxides, as compared to oTC. Analyses of the physicochemical properties of the composted PE-MPs indicated that increased •OH generation could largely accelerate the oxidative degradation of MPs. This work, for the first time, proposes a feasible strategy to enhance the reduction efficiency of MPs abundance during composting through the regulation of •OH production.

Reactive oxygen species accelerate humification process during iron mineral-amended sludge composting.

The production of hydroxyl radicals (OH) has been documented during composting. However, the effect of OH on composting efficiency remains unclear. Here, iron mineral supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing OH production and accelerating the maturation of composting. The results indicated that the maximum OH production of imTC was 1922.74 µmol·kg-1, which increased by 1.39 times than that of ordinary thermophilic composting (oTC). Importantly, the increase of OH could greatly enhance organic matter degradation and humic substances formation during imTC, resulting in shorting the maturity time by 25 %. Enrichment of laccase-producing bacteria resulted in higher laccase activity (31.85 U·g-1) in imTC compared with oTC (23.82 U·g-1), which may have contributed to the higher level of humification in imTC treatment. This work, for the first time, proposes a feasible strategy for improving composting efficiency through the regulation of OH production during aerobic composting.

Farmers' tea and nation's trees: A framework for eco-compensation assessment based on a subjective-objective combination analysis.

The effectiveness and sustainability of eco-compensation policy implementation are essential to ecosystem service protection. However, a purely subjective standpoint causes deviations from the compensation benchmark, while decision-making based solely on an objective standpoint fails to offer a profound understanding of local stakeholder conflicts. Therefore, local authorities find it difficult to set reasonable and effective eco-compensation implementation standards. An assessment framework for eco-compensation, defined as the subjective-objective combination analysis (SOCA), which considers both the subjective and objective positions of stakeholders is proposed. Focusing on a typical eco-compensation case, "Returning Tea to Forest", a compensation range is finally quantified from $443/ha to $2114/ha per year using the SOCA framework. SOCA quantification from multiple perspectives optimized the eco-compensation benchmark determinations and the eco-protection decision-making process.

Homogeneous activation of peroxymonosulfate using a low-dosage cross-bridged cyclam manganese(II) complex for organic pollutant degradation via a nonradical pathway.

The high dosage of catalyst requirement and weak anti-interference ability limit current heterogeneous manganese (Mn) catalyst/peroxymonosulfate (PMS) systems to remediate the organic polluted wastewater in complicated environment. Inspired by the concept of atom economy, herein, a homogenous manganese complex bearing a cross-bridged cyclam ligand Mn(cbc)Cl2 (MnL, L = cbc = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)) is capable of activating PMS for reactive brilliant red K-2BP (RBR K-2BP) degradation. The dosage of MnL for PMS activation was low, in a range of 0.38∼3.8 mg/L. The quenching experiments demonstrated that the degradation was a nonradical-controlled process. Using methyl phenyl sulfoxide (PMSO) as a probe, the dominated degradation process of substrate was via an oxygen transfer pathway. Moreover, a high-valent Mn-oxo [(O)MnVLCl2]+ was directly detected using electrospray ionization mass spectrometry (ESI/MS). This system showed excellent anti-interference ability to both anions and humic acid, a typical natural organic matter. The atom economy, represented by an index ((mg pollutant)/h/(g catalyst)), showed that MnL 22737 in PMS activation was much higher than those of Mn-based heterogeneous catalytic systems 67∼960 and was only behind that of iron-tetraamidomacrocyclic ligand Fe-TAML 59139. This work provides insights into designing an atom-economic Mn-based PMS activator for efficient treatments for organic pollutants in a complicated environment.

Cysteine-Accelerated Methanogenic Propionate Degradation in Paddy Soil Enrichment.

Propionate degradation is a critical step during the conversion of complex organic matter under methanogenic conditions, and it requires a syntrophic cooperation between propionate-oxidizing bacteria and methanogenic archaea. Increasing evidences suggest that interspecies electron transfer for syntrophic metabolism is not limited to the reducing equivalents of hydrogen and formate. This study tested the ability of an electron shuttle to mediate interspecies electron transfer in syntrophic methanogenesis. We found that cysteine supplementation (100, 400, and 800 µM) accelerated CH4 production from propionate in paddy soil enrichments. Of the concentrations tested, 100 µM cysteine was the most effective at enhancing propionate degradation to CH4, and the rates of CH4 production and propionate degradation were increased by 109 and 79%, respectively, compared with the cysteine-free control incubations. We eliminated the possibility that the stimulatory effect of cysteine on methanogenesis was attributable to the function of cysteine as a methanogenic substrate in the presence of propionate. The potential catalytic effect involved cysteine serving as an electron carrier to mediate interspecies electron transfer in syntrophic propionate oxidization. The redox potential of cystine/cysteine, which is dependent on the concentration, might be more suitable to facilitate interspecies electron transfer between syntrophic partners at a concentration of 100 µM. Pelotomaculum, obligately syntrophic, propionate-oxidizing bacteria, and hydrogenotrophic methanogens of the family Methanobacteriaceae are predominant in cysteine-mediated methanogenic propionate degradation. The stimulatory effect of cysteine on syntrophic methanogenesis offers remarkable potential for improving the performance of anaerobic digestion and conceptually broaden strategies for interspecies electron transfer in syntrophic metabolism.

Secondary Mineralization of Ferrihydrite Affects Microbial Methanogenesis in Geobacter-Methanosarcina Cocultures.

UNLABELLED: The transformation of ferrihydrite to stable iron oxides over time has important consequences for biogeochemical cycling of many metals and nutrients. The response of methanogenic activity to the presence of iron oxides depends on the type of iron mineral, but the effects of changes in iron mineralogy on methanogenesis have not been characterized. To address these issues, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. In this system, secondary mineralization products from ferrihydrite are regulated by the presence or absence of phosphate. In cultures producing magnetite as the secondary mineralization product, the rates of methanogenesis from acetate and ethanol increased by 30.2% and 135.3%, respectively, compared with a control lacking ferrihydrite. Biogenic magnetite was proposed to promote direct interspecies electron transfer between Geobacter and Methanosarcina in a manner similar to that of c-type cytochrome and thus facilitate methanogenesis. Vivianite biomineralization from ferrihydrite in the presence of phosphate did not significantly influence the methanogenesis processes. The correlation between magnetite occurrence and facilitated methanogenesis was supported by increased rates of methane production from acetate and ethanol with magnetite supplementation in the defined cocultures. Our data provide a new perspective on the important role of iron biomineralization in biogeochemical cycling of carbon in diverse anaerobic environments. IMPORTANCE: It has been found that microbial methanogenesis is affected by the presence of iron minerals, and their influences on methanogenesis are associated with the mineralogical properties of the iron minerals. However, how changes in iron mineralogy affect microbial methanogenesis has not been characterized. To address this issue, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. The experimental results led to two contributions, i.e., (i) the transformation of iron minerals might exert an important influence on methanogenesis under anaerobic conditions and (ii) both biogenic and chemical magnetite can accelerate syntrophic ethanol oxidization between Geobacter metallireducens and Methanosarcina barkeri This study sheds new light on the important role of iron biomineralization in the biogeochemical cycling of carbon in diverse anaerobic environments, particularly in iron-rich natural and agricultural wetland soils.