N2O Production Rates Research Articles

Unveiling the role of oxygen in ammonia coal combustion: A DFT study on NOx emission mechanism

Ammonia-coal combustion mitigates CO2 emissions, yet nitrogen oxide emissions and char nitrogen oxidation mechanisms require further study. Our research employs density functional theory to explore coal char interactions with NO, NH3, and the impact of hydroxyls (–OH) and oxygen on reduction–oxidation processes. Findings indicate oxygen aids in forming hydroxyls on coal char, facilitating NO to NO2 conversion, lowering the activation energy for ammonia-coal oxidation to NO2. Oxygen also promotes char nitrogen oxidation to NO, reducing its activation energy. In NH3/coal/O2 systems, NH3 oxidation initiates NO formation. With the increase of the temperature, the reduction rate of NO by ammonia is always higher than the production rate of NO.

Labile organic matter favors a low N2O yield during nitrogen removal in estuarine sediments

Estuary harbors the active sediment denitrification and nitrous oxide (N2O) emission, while the knowledge of environmental controls on the denitrification-derived N2O yield remains underexplored. Here, we quantitatively assess the potential and in situ rates of N2O production during sediment denitrification in the Pearl River Estuary (PRE), China. Organic matter determines the product stoichiometry and capacity of nitrogen removal. In particular, labile organic matter (LOM) reduces N2O yield via enhancing the complete coupled nitrification-denitrification. Our results reveal that the chain processes, primary production-LOM settling-sedimentary respiration-coupled nitrification-denitrification, control the sediment denitrification and N2O production, linking the carbon and nitrogen biogeochemical cycles in the atmosphere-water column-sediment continuum. The PRE sediments serve as nitrogen removal hotspots but with low efficiency (~25 % of riverine input) and strong N2O release (~66 % of daily sea-air N2O efflux). These findings contribute to policy makers to develop knowledge-based management actions for achieving sustainable coastal environments and mitigating N2O emission.

In vitro inhibitory effect of berberine against rotavirus combined with its antioxidant, anti-inflammatory, and cytotoxicity activities.

Although berberine (BBR) is well known as a traditional medicine used in treatment of gastrointestinal diseases, its potent against viral gastroenteritis has not been specifically reported. This study aims to investigate the antiviral activity of BBR against rotavirus and evaluate its cytotoxicity and pharmacological efficacies, including antioxidant and anti-inflammatory activities in vitro. Using ultraviolet-visible absorption spectroscopy, the saturation concentration of BBR was determined as 2261 µg/mL, indicating that BBR is a poor water-soluble compound. The inhibition rate of NO production of BBR solution at a concentration of 238 µg/mL was similar to that of Cardamonin 0.3 µM with a cell viability of 92,46±0.35%, revealing the anti-inflammatory activity of BBR. The cytotoxicity of BBR solution depended on its concentration, whereby the 50% cytotoxicity concentration (CC50) of BBR after 96 h exposure was 664 µg/mL. Investigation of cytopathic effects (CPE) of MA104 cells treated with BBR and BBR-incubated rotavirus indicates that BBR could effectively inhibit the replication of rotavirus. CPEs were not observed in the cells inoculated with rotavirus (100TCID50) which was pre-incubated with BBR for 96 hours at BBR concentration of 283 µg/mL. Therefore, the study provides reliable results to demonstrate the ability of BBR to inhibit the replication of rotavirus.

Temperature differentially regulates estuarine microbial N2O production along a salinity gradient

Nitrous oxide (N2O) is atmospheric trace gas that contributes to climate change and affects stratospheric and ground-level ozone concentrations. Ammonia oxidizers and denitrifiers contribute to N2O emissions in estuarine waters. However, as an important climate factor, how temperature regulates microbial N2O production in estuarine water remains unclear. Here, we have employed stable isotope labeling techniques to demonstrate that the N2O production in estuarine waters exhibited differential thermal response patterns between nearshore and offshore regions. The optimal temperatures (Topt) for N2O production rates (N2OR) were higher at nearshore than offshore sites. 15N-labeled nitrite (15NO2-) experiments revealed that at the nearshore sites dominated by ammonia-oxidizing bacteria (AOB), the thermal tolerance of 15N-N2OR increases with increasing salinity, suggesting that N2O production by AOB-driven nitrifier denitrification may be co-regulated by temperature and salinity. Metatranscriptomic and metagenomic analyses of enriched water samples revealed that the denitrification pathway of AOB is the primary source of N2O, while clade II N2O-reducers dominated N2O consumption. Temperature regulated the expression patterns of nitrite reductase (nirK) and nitrous oxide reductase (nosZ) genes from different sources, thereby influencing N2O emissions in the system. Our findings contribute to understanding the sources of N2O in estuarine waters and their response to global warming.

Study of NO and CO Formation Pathways in Jet Flames with CH4/H2 Fuel Blends

The existing natural gas transportation pipelines can withstand a hydrogen content of 0 to 50%, but further research is still needed on the pathways of NO and CO production under moderate or intense low oxygen dilution (MILD) combustion within this range of hydrogen blending. In this paper, we present a computational fluid dynamics (CFD) simulation of hydrogen-doped jet flame combustion in a jet in a hot coflow (JHC) burner. We conducted an in-depth study of the mechanisms by which NO and CO are produced at different locations within hydrogen-doped flames. Additionally, we established a chemical reaction network (CRN) model specifically for the JHC burner and calculated the detailed influence of hydrogen content on the mechanisms of NO and CO formation. The findings indicate that an increase in hydrogen content leads to an expansion of the main NO production region and a contraction of the main NO consumption region within the jet flame. This phenomenon is accompanied by a decline in the sub-reaction rates associated with both the prompt route and NO-reburning pathway via CHi=0–3 radicals, alongside an increase in N2O and thermal NO production rates. Consequently, this results in an overall enhancement of NO production and a reduction in NO consumption. In the context of MILD combustion, CO production primarily arises from the reduction of CO2 through the reaction CH2(S) + CO2 ⇔ CO + CH2O, the introduction of hydrogen into the system exerts an inhibitory effect on this reduction reaction while simultaneously enhancing the CO oxidation reaction, OH + CO ⇔ H + CO2, this dual influence ultimately results in a reduction of CO production.

Impacts of O2:CH4 ratios and CH4 concentrations on the denitrification and CH4 oxidations of a novel AME-AD system

Aerobic methane (CH4) oxidation coupled to denitrification (AME-D) is a promising process for the denitrification of low C/N wastewater. Compared with anaerobic denitrifying bacteria, aerobic denitrifying bacteria may enable AME-D have high denitrification ability under aerobic conditions. This study constructed a novel aerobic methane oxidation coupled to aerobic denitrification (AME-AD) system using the typical aerobic denitrifying bacteria Paracoccus pantotrophus ATCC35512 and the typical aerobic methane oxidizing bacteria Methylosinus trichosporium OB3b. The denitrification and CH4 oxidations of AME-AD with different O2:CH4 ratios (0:1, 0.25:1, 0.5:1, 0.75:1, 1:1 and 1.25:1) and CH4 concentrations (0, 14000, 28000, 42000, 56000 and 70000 mg m−3) were investigated in batch experiments. Higher O2:CH4 ratios can significantly improve the denitrification and CH4 oxidations of the AME-AD (P < 0.05). The treatment with an O2:CH4 ratio of 1.25:1 had the highest denitrification rate (0.036 mg h−1) and highest CH4 oxidation rate (0.20 mg h−1). The CH4 concentration in the headspace was positively correlated with the AME-AD denitrification rate. The calculated CH4/NO3−(mol/mol) in most treatments ranged from 5.76 to 6.84. In addition, excessively high O2 and CH4 concentrations can lead to increased nitrous oxide (N2O) production in AME-AD. The N2O production rate was up to 1.00 μg h−1 when the O2:CH4 was 1.25:1. These results can provide data support for the application of AME-AD for low-C/N wastewater treatment and greenhouse gas emission reduction.

Selective increase of antibiotic-resistant denitrifiers drives N2O production in ciprofloxacin-contaminated soils

Agricultural systems significantly contribute to global N2O emissions, which is intensified by excessive fertilization and antibiotic residues, attracting global concerns. However, the dynamics and pathways of antibiotics-induced soil N2O production coupled with microbial metabolism remain controversial. Here, we explored the pathways of N2O production in agricultural soils exposed to ciprofloxacin (CIP), and revealed the underlying mechanisms of CIP degradation and the associated microbial metabolisms using 15N-isotope labeling and molecular techniques. CIP exposure significantly increases the total soil N2O production rate. This is attributed to an unexpected shift from heterotrophic and autotrophic nitrification to denitrification and an increased abundance of denitrifiers Methylobacillus members under CIP exposure. The most striking strain M. flagellatus KT is further discovered to harbor N2O-producing genes but lacks a N2O-reducing gene, thereby stimulating denitrification-based N2O production. Moreover, this denitrifying strain is probably capable of utilizing the byproducts of CIP as carbon sources, evidenced by genes associated with CIP resistance and degradation. Molecular docking further shows that CIP is well ordered in the catalytic active site of CotA laccase, thus affirming the potential for this strain to degrade CIP. These findings advance the mechanistic insights into N2O production within terrestrial ecosystems coupled with the organic contaminants degradation.

Biodegradable microplastics aggravate greenhouse gas emissions from urban lake sediments more severely than conventional microplastics

Freshwater ecosystems, such as urban lake sediments, have been identified as important sources of greenhouse gases (GHGs) to the atmosphere, as well as persistent sinks for ubiquitous microplastics due to the high population density and frequent anthropogenic activity. The potential impacts of microplastics on GHG production, however, remain underexplored. In this study, four types of common biodegradable microplastics (BMPs) versus four conventional non-biodegradable microplastics (NBMPs) were artificially exposed to urban lake sediments to investigate the responses of nitrous oxide (N2O) and methane (CH4) production, and make a comparison regarding how the biodegradability of microplastics affected GHG emissions. Importantly, results suggested that BMPs aggravated N2O and CH4 production in urban lake sediments more severely than conventional NBMPs. The production rates of N2O and CH4 increased by 48.78–71.88 % and 30.87–69.12 %, respectively, in BMPs groups, while those increased by only 0–25.69 % and 6.46–10.46 % with NBMPs exposure. Moreover, BMPs insignificantly affected nitrification but facilitated denitrification, while NBMPs inhibited both processes. BMPs not only created more oxygen-limited microenvironment, greatly promoting N2O production via nitrifier denitrification pathway, but also provided dissolved organic carbon favoring heterotrophic denitrification, which was primarily supported by the enriched denitrifiers and functional genes. In contrast, NBMPs slightly upregulated nitrifier denitrification pathway to generate N2O, and showed a toxic inhibition on both nitrifiers and denitrifiers. In addition, both BMPs and NBMPs promoted hydrogen-dependent methanogenic pathway but suppressed acetate-dependent pathway. The greater enhancement of CH4 production with BMPs exposure was attributed to the additional organic carbon substrates derived from BMPs and the stimulated microbial methane metabolism activities.

Aquacultural source of nitrous oxide revealed by nitrogen isotopes

The rapid expansion of coastal aquaculture has led to an increase in the coverage of aquaculture ponds, where intense feed-derived nitrogen is causing significant emissions of nitrous oxide (N2O). Multiple N2O production pathways and the relative importance of water column vs. sedimentary production in aquaculture ponds remain uncertain. Clarifying these pathways is vital for sustainable aquaculture development. Using 15N-labeled dissolved inorganic nitrogen, the pathways and rates of N2O production in subtropical aquaculture ponds located in south China, cultivating whiteleg shrimp, Japanese seabass, and giant river prawn, were successfully characterized. Total N2O production rates ranged from 6 to 70 µmol-N m−2 d−1, with the shrimp pond exhibiting the highest total N2O production rates, followed by ponds for seabass and prawn. These differences are primarily due to varying feed amounts causing differences in dissolved nutrients in water column and sediment. Particularly, nutrient and organic matter accumulation at the surface sediment stimulated N2O production. The oxygenated sediment on a centimeter scale could produce substantially more N2O compared to the water column above on a meter scale. Partial denitrification, i.e., nitrate and nitrite reduction to N2O, was more important (> 60 %) for N2O production in aquaculture ponds. The availability of nitrite is likely a major factor driving partial denitrification for both sedimentary and water column N2O production.

Effects of Long-term Biochar Addition on Denitrification N2O Emissions from Bacteria and Fungi in Paddy Soil

Denitrification driven by bacteria and fungi is the main source of nitrous oxide （N2O） emissions from paddy soil. It is generally believed that biochar reduces N2O emissions by influencing the bacterial denitrification process, but the relevant mechanism of its impact on fungal denitrification is still unclear. In this study, the long-term straw carbonization returning experimental field in Changshu Agricultural Ecological Experimental Base of the Chinese Academy of Sciences was taken as the object. Through indoor anaerobic culture and molecular biology technology, the relative contributions of bacteria and fungi to denitrifying N2O production in paddy soil and the related microorganism mechanism were studied under different long-term biochar application amounts （blank, 2.25 t·hm-2, and 22.5 t·hm-2, respectively, expressed by BC0, BC1, and BC10）. The results showed that compared with that in BC0, biochar treatment significantly reduced N2O emission rate, denitrification potential, and cumulative N2O emissions, and the contribution of bacterial denitrification was greater than that of fungal denitrification in all three treatments. Among them, the relative contribution rate of bacterial denitrification in BC10 （62.9%） was significantly increased compared to BC0 （50.8%）, whereas the relative contribution rate of fungal denitrification in BC10 （37.1%） was significantly lower than that in BC0 （49.2%）. The application of biochar significantly increased the abundance of bacterial denitrification functional genes （nirK, nirS, and nosZ） but reduced the abundance of fungal nirK genes. The contribution rate of fungal denitrification was significantly positively correlated with the N2O emission rate and negatively correlated with soil pH, TN, SOM, and DOC. Biochar may have inhibited the growth of denitrifying fungi by increasing pH and carbon and nitrogen content, reducing the abundance of related functional genes, thereby weakening the reduction ability of NO to N2O during fungal denitrification process. This significantly reduces the contribution rate of N2O production during the fungal denitrification process and the denitrification N2O emissions from paddy soil. This study helps to broaden our understanding of the denitrification process in paddy soil and provides a theoretical basis for further regulating fungal denitrification N2O emissions.

Isotopomer labeling and oxygen dependence of hybrid nitrous oxide production

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas and ozone depletion agent, with a significant natural source from marine oxygen-deficient zones (ODZs). Open questions remain, however, about the microbial processes responsible for this N2O production, especially hybrid N2O production when ammonia-oxidizing archaea are present. Using 15N-labeled tracer incubations, we measured the rates of N2O production from ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-) in the eastern tropical North Pacific ODZ and the isotopic labeling of the central (α) and terminal (β) nitrogen (N) atoms of the N2O molecule. We observed production of both doubly and singly labeled N2O from each tracer, with the highest rates of labeled N2O production at the same depths as the near-surface N2O concentration maximum. At most stations and depths, the production of 45N2Oα and 45N2Oβ were statistically indistinguishable, but at a few depths there were significant differences in the labeling of the two nitrogen atoms in the N2O molecule. Implementing the rates of labeled N2O production in a time-dependent numerical model, we found that N2O production from NO3- dominated at most stations and depths, with rates as high as 1600 ± 200 pM N2O d−1. Hybrid N2O production, one of the mechanisms by which ammonia-oxidizing archaea produce N2O, had rates as high as 230 ± 80 pM N2O d−1 that peaked in both the near-surface and deep N2O concentration maxima. Based on the equal production of 45N2Oα and 45N2Oβ in the majority of our experiments, we infer that hybrid N2O production likely has a consistent site preference, despite drawing from two distinct substrate pools. We also found that the rates and yields of hybrid N2O production were enhanced at low dissolved oxygen concentrations ([O2]), with hybrid N2O yields as high as 20 % at depths where [O2] was below detection (880 nM) but nitrification was still active. Finally, we identified a few incubations with [O2] up to 20 µM where N2O production from NO3- was still active. A relatively high O2 tolerance for N2O production via denitrification has implications for the feedbacks between marine deoxygenation and greenhouse gas cycling.

Long-term addition of organic manure stimulates the growth and activity of comammox in a subtropical Inceptisol

The discovery of complete ammonia oxidizers (comammox) has dramatically altered our perception of nitrogen (N) biogeochemistry. However, their functional importance vs. the canonical ammonia oxidizers (i.e., ammonia oxidizing-archaea (AOA) and bacteria (AOB)) in agroecosystems is still poorly understood. Accordingly, a new assay using acetylene, 3,4-dimethylpyrazole phosphate (DMPP), and 1-octyne was adopted to assess the ammonia (NH3) oxidation and nitrous oxide (N2O) production activity of these functional guilds in a subtropical Inceptisol under long-term different fertilization regimes. These regimes include CK (no fertilizer control), synthetic fertilizer only (NPK), organic manure only (M) and organic manure plus synthetic fertilizer (MNPK). AOA dominated NH3 oxidation in the M treatment, while AOB dominated both NH3 oxidation and N2O production in all treatments except M. Comammox always played a minor role in both NH3 oxidation and N2O production across all treatments. Both M and MNPK treatments significantly increased the activity and growth of comammox. Compared to NPK, comammox exhibited increases of 270 % and 326 % in the NH3 oxidation rates, and increases of 1472 % and 563 % in the N2O production rates in M and MNPK, respectively. Random forest model revealed that copper (Cu), comammox abundance, and dissolved organic nitrogen (DON) were the most important predictors for the NH3 oxidation rates of comammox. Redundancy analyses (RDA) showed that fertilizer treatments significantly altered the community composition of NH3 oxidizers, and pH was the overarching parameter underpinning the community shift of the NH3 oxidizers. Overall, this study provides evidence that comammox play a minor yet unneglectable role in the nitrification of agroecosystems, and the long-term addition of organic manure stimulates the growth and activity of comammox in a subtropical Inceptisol.

The effect of lightning on the atmospheric chemistry of exoplanets and potential biosignatures

Context. Lightning has been suggested to play a role in triggering the occurrence of bio-ready chemical species. Future missions such as PLATO, ARIEL, HWO, and LIFE, as well as ground-based extremely large telescopes (ELTs), will carry out investigations of the atmospheres of potentially habitable exoplanets. Aims. We aim to study the effect of lightning on the atmospheric chemistry. We also consider how it affects false-positive and false-negative biosignatures and whether these effects would be observable on exo-Earth and TRAPPIST-1 planets. Methods. We utilised a combination of laboratory experiments and photochemical and radiative transfer modelling. We conducted spark discharge experiments in N2−CO2−H2 gas mixtures, representing a range of possible rocky-planet atmospheres. We investigated the production of potential lightning signatures (CO and NO), possible biosignature gases (N2O, NH3, and CH4), and important prebiotic precursors (HCN and urea). Using the measured CO and NO production rates, we conducted photochemical simulations for oxygen-rich and anoxic atmospheres for rocky planets orbiting in the habitable zones of the Sun and TRAPPIST-1 for a range of lightning flash rates. Synthetic spectra were calculated using SMART to study the atmosphere’s reflectance, along with the emission and transmission spectra. Results. Lightning enhances the spectral features of NO, NO2, and (in some cases) CO through direct production; whereas CH4 and C2H6 may be enhanced indirectly. Lightning at a flash rate slightly higher than on modern-day Earth is able to mask the ozone features of an oxygen-rich, biotic atmosphere, making it harder to detect the biosphere of such a planet. Similarly, lightning at a flash rate at least ten times higher than on modern-day Earth is also able to mask the presence of ozone in the anoxic, abiotic atmosphere of a planet orbiting a late M dwarf, reducing the potential for a false-positive life detection. Conclusions. The threshold lightning flash rates to eliminate oxygen (&gt;0.1%) and ozone false positive biosignatures on planets orbiting ultra-cool dwarfs is up to ten times higher than the modern flash rate. This result indicates that lightning cannot always prevent these false-positive scenarios.

Impact of organic carbon on sulfide-driven autotrophic denitrification: Insights from isotope fractionation and functional genes

Additional organics are generally supplemented in the sulfide-driven autotrophic denitrification system to accelerate the denitrification rate and reduce sulfate production. In this study, different concentrations of sodium acetate (NaAc) were added to the sulfide-driven autotrophic denitrification reactor, and the S0 accumulation increased from 7.8% to 100% over a 120-day operation period. Batch experiments revealed a threefold increase in total nitrogen (TN) removal rate at an Ac−-C/N ratio of 2.8 compared to a ratio of 0.5. Addition of organic carbon accelerated denitrification rate and nitrite consumption, which shortened the emission time of N2O, but increased the N2O production rate. The lowest N2O emissions were achieved at the Ac−-C/N ratio of 1.3. Stable isotope fractionation is a powerful tool for evaluating different reaction pathways, with the 18ε/15ε values in nitrate reduction ranging from 0.5 to 1.0. This study further confirmed that isotope fractionation can reveal denitrifying nutrient types, with the 18ε (isotopic enrichment factor of oxygen)/15ε (isotopic enrichment factor of nitrogen) value approaching 1.0 for autotrophic denitrification and 0.5 for heterotrophic denitrification. Additionally, the 18ε/15ε values can indicate changes in nitrate reductase. There is a positive correlation between the 18ε/15ε values and the abundance of the functional gene napA, and a negative correlation with the abundance of the gene narG. Moreover, 18ε and 15ε were associated with changes in kinetic parameters during nitrate reduction. In summary, the combination of functional gene analysis and isotope fractionation effectively revealed the complexities of mixotrophic denitrification systems, providing insights for optimizing denitrification processes.

A novel method for quantifying variations in NO formation pathways using a sub-mechanism accounting and reaction tracing algorithm

This work presents a new implementation of reaction path analysis that traces molar fluxes attributable to various sub-mechanisms from inception through to their final product. The post-processing procedure involves creating a network of these fluxes and quantifying the contributions made by the specified formation and destruction mechanisms through an iterative process starting from the individual initiation reactions. A key distinction of this approach is that the reaction fluxes are directly correlated to their initiation reaction, which is then followed throughout the entire reaction network. This allows for the distinction of contribution to the formation of a target species from an arbitrary number of sources. The effectiveness of this approach is demonstrated by examining the formation of NO in three different case studies: (1) the impact of equivalence ratio on methane/air premixed counterflow flames, (2) the effect of hydrogen addition on ultra-lean methane/air premixed counter flames, and (3) the influence of pressure elevation in partially premixed methane/air flames. The results are presented in emission indexes, NO production rates throughout the flame, and multidigraphs illustrating the allocated flows between the species. Compared to replicated analysis methods previously used for these case studies, this new approach provides a more comprehensive and detailed analysis for several reasons. Firstly, the method does not require duplicated simulations with modified kinetic mechanisms, but is applied purely post-processing. This avoids the previous problems of needing to re-simulate the flame multiple times and allows for the fully coupled chemistry set. Secondly, the method allows for an arbitrarily defined set of initiation pathways which propagate through all possible routes within the network. This allows for the identification of spatial/temporal variability in the sub-mechanisms and thereby yields more information than the integral values of previous methods.Novelty and significance statementUnderstanding reaction pathways that lead to the formation of pollutants such as NO is an essential aspect in the development of new sustainable and low-emission combustion concepts. However, evaluating the different underlying sub-mechanisms is difficult due to the high degree of interconnectedness and spatial/temporal overlap of the reaction pathways. This work, therefore, presents a new algorithm that can be used to investigate the contributions of an arbitrary number of sub-mechanisms to the formation or decomposition of a species. The results can be expressed not only as integral values, but also as spatially and/or temporally resolved production rates and reaction path figures and graphs, leading to a more comprehensive and detailed analysis. The approach is also applied as a purely post-processing technique, which does not require multiple simulations with different chemical kinetic mechanisms as has previously be applied.

Effects of microplastics on N2O production and reduction potential in crop soils of northern China

Microplastics (MPs) pollution are found to be increasing in vegetable soils and potentially affecting N2O production and their associated pathways; however, its specific effects remain unclear. Here, we selected two common MPs, PE and PP at four different concentration levels of 0, 0.5, 1.5 and 3%, and conducted several incubation experiments aiming to explore soil bacterial and fungal N2O production. Results showed that the bacteria were the main contributors for the production of N2O, regardless of the absence or presence of MPs; and its contribution was decreased with increasing concentrations of PE and PP. The nosZ clade I and II genes were positively correlated with N2O reduction rates, indicating a combined regulation on soil N2O reduction. PE significantly inhibited the bacterial nitrification and denitrification, but did not affect the total N2O production rates; while PP significantly reduced both the bacterial and fungal N2O production rates. The resistance of fungal N2O production to MPs pollution was stronger than that of the bacterial N2O production. It highlights that the MPs pollution could reduce the potential of N2O production and reduction, and thus disturb soil nitrogen cycling system; while the inhibition on N2O production via bacteria and fungi varies with different types of MPs. This study is conducive to an improved and more comprehensive understanding of the ecological impacts of MPs within the agroecosystem.

Efficacy of grape seed procyanidins for inhibiting denitrification varies by source, soil texture, and cropping history

Plant-derived denitrification inhibitors, such as procyanidins derived from grape seed extract (GSE), hold potential in mitigating nitrous oxide (N2O) emissions, a potent greenhouse gas and stratospheric ozone depleter. A deeper understanding of the effects of GSE – considering aspects like rate, source, application timing, storage, and interactions with soil properties and cropping histories – on denitrification inhibition remains elusive. We conducted a series of laboratory microcosm experiments to assess these effects using denitrification enzyme activity (DEA) and measurements of N2O and carbon dioxide (CO2) production rates under both anaerobic and aerobic conditions, soil inorganic nitrogen (N), and other major soil properties. Our results revealed that one commercial GSE brand (USP GSE) inhibited DEA, while another source was ineffective. Two non-procyanidin compounds in commercial GSE mixtures, tartaric acid and gallic acid, actually enhanced DEA. Inhibition efficiency of the USP GSE varied significantly across soils with differing crop histories and physical properties, exhibiting a positive dose-response in three out of the five soils examined. Greater efficiency was observed in sandy soils compared to silt loam soils and in soils with a history of continuous corn production as opposed to soybean. The GSE application timing relative to urea addition and a one-week room temperature storage had minor effects on denitrification inhibition. In corn-cultivated soil, co-application of GSE and urea reduced cumulative N2O production by 27 % compared to soils treated with urea alone. The CO2 production and nitrate levels remained largely unaffected by GSE application. These findings supported the potential of GSE as a soil amendment to reduce N2O emissions in corn-cultivated soils. However, challenges including purity of procyanidins, cost-effectiveness, and inconsistent performance under various systems warrant consideration for broader field applications.

Smaller Aerobic Granules Significantly Reduce N2O Production by Ammonia-Oxidizing Bacteria: Evidences from Biochemical and Isotopic Analyses.

The mitigation of nitrous oxide (N2O) is of primary significance to offset carbon footprints in aerobic granular sludge (AGS) systems. However, a significant knowledge gap still exists regarding the N2O production mechanism and its pathway contribution. To address this issue, the impact of varying granule sizes, dissolved oxygen (DO), and nitrite (NO2-) levels on N2O production by ammonia-oxidizing bacteria (AOB) during nitrification in AGS systems was comprehensively investigated. Biochemical and isotopic experiments revealed that increasing DO or decreasing NO2- levels reduced N2O emission factors (by 13.8 or 19.5%) and production rates (by 0.08 or 0.35 mg/g VSS/h) via weakening the role of the AOB denitrification pathway since increasing DO competed for more electrons required for AOB denitrification. Smaller granules (0.5 mm) preferred to diminish N2O production via enhancing the role of NH2OH pathway (i.e., 59.4-100% in the absence of NO2-), while larger granules (2.0 mm) induced conspicuously higher N2O production via the AOB denitrification pathway (approximately 100% at higher NO2- levels). Nitrifying AGS systems with a unified size of 0.5 mm achieved 42% N2O footprint reduction compared with the system with mixed sizes (0.5-2.0 mm) under optimal conditions (DO = 3.0 mg-O2/L and NO2- = 0 mg-N/L).

Reshaping the plastisphere upon deposition: Promote N2O production through affecting sediment microbial communities in aquaculture pond

Microplastics (MPs) could provide vector for microorganisms to form biofilm (plastisphere), but the shaping process of MPs biofilm and its effects on the structure and function of sedimentary microbial communities especially in aquaculture environments are not reported. For this, we incubated MPs biofilm in situ in an aquaculture pond and established a sediment microcosm with plastisphere. We found that the formation of MPs biofilm in surface water was basically stable after 30 d incubation, but the biofilm communities were reshaped after deposition for another 30 d, because they were more similar to plastisphere communities incubated directly within sediment but not surface water. Moreover, microbial communities of MPs-contaminated sediment were altered, which was mainly driven by the biofilm communities present on MPs, because they but not sediment communities in proximity to MPs had a more pronounced separation from the control sediment communities. In the presence of MPs, increased sediment nitrification, denitrification and N2O production rates were observed. The K00371 (NO2-⇋NO3-) pathway and elevated abundance of nxrB and narH genes were screened by metagenomic analysis. Based on structural equation model, two key bacteria (Alphaproteobacteria bacterium and Rhodobacteraceae bacterium) associated with N2O production were further identified. Overall, the settling of MPs could reshape the original biofilm and promote N2O production by selectively elevating sedimental microorganisms and functional genes in aquaculture pond.

Particle-associated denitrification is the primary source of N2O in oxic coastal waters

The heavily human-perturbed coastal oceans are hotspots of nitrous oxide (N2O) emission to the atmosphere. The processes underpinning the N2O flux, however, remain poorly understood, leading to large uncertainties in assessing global N2O budgets. Using a suite of nitrogen isotope labeling experiments, we show that multiple processes contribute to N2O production throughout the estuarine-coastal gradient, sustaining intensive N2O flux to the atmosphere. Unexpectedly, denitrification, rather than ammonia oxidation as previously assumed, constitutes the major source of N2O in well-oxygenated coastal waters. Size-fractionated manipulation experiments with gene analysis further reveal niche partitioning of ammonia oxidizers and denitrifiers across the particle size spectrum; denitrification dominated on large particles and ammonia oxidizers on small particles. Total N2O production rate increases with substrate and particle concentrations, suggesting a crucial interplay between nutrients and particles in controlling N2O production. The controlling factors identified here may help understand climate feedback mechanisms between human activity and coastal oceans.