The quantification of N2O reduction during denitrification is crucial to take measures reducing N2O emissions from arable soils. The analysis of site specific N2O isotopic composition may help to ...quantify the pathway of N2O reduction to N2 during denitrification process. In manure-amended soil (chicken manure, cow manure and sheep manure), N2O reduction was evaluated by examining the N2O emissions in the presence of acetylene (C2H2) and by analyzing the N2O isotopocule deltas. The results indicated that the three manures had no significant differences for the N2O emission rates and N2O isotopocule deltas. The extent of N2O reduction to N2 was 81–84% using the mapping of Δδ18O(N2O-H2O/N2O-NO3-) (different value of δ18O between the N2O and H2O or NO3−) vs. SP (15N site preference in N2O) and approximately 76% using C2H2 (10% v/v) inhibition method under 60% WFPS (water–filled pore space). Moreover, complete N2O reduction held η18OR and SPR (net isotopocule effect of N2O reduction to N2) values of −13.6‰ and −6.7‰, respectively. It was also found that oxygen exchange between N2O and soil water was approximately 92%. In summary, the mapping of Δδ18O(N2O-H2O/N2O-NO3-) vs. SP was very useful to distinguish the production and consumption pathways of N2O during denitrification. The extent of N2O reduction was underestimated by the C2H2 method. These results provide guidance in correcting the acetylene effect, which is important in evaluating the impact of manure on the N2O reduction.
•The mapping of Δδ18O(N2O-H2O/N2O-NO3-) vs. SP was more accurate for N2O source partitioning.•The isotopocule effect of Oxygen and SP during N2O reduction were −13.6‰ and −6.7‰, respectively.•Acetylene method underestimated the N2O reduction extent from manure-amended soil under 60% WFPS.•The extent of oxygen exchange between N2O and soil water was approximately 92%.
•Indirect N2O emissions were measured in a typic agricultural-urban gradient river.•Suburban agriculture increased river N loading but decreased indirect N2O emissions.•High DOC reduced the ...denitrification source N2O by favoring complete denitrification.•DOC factor can improve our EF5r prediction in the agricultural-urban gradient river.
The effects of land use on riverine N2O emissions are not well understood, especially in suburban zones between urban and rural with distinct anthropogenic perturbations. Here, we investigated in situ riverine N2O emissions among suburban, urban, and rural sections of a typical agricultural-urban gradient river, the Qinhuai River of Southeastern China from June 2010 to September 2012. Our results showed that suburban agriculture greatly increased riverine N concentration compared to traditional agricultural rivers (TAR). The mean total dissolved nitrogen (TDN) concentration was 8.18 mg N L−1 in the suburban agricultural rivers (SUAR), which was almost the same as that in the urban rivers (UR, of 8.50 mg N L−1), compared to that in TAR (0.92 mg N L−1). However, the annual average indirect N2O flux from the SUAR was only 27.15 μg N2O-N m−2 h−1, which was slightly higher than that from the TAR (13.14 μg N2O-N m−2 h−1) but much lower than that from the UR (131.10 μg N2O-N m−2 h−1). Moreover, the average N2O emission factor (EF5r, N2O-N/DIN-N) in the SUAR (0.0002) was significantly lower than those in the TAR (0.0028) and UR (0.0004). The limited indirect N2O fluxes from the SUAR are best explained by the high riverine dissolved organic carbon (DOC) and low dissolved oxygen, which probably reduced the denitrification source N2O by favoring complete denitrification to produce N2 and inhibited the nitrification source N2O, respectively. An exponential decrease model incorporating dissolved inorganic nitrogen and DOC could greatly improve our EF5r predictions in the agricultural-urban gradient river. Given the unprecedented suburban agriculture in the world, more studies in suburban agricultural rivers are needed to further refine the EF5r and better reveal the mechanisms behind indirect N2O emissions as influenced by suburban agriculture.
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Soilless culture systems (SCS) play an increasing role in greenhouse vegetable production. In the SCS, soilless substrates serve as the major substitute for soil, supplying nutrients to plants but ...releasing greenhouse gases into the atmosphere. Remarkably, there is a serious problem of N2O emission due to excessive input of N fertilizer. However, the microbial processes of N2O production and consumption in soilless substrates have been rarely studied resulting in difficultly interpreting for its global warming potential. Therefore, these pathways from two classic soilless substrates under two irrigation patterns were investigated by stable isotope technology combined with qPCR analysis in present study. The results according to the dual isotopocule plot of δ15NSP vs. δ18O showed that the mean contribution of denitrification and the mean extent of N2O reduction of case i (Reduction–Mixing) were 26.2 and 81.2 % for the treatment of peat based substrate under drip irrigation (PD), 47.7 and 70.3 % for the treatment of coir substrate under drip irrigation (CD), 29.0 and 80.8 % for the treatment of peat based substrate under tidal irrigation (PT), and 50.8 and 47.4 % for the treatment of coir substrate under tidal irrigation (CT). These results were also further confirmed by the abundance of major functional genes including AOA amoA, nirK and nosZ. Altogether, N2O emission and its microbial processes are determined by substrate types instead of irrigation patterns. For detail, denitrification dominated in the peat based substrate and nitrification dominated in the coir substrate. Compared to the coir substrate, the peat based substrate had higher abundance of functional genes and stronger denitrification and thus generated more N2O. For the two soilless substrates, moreover, the microbiome replaced the mineral N content as the limiting factor for N2O emission. In the SCS, in summary, the two soilless substrates play an important role in tomato growth, but might suffer from inorganic nutrient surplus and microbial shortage. More importantly, the combined analysis of N2O isotopocule deltas and functional genes is a robust tool and provides reliable conclusions for clarifying the microbial processes of N2O production and consumption, thus it is also recommended for use in environments other than soilless substrates.
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•N2O production and consumption pathways in soilless culture systems were studied for the first time.•Denitrification dominated in peat based substrate and nitrification dominated in coir substrate.•Microbiome replaced mineral N content as the limiting factor for N2O emission from soilless substrates.•Combined analysis of N2O isotopocule deltas and functional genes is a robust tool and provides reliable conclusions.
Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (N2O) and methane (CH4). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), ...extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called bomas in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked N2O emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first in-situ isotope measurements of N2O fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted N2O from bomas suggests that on average 91 ± 8% N2O was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of N2O reduction to N2 across all sample sites (81 ± 9%), indicating high levels of N2O consumption. The abundances of denitrification-related genes (nirK and narG) were significantly higher than those of nitrification-related genes (amoA: AOA and AOB) in the cattle manure samples taken from the bomas, corroborating N2O emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene (nosZ) also corroborated the high potential for microbial N2O reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern N2O emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions.
•Natural abundance dual-isotope measurements were combined with functional gene analyses to explore processes of N2O formation in cattle bomas.•Denitrification dominated N2O emissions in cattle bomas.•Higher abundance of denitrification-related genes (nirK and narG) than nitrification-related genes (amoA) were observed in cattle bomas.•A high reduction (81% ± 9%) of N2O to N2 was observed in cattle bomas.
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•Development of NH3-fuel demands catalytic de-N2O unit for stack gas treatment.•ZnxCo1−xCo2O4 spinel catalysts were evaluated for low-temperature de-N2O.•T50 of 203.3 °C and XN2O of ...94.2 % at 250 °C were achieved when x = 0.73.•Zn induced the formation of oxygen vacancies, enhancing the resistance to O2.•Zn strengthen the bond between Co and –NO species.
The recent advancement of NH3-based fuel demands the development of catalysts that can decompose N2O at low temperatures and are stable against various inhibitors. Zn-doped cobalt spinel (ZnxCo1−xCo2O4) catalysts have demonstrated superior activity for N2O decomposition at low temperatures. However, their optimization and deactivation mechanisms with respect to Zn loading when inhibitors are present require further investigation. Herein, we reviewed the effects of Zn loading on catalysts at low temperatures without or with the presence of inhibitors (3 vol% O2, 6 vol% H2O, 200 ppm NO). The results showed that adding an appropriate amount of Zn into Co3O4 spinel catalysts improves their N2O decomposition activity. The Zn-induced enhancement of the catalysts’ redox properties, and reducibility was the underlying mechanism behind the activity promotion. The presence of structural defects created through the addition of Zn enhanced the catalyst’s resistance to O2. The deactivation by H2O and NO upon the addition of Zn could be correlated with the reduced availability of surface Co species and Co2+ as adsorption-active sites and the stronger bond of Co with –NO, respectively. This study underscores the importance of controlling the Zn loading as a bulk redox promoter in ZnxCo1−xCo2O4 spinel catalysts for practical applications.
Nitrifier denitrification is the reduction of nitrite (NO2−) by ammonia-oxidizing bacteria. This process may account for up to 100% of nitrous oxide (N2O) emissions from ammonium (NH4+) in soils and ...is more significant than classical denitrification under some conditions. Investigations of nitrifier denitrification have expanded in the last decade but many aspects are still not understood. In this review, we revisit our 2001 paper, present a comprehensive summary of current knowledge concerning nitrifier denitrification, and identify the many research needs. Nitrifier denitrification can be distinguished from other routes of N2O production using isotopic methods: either isotopomer techniques or a combination of 15N and 18O tracers. Our understanding of the regulation and conditions favouring nitrifier denitrification has improved over the last decade as a result of adopting molecular and modelling approaches. Environments low in oxygen, and especially those with fluctuating aerobic-anaerobic conditions, promote N2O production by nitrifier denitrification. Also, large NO2− concentrations, which often arise following inputs of ammonium or urea, may be linked to changes in aerobicity and high pH and favour nitrifier denitrification. The effects of temperature and carbon contents on nitrifier denitrification are incompletely understood and future research needs include: the study of pathways similar to nitrifier denitrification in archaea and nitrite oxidizers; the effects of interactions among microorganisms and between microorganism and plants; and the regulation and importance of the enzymes involved. A comparison and evaluation of the methods used for differentiating the sources of N2O is urgently needed. Furthermore, results from studies of freshwater and marine environments as well as wastewater treatment, where nitrifier denitrification is also known as nitrous aerobic denitritation (up to N2O) or aerobic denitritation (up to N2), will further advance our understanding.
Laboratory experiments were conducted to examine the effect of charcoal addition on N₂O emissions resulting from rewetting of air-dried soil. Rewetting the soil at 73% and 83% of the water-filled ...pore space (WFPS) caused a N₂O emission peak 6 h after the rewetting, and the cumulative N₂O emissions throughout the 120-h incubation period were 11 ± 1 and 13 ± 1 mg N m⁻², respectively. However, rewetting at 64% WFPS did not cause detectable N₂O emissions (-0.016 ± 0.082 mg N m⁻²), suggesting a severe sensitivity to soil moisture. When the soils were rewetted at 73% and 78% WFPS, the addition of charcoal to soil at 10 wt% supressed the N₂O emissions by 89% . In contrast, the addition of the ash from the charcoal did not suppress the N₂O emissions from soil rewetted at 73% WFPS. The addition of charcoal also significantly stimulated the N₂O emissions from soil rewetted at 83% WFPS compared with the soil without charcoal addition (P < 0.01). Moreover, the addition of KCl and K₂SO₄ did not show a clear difference in the N₂O emission pattern, although Cl⁻ and graphic removed , which were the major anions in the charcoal, had different effects on N₂O-reducing activity. These results indicate that the suppression of N₂O emissions by the addition of charcoal may not result in stimulation of the N₂O-reducing activity in the soil because of changes in soil chemical properties.
Forest soils are an important source of nitrous oxide (N2O), however, field observations of N2O emission have often exhibited large variabilities when compared with managed agricultural lands. In the ...last decade, the number of forest N2O studies has increased more than tenfold, but only a few of them have looked into the interannual flux variabilities from the regional scale. Here, we have collected 30 long-term N2O monitoring studies (≥ 2 years) based on a global database, and extracted variabilities (VARFlux) as well as relative variabilities (VAR%, in proportions) of annual N2O fluxes. The relationship of mean annual precipitation (MAP), mean annual temperature (MAT), and nitrogen (N) deposition with flux variabilities was examined to explore the underlying mechanisms for N2O emission on a long-term scale. Our results show that mean VARFlux is 0.43 kg N ha−1 yr−1 and VAR% is 28.68%. Across climatic zones, the subtropical forests have the largest annual N2O fluxes, as well as the largest fluctuations among annual budgets, while the tropics were the smallest. We found that the regulating factors for VARFlux and VAR% are fundamentally different, i.e., MAT and N input determine the annual fluxes as well as VARFlux while MAP and other limiting soil parameters determine VAR%. The relative contributions of different seasons to flux variabilities were also explored, indicating that N2O fluxes of warm and cool seasons are more responsible for the fluctuations in annual fluxes of the (sub)tropical and temperate forests, respectively. Overall, despite the limitation in interpretations due to few long-term studies from literature, this work highlights that significant interannual variabilities are common phenomena for N2O emission from different climatic zones forest soils; by unraveling the divergent drivers for VARFlux and VAR%, we have provided the possibility of improving N2O simulation models for constraining the heterogeneity of N2O emission processes from climatic zones forest soils.
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•The mean uncertainty of annual N2O fluxes is 0.43 kg N ha−1 yr−1.•The relative fluctuation of annual N2O fluxes contributes 28.68 % uncertainty.•Divergent factors are driving flux and percentage variabilities.
Sulfonamides, quinolones, tetracyclines, and macrolides are the most prevalent classes of antibiotics used in both medical treatment and agriculture. The misuse of antibiotics leads to their ...extensive dissemination in the environment. These antibiotics can modify the structure and functionality of microbial communities, consequently impacting microbial-mediated nitrogen cycling processes including nitrification, denitrification, and anammox. They can change the relative abundance of nirK/norB contributing to the emission of nitrous oxide, a potent greenhouse gas. This review provides a comprehensive examination of the presence of these four antibiotic classes across different environmental matrices and synthesizes current knowledge of their effects on the nitrogen cycle, including the underlying mechanisms. Such an overview is crucial for understanding the ecological impacts of antibiotics and for guiding future research directions. The presence of antibiotics in the environment varies widely, with significant differences in concentration and type across various settings. We conducted a comprehensive review of over 70 research articles that compare various aspects including processes, antibiotics, concentration ranges, microbial sources, experimental methods, and mechanisms of influence. Antibiotics can either inhibit, have no effect, or even stimulate nitrification, denitrification, and anammox, depending on the experimental conditions. The influence of antibiotics on the nitrogen cycle is characterized by dose-dependent responses, primarily inhibiting nitrification, denitrification, and anammox. This is achieved through alterations in microbial community composition and diversity, carbon source utilization, enzyme activities, electron transfer chain function, and the abundance of specific functional enzymes and antibiotic resistance genes. These alterations can lead to diminished removal of reactive nitrogen and heightened nitrous oxide emissions, potentially exacerbating the greenhouse effect and related environmental issues. Future research should consider diverse reaction mechanisms and expand the scope to investigate the combined effects of multiple antibiotics, as well as their interactions with heavy metals and other chemicals or organisms.
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•Microbial nitrogen cycling and N2O emissions under antibiotics were summarized.•μg/L or mg/kg of antibiotics inhibited nitrification, denitrification and anammox.•Antibiotics changed ratio of nirK/norB and increased nitrous oxide emissions.•Microbial community, electron transfer system & ARGs were altered by antibiotics.
•An increase in the fertilizer N rate increased N2O emissions in irrigated corn.•No-tillage significantly increased soil N2O emission at the highest N-fertilizer rate.•Denitrification was the main ...pathway under no-tillage for N2O emission.•The use 200 kg N ha−1 reduced the yield-scaled N2O emissions in the first out of three years.•The emission factor was much lower than 1% proposed by IPCC.
In irrigated Mediterranean conditions there is a lack of knowledge about the best combination of tillage and N fertilization practices to reduce soil nitrous oxide (N2O) emissions while maintaining maize productivity. The aim of this work was to investigate the effects of different soil management practices and synthetic N fertilization rates on soil N2O emissions and their relationship with maize grain yield to determine the best management system to reduce yield-scaled N2O emissions (YSNE) in a semiarid area recently converted to irrigation under Mediterranean conditions. A long-term tillage and N rate field experiment established in 1996 under barley (Hordeum vulgare L.) rainfed conditions, was converted to irrigated maize (Zea mays L.) in 2015. After the transformation to irrigation, the field experiment maintained the same tillage treatments and N fertilization rates. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha−1) were compared during three years (2015–2017) in a randomized block design with three replications. Soil N2O emissions, water-filled pore space, soil temperature, mineral N content (as NH4+ and NO3−), denitrification potential and maize grain yield and above-ground N uptake were quantified. Moreover, the emission factor (EF) and YSNE were calculated. The results showed that the combination of NT and the highest rate of N fertilization led to greater N2O emissions. Furthermore, the lowest N2O fluxes were observed in CT when WFPS was below 40% and the highest N2O fluxes were seen in NT when WFPS was above 60% coinciding with the greatest denitrification potential. Cumulative N2O emissions in 2017 and 2015 followed the order 400 > 200 > 0 kg N ha−1, while in 2016, rate of 400 and 200 kg N ha−1 showed greater cumulative N2O emission compared to the control. Only RT showed differences between growing seasons on cumulative N2O emissions, with greater values in 2017 compared to 2015, and intermediate values in 2016. In all treatments, the N2O EF was much lower than the default IPCC emission factor (1%). NT and RT increased the grain production compared to CT which was affected by severe soil crusting causing water deficit. Likewise, N fertilizer treatments significantly affected the YSNE, increasing with increasing fertilizer N application rate in the first year of study. Our data show that the use of NT or RT does not lead to more yield-scaled N2O emissions than CT in Mediterranean agroecosystems recently converted to irrigation.
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