Modeling nitrous oxide emission from rivers: a global assessment

Estimates of global riverine nitrous oxide (N₂O) emissions contain great uncertainty. We conducted a meta‐analysis incorporating 169 observations from published literature to estimate global riverine N₂O emission rates and emission factors. Riverine N₂O flux was significantly correlated with NH₄, NO₃ and DIN (NH₄ + NO₃) concentrations, loads and yields. The emission factors EF(a) (i.e., the ratio of N₂O emission rate and DIN load) and EF(b) (i.e., the ratio of N₂O and DIN concentrations) values were comparable and showed negative correlations with nitrogen concentration, load and yield and water discharge, but positive correlations with the dissolved organic carbon : DIN ratio. After individually evaluating 82 potential regression models based on EF(a) or EF(b) for global, temperate zone and subtropical zone datasets, a power function of DIN yield multiplied by watershed area was determined to provide the best fit between modeled and observed riverine N₂O emission rates (EF(a): R² = 0.92 for both global and climatic zone models, n = 70; EF(b): R² = 0.91 for global model and R² = 0.90 for climatic zone models, n = 70). Using recent estimates of DIN loads for 6400 rivers, models estimated global riverine N₂O emission rates of 29.6–35.3 (mean = 32.2) Gg N₂O–N yr⁻¹ and emission factors of 0.16–0.19% (mean = 0.17%). Global riverine N₂O emission rates are forecasted to increase by 35%, 25%, 18% and 3% in 2050 compared to the 2000s under the Millennium Ecosystem Assessment's Global Orchestration, Order from Strength, Technogarden, and Adapting Mosaic scenarios, respectively. Previous studies may overestimate global riverine N₂O emission rates (300–2100 Gg N₂O–N yr⁻¹) because they ignore declining emission factor values with increasing nitrogen levels and channel size, as well as neglect differences in emission factors corresponding to different nitrogen forms. Riverine N₂O emission estimates will be further enhanced through refining emission factor estimates, extending measurements longitudinally along entire river networks and improving estimates of global riverine nitrogen loads.     

Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape

Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification – a potential source of the potent greenhouse gas, nitrous oxide (N₂O) – and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N₂O. Measurements of net N₂O fluxes alone yield little insight into the different effects of redox conditions on N₂O production and consumption. We used in situ measurements of gross N₂O fluxes across a salt marsh elevation gradient to determine how soil N₂O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes (P < 0.001 for both). In addition, soil oxygen concentrations were lower in the low and mid‐marshes relative to the high marsh (P < 0.001). Net N₂O fluxes differed significantly among marsh zones (P = 0.009), averaging 9.8 ± 5.4 μg N m^?2 h^?1, ?2.2 ± 0.9 μg N m^?2 h^?1, and 0.67 ± 0.57 μg N m^?2 h^?1 in the low, mid, and high marshes, respectively. Both net N₂O release and uptake were observed in the low and high marshes, but the mid‐marsh was consistently a net N₂O sink. Gross N₂O production was highest in the low marsh and lowest in the mid‐marsh (P = 0.02), whereas gross N₂O consumption did not differ among marsh zones. Thus, variability in gross N₂O production rates drove the differences in net N₂O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N₂O in salt marshes to improve our predictions of changes in net N₂O fluxes caused by future sea level rise.     

福建漳江口红树林和盐沼湿地的多毛类动物群落

为了比较漳江口4种植物生境之间多毛类动物群落的差异性,2010年对漳江口潮间带秋茄、桐花树、白骨壤和互花米草4种植物生境的多毛类动物进行4个季度的定量取样.共获得15种多毛类动物,4个季度在4种植物生境中均出现三角洲双须虫、溪沙蚕、拟突齿沙蚕、凿贝才女虫、小头虫和加州中蚓虫.多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数的季节变化不明显;但4种植物生境之间多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数有显著差异,且互花米草生境与3种红树林生境之间多毛类动物优势种不同.Pearson相关分析表明,漳江口红树林和盐沼湿地除了多毛类物种数与泥温显著相关外,多毛类动物栖息密度、生物量、丰度指数、均匀度指数和多样性指数均与泥温、盐度、总有机碳、总氮无显著相关关系,其原因是漳江口4种植物生境多毛类动物常见种小头虫、加州中蚓虫和溪沙蚕均是广温、广盐及耐高有机质含量的种类.     

垃圾填埋场N2O排放通量及测定方法研究进展

氧化亚氮(N₂O)是第三大温室气体和最主要的臭氧层破坏气体.填埋是目前城市生活垃圾处理处置的主要方式,而垃圾填埋场是N₂O的排放源之一.实验室研究和现场测定均表明,生活垃圾填埋场可以有高的N₂O释放通量,但不同填埋场测定数据差异很大.目前,对生活垃圾填埋场N₂O排放量的原位准确测定以及排放机理和重要性的认识仍有很多不足.本文概述了生活垃圾填埋场N₂O排放研究现状,从垃圾堆体和覆土层两部分探讨了传统厌氧卫生填埋场的N₂O产生和排放机理,并就此对新型脱氮型生物反应器填埋场做了相应探讨.最后,就静态箱法、涡度相关法等N₂O通量测定方法在填埋场的适用性进行了讨论,并展望了填埋场N₂O排放的研究方向.     

Nitrous oxide emissions from grass swards during the eighth year of elevated atmospheric pCO2 (Swiss FACE)

Emissions of N₂O were measured during the growth season over a year from grass swards under ambient (360 μL L^?1) and elevated (600 μL L^?1) CO₂ partial pressures at the Free Air Carbon dioxide Enrichment (FACE) experiment, Eschikon, Switzerland. Measurements were made following high (56 g N m^?2 yr^?1) and low (14 g N m^?2 yr^?1) rates of fertilizer application, split over 5 re‐growth periods, to Lolium perenne, Trifolium repens and mixed Lolium/Trifolium swards. Elevated pCO₂ increased annual emissions of N₂O from the high fertilized Lolium and mixed Lolium/Trifolium swards resulting in increases in GWP (N₂O emissions) of 179 and 111 g CO₂ equivalents m^?2, respectively, compared with the GWP of ambient pCO₂ swards, but had no significant effect on annual emissions from Trifolium monoculture swards. The greater emissions from the high fertilized elevated pCO₂Lolium swards were attributed to greater below‐ground C allocation under elevated pCO₂ providing the energy for denitrification in the presence of excess mineral N. An annual emission of 959 mg N₂O‐N m^?2 yr^?1 (1.7% of fertilizer N applied) was measured from the high fertilized Lolium sward under elevated pCO₂. The magnitude of emissions varied throughout the year with 84% of the total emission from the elevated pCO₂Lolium swards measured during the first two re‐growths (April–June 2001). This was associated with higher rainfall and soil water contents at this time of year. Trends in emissions varied between the first two re‐growths (April–June 2001) and the third, fourth and fifth re‐growths (late June–October 2000), with available soil NO₃^? and rainfall explaining 70%, and soil water content explaining 72% of the variability in N₂O in these periods, respectively. Caution is therefore required when extrapolating from short‐term measurements to predict long‐term responses to global climate change. Our findings are of global significance as increases in atmospheric concentrations of CO₂ may, depending on sward composition and fertilizer management, increase greenhouse gas emissions of N₂O, thereby exacerbating the forcing effect of elevated CO₂ on global climate. Our results suggest that when applying high rates of N fertilizer to grassland systems, Trifolium repens swards, or a greater component of Trifolium in mixed swards, may minimize the negative effect of continued increasing atmospheric CO₂ concentrations on global warming.     

Nitrous oxide fluxes from savanna (miombo) woodlands in Zimbabwe

Aim We test the hypothesis that land use and climate are important controls of nitrous oxide (N₂O) emissions from savanna ecosystems, and that these emissions can be represented by a mechanistic model of carbon (C) and nitrogen (N) transformations. Location Miombo woodlands in Zimbabwe are part of widespread woody savanna formations in southern and central Africa that cover more than 2.7 million km². The rainfall in this region is around 800 mm and is concentrated in the period between November and March. Methods Losses of N₂O were measured along transects in two field areas using static chambers over a period of 1 year. The vegetation in both areas was dominated by Julbernardia globiflora and Brachystegia spiciformis, but had differing management systems (burned and unburned), soil properties and site characteristics (slope and drainage). The effects of simulated rainfall and fertilizer additions were studied in laboratory incubations. Results Patterns of N₂O emissions were strongly linked to rainfall. The highest fluxes at both sites were measured within 18 days of the onset of the first rains in November, with fluxes of up to 42 μg N m^?2 h^?1. During the dry season, fluxes were lower, but a large proportion (R² values between 0.8 and 0.95, P < 0.001) of the N₂O flux could be predicted by variations in soil moisture. Soil columns were set up in the laboratory to which simulated rainwater was added, and the amounts and timing of rainwater addition were varied. Losses of N₂O were highest within the first week of the laboratory study. Altering the amount of rainwater addition did not significantly affect N₂O loss; however, a continuous addition of water resulted in higher losses of N₂O (up to 79 μg N m^?2 h^?1) than periodic addition of the same amount. A model (denitrification–decomposition) was used to simulate N₂O release over a 12 month period, using meteorological data recorded in the vicinity of the field site. The simulations and field data suggest that nitrification was the main process responsible for N₂O release during the dry season but that denitrification was more important during the wet season. Main conclusions The release of N₂O from dryland savannas was shown to constitute an important nutrient flux, and emissions were strongly linked to patterns of rainfall; however, there was evidence to suggest that the magnitude of fluxes is also influenced locally by differences in soil organic matter concentration and drainage.     

Nitrous oxide production, its source and distribution in urine patches on grassland on peat soil

Urine patches are considered to be important sites for nitrous oxide (N₂O) production through nitrification and denitrification due to their high concentration of nitrogen (N). The aim of the present study was to determine the microbial source and size of production of N₂O in different zones of a urine patch on grassland on peat soil. Artificial urine was applied in elongated patches of 4.5 m. Four lateral zones were distinguished and sampled for four weeks using an intact soil core incubation method. Incubation of soil cores took place without any additions to the headspace to determine total N₂O production, with acetylene addition to determine total denitrification (N₂O+N₂), and with methyl fluoride to determine the N₂O produced through denitrification.Nitrous oxide production was largest in the centre and decreased towards the edge of the patch. Maximum N₂O production was about 50 mg N m^–2 d^–1 and maximum denitrification activity was 70 mg N m^–2 d^–1. Nitrification was the main N₂O producing process. Nitrous oxide production through denitrification was only of significance when denitrification activity was high. Total N loss through nitrification and denitrification over 31 days was 4.1 g N per patch which was 2.2% of the total applied urine-N.     

Effect of ammonium and nitrate application on the NO and N2O emission out of different soils

The effect of nitrate and ammonium application (0, 50, 100 and 150 mg N kg^-1 soil) was studied in an incubation experiment. Four Belgian soils, selected for different soil characteristics, were used. The application of both nitrate and ammonium caused an increase of the NO and N₂O emission. The NO production from nitrate and ammonium was found to be of the same order of magnitude. At low pH the NO production was found to be highest from nitrate, at higher pH values the production was found to be higher from ammonium. This seems to be the result of the negative effect of low pH on nitrification.The ANOVA analysis was carried out to separate the effect of the form of nitrogen, quantily of N applied and soil characteristics. The total production of NO was found to depend for 97% on the soil characteristics and for 3% on the quantity of N added. The total N₂O production depended for 100% on the soil characteristics.Stepwise regression analysis showed that the total NO production was best predicted by a combination of the factors CaCO₃ content and NH₄ ⁺ concentration in the soil. Total N₂O production was best described by a combination of CaCO₃, water soluble carbon (WSC) and sand-content.The N₂O/NO ratio was found to be highly variable, indicating that their productions react differently to changes in conditions, or are partly independent.It may be concluded that to NO and N₂O from soils both nitrification and denitrification may be equally important, their relative importance depending on local conditions such as substrate availability, water content of the soil etc. However, the NO production seems to be more nitrification dependent than the N₂O production. ei]{gnE}{fnMerckx}{edSection editor}     

Nitrous oxide fluxes over establishing biofuel crops: Characterization of temporal variability using the cross‐wavelet analysis

Emissions of nitrous oxide (N₂O) over croplands are a major source of greenhouse gases to the atmosphere. The precise accounting of sources of N₂O is essential to national and global budgets, as well as the understanding of the spatial and temporal relationships with environmental variables such as rainfall, air and soil temperature, and soil moisture. The objective of this work was to investigate the temporal correlations of N₂O fluxes with soil and air temperatures, as well as soil moisture. N₂O fluxes were measured over four biofuel crops in Central Illinois during their establishment phase. Measurements were carried out from 2009 to 2011 using a trace gas analyzer (TGA) with tunable laser technology. Measurements of concentrations of N₂O and CO₂ were taken at the center of four plots of maize/soybean rotation, miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum) and a mixture of native prairie plants. Cumulative fluxes indicate an average emission of nitrogen via N₂O fluxes on the order of 1.5 kg N ha^?1 year^?1, in agreement with chamber measurements previously reported for the site. N₂O fluxes were associated with peaks in soil and air temperature, and soil moisture, particularly during spring and winter thaws. Cross‐wavelet analysis was used to investigate the correlation between N₂O fluxes and those variables. Results indicate that N₂O fluxes and meteorological variables have significant covariance in time scales ranging from 4 to 32 days. In addition, temporal delays of 1–8 days were found in those relationships. Cross‐wavelet patterns were similar when relating N₂O fluxes with soil temperature, air temperature and soil moisture. The temporal patterns of fluxes and environmental variables reported here support the modeling of emissions and highlight the importance of considering the timing of fluxes in relation to trends in meteorological variables.     

Environmental factors function as constraints on soil nitrous oxide fluxes in bioenergy feedstock cropping systems

Nitrous oxide (N₂O) is a potent greenhouse gas and major component of the net global warming potential of bioenergy feedstock cropping systems. Numerous environmental factors influence soil N₂O production, making direct correlation difficult to any one factor of N₂O fluxes under field conditions. We instead employed quantile regression to evaluate whether soil temperature, water‐filled pore space (WFPS), and concentrations of soil nitrate () and ammonium () determined upper bounds for soil N₂O flux magnitudes. We collected data over 6 years from a range of bioenergy feedstock cropping systems including no‐till grain crops, perennial warm‐season grasses, hybrid poplar, and polycultures of tallgrass prairie species each with and without nitrogen (N) addition grown at two sites. The upper bounds for soil N₂O fluxes had a significant and positive correlation with all four environmental factors, although relatively large fluxes were still possible at minimal values for nearly all factors. The correlation with was generally weaker, suggesting it is less important than in driving large fluxes. Quantile regression slopes were generally lower for unfertilized perennials than for other systems, but this may have resulted from a perpetual state of nitrogen limitation, which prevented other factors from being clear constraints. This framework suggests efforts to reduce concentrations of in the soil may be effective at reducing high‐intensity periods—”hot moments”—of N₂O production.     

稻鸭共作生态系统中N2O排放及经济效益评价

稻鸭共作技术是中国传统农业的精华,研究稻鸭共作生态系统中N2O排放产生的环境效应并对其经济价值进行评价,为进一步开发利用这一经典农艺提供理论基础和实践依据.采用静态箱技术,研究稻鸭共作生态系统N2O排放规律,并运用增温潜势对稻鸭共作生态系统N2O排放的温室效应及经济效益进行了估算.结果表明,稻鸭共作生态系统N2O排放呈现明显的日变化和季节变化.N2O日变化与鸭子的活动呈现明显的相关性,其排放峰值出现在清晨和16:00;N2O季节变化幅度较大,排放峰值出现在水稻成熟期.在施用等量基肥条件下,稻鸭稻田排放的N2O高于常规稻田,其平均排放通量分别为(149 46±25.81)μg·m-2·h-1和(138.84±25.26)μg·m-2·h-1,产生的温室效应成本分别为283.14yuan·hm-2和265.47yuan·hm-2.除去N2O排放产生温室效应的环境成本,采用稻鸭生态种养技术的经济效益为7687.66yuan·hm-2,比常规不养鸭稻田增加1932.33 yuan·hm-2.可见,稻鸭共作技术仍具有较好的推广价值.     

Riparian nitrogen dynamics in two geomorphologically distinct tropical rain forest watersheds: nitrous oxide fluxes

Fluxes of N₂O at the soil surface, dissolved N₂O in near-surface groundwater, and potential N₂O production rates were measured across riparian catenas in two rain forest watersheds in Puerto Rico. In the Icacos watershed, mean N₂O fluxes were highest at topographic breaks in the landscape (≃ 40–300 μg N₂O-N m⁻² h⁻¹). At other locations in the riparian zone and hillslope, fluxes were lower (⩽ 2 μg N₂O-N m⁻² h⁻¹). This pattern of surface N₂O fluxes was persistent. In the Bisley watershed, mean suface N₂O fluxes were lower (<40 μg N₂O-N m⁻² h⁻¹) and no identifiable spatial or temporal pattern. Although the spatial patterns and intensities of N₂O emissions differed between the two watersheds, surface soils from both sites had a high potential to reduce NO₃ to N₂O (and perhaps N₂). This potential declined sharply with depth as did soil %C, %N, and potential N-mineralization. Simple controls on denitrification (i.e. aeration, nitrate, and carbon) explained characteristics of potential N₂O production in surface and deep soils from riparian and upslope locations. In the field, spatial patterns in these controlling variables were defined by geomorphological differences between the two watersheds, which then explained the spatial patterns of observed N₂O flux     

The potential to mitigate global warming with no-tillage management is only realized when practised in the long term

No‐tillage (NT) management has been promoted as a practice capable of offsetting greenhouse gas (GHG) emissions because of its ability to sequester carbon in soils. However, true mitigation is only possible if the overall impact of NT adoption reduces the net global warming potential (GWP) determined by fluxes of the three major biogenic GHGs (i.e. CO₂, N₂O, and CH₄). We compiled all available data of soil‐derived GHG emission comparisons between conventional tilled (CT) and NT systems for humid and dry temperate climates. Newly converted NT systems increase GWP relative to CT practices, in both humid and dry climate regimes, and longer‐term adoption (>10 years) only significantly reduces GWP in humid climates. Mean cumulative GWP over a 20‐year period is also reduced under continuous NT in dry areas, but with a high degree of uncertainty. Emissions of N₂O drive much of the trend in net GWP, suggesting improved nitrogen management is essential to realize the full benefit from carbon storage in the soil for purposes of global warming mitigation. Our results indicate a strong time dependency in the GHG mitigation potential of NT agriculture, demonstrating that GHG mitigation by adoption of NT is much more variable and complex than previously considered, and policy plans to reduce global warming through this land management practice need further scrutiny to ensure success.     

Mangrove transgression into saltmarsh environments in south-east Australia

The landward transgression of man- groves into saltmarsh environments in the estuaries of south-east Australia over the last five decades is established as a widespread trend through a review of a number of independent studies. This process is occurring in a range of geomorphic settings, and in some cases reversing the direction of longer-term vegetation change. Several hypotheses are advanced to explain this occurrence, including increases in rainfall, revegetation of areas cleared for agriculture, altered tidal regimes or estuary water levels, and increases in nutrient levels and sedimentation.     

Using kinetics and modeling to predict denitrification fluxes in elemental-sulfur-based biofilms

Elemental sulfur (S⁰) can serve as an electron donor for water and wastewater denitrification, but few researchers have addressed the kinetics of S ⁰–based reduction of nitrate (NO ₃ ⁻), nitrite (NO ₂ ⁻), and nitrous oxide (N ₂O). In addition, S ⁰-based denitrifying biofilms are counter-diffusional. This is because the electron donor (S ⁰) is supplied from the biofilm attachment surface while the acceptor, for example, NO ₃ ⁻, is supplied from the bulk liquid. No existing mathematical model for S ⁰-based denitrification considers this behavior. In this study, batch tests were used to determine the kinetic parameters for the reduction of NO ₃ ⁻, NO ₂ ⁻, and N ₂O. Additionally, a biofilm model was developed to explore the effects of counter-diffusion on overall fluxes, that is, the mass of NO ₃ ⁻ or NO ₂ ⁻ removed per unit biofilm support area per unit time. The maximum specific substrate utilization rates () for NO ₃ ⁻, NO ₂ ⁻, and N ₂O were 3.54, 1.98, and 6.28 g N g COD ⁻¹·d ⁻¹, respectively. The maximum specific growth rates () were 0.71, 1.21, and 1.67 d ⁻¹ for NO ₃ ⁻ to NO ₂ ⁻, NO ₂ ⁻ to N ₂O, and N ₂O to N ₂, respectively. Results suggest that the observed NO ₂ ⁻ accumulation during S ⁰-based denitrification results from a low for NO ₂ ⁻ relative to that for NO ₃ ⁻. The high for N ₂O, relative to that for NO ₃ ⁻ and NO ₂ ⁻, suggest that little N ₂O accumulation occurs during denitrification. A counter-diffusional biofilm model was used to predict trends for NO ₃ ⁻ fluxes, and confirmed NO ₂ ⁻ accumulation in S ⁰-based denitrification biofilms. It also explains the observed detrimental effects of biofilm thickness on denitrification fluxes. This study allows a more accurate prediction of NO ₃ ⁻, NO ₂ ⁻, and N ₂O transformations in S ⁰-based denitrification.     

Rapid Conversion of Added Nitrate to Nitrous Oxide and Dinitrogen in Northern Forest Soil

The aims of this study were to simulate wet deposition of atmospheric nitrate (NO₃^?) onto forest soils and trace its fate via conversion spatially and temporally into gaseous products nitrous oxide (N₂O) and dinitrogen (N₂). The most likely mechanism is microbial denitrification, but an intermediate product nitrite (NO₂^?) can fuel N₂O production via a chemical pathway involving reactions with iron and/or organic matter referred to as chemodenitrification. During summer months, we applied tracer amounts of ¹⁵N-labeled NO₃^? onto forest soils (pH ～ 4) at three sites in the White Mountain Region of New Hampshire, USA. We recovered ¹⁵N as N₂O in 210 of 504 measurements (42%) versus ¹⁵N as N₂ in 51 of 504 measurements (10%), suggesting partial microbial denitrification and/or chemodenitrification. When recovery occurred, the mean percent recovery of added ¹⁵N was just 1.1% as N₂O, although N₂ recovery was 33%. A site with old-growth trees had a larger percentage recovery as N₂ (48%), whereas a site that had burned 100 years ago had a small percentage recovery as N₂O (0.24%). The ¹⁵N composition of N₂O in ambient air, collected before addition of the label, was markedly enriched in ¹⁵N. Since flux measurements were made 2 h after the addition, the results suggest that denitrification enzymes and conditions for chemodenitrification are present throughout the summer months but account for small amounts of NO₃^? conversion into N₂O and N₂.     

Effect of oxic and anoxic conditions on nitrous oxide emissions from nitrification and denitrification processes

A lab-scale sequencing batch reactor fed with real municipal wastewater was used to study nitrous oxide (N(2)O) emissions from simulated wastewater treatment processes. The experiments were performed under four different controlled conditions as follows: (1) fully aerobic, (2) anoxic-aerobic with high dissolved oxygen (DO) concentration, (3) anoxic-aerobic with low DO concentration, and 4) intermittent aeration. The results indicated that N(2)O production can occur from both incomplete nitrification and incomplete denitrification. N(2)O production from denitrification was observed in both aerobic and anoxic phases. However, N(2)O production from aerobic conditions occurred only when both low DO concentrations and high nitrite concentration existed simultaneously. The magnitude of N(2) O produced via anoxic denitrification was lower than via oxic denitrification and required the presence of nitrite. Changes in DO, ammonium, and nitrite concentrations influenced the magnitude of N(2)O production through denitrification. The results also suggested that N(2)O can be produced from incomplete denitrification and then released to the atmosphere during aeration phase due to air stripping. Therefore, biological nitrogen removal systems should be optimized to promote complete nitrification and denitrification to minimize N(2)O emissions.     

Effects of biochar application on soil greenhouse gas fluxes: a meta‐analysis

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta‐analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO₂, CH₄, and N₂O) in response to biochar application. Our results showed that biochar application significantly increased soil CO₂ fluxes by 22.14%, but decreased N₂O fluxes by 30.92% and did not affect CH₄ fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO₂ fluxes. However, soil CO₂ fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO₂ fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation.