Impact of 13-years of nitrogen addition on nitrous oxide and methane fluxes and ecosystem respiration in a temperate grassland

Towards climate neutrality in the Spanish N-fertilizer sector: A study based on radiative forcing

Agricultural systems in the 21st Century face the double challenge of achieving climate neutrality while maintaining food security. Synthetic fertilizers rich in nitrogen (N-fertilizers) boost agricultural production at the expense of increasing climate impact. Public policies, such as the Farm-to-Fork (F2F) Strategy, aim to reduce the extensive use of N-fertilizers with the ultimate goal of achieving a climate neutral European Union (EU). However, the strong link between N-fertilizers and GHG emissions (i.e., CO2, CH4 and, especially, N2O) highlights the need to better understand the climate impact of this sector. The present study conducts a climate impact analysis of Spanish N-fertilizer sector for two periods: (i) from 1960 to 2020 using real data and (ii) from 2021 to 2100 considering five forecasted scenarios. The scenarios range from business-as-usual practices to a full accomplishment of the goals pursued by the EU's F2F strategy. The system's climate stability and neutrality are analysed for the different scenarios based on radiative forcing (RF) metrics. Additionally, the study evaluates the short-term impact of the EU decarbonization goals on the climate impact of the Spanish N-fertilizer sector. The results of the study illustrate that the long-lasting climate impact of N2O and CO2 emissions compromise the capacity of N-fertilizer sector to achieve climate stability and approach climate neutrality. However, the decarbonisation of transport and N-fertilizer production activities is an important driver to substantially reduce the life cycle CH4 and CO2 emissions in the Spanish N-fertilizer sector. The results also highlight that more severe reductions on N-cycles than those suggested by the EU's F2F are required, especially to reduce the long-lasting N2O emissions in the N-fertilizer sector. Overall, the study concludes that using RF-based metrics increases robustness and transparency of climate assessments, which is necessary for a higher integration of climate science within public policymaking.

The effect of nitrogen input on N2O emission depends on precipitation in a temperate desert steppe

Nitrous oxide (N2O) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect N2O emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on N2O emission. The study result showed that N2O emission in this desert steppe was relatively small and did not show significant seasonal change. The annual N2O emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17th 2019) on N2O emission was greatly amplified by nearly 17-46 times by an extreme precipitation event on June 24th 2019. In contrast, this greatly promoting effect of high N input on N2O emission was not observed on September 26th 2019 by a similar extreme precipitation event. Further analysis showed that soil NH4+-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting N2O emission. Soil moisture played an important indirect role in regulating N2O emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on N2O emission was greatly increased by high N input. Furthermore, in this desert steppe, annual N2O flux is co-managed through soil nitrification substrate concentration (NH4+-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future N2O emissions from desert steppes.

Enhanced CO2 uptake is marginally offset by altered fluxes of non-CO2 greenhouse gases in global forests and grasslands under N deposition

Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO2 exchange and the emission or uptake of non-CO2 GHGs (CH4 and N2 O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom-up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH4 and N2 O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration (RH ) in both forests and grasslands, while a significant N-induced increase in soil CO2 fluxes (RS , soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N2 O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH4 , suggesting a declined sink capacity of forests and grasslands for atmospheric CH4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production-based method (forest, 1.28 Pg CO2 -eq year-1 vs. grassland, 0.58 Pg CO2 -eq year-1 ) was greater than those estimated using the SOC-based method (forest, 0.32 Pg CO2 -eq year-1 vs. grassland, 0.18 Pg CO2 -eq year-1 ) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%-4.8%) by the combined effects of its stimulation of N2 O emissions together with the reduced soil uptake of CH4 .

Decrease of nitrogen cycle gene abundance and promotion of soil microbial-N saturation restrain increases in N2O emissions in a temperate forest with long-term nitrogen addition

Increases in soil available nitrogen (N) influence N-cycle gene abundances and emission of nitrous oxide (N2O), which is primarily due to N-induced soil acidification in forest. Moreover, the extent of microbial-N saturation could control microbial activity and N2O emission. The contributions of N-induced alterations of microbial-N saturation and N-cycle gene abundances to N2O emission have rarely been quantified. Here, the mechanism underlying N2O emission under N additions (three chemical forms of N, i.e., NO3--N, NH4+-N and NH4NO3-N, and each at two rates, 50 and 150 kg N ha-1 year-1, respectively) spanning 2011-2021 was investigated in a temperate forest in Beijing. Results showed N2O emissions increased at both low and high N rates of all the three forms compared with control during the whole experiment. However, N2O emissions were lower in high rate of NH4NO3-N and NH4+-N treatments than the corresponding low N rates in the recent three years. Effects of N on microbial-N saturation and abundances of N-cycle genes were dependent on the N rate and form as well as experimental time. Specifically, negative effects of N on N-cycle gene abundances and positive effects of N on microbial-N saturation were demonstrated in high N rate treatments, particularly with NH4+ addition during 2019-2021. Such effects were associated with soil acidification. A hump-backed trend between microbial-N saturation and N2O emissions was observed, suggesting N2O emissions decreased with increase of the microbial-N saturation. Furthermore, N-induced decreases in N-cycle gene abundances restrained N2O emissions. In particular, the nitrification process, dominated by ammonia-oxidize archaea, is critical to determination of N2O emissions in response to the N addition in the temperate forest. We confirmed N addition promoted soil microbial-N saturation and reduced N-cycle gene abundances, which restrained the continuous increase in N2O emissions. It is important for understanding the forest-N-microbe nexus under climate change.

Effects of grazing and nitrogen application on greenhouse gas emissions in alpine meadow

Overgrazing and injudicious nitrogen applications have increased emissions of greenhouse gases from grassland ecosystems. To explore the effects and potential mechanisms of grazing, nitrogen application, and their interaction with greenhouse gas (GHG) emissions, field experiments were conducted on the Qinghai-Tibet Plateau for three consecutive years. Alpine meadow plots were subjected to light (8 sheep ha^-1) and heavy (16 sheep ha^-1) stocking rates, with or without ammonium nitrate (NH₄NO₃) (90 kg N ha^-1 yr^-1) treatment to simulate soil nitrogen deposition. During early warm growth season (May-June), peak growth season (July-September), and early cold season (October-November), static-chamber gas chromatography was used to analyze the soil's greenhouse gas emissions (CO₂, N₂O, and CH₄). Results indicated that light stocking rate (LG) led to an increase in cumulative CO₂ and N₂O emissions, while also promoting CH₄ uptake. Conversely, heavy stocking rate (HG) produced contrasting outcomes. Additionally, nitrogen applications significantly increased the short-term CO₂ and N₂O fluxes peaks. Combined treatment of nitrogen application and light stocking rate (LG + N) resulted in increased CO₂ and N₂O emissions while decreased CH₄ uptake, consequently leading to a significant increase in global warming potential. According to the structural equation model, we discovered that nitrogen application and grazing affected GHG fluxes both directly and indirectly through their impact on the environmental factors. Our findings suggest that in the context of increasing nitrogen deposition in the Qinghai-Tibet Plateau, a moderate increase in stocking rate is more effective than reducing grazing intensity for mitigating global warming potential in alpine meadow.

Variation in methane uptake by grassland soils in the context of climate change - A review of effects and mechanisms

Grassland soils are climate-dependent ecosystems that have a significant greenhouse gas mitigating function through their ability to store large amounts of carbon (C). However, what is often not recognized is that they can also exhibit a high methane (CH₄) uptake capacity that could be influenced by future increases in atmospheric carbon dioxide (CO₂) concentration and variations in temperature and water availability. While there is a wealth of information on C sequestration in grasslands there is less consensus on how climate change impacts on CH₄ uptake or the underlying mechanisms involved. To address this, we assessed existing knowledge on the impact of climate change components on CH₄ uptake by grassland soils. Increases in precipitation associated with soils with a high background soil moisture content generally resulted in a reduction in CH₄ uptake or even net emissions, while the effect was opposite in soils with a relatively low background moisture content. Initially wet grasslands subject to the combined effects of warming and water deficits may absorb more CH₄, mainly due to increased gas diffusivity. However, in the longer-term heat and drought stress may reduce the activity of methanotrophs when the mean soil moisture content is below the optimum for their survival. Enhanced plant productivity and growth under elevated CO₂, increased soil moisture and changed nutrient concentrations, can differentially affect methanotrophic activity, which is often reduced by increasing N deposition. Our estimations showed that CH₄ uptake in grassland soils can change from -57.7 % to +6.1 % by increased precipitation, from -37.3 % to +85.3 % by elevated temperatures, from +0.87 % to +92.4 % by decreased precipitation, and from -66.7 % to +27.3 % by elevated CO₂. In conclusion, the analysis suggests that grasslands under the influence of warming and drought may absorb even more CH₄, mainly because of reduced soil water contents and increased gas diffusivity.

Suppression of methane uptake by precipitation pulses and long-term nitrogen addition in a semi-arid meadow steppe in northeast China

In the context of global change, the frequency of precipitation pulses is expected to decrease while nitrogen (N) addition is expected to increase, which will have a crucial effect on soil C cycling processes as well as methane (CH₄) fluxes. The interactive effects of precipitation pulses and N addition on ecosystem CH₄ fluxes, however, remain largely unknown in grassland. In this study, a series of precipitation pulses (0, 5, 10, 20, and 50 mm) and long-term N addition (0 and 10 g N m^-2 yr^-1, 10 years) was simulated to investigate their effects on CH₄ fluxes in a semi-arid grassland. The results showed that large precipitation pulses (10 mm, 20 mm, and 50 mm) had a negative pulsing effect on CH₄ fluxes and relatively decreased the peak CH₄ fluxes by 203-362% compared with 0 mm precipitation pulse. The large precipitation pulses significantly inhibited CH₄ absorption and decreased the cumulative CH₄ fluxes by 68-88%, but small precipitation pulses (5 mm) did not significantly alter it. For the first time, we found that precipitation pulse size increased cumulative CH₄ fluxes quadratically in both control and N addition treatments. The increased soil moisture caused by precipitation pulses inhibited CH₄ absorption by suppressing CH₄ uptake and promoting CH₄ release. Nitrogen addition significantly decreased the absorption of CH₄ by increasing NH₄ ⁺-N content and NO₃ ^--N content and increased the production of CH₄ by increasing aboveground biomass, ultimately suppressing CH₄ uptake. Surprisingly, precipitation pulses and N addition did not interact to affect CH₄ uptake because precipitation pulses and N addition had an offset effect on pH and affected CH₄ fluxes through different pathways. In summary, precipitation pulses and N addition were able to suppress the absorption of CH₄ from the atmosphere by soil, reducing the CH₄ sink capacity of grassland ecosystems.

Nitrogen deposition stimulated winter nitrous oxide emissions from bare sand more than biological soil crusts in cold desert ecosystem

Dryland ecosystems are often nitrogen-limited, and small nitrogen inputs may produce large responses to dryland ecological processes, such as gaseous nitrogen emission. The effect of increased anthropogenic nitrogen deposition on N₂O and NO emissions in desert ecosystems is unclear, especially in non-growing seasons when the surface is covered with snow. In this study, nitrogen applications were performed on biological soil crusts (lichen crust and moss crust, bare sand for control) in the Gurbantunggut Desert, Northwest China. We measured the fluxes of N₂O and NO and related nitrogen cycle functional gene abundances in winter for three-years period. Nitrogen addition significantly affected N₂O emissions and increased the abundances of key functional gene for nitrogen cycle, while it only slightly influenced NO emissions. These effects of nitrogen addition depended on composition of biological soil crusts. For bare sand and lichen crust, nitrogen addition significantly increased N₂O emissions, whereas for moss crust, only a negligible effect was observed. Meanwhile, significant differences in nitrogen cycle functional gene abundances were found among different composition of biological soil crusts. Abundance of amoA, narG, and nosZ genes were highly related to N₂O and NO emissions. Thus, our results indicate that gaseous nitrogen emissions were generally increased by nitrogen addition through their effects on related functional microbial groups. The effects were regulated by composition of biological soil crusts which can buffer the effects of increasing nitrogen addition during winter.

Soil Enzyme Activity Regulates the Response of Soil C Fluxes to N Fertilization in a Temperate Cultivated Grassland

Exogenous nitrogen (N) inputs greatly change the emission and uptake of carbon dioxide (CO2) and methane (CH4) from temperate grassland soils, thereby affecting the carbon (C) budget of regional terrestrial ecosystems. Relevant research focused on natural grassland, but the effects of N fertilization on C exchange fluxes from different forage soils and the driving mechanisms were poorly understood. Here, a three-year N addition experiment was conducted on cultivated grassland planted with alfalfa (Medicago sativa) and bromegrass (Bromus inermis) in Inner Mongolia. The fluxes of soil-atmospheric CO2 and CH4; the content of the total dissolved N (TDN); the dissolved organic N (DON); the dissolved organic C (DOC); NH4+–N and NO3−–N in soil; enzyme activity; and auxiliary variables (soil temperature and moisture) were simultaneously measured. The results showed that N fertilization (>75 kg N ha−1 year−1) caused more serious soil acidification for alfalfa planting than for brome planting. N fertilization stimulated P-acquiring hydrolase (AP) in soil for growing Bromus inermis but did not affect C- and N-acquiring hydrolases (AG, BG, CBH, BX, LAP, and NAG). The oxidase activities (PHO and PER) of soil for planting Bromus inermis were higher than soil for planting Medicago sativa, regardless of N, whether fertilization was applied or not. Forage species and N fertilization did not affect soil CO2 flux, whereas a high rate of N fertilization (150 kg N ha−1 year−1) significantly inhibited CH4 uptake in soil for planting Medicago sativa. A synergistic effect between CO2 emission and CH4 uptake in soil was found over the short term. Our findings highlight that forage species affect soil enzyme activity in response to N fertilization. Soil enzyme activity may be an important regulatory factor for C exchange from temperate artificial grassland soil in response to N fertilization.

Exploring wheat-based management strategies to balance agricultural production and environmental sustainability in a wheat-maize cropping system using the DNDC model

Faced with the great challenge of food demand and environmental pollution, optimizing agricultural practices can potentially balance food security and environmental protection. In this study, the DeNitrification-DeComposition (DNDC) model was applied to explore the effect of wheat-based management strategies on crop productivity and greenhouse gas emissions in the wheat-maize system. The DNDC model was tested against crop yield, daily nitrous oxide (N₂O) fluxes, and cumulative N₂O emissions determined from field measurements in a typical winter wheat-summer maize cropping system. Model evaluations demonstrated a good agreement between the observations and simulated crop yield (4.4%≤NRMSE≤8.0%), daily N₂O fluxes (0.68 ≤ d ≤ 0.88), and cumulative N₂O emissions (4.9%≤NRMSE≤11.9%). By adopting sensitivity analysis, the DNDC model then assessed the impacts on crop yield and cumulative N₂O emissions of multiple management practices from the winter wheat season. Delaying the sowing date from October 7 to November 4 reduced annual yield by 1.9%, while cumulative N₂O emissions were increased by 10.4%. Furthermore, postponing the supplementary irrigation date from April 1 to May 20 decreased annual yield by 2.4% without affecting cumulative N₂O emissions. An N fertilizer rate of 120-150 kg N ha^-1 was able to reduce N usage and cumulative N₂O emissions without sacrificing annual yield. Despite an improvement in the annual yield at the 0-30 cm tillage depth by 2.9%, cumulative N₂O emissions increased by 11.6%. The results suggest that sowing in early October, applying supplementary irrigation in early April, an N fertilizer rate of 120-150 kg N ha^-1, and no-tillage from the winter wheat season can improve crop yield and mitigate N₂O emissions. This is conducive to the synergism of agricultural production and environmental sustainability.

The impacts of nitrogen addition on upland soil methane uptake: A global meta-analysis

Elevated nitrogen (N) addition from anthropogenic activities has great impacts on soil methane (CH₄) uptake, which could interrupt the existing global CH₄ balance and cause feedbacks to climate and biogeochemical processes. Previous studies have come to inconsistent conclusions on both the quantification of the response of CH₄ uptake to N addition and understanding of its underlying mechanisms, probably due to the lack of experimental data. Here, we conduct a broad meta-analysis of 90 papers to quantify the responses of CH₄ uptake to N addition in upland soil. The results show that N addition has a significant negative impact on soil CH₄ uptake (-19.25%), which is termed the N inhibition effect. Soil pH is identified as the dominant factor, with the other factors affecting the CH₄ uptake through the alteration of soil pH. The N inhibition effect is observed to be large and significant in forest and grassland, but small and insignificant in farmland, because of the distinct composition of their methanotrophic communities. A threshold of the N addition level is identified at about 68 kg N ha^-1 year^-1, which indicates the lowest N inhibition effect. Furthermore, the convex relationship between response ratio of CH₄ uptake (negative) and N addition duration indicates that a medium level of N addition duration has the largest N inhibition effect, and longer or shorter durations will both reduce the effect. Our analysis of the N inhibition effect implies that controlling the N addition level could effectively reduce the CH₄ concentration in the atmosphere and thus relieve global warming.

Effects of increasing organic nitrogen inputs on CO2, CH4, and N2O fluxes in a temperate grassland

Understanding future climate change requires accurate estimates of the impacts of atmospheric nitrogen (N) deposition, composed of both inorganic and organic compounds, on greenhouse gas (GHG) fluxes in grassland ecosystems. However, previous studies have focused on inorganic compounds and have not considered the potential effects of organic N sources. Here, we conducted a grassland experiment that included organic, inorganic N, and a mix of them at a ratio of 4:6, with two input rates, to study N inputs induced CO₂, CH_4, and N₂O fluxes, as well as the potential abiotic and biotic mechanisms driving the fluxes. We found that N compositions significantly affected fluxes each of the three GHGs. Greater organic N decreased the impacts of N addition on CO₂ and N₂O emissions, caused primarily by low rates of increase in substrates (soil available N) for production of CO₂ and N₂O resulting from high ammonia volatilization rather than changes in microbial activity. Also, greater organic N slightly stimulated CH₄ uptake. Nitrogen composition effects on CO₂ emissions and CH₄ uptake were independent of N input rates and measurement dates, but N₂O emissions showed stronger responses to inorganic N under high N addition and in June. These results suggest that future studies should consider the source of N to improve our prediction of future climate impact of N deposition, and that management of N fertilization can help mitigate GHG emissions.

Salt stress alters the short-term responses of nitrous oxide emissions to the nitrogen addition in salt-affected coastal soils

Increasing nitrogen deposition has become one of major environmental concerns in coastal wetlands. However, little is known about the response of soil nitrous oxide (N₂O) emissions, a powerful greenhouse gas, to the different levels and forms of nitrogen addition, in salt-affected coastal soils. To close the knowledge gap, a laboratory factorial incubation experiment with four nitrogen addition levels (0, no N addition; low-N, 45; medium-N, 90; high-N, 270 mg N kg^-1), three forms (NO₃^- (KN); NH₄⁺ (NH); DN, NH₄NO₃ (DN)), and three levels of salt addition (0, no salt addition; 12 ppt, low-salt; 35 ppt, high-salt) was carried out in two coastal soils with different initial salinity levels (LW: lower salinity wetlands; HW: higher salinity wetlands) in the Yellow River Delta, China. Results showed that, in no salt addition treatments, the cumulative N₂O emissions were linearly related to nitrogen addition, and high nitrogen addition significantly promoted N₂O emissions by 213% in LW soils and 848% in HW soils (p < 0.05), indicating that the mitigate effects of nitrogen addition to the deleterious salt stress were stronger in HW soils. Meanwhile, the promoting effects of DN and KN treatments were more obvious than NH treatments, suggesting that denitrification was responsible for the N₂O emission. However, with salt addition, the nonlinear response pattern and reduced response sizes were observed for KN and DN treatments (p < 0.05), suggesting the alteration in responses of N₂O emission to nitrogen addition by salt stress. In addition, the reduction and modification of response pattern was more obvious in soil with lower initial salinity. The findings of this work suggest the uniqueness and complexity of N₂O emission responses to nitrogen inputs related to the salinity levels in coastal wetlands.

Effects of domestic sewage from different sources on greenhouse gas emission and related microorganisms in straw-returning paddy fields

Reusing domestic sewage for crop irrigation is a promising practice, particularly in developing countries, since it is a substitute for chemical fertilizer and reduces water contamination. More attention was paid to the effect of sewage irrigation on crop yield and soil nutrients, but little attention was paid to greenhouse gas (GHG) emission from straw-returning paddy fields. In this study, a soil column monitoring experiment was conducted to assess the effects of untreated domestic sewage (dominated with ammonia) and treated domestic sewage (dominated with nitrate) irrigation on methane (CH₄), nitrous oxide (N₂O) emission, and related soil microorganisms in straw-returning paddy fields. Results showed that straw-returning dramatically promoted CH₄ emission but had little effect on N₂O emission. Both untreated and treated domestic sewage irrigation decreased CH₄ emission of straw-returning paddy whether nitrogen fertilizer applied or not. The mitigating effect of treated sewage irrigation on CH₄ emission was greater than untreated sewage irrigation. CH₄ emission had a significant correlation with the abundance of soil methanogens and methanogens/methanotrophs. N₂O emission increased with untreated or treated domestic sewage irrigation, although the total N input, including the N carried by sewage water, was the same for all treatments. No significant correlation between N₂O and denitrification functional genes was found in this study. Treated domestic sewage irrigation reduced the global warming potential (GWP) by 66.7%, but untreated domestic sewage had no evident influence on the GWP. Results indicated that treated domestic sewage irrigation could significantly inhibit CH₄ emission and the GWP by decreasing the ratio of methanogens to methanotrophs, and is promising in mitigating GWP from straw-returned paddy fields.

Grazing offsets the stimulating effects of nitrogen addition on soil CH4 emissions in a meadow steppe in Northeast China

Grazing is the most common land use type for grasslands, and grazing may alter the impacts of the predicted enhancement of nitrogen deposition on soil CH4 flux. To understand the effects of nitrogen addition, grazing, and their interactions on soil CH4 flux, we conducted a field study on CH4 flux in a meadow steppe in Northeast China from 2017 to 2018. We measured the soil CH4 flux and soil physiochemical and vegetation parameters. The studied meadow steppe soil acted as a CH4 source due to the legacy effects of an extreme rainfall event. During the experimental period, the average CH4 fluxes were 7.8 ± 1.0, 5.8 ± 0.5, 9.3 ± 0.9 and 7.6 ± 0.6 μg m-2 h-1 for the CK (control), G (grazing), N (nitrogen addition) and NG (grazing and nitrogen addition) treatments, respectively. The cumulative CH4 fluxes were 24.9 ± 2.6, 11.5 ± 4.9, 28.8 ± 4.2 and 17.8 ± 3.5 μg m-2 yr-1 for the CK, G, N and NG treatments, respectively. The N addition increased the average CH4 flux by 19%, and the grazing treatment reduced it by 25%. The soil CH4 flux was positively correlated with the 0-10 cm soil water filled pore space (P < 0.01), soil NH4+-N (P < 0.01) and soil NO3--N (P < 0.01), but negatively correlated with the 0-10 cm soil temperature (P < 0.01), except for the sampling dates that were strongly influenced by the extreme rainfall event. The average CH4 flux was significantly (P < 0.05) affected by the grazing and N addition treatments with the N addition treatment significantly (P < 0.05) increased the CH4 flux, whereas grazing significantly (P < 0.05) decreased the CH4 flux. Grazing offset the stimulating effects of N addition on CH4 flux, and there was no difference (P = 0.79) in the CH4 flux between the CK and NG plots. In summary, moderate grazing has the potential to reduce the negative impacts of N addition on CH4 flux and can increase the capacity of the soil CH4 sink in the studied meadow steppe.