Methane Uptake Research Articles

The Effect of Multi-Years Reclaimed Water Irrigation on Dryland Carbon Sequestration in the North China Plain

Reclaimed water is an alternative water source which could alleviate the shortage of water resources in agricultural systems. Many researchers have studied the effect of reclaimed water on soil environment, crop yield, etc. However, carbon sequestration in reclaimed water irrigated agricultural systems is less studied. This study investigates methane uptake and photosynthesis in reclaimed water irrigation systems contributing to carbon sequestration estimation and analyzes the important factors impacting them. The results show that CH4 uptake is related to soil water-filled pore space (WFPS) with a quadratic and it has the highest uptake when WFPS is between 40 and 50%. Long-term reclaimed water irrigation could significantly decrease (p < 0.05) CH4 uptake and macroaggregate stability in the topsoil. However, reclaimed water had no significant impact on photosynthesis in comparison. The type of fertilizer is an important factor which impacts CH4 emission from soil; urea had a lower CH4 uptake and a higher CO2 emission than slow-released fertilizer. Overall, reclaimed water irrigation could effectively decrease soil carbon sequestration. A soil wetted proportion level of 40–50% was recommended in this study for favorable methane oxidation. Slow-released fertilizer in reclaimed water irrigated agriculture could better control soil carbon emission and soil carbon absorption.

Exploring Methane Emissions from Africa’s Tropical Forests

Global methane budgets suffer from a lack of field studies in African forests, but new research sheds light on methane emissions and uptake from upland forests in the Congo Basin.

Grassland restoration measures alter soil methane uptake by changing community phylogenetic structure and soil properties

Grassland restoration can play a critical role in regulating ecosystem carbon cycling, especially for changes in methane (CH4) flux. However, how grassland restoration measures affect soil CH4 flux remains poorly understood. Here, we investigated the relationships between soil CH4 flux and properties of both plant communities and soil under different grassland restoration measures (shallow ploughing, harrowing and natural recovery) in a field experiment conducted during the growing season in a semiarid grassland in northern China using the static chamber method. Soil was a CH4 sink across all three restoration measures. Compared to natural recovery, shallow ploughing significantly enhanced and harrowing significantly decreased soil CH4 uptake. The rates of soil CH4 uptake were positively associated with litter production and belowground biomass and negatively associated with plant taxonomic and phylogenetic diversity. Soil temperature, NH4+-N concentration, and soil organic matter quality had positive effects on CH4 uptake rate, but soil moisture and NO3−-N concentration had negative effects on CH4 uptake rate. Our results elucidate the pathway through which shallow ploughing facilitates soil CH4 uptake in a semiarid grassland and thus highlights its role in sustaining ecosystem multifunctionality as a measure for grassland restoration.

Effects of pyrrolidine on methane hydrate formation: Thermodynamic, kinetic, and morphology perspectives

Solidified natural gas (SNG) via clathrate hydrates has been proposed as an alternative approach for natural gas storage and transportation. In this work, the roles of 5.56 mol% pyrrolidine were investigated for the methane hydrate formation in terms of thermodynamics and kinetics along with morphology. The results showed that pyrrolidine generally improved the thermodynamic stability of mixed methane hydrates, enhancing the formation at milder conditions than those of pure methane hydrates. To demonstrate the kinetic performance of pyrrolidine, the experiments were performed at 8 MPa and 285.2 K in a quiescent configuration. The results showed that a very short induction time and a rapid rate of hydrate formation with desirable methane uptake were achieved. In addition, a distinct methane bubble with breathing effect, assisting methane gas to interact with the bulk solution, was observed during the hydrate formation morphology. The comparative kinetic study with 5.56 mol% tetrahydrofuran (THF) was also carried out under the same driving force and the same experimental condition. Surprisingly, although THF gave a high methane uptake, pyrrolidine could give more than 10 times higher rate of hydrate formation at the same driving force; moreover, it provided a competitive rate with THF at the similar formation condition.

Aerobic Methanotrophy and Co-occurrence Networks of a Tropical Rainforest and Oil Palm Plantations in Malaysia

Oil palm (OP) plantations are gradually replacing tropical rainforest in Malaysia, one of the largest palm oil producers globally. Conversion of lands to OP plantations has been associated with compositional shifts of the microbial community, with consequences on the greenhouse gas (GHG) emissions. While the impact of the change in land use has recently been investigated for microorganisms involved in N2O emission, the response of the aerobic methanotrophs to OP agriculture remains to be determined. Here, we monitored the bacterial community composition, focusing on the aerobic methanotrophs, in OP agricultural soils since 2012, 2006, and 1993, as well as in a tropical rainforest, in 2019 and 2020. High-affinity methane uptake was confirmed, showing significantly lower rates in the OP plantations than in the tropical rainforest, but values increased with continuous OP agriculture. The bacterial, including the methanotrophic community composition, was modified with ongoing OP agriculture. The methanotrophic community composition was predominantly composed of unclassified methanotrophs, with the canonical (Methylocystis) and putative methanotrophs thought to catalyze high-affinity methane oxidation present at higher relative abundance in the oldest OP plantation. Results suggest that the methanotrophic community was relatively more stable within each site, exhibiting less temporal variations than the total bacterial community. Uncharacteristically, a 16S rRNA gene-based co-occurrence network analysis revealed a more complex and connected community in the OP agricultural soil, which may influence the resilience of the bacterial community to disturbances. Overall, we provide a first insight into the ecology and role of the aerobic methanotrophs as a methane sink in OP agricultural soils.

Biochar dose determines methane uptake and methanotroph abundance in Haplic Luvisol

Biochar promotes C sequestration and improvement of soil properties. Nevertheless, the effects of biochar addition on soil condition are poorly understood, especially with respect to greenhouse gas (GHG) emissions. A large proportion of GHG emissions derive from agriculture and, thus, recognition of the effect of biochar addition to soil on GHG emissions from terrestrial ecosystems is an important issue. The purpose of our study was to evaluate the short- and long-term effects of biochar application on soil in aspects of: GHG exchange (CH4 and CO2), basic physicochemical soil properties and structure of microbial communities in Haplic Luvisol. Soil was collected from fallow fields enriched with three doses of wood offcuts biochar (10, 20 and 30 Mg ha−1) and incubated at two moisture levels (60 and 100% WHC) with the addition of 1% CH4. To evaluate the influence of biochar aging in soil, the samples were analysed directly (short-term response) and five years (long-term response) after amendment. Generally, biochar addition increased soil pH, redox potential (Eh), organic carbon (SOC) and dissolved organic carbon (DOC) contents. Under 60% WHC, direct biochar application to the soil resulted in a clear improvement in the CH4 uptake rate. In contrast to that (at 100% WHC) methane uptake rates were twofold decreased. The positive effect was reduced due to biochar aging in the soil, but five years after application, at 60% WHC and the highest biochar dose (30 Mg ha−1) still significantly enhanced CH4 oxidation. From a short-term perspective, biochar application increased CO2 emissions, but after five years this effect was not observed. Microbial tests confirmed that the improvement in CH4 oxidation was correlated with methanotroph abundance in the soil. Moreover, an increase of Methylocystis abundance in the soil enriched with biochar along with enhanced CH4 uptake rates confirm the positive biochar influence on methanotrophic communities.

Interactions between maize plants and nitrogen impact on soil profile dynamics and surface uptake of methane on a dryland farm

To determine the role of maize plants and their interaction with nitrogen (N) fertilizer in regulating subsoil methane (CH4) fluxes, we conducted a two-year field experiment on a semiarid farm in northwestern China. Four treatments were evaluated: unplanted soil without (C0) or with (CN) N fertilization and planted maize without (P0) or with (PN) N fertilization. Soil surface fluxes and profile dynamics of CH4 at depths of 0–50 cm in situ were monitored. The CH4 concentrations decreased with increasing soil depth. Seasonal and vertical variations in CH4 diffusive fluxes varied with maize phenology. The CH4 fluxes in the 0–20 cm layers accounted for 48.9–57.5% of the total fluxes in the 0–50 cm layers. The surface CH4 uptake was positively correlated with soil temperature during the fallow season and negatively correlated with soil water-filled pore space (WFPS) and exchangeable NH4+ concentration during the growing season. Compared with the unplanted treatments, the presence of maize plants significantly decreased soil WFPS and increased surface CH4 uptake during the growing season. The two-year mean cumulative diffusive CH4 fluxes were also significantly increased by 33.1–36.3% at depths of 10–30 cm and by 15.8–66.4% at depths of 10–40 cm in the P0 and PN treatments, respectively. Compared with the P0 treatment, the PN treatment significantly increased the surface CH4 uptake and cumulative CH4 uptake at depths of 0–40 cm in 2015. There was no significant difference in the CH4 surface and subsoil fluxes between the C0 and CN treatments. Our results suggested that N fertilization stimulated CH4 diffusion and uptake mainly by promoting maize growth and subsequently the soil water consumption on a dryland farm.

Responses of ecosystem respiration, methane uptake and nitrous oxide emission to drought in a temperate desert steppe

AimsDrought significantly impacts ecosystem structure and function, especially the transformation rates of soil carbon and nitrogen. This study explores how drought affects ecosystem respiration (Re), methane (CH4) uptake and nitrous oxide (N2O) emissions in temperate desert steppes and the underlying mechanisms.MethodsAn in-situ experiment was conducted in the Inner Mongolia desert steppe in northern China to study the effect of drought on Re, CH4 and N2O fluxes. Structural equation modeling (SEM) was used to establish the relationship between Re, CH4 uptake and N2O emissions and plant functional traits and environmental factors.ResultsEcosystem respiration and CH4 uptake were both significantly reduced by chronic drought (66 % precipitation reduction from 1 May to 31 August) but not by pulse drought (100 % precipitation reduction in June and July). In contrast, no significant impact on N2O emissions was observed under chronic or pulse drought. There were no significant direct effects of soil moisture on Re, CH4 uptake or N2O emissions. However, soil moisture had an important indirect effect on Re, CH4 uptake and N2O emissions, mainly through its influence on plant functional traits, plant above-ground biomass and soil nutrients. Plant biomass and soil temperature were the key indicators of Re, and plant leaf nitrogen content was the key plant trait associated with N2O emissions. In contrast, plant specific leaf area and biomass were the key traits associated with CH4 uptake.ConclusionsOverall, Re and CH4 uptake were reduced by chronic drought in this desert steppe, but there was no significant effect on N2O emissions. Ecosystem respiration, CH4 uptake and N2O emissions were associated with plant functional traits. This provides new insight for the understanding of soil carbon and nitrogen dynamics in desert steppe systems under drought conditions and an important theoretical basis for the revision of model parameters.

Comparing Soil Nitrous Oxide and Methane Fluxes From Oil Palm Plantations and Adjacent Riparian Forests in Malaysian Borneo

Riparian forests are often kept as buffers between rivers and oil palm plantations. Many benefits of riparian forests, such as increasing biodiversity and providing a travel corridor for wildlife have been documented. Conversely, data on fluxes of the greenhouse gases nitrous oxide (N2O) and methane (CH4) from riparian forests are sparse. Nitrogen (N) from fertilizer applied in the oil palm plantations leached to the adjacent riparian forests, may increase emissions of N2O. Methane (CH4) fluxes might also differ between oil palm plantations and riparian forests due to carbon (C) availability. In this scoping study, we installed transects from three mature oil palm plantations to adjacent riparian forests within the SAFE project landscape in Sabah, Malaysia (https://www.safeproject.net) for measurements of greenhouse gases and associated parameters every 2 months for 13 months. Emissions of N2O were higher from riparian forests with 40.4 [95% confidence intervals (CI): 35.7–44.6] μg N2O-N m–2 h–1 than from an equivalent area of oil palm plantation 27.6 (CI: 23.1–32.3) μg N2O-N m–2 h–1. Methane uptake was significantly higher from the riparian forest with −14.7 (CI: −21.1 to −8.3) μg CH4-C m–2 h–1 compared to slight positive emission in the oil palm plantations of 6.3 (CI: 1.1–11.4) μg CH4-C m–2 h–1. We are contributing urgently needed flux data for less well studied riparian forests in the Tropics, however, additional long-term studies are needed to be able to draw wider conclusions than possible from this scoping study alone.

Observed Methane Uptake and Emissions at the Ecosystem Scale and Environmental Controls in a Subtropical Forest

Methane (CH4) is one of the three most important greenhouse gases. To date, observations of ecosystem-scale methane (CH4) fluxes in forests are currently lacking in the global CH4 budget. The environmental factors controlling CH4 flux dynamics remain poorly understood at the ecosystem scale. In this study, we used a state-of-the-art eddy covariance technique to continuously measure the CH4 flux from 2016 to 2018 in a subtropical forest of Zhejiang Province in China, quantify the annual CH4 budget and investigate its control factors. We found that the total annual CH4 budget was 1.15 ± 0.28~4.79 ± 0.49 g CH4 m−2 year−1 for 2017–2018. The daily CH4 flux reached an emission peak of 0.145 g m−2 d−1 during winter and an uptake peak of −0.142 g m−2 d−1 in summer. During the whole study period, the studied forest region acted as a CH4 source (78.65%) during winter and a sink (21.35%) in summer. Soil temperature had a negative relationship (p < 0.01; R2 = 0.344) with CH4 flux but had a positive relationship with soil moisture (p < 0.01; R2 = 0.348). Our results showed that soil temperature and moisture were the most important factors controlling the ecosystem-scale CH4 flux dynamics of subtropical forests in the Tianmu Mountain Nature Reserve in Zhejiang Province, China. Subtropical forest ecosystems in China acted as a net source of methane emissions from 2016 to 2018, providing positive feedback to global climate warming.

Methane hydrate production using a novel spiral‐agitated reactor: Promotion of hydrate formation kinetics

AbstractTo enhance hydrate formation kinetics, we presented a novel spiral‐agitated reactor, where hydrates were synthetized in pure water systems, and fast hydrate kinetics was observed under extremely mild conditions. Hydrates can nucleate within 4 min under 3.5 MPa and 275.15 K at a rotating speed of 60 rpm, and large water‐to‐hydrate conversion (>85%) was obtained at a moderate condition of 4.85 MPa, 275.15 K, and 30 rpm with an average methane uptake of 139.78 V/V, demonstrating that pure water systems are feasible for hydrate‐based solidified natural gas (SNG) technology. Numerical simulations of flow fields inner the reactor were carried out, and four mechanisms behind the excellent promotion were proposed, dual‐agitation, two‐way convection, interfacial impact and micro bubbles, which significantly improve mass transfer, giving rise to fast hydrate nucleation and growth kinetics. These findings suggest extraordinary performance of spiral agitation, and this may pave way on the industrial application of hydrate‐based SNG technology.

Precipitation changes regulate the annual methane uptake in a temperate desert steppe

Desert soils are an important sink of atmospheric methane (CH4) and regulate the global CH4 budget. However, it is still unclear how CH4 fluxes respond to precipitation changes in desert-steppe soils. Therefore, a two-year in situ control experiment was conducted to investigate the effect of precipitation changes on CH4 uptake in desert steppe of Inner Mongolia in northwest China and its driving mechanism. The result showed that this desert steppe was an important sink of CH4, with an annual uptake of 2.93 (2.64–3.22) kg C ha−1. It was found that CH4 uptake was reduced significantly for decreasing precipitation, especially in spring and summer. In contrast, an increasing trend of CH4 uptake was observed for increasing precipitation, although it was not statistically significant. Further analyses found that CH4 uptake was more sensitive to decreasing precipitation than increasing precipitation. This may be mainly due to the fact that only moderate water-filled pore space (WFPS) induced by precipitation promoted CH4 uptake, while too-high (>32%) or too-low WFPS inhibited its uptake. A structural equation model showed that the copy number of the pmoA functional gene was the most important factor affecting CH4 uptake. In contrast, soil moisture had a very important indirect effect on CH4 uptake, mainly through significantly affected soil porosity, the above-ground plant biomass and NO3−-N content, further affected CH4 uptake. Overall, CH4 sinks in desert steppe was still mainly controlled by methane-oxidizing bacteria containing the key functional gene pmoA and WFPS. Therefore, precipitation plays an important role in regulating the intensity of CH4 sinks in desert steppe, while it is worth noting that too-little precipitation will significantly weaken CH4 sinks.

Urbanization degree rather than methanotrophic abundance decreases soil CH4 uptake

Urbanization has been increasing worldwide, which can greatly influence ecosystem functions such as soil methane (CH4) uptake. However, little information is available for quantifying the effects of urbanization on soil CH4 uptake and the underlying microbial mechanisms. By conducting a meta-analysis of soil CH4 uptake under urbanization worldwide in combination with measurements of potential soil CH4 uptake from 134 samples along an urbanization gradient across Shanghai, China, we found that urbanization significantly decreased soil CH4 uptake with greater inhibition under higher urbanization levels. Urbanization degree, index of urbanization levels, explained large variations of soil CH4 uptake, and urbanization decoupled the relationships between methanotrophic abundance and soil CH4 uptake, which was often neglected in previous research. To our knowledge, this is the first study to quantify the effects of urbanization degree on soil CH4 uptake, which need to be incorporated into Earth system models for estimating the global CH4 budget more accurately.

Residual Guest-Assisted MOF-5 Powder Densification.

Powder densification for specified shaped metal-organic frameworks (MOFs) is desirable for most applications. The obtainment of such properties is challenging, one of which is the rapid crystal-to-amorphous transition (framework collapse) of MOFs under pressure. Herein, we found that the residual guests of the MOF-5 synthesis process could form binding groups based on the hydrogen-bonding networks of water. The improved processability and ease of compression, which did not promote rapid structure collapse, can be achieved in the guest-loaded MOF-5. Correspondingly, enhanced volumetric specific surface area and methane uptake of MOF-5 were obtained. This work focuses on a commonly neglected but positive function of the residual guests in MOFs, besides supporting the framework. MOFs loaded with multiple types of guests show attractive mechanical properties via guest-guest and guest-host interactions for powder densification, highlighting their commercial applications.

Nitrogen and Phosphorus Control Soil Methane Uptake in Tropical Montane Forests

AbstractTropical forests contribute about one third to global annual CH4 uptake by soils. Understanding the factors that control the soil‐atmosphere exchange of CH4 at a large scale is a critical step to improve the CH4 flux estimate for tropical soils, which is presently poorly constrained. Since tropical forest degradation often involves shifts in nutrient availabilities, it is critical to evaluate how this will affect soil CH4 flux. Here, we report how nitrogen (N; 50 kg N ha−1 yr−1), phosphorus (P; 10 kg P ha−1 yr−1), and combined N + P additions affect soil CH4 fluxes across an elevation gradient of tropical montane forests. We measured soil CH4 fluxes in a nutrient application experiment at different elevations over a period of 5 years. Nutrient additions increased soil CH4 uptake after 4–5 years of treatment but effects were not uniform across elevations. At 1,000 m, where total soil P was high, we detected mainly N limitation of soil CH4 uptake. At 2,000 m, where total soil P was low, a strong P limitation of soil CH4 uptake was observed. At 3,000 m, where total P was low in the organic layer but high in mineral soil, we found N limitation of soil CH4 uptake. Our results show that projected increases of N and P depositions may increase soil CH4 uptake in tropical montane forests but the direction, magnitude, and timing of the effects will depend on forests' nutrient status and plant‐microbial competition for N and P.

Effects of land-use conversion from Masson pine forests to tea plantations on net ecosystem carbon and greenhouse gas budgets

A five-year in situ field experiment was conducted to explore the effects of land-use conversion from Masson pine forests to tea plantations on the net ecosystem carbon balance (NECB) and net greenhouse gas (GHG) budget. Compared with forests, tea plantations decreased soil methane (CH4) uptake by 23.3–73.1% and increased heterotrophic respiration (Rh) and nitrous oxide (N2O) emissions by 1.4–60.0% and 263.2–2796.7%, respectively, over the five-year study period. The forests acted as net carbon sinks (0.04 Mg C ha−1 yr−1 on average). Converting the forests to tea fields in the first and second years led to net carbon losses of 27.94 and 2.28 Mg C ha−1 yr−1, respectively. These losses could primarily be attributed to the sharp decrease in net primary productivity (NPP) by removal of the forests and increase in Rh outweighing organic fertilizer application in the first year, and Rh exceeding NPP in the second year. Tea plantations served as net carbon sinks (0.27–0.69 Mg C ha−1 yr−1) in the third to fifth years following land-use conversion, which was mainly due to organic fertilizer application and NPP outweighing Rh. The forests showed net GHG uptake (−0.07 Mg CO2-eq. ha−1 yr−1 on average). However, tea plantations functioned as net GHG emissions for the first and second years (104.3 and 8.9 Mg CO2-eq. ha−1 yr−1, respectively) following their conversion from the forests primarily due to net C losses and N2O emissions. Subsequently, tea fields transformed into net GHG sinks (−0.29 to −0.06 Mg CO2-eq. ha−1 yr−1) from the third to fifth years following land-use conversion, primarily due to the NECB overweighing N2O emissions. On a 5-year average, converting Masson pine forests to tea plantations resulted in net C losses and net GHG emissions of 5.76 Mg C ha−1 yr−1 and 22.53 Mg CO2-eq. ha−1 yr−1, respectively. In conclusion, net C losses and net GHG emissions in the first two years following the conversion of Masson pine forests to tea plantations should be considered when assessing the environmental impacts on land-use conversion.

In Silico Evolution of High-Performing Metal Organic Frameworks for Methane Adsorption.

The increased use of transition fuels, such as natural gas, and the resulting increase in methane emissions have resulted in a need for novel methane storage materials. Metal-organic frameworks (MOFs) have shown promise as efficient storage materials. A virtually limitless number of potential MOFs can be hypothesized, which exhibit a wide variety of different structural and chemical characteristics. Because of the numerous possibilities, identification of the best MOF for methane storage can be a potentially challenging problem. In this work, determination of the best such MOF was cast as an inverse function problem. The function, a random forest (RF) model using 12 structural and chemical descriptors, was trained on 10% of a data set consisting of 130 398 hypothetical MOFs (hMOFs) to predict simulated methane uptake. The RF model was tested on the remaining 90% of the data. After validation, a genetic algorithm (GA) was used to evolve in silico the best MOFs for methane adsorption. The RF model was imbedded into the GA as the fitness function to predict the methane uptake of the evolved MOFs (eMOFs). The best 15 eMOFs matched hMOFs found in the top 1% of the database. Nine of the 15 eMOFs were found in the top 0.1%. More impressively, two of the eMOFs matched the top two hypothetical MOFs with the highest methane uptake values out of the entire database of 130 398 MOFs. Further, by leveraging the ensemble nature of the GA, it was possible to characterize the importance of the different material properties for methane adsorption, providing fundamental insight for future material design strategies.

Effects of experimental fire in combination with climate warming on greenhouse gas fluxes in Arctic tundra soils

The frequency and severity of fire is increasing in Arctic tundra regions with climate change. Here we investigated effects of experimental low-intensity fire and shrub cutting, in combination with warming, on soil biogeochemical cycles and post-fire greenhouse gas (GHG) emissions in a dry heath tundra, West Greenland. We performed in vitro incubation experiments based on soil samples collected for up to two years after the fire. We observed tendency for increased soil nitrate (14-fold) and significant increases in soil ammonium and phosphate (four-fold and five-fold, respectively) two years after the fire, but no effects of shrub cutting on these compounds. Thus, changes appear to be largely due to fire effects rather than indirect effects by vegetation destruction. Two years after fire, nitrous oxide (N2O) and carbon dioxide (CO2) production was significantly increased (three-fold and 32% higher, respectively), in burned than unburned soils, while methane (CH4) uptake remained unchanged. This stimulated N2O and CO2 production by the fire, however, was only apparent under conditions when soil was at maximum water holding capacity, suggesting that fire effects can be masked under dry conditions in this tundra ecosystem. There were positive effects by modest 2.5 °C warming on CO2 production in control but not in burned soils, suggesting that fire may decrease the temperature response in soil respiration. Methane uptake was neither altered by the modest warming in shrub-cut nor in burned soils after two years, suggesting that the removal of vegetation may play a key role in controlling future temperature response of CH4 oxidation. Altogether, our results show that post-fire tundra soils have the potential to enhance soil GHG emissions (e.g. N2O and CO2) especially during episodes with wet soil conditions. On the other hand, the lack of warming responses in post-fire soil respiration may weaken this positive feedback to climate change.

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.

Global Uptake of Atmospheric Methane by Soil From 1900 to 2100

AbstractSoil methanotrophy is the only biological process that removes methane (CH4) from the atmosphere. There is good agreement about the size of the global sink but great uncertainty about its interannual variability and regional responses to changes in key environmental drivers. We used the process‐based methanotrophy model Methanotrophy Model (MeMo) v1.0 and output from global climate models to simulate regional and global changes in soil uptake of atmospheric CH4 from 1900 to 2100. The annual global uptake doubled from 17.1 ± 2.4 to 37.2 ± 3.3 Tg yr−1 from 1900‐2015 and could increase further to 82.7 ± 4.4 Tg yr−1 by 2100 (RCP8.5), primarily due to enhanced diffusion of CH4 into soil as a result of increases in atmospheric CH4 mole fraction. We show that during the period 1980–2015 temperature became an important influence on the increasing rates of soil methanotrophy, particularly in the Northern Hemisphere. In RCP‐forced simulations the relative influence of temperature on changes in the uptake continues to increase, enhancing the soil sink through higher rates of methanotrophic metabolic activity, increases in the global area of active soil methanotrophy and length of active season. During the late 21st century under RCP6.0, temperature is predicted to become the dominant driver of changes in global mean soil uptake rates for the first time. Regionally, in Europe and Asia, nitrogen inputs dominate changes in soil methanotrophy, while soil moisture is the most important influence in tropical South America. These findings highlight that the soil sink could change in response to drivers other than atmospheric CH4 mole fraction.