Methane Emissions Research Articles

Identification of key factors for the successful development of agricultural biogas plants in Poland

In Poland, the potential for biogas production is high. important source of renewable energy and contributes to reducing the emissions of methane, a greenhouse gas. In this article, based on materials from the National Agricultural Advisory Centre (KOWR), literature, and statistical data, the implementation of the agrigas plant construction programme was evaluated in individual voivodeships. Based on the collected data, it was concluded that the most meaningful factors for the successful development of Polish agricultural biogas plants are biogas production technology, substrate availability, energy price from renewable energy sources, waste disposal costs, population density in the commune, and allocation of places in local spatial development plans (MPZP). DEMATEL technique was used to identify key development factors. The results of the study provide useful information for both government and local authorities in the search for effective ways to drive the sector's development.

Beef’s intersection with ESG Metrics

Environmental, social and governance (ESG) metrics are in­creasingly important to businesses for evaluating their perfor­mance in non-financial indicators to investors. Currently, the largest intersection of the beef industry with ESG metrics is re­lated to the area of greenhouse gas emissions (GHG) reporting and goals and targets. Many companies that sell beef products have made public commitments to reduce Scope 3 GHG emis­sions, which includes GHG emissions from all inputs, including emissions associated with the raising of cattle for beef. Cur­rently, there is a gap between company commitments and the U.S. beef supply’s ability to document and mitigate greenhouse gas emissions from cattle production. Research filling these gaps, including improving models used for reporting and find­ing practical and scalable solutions to mitigate enteric methane emissions is a key focus of Colorado State University’ AgNext. Animal health and veterinary medicine is a key part of main­taining and achieving ESG metrics outcome goals, as lower rates of morbidity and mortality can lower resource inputs and GHG emissions per pound of beef produced. Additionally, animal health and well-being are fundamental components of the social license to operate for beef supply chains, thus bovine veterinari­ans can play a key role in ESG metrics related to beef production.

CH4 emissions from runoff water of Alaskan mountain glaciers

Recent studies have observed high methane concentrations in runoff water and the ambient air at various glacier sites, including the Greenland Ice Sheet, the glacier forefield in Svalbard, and the ice cap in Iceland. This study extends these findings to smaller mountain glaciers in Alaska. Methane and carbon dioxide concentrations in the ambient air near the meltwater outlet, fluxes of these gases at the surface of runoff water and riverbank sediments, and dissolved methane content in the runoff water were measured at four glaciers. Three of the four glaciers showed conspicuous signals of methane emissions from runoff water, with the Castner Glacier terminus exhibiting a methane concentration three times higher than background levels, along with elevated dissolved methane levels in the runoff water. This study marks the detection of significant methane emissions from small mountain glacier runoff, contributing to the understanding that mountain glaciers also release methane into the atmosphere.

Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH4) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 106 copies g−1) was significantly higher than that of NC10 bacteria (2.1 × 106 copies g−1), the average potential rates of nitrite-DAMO (4.59 nmol 13CO2 g−1 d−1) and nitrate-DAMO (5.01 nmol 13CO2 g−1 d−1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH4 m−2 d−1, respectively, which accordingly achieved 15.07–24.95 mg m−2 d−1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH4 mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.

Measurement-based carbon intensity of US offshore oil and gas production

Abstract The United States (US) produces oil and gas from six offshore regions: the North Slope of Alaska, Cook Inlet in Alaska, offshore California, and three Gulf of Mexico (GOM) sub-regions: state shallow, federal shallow, and deep waters. Measurement-based assessment of direct greenhouse gas emissions from this production can provide real-world information on carbon emissions to inform decisions on current and future production. In evaluating the climate impact of production, the Carbon Intensity (CI, the ratio of greenhouse gases emitted compared to the energy of fuels produced) is often used, though it is rarely quantified with measurements. Here, we complete an observational evaluation of the US offshore sector and present the largest current set of measurement-based CIs. We collected airborne measurements of methane, carbon dioxide, and nitrogen oxides from the North Slope, Cook Inlet, and California and combined with prior GOM results. For Alaska and California, we found emissions agree with facility-level inventories, however, the inventories miss some facilities. The US offshore CI, on a 100-year GWP basis, is 5.7 gCO2e/MJ[4.5, 6.8, 95% confidence interval]. This is greater than double the CI based on the national US inventory, with the discrepancy attributed primarily to methane emissions from GOM shallow waters, with a methane dominated CI of 16[12, 22] for GOM federal shallow waters and 43[25-65] for state shallow waters. Regional intensities vary, with carbon dioxide emissions largely responsible for CI on the North Slope 11[7.5, 15], in Cook Inlet 22[13, 34], offshore California 7.2[3.2, 13], and in GOM deep waters 1.1[1.0, 1.1]. These observations indicate offshore operations outside of the GOM in the US have modest methane emissions, but the CI can still be elevated due to direct carbon dioxide emissions. Accurate assessment of different offshore basins, with differing characteristics and practices, is important for the climate considerations of expanded production.

Methane emissions in cattle production: biology, measurement and mitigation strategies in smallholder farmer systems

Methane emissions in cattle production: biology, measurement and mitigation strategies in smallholder farmer systems

Improving the biowaste management in Egypt and Jordan to mitigate methane emissions from the waste sector

Improving the biowaste management in Egypt and Jordan to mitigate methane emissions from the waste sector

Methane Emissions, Nowhere to Hide from Detection and Compliance Monitoring with Newly Launched Satellite

Climate change is often synonymous with carbon dioxide (CO2) emissions. But there is another greenhouse gas (GHG) that is also a contributor: methane (CH4), a short‐lived but extremely potent GHG. Methane emissions behave differently than CO2 emissions when emitted into the atmosphere. The warming effects of CH4 wear off quickly compared to CO2, which remains in the atmosphere for centuries. But what it lacks in retention time, it makes up for in potency: CH4 has approximately 80 times the warming impact of CO2 over a 20‐year period. That means it has a greater impact on near‐term (20‐year) temperature change. When CH4 escapes (or is released) into the atmosphere, it acts as a heavy blanket in the atmosphere, trapping the sun's heat and warming the world.

Spatiotemporal variations and influencing factors of methane emissions from livestock in China: A spatial econometric analysis

In recent years, China has been implementing policies to improve the livestock industry in response to the global trend toward green and low-carbon development. These policies include the establishment of demonstration zones for high-standard agriculture, the relocation of farms to the north, etc. This study aims to investigate the impact of changes in the spatial structure of the livestock industry on methane emissions. It used panel data from 31 provinces in China from 2001 to 2021 and applied the IPCC methodology to quantify methane emissions at both the national and provincial levels. In addition, a spatial econometric model was used to analyze the impact of changes in the spatial structure of the livestock industry on methane emissions. The results show that methane from livestock in China decreased from 13.85 million tons in 2001 to 11.82 million tons in 2021. In addition, methane emissions from livestock in China show a significant spatial gradient and correlation. The Southwest has the highest methane emissions, accounting for 24 % of the total emissions. After controlling for spatial correlation and other factors in the model, it was found that the spatial structure of the livestock industry has a different influence on methane emissions both in the province and in neighboring provinces. To improve methane emission efficiency in the future, policies such as establishing functional zones for livestock farming, strengthening technological innovation and sharing for green development in agriculture, and promoting the optimization of agricultural and rural management structures should be implemented.

Ration particle size has different effects on digestive but not production parameters in higher-yielding (Holstein) compared to lower-yielding (Girolando) cows.

The aim of the study was to evaluate the effect of total mixed ration particle size (length) and breed of cow on intake dynamics, animal performance and CH4 emissions, comparing high yielding Holstein and low yielding Girolando cows. The experimental design was 2 × 2 Latin Square arranged as a crossover factorial scheme with two diets (short particle size, SPS and long particle size, LPS) and the two breed compositions. The design comprised two periods of 26 d each, where all data collection was performed at cow level. No influence of the particle size occurred for the passage rate, neutral detergent fiber digestibility, performance and milk composition, methane emissions or ruminal fermentation parameters. Girolando cows had greater dry matter intake (DMI) when fed SPS, while Holsteins had the same (P < 0.05). Girolando cows had lower dry matter digestibility when fed LPS compared to SPS, while Holsteins had the opposite effect (P < 0.05). Also, the digestibility of crude protein and non-fibrous carbohydrates decreased in Girolando cows fed LPS, but not in Holsteins (P < 0.05). Girolando cows reduced DMI by 10.6% when fed LPS diet (P < 0.05). Girolando had an increased eating rate (+24 g of DM/min; P < 0.05) compared to Holstein cows, but Holstein cows had a lower CH4 intensity (by 29.7%: P < 0.05). Girolando cows increased the dry matter intake when fed a diet with short particle size, while the same did not happen in Holsteins. Dry matter digestibility increased in Holsteins when fed long particle size, while the opposite was observed in Girolando cows. Nutrient digestibility was reduced in Girolando cows when fed short particle size. Particle size did not influence eating time, eating rate, feed trough visits, visits with intake, milk yield and composition regardless of the breed. Reducing particle size increased CH4 intensity in both breeds.

9 Use of new technology to measure methane emissions

Abstract Over recent decades, the impact of human-induced climate change and the role of ruminant agriculture has been of growing concern for both the public and the scientific community. This has led to rapid advancements in technology needed to measure methane emissions accurately and precisely. Primarily, these advancements have been focused on measurements of enteric methane, with the proliferation of GreenFeed emission measurement systems (GEM; C-Lock, Inc; Rapid City, SD) being utilized by animal scientists across the world. The GEM relies on spot measurements collected in a portable head-box, either in a freestall or on a trailer. The GEM uses bait feed to entice animals to place their head into the head-box to collect measurements. Use of respiration chambers or head-boxes are still considered the “gold standard”, but the GEM allows for quantification in production environments and with greater number of animals. While enteric emissions are the primary source of methane from ruminant agriculture, manure methane emissions account for 15.8% of direct emissions from cattle in the U.S. This emission source is a significant contributor to confined feeding operations’ greenhouse gas emissions (GHG), where consolidation and changes in manure handling practices have occurred over the last several decades. From 2010 to 2020, manure methane emissions were a larger contributor to climate warming than enteric methane (90.8 MMT CO2-we vs. 89.2 MMT CO2-we, respectively) when calculated using the new GWP* metric. However, few advancements have been made in quantifying emissions from manure, with the cost-effective static chamber methodology still widely used. This technique allows for the determination of temporal gas concentration change in a known volume of air with a PVC cylinder, inserted 5-10 cm in the soil and posteriorly closed with a PVC lid to generate “known volume” headspace. However, this method does have known limitations on spatial and temporal flux calculations. These limitations include: the PVC chamber may alter the soil microenvironment thereby altering soil GHG flux estimates; they have potential for technician bias; and are short term monitoring, limiting interpretations to that snapshot in time and making comparisons across experiments difficult. Differing measuring techniques, such as eddy covariance and dual-comb, that more accurately and precisely monitor the soil-atmosphere interface may help better understand gas fluxes from livestock systems. Key Word: cattle, enteric, manure, methane

Assessing paddy methane emissions through the identification of rice and winter crop areas using Sentinel-2 imagery in Korea

AbstractThe global efforts on reducing methane (CH4) emissions was emphasized in COP 28 and the potential for improved estimation became feasible through bottom-up data acquisition with advanced remote sensing technology. The objectives of this study were to extract summer rice and winter crop cultivation areas based on satellite images and to incorporate into estimating CH4 emissions in South Korea for the year 2020. Satellite images of Sentinel-1 and Sentinel-2 were acquired from European Space Agency. Rice paddy was classified with backscattering coefficient from Sentinel-1 images, while the normalized difference vegetation index from Sentinel-2 images was used to identify winter cropping field. The equation of IPCC guidelines was used to estimate CH4 emissions by incorporating the areas of rice paddy and winter crop extracted with the respective satellite image. National farming statistics were used to determine the scaling factors for paddy organic matter and water management practices. The estimated areas for rice paddy and winter crop cultivation were 712,237 ha and 117,840 ha, respectively. The rice paddy areas were primarily concentrated in the western regions of the Korean peninsula, whereas winter crop cultivation was predominantly found in southern part of the country. The total amount of CH4 emissions was 6272 Gg CO2 eq./yr when considering rice straw and winter cropping practices into estimation (modified Tier 2 method). This represents a 7% increase compared to the method that considered solely the rice straw incorporation (current Tier 2 method). The CH4 emissions per unit area were also 8.82 tons CO2 eq./ha/yr with the modified Tier 2 method, indicating a 10% greater compared to the current Tier 2 method. Substantial CH4 emissions were primarily concentrated in western regions where extensive rice paddy cultivation occurs, while greater CH4 emissions per unit area were predominantly found in southern regions with substantial winter crop cultivation. The study findings hold importance for improving the accuracy of CH4 emissions estimation by employing bottom-up approach that utilizes satellite imagery to assess rice paddy and winter cropping areas. Further study would be needed to incorporate field-based data on rice crop management practices, such as rice straw and water management, to further refine CH4 emission estimation method.

5 Rumen microbiome and metabolome in dairy cattle performance

Abstract Cattle rumen microbiome converts fibrous feed to nutrients that directly influence cattle’s growth and performance. Recent research has revealed the composition and function of rumen microbiome can affect many economically important traits in cattle such as feed efficiency, milk/meat yield and quality, methane emission, metabolic health and so on. In this presentation, the research on the assessment of to what extent the rumen microbiome and its metabolites, as well as host metabolites contribute to milk production and quality traits will be focused and discussed. It has been evident that some dairy cows can produce large amounts of milk under the same nutritional and management conditions. Recent research has revealed that in addition to host genetics and diet, parity and days in milk of dairy cows can affect the rumen microbiota, and both core and pan rumen bacteriome can potentially contribute to variations of milk production traits. Additionally, the analysis of rumen metagenomics and metabolomics of dairy cows with varied milk production yield showed that some key bacterial taxa (for example, Prevotella species), and their functions (such as branched-chain amino acids biosynthesis, methanogenesis), some rumen microbial metabolites (mainly amino acids, carboxylic acids, and fatty acids) significantly differed between high and low production cows. Further integrated analysis with serum metabolomics of the cos revealed the varied contributions of rumen microbial composition, functions, metabolites, and the serum metabolites to the milk protein yield of a dairy cow, a potential new trait that can be used for high-quality milk production, respectively. The fundamental understanding of the role of rumen microbiome and its metabolome contributing to milk yield and protein yield traits can provide novel insights into future manipulation of rumen microbiome to enhance milk production and quality.

The Relationship Between Environmental Degradation and Per Capita Income in ASEAN Countries

This study aims to analyze the relationship between environmental degradation, namely carbon dioxide (CO2) and methane (CH4) emissions, and the per capita income in ASEAN countries. The data used is secondary data in the form of panel data for 1993–2020 originating from the World Bank and Our World in Data. The method used is quantitative descriptive analysis with the Granger Causality Test. The results of the study indicate that there is a one-way relationship that flows from environmental degradation in the form of CO2 and CH4 emissions to per capita income in ASEAN countries, but the reverse does not apply. Keywords: environmental degradation, carbon dioxide emissions, methane emissions, per capita income

Organic Matter Accumulation and Hydrology as Drivers of Greenhouse Gas Dynamics in Newly Developed Artificial Channels.

Artificial channels, common features of inland waters, have been suggested as significant contributors to methane (CH4) and carbon dioxide (CO2) dynamics and emissions; however, the magnitude and drivers of their CH4 and CO2 emissions (diffusive and ebullitive) remain unclear. They are characterized by reduced flow compared to the donor river, which results in suspended organic matter (OM) accumulation. We propose that in such systems hydrological controls will be reduced and OM accumulation will control emissions by promoting methane production and outgassing. Here, we monitored summertime CH4 and CO2 concentrations and emissions on six newly constructed river-fed artificial channels, from bare riparian mineral soil to lotic channels, under two distinct flow regimes. Chamber-based fluxes were complemented with hydrology, total fluxes (diffusion + ebullition), and suspended OM accumulation assessments. During the first 6 weeks after the flooding, inflowing riverine water dominated the emissions over in-channel contributions. Afterwards, a substantial accumulation of riverine suspended OM (≥50% of the channel's volume) boosted in-channel methane production and led to widespread ebullition 10× higher than diffusive fluxes, regardless of the flow regime. Our finding suggests ebullition as a dominant pathway in these anthropogenic systems, and thus, their impact on regional methane emissions might have been largely underestimated.

Including Methane Emissions from Agricultural Ponds in National Greenhouse Gas Inventories.

Agricultural ponds are a significant source of greenhouse gases, contributing to the ongoing challenge of anthropogenic climate change. Nations are encouraged to account for these emissions in their national greenhouse gas inventory reports. We present a remote sensing approach using open-access satellite imagery to estimate total methane emissions from agricultural ponds that account for (1) monthly fluctuations in the surface area of individual ponds, (2) rates of historical accumulation of agricultural ponds, and (3) the temperature dependence of methane emissions. As a case study, we used this method to inform the 2024 National Greenhouse Gas Inventory reports submitted by the Australian government, in compliance with the Paris Agreement. Total annual methane emissions increased by 58% from 1990 (26 kilotons CH4 year-1) to 2022 (41 kilotons CH4 year-1). This increase is linked to the water surface of agricultural ponds growing by 51% between 1990 (115 kilo hectares; 1,150 km2) and 2022 (173 kilo hectares; 1,730 km2). In Australia, 16,000 new agricultural ponds are built annually, expanding methane-emitting water surfaces by 1,230 ha yearly (12.3 km2 year-1). On average, the methane flux of agricultural ponds in Australia is 0.238 t CH4 ha-1 year-1. These results offer policymakers insights into developing targeted mitigation strategies to curb these specific forms of anthropogenic emissions. For instance, financial incentives, such as carbon or biodiversity credits, can mobilize widespread investments toward reducing greenhouse gas emissions and enhancing the ecological and environmental values of agricultural ponds. Our data and modeling tools are available on a free cloud-based platform for other countries to adopt this approach.

Divergent effects of copper oxide nanoparticles on methanotrophs: Stimulation at low concentrations and inhibition at high concentrations

Methanotrophs represent pivotal microorganisms, integral to the regulation of global methane emissions. Upon introduction into the environment, copper oxide nanoparticles (CuO NPs), a frequently employed category of inorganic nanomaterials, possess the potential to exert influences on methanotrophs. This study investigated the impact of CuO NPs on methanotrophs, showing a clear concentration-dependent response. Under high concentrations, exposure of methanotrophs to CuO NPs induced the production of reactive oxygen species, compromised cell membrane integrity, and resulted in the substantial release of lactate dehydrogenase. The expressions of genes encoding methane monooxygenase were obviously down-regulated. Whereas under low concentrations, a distinct enhancement of bacterial growth and metabolism was observed. The presence of methanotrophs facilitated the release of Cu2+ from CuO NPs, and the Cu2+ stimulated the biosynthesis of particulate methane monooxygenase reversely. Compared to the cellular toxicity of CuO NPs as nanoparticles, the released Cu2+ exerted a more pronounced promoting effect on methanotrophs growth, resulting in an overall strengthened methane metabolism. Significant alterations were observed in genes encoding copper uptake and resistance, cytochrome-related and heme-related proteins. This study provides novel insights into interactions between methanotrophs and nanoparticles, thereby advancing our comprehension of the impact of CuO NPs on methane emissions within an environmental context.

A Meta-analysis of probiotic interventions to mitigate ruminal methane emissions in cattle: implications for sustainable livestock farming

In recent years, the significant impact of ruminants on methane emissions has garnered international attention. While dietary strategies have been implemented to solve this issue, probiotics gained the attention of researchers due to their sustainability. However, it is challenging to ascertain their effectiveness as an extensive range of strains and doses have been reported in the literature. Hence, the objective of this experiment was to perform a meta-analysis of probiotic interventions aiming to reduce ruminal methane emissions from cattle. From 362 articles retrieved from scientific databases, 85 articles were assessed independently by 2 reviewers, and 20 articles representing 49 comparisons were found eligible for meta-analysis. In each study, data such as mean, standard deviation, and sample sizes of both the control and probiotic intervention groups were extracted. The outcomes of interest were methane emission, methane yield, and methane intensity. For the meta-analysis, effect sizes were pooled using a fixed effect or a random effect model depending on the heterogeneity. Afterward, sensitivity analyses were conducted to confirm the robustness of the findings. Overall pooled standardized mean differences (SMD) with their confidence intervals (CIs) did not detect significant differences in methane emission (SMD = -0.04; 95% CI = -0.18 to 0.11; p = 0.632), methane yield (SMD = -0.08; 95% CI = -0.24 to 0.07; p = 0.291), and methane intensity (SMD = -0.22; 95% CI = -0.50 to 0.07; p = 0.129) between cattle supplemented with probiotics and the control group. However, subgroup analyses revealed that multiple-strain bacterial probiotics (SMD = -0.36; 95% CI = -0.62 to -0.11; p = 0.005), specifically the combination of bacteria involved in reductive acetogenesis and propionate production (SMD = -0.71; 95% CI = -1.04 to -0.36; p = 0.001), emerged as better interventions. Likewise, crossbreeds (SMD = -0.48; 95% CI = -0.78 to -0.18; p = 0.001) exhibited a more favorable response to the treatments. Furthermore, meta-regression demonstrated that longer periods of supplementation led to significant reductions in methane emissions (p = 0.001), yield (p = 0.032), and intensity (p = 0.012) effect sizes. Overall, the results of the current study suggest that cattle responses to probiotic interventions are highly dependent on the probiotic category. Therefore, extended trials performed with probiotics containing multiple bacterial strains are showing the most promising results. Ideally, further trials focusing on the use of probiotics to reduce ruminal methane in cattle should be conducted to complete the available literature.

Enhancing bioelectricity generation and mitigating methane emissions in paddy fields: A novel approach using activated biochar in plant microbial fuel cells

In the innovative realm of green energy solutions, plant microbial fuel cells (PMFCs) have emerged as a promising frontier, embodying a greener technological approach. However, PMFC is not yet viable for large-scale application due to its low voltage generation. This study explores the integration of PMFC technology in paddy field, using activated biochar as electrode material to enhance voltage production while reducing methane emission. According to the findings, rice PMFCs equipped with activated biochar achieved the highest power density, reaching an impressive 106.67 mW m−2 of anode area, significantly outperforming SMFCs, which peaked at 38.28 mW m−2 when integrated with a biochar anode. Additionally, rice-PMFCs emitted 38 % less methane than the normal rice plant, while the reduction was 27.1 % for rice plants equipped with activated biochar, with no significant change in plant yield observed. Furthermore, PMFCs reduced greenhouse gas emissions by 70 % and 67 % compared to traditional coal and natural gas-based power plants, respectively. In summary, activated biochar shows promise as a potent alternative to traditional graphite electrodes in PMFCs.

Tree stem methane emissions: Global patterns and controlling factors

Growing evidence suggests that methane (CH4) emissions from tree stems are a potentially significant atmospheric source. However, a comprehensive global assessment of the general pattern and the controlling factors of stem CH4 emissions is still unavailable. Here, we present a global data-synthesis of 1081 observations from 62 studies to explore the patterns of stem CH4 emission rate in upland and wetland ecosystems and their controlling factors. The global average stem CH4 emission rate in uplands was 2.04 ± 0.61 nmol m−2s−1, which was significantly lower than in wetlands (87.08 ± 19.49 nmol m−2s−1). Angiosperm stem CH4 emission rates were significantly higher than gymnosperm in both upland and wetland ecosystems. Meanwhile, stem CH4 emission rate in inland wetlands (101.78 ± 27.44 nmol m−2s−1) was significantly higher than in coastal wetlands (56.21 ± 19.23 nmol m−2s−1). In both wetland and upland ecosystems, stem CH4 emission rate decreased with increasing sampling height, but increased as soil CH4 emission rate increased. However, the relationship between stem CH4 emissions and soil CH4 fluxes was much weaker for uplands, but very strong for wetlands. In wetlands, stem CH4 emission rate was also regulated by plant properties, as it was negatively correlated with wood specific density, but positively correlated with stem lenticel density. In uplands, tree diameter negatively affected stem CH4 emission rate. Overall, our results shed light on the magnitude and controlling factors of stem CH4 emissions in upland and wetland ecosystems and could facilitate their upscaling to ecosystems and identify the role of stem CH4 emissions in global CH4 budgets.