Increased CH4 Emissions Research Articles

Divergent impacts of animal bioturbation on methane and nitrous oxide emissions from mariculture ponds.

Aquaculture systems are of increasing concern as an important source of atmospheric methane (CH4) and nitrous oxide (N2O). However, the role of animals in regulating CH4 and N2O emissions from aquaculture systems remains unclear. Here, we established mesocosm trials to investigate impacts of bioturbation of different aquaculture species (i.e., clam, shrimp, and crab) on CH4 and N2O fluxes in a mariculture pond. Across the initial, middle, and final culturing stages, mean CH4 flux in mesocosm without animals was 4.81 ± 0.09 µg CH4 m‒2 h‒1, while the existence of clam, shrimp, and crab significantly increased CH4 flux by 35.3 %, 80.6 %, and 138 %, respectively. Bioturbation significantly decreased dissolved oxygen (DO) concentration by 5.19‒44.8 % but increased porewater CH4 concentration by 14.1‒59.9 %, indicating that lowered DO caused by animal respiration promoted CH4 production in sediment. Moreover, bioturbation of animals significantly increased ebullitive CH4 fluxes by 41.0‒216 %, contributing 57.4‒77.2 % of the increased CH4 emission in mesocosms with animals. However, shrimp and crab significantly reduced N2O flux by 30.3 % and 42.5 %, respectively, primarily due to lowered DO conditions suppressing nitrification and limiting NO3‒ supply for denitrification. By contrast, clam significantly increased N2O emission by 181 % because its filter-feeding behavior excreted more NH4+ and NO3‒ into overlying water and thereby facilitating N2O production. The N2O concentration in overlying water was 1.72‒2.83-fold of that in porewater, and the calculated diffusive N2O flux was 1.80‒37.5 % greater than chamber-measured N2O efflux. This implied that N2O might be primarily produced in overlying water rather than sediments, and the produced N2O can either evade as water-air fluxes or diffuse downwards into sediments to be consumed. Overall, our study advocates that aquaculture-related climate mitigation strategies should place more attention on the divergent impacts of animal bioturbation on CH4 and N2O emissions.

Long-Term Grazing and Nitrogen Management Impacted Methane Emission Potential and Soil Microbial Community in Grazing Pastures.

Achieving sustainable development in livestock agriculture by balancing livestock production, reduction of greenhouse gas (GHG) emissions, and effective utilization of nitrogen nutrient has indeed been challenging. This study investigated the long-term effects of continuous cattle grazing, stocking rates, and fertilization regimens on methane (CH4) emissions, soil microbial communities, and soil organic carbon (SOC) stocks in Bermudagrass pastures in East Texas, USA. Pastures were subjected to high or low stocking rates for over 50 years, with further subdivision based on fertilization: nitrogen-based fertilizer application or no fertilizer but with the growth of annual clover. Seasonal soil cores (0-60 cm) were collected, and laboratory microcosm incubation studies revealed unexpectedly high in vitro CH4 emissions in surface soils, particularly in the top 0-5 cm soil layer, reaching up to 300 nmol of CH4 mL-1. Higher CH4 emissions and methanogen abundance, along with lower SOC stocks, were observed in pastures subjected to high stocking rates compared to those with low stocking rates and in clover pastures compared to those with N-fertilized ryegrass. On the contrary, in low-stocked, N-fertilized annual ryegrass pastures, methanogen abundance was lowest, CH4 emissions were negligible, and SOC stocks were highest. Furthermore, animal excreta deposition significantly contributed to increased CH4 emissions. Prokaryotic and potential methanotrophic taxa, as compared to fungi, exhibited greater responsiveness to N-fertilization than to cattle stocking treatments with higher levels of methanotrophs observed in pastures subjected to high stocking rates and clover growth. This study suggests that strategic management practices such as optimal grazing and nitrogen management could effectively mitigate CH4 emissions in grazing lands.

Modelling mixed crop-livestock systems and climate impact assessment in sub-Saharan Africa

Climate change significantly challenges smallholder mixed crop-livestock (MCL) systems in sub-Saharan Africa (SSA), affecting food and feed production. This study enhances the SIMPLACE modeling framework by incorporating crop-vegetation-livestock models, which contribute to the development of sustainable agricultural practices in response to climate change. Applying such a framework in a domain in West Africa (786,500 km2) allowed us to estimate the changes in crop (Maize, Millet, and Sorghum) yield, grass biomass, livestock numbers, and greenhouse gas emission in response to future climate scenarios. We demonstrate that this framework accurately estimated the key components of the domain for the past (1981–2005) and enables us to project their future changes using dynamically downscaled Global Circulation Model (GCM) projections (2020–2050). The results demonstrate that in the future, the northern part of the study area will likely experience a significant decline in crop biomass (up to -56%) and grass biomass (up to -57%) production leading to a decrease in livestock numbers (up to -43%). Consequently, this will impact total emissions (up to -47% CH4) and decrease of -41% in milk production, and − 47% in meat production concentrated in the Sahelian zone. Whereas, in pockets of the Sudanian zone, an increase in livestock population and CH4 emission of about + 24% has been estimated, indicating that variability in climate change impact is amplifying with no consistent pattern evident across the study domain.

How does the chemical composition of dung affect nitrous oxide and methane emissions in pasture soils?

There is an important gap in how variations in herbivore dung composition affect GHG emissions on pastures, especially due to differences in dry matter (DM) and nitrogen contents. Oversimplifications can compromise the accuracy of mitigation strategies. This study aims to address this gap by investigating how the chemical composition of dung from different species influences GHG emissions in pasture systems. The results showed that drier dung led to higher cumulative N₂O emissions. The highest emissions were observed from goat at 9.47 mg N-N₂O g⁻1 dry soil, followed by sheep at 5.95 mg N-N₂O g⁻1 dry soil, beef cattle at 5.44 mg N₂O g⁻1 dry soil, dairy cattle at 2.67 mg N₂O g⁻1 dry soil, and horse at 0.83 mg N₂O g⁻1 dry soil. It was observed that higher dung moisture content generally corresponded to increased CH₄ emissions, except for horse dung. The highest cumulative CH₄ emission was for dairy cattle dung (8.29 mg C-CH₄ g⁻1 dry soil), followed by beef cattle (3.89 mg C-CH₄ g⁻1 dry soil), sheep (2.32 mg C-CH₄ g⁻1 dry soil), goats (1.89 mg C-CH₄ g⁻1 dry soil), and horses (1.66 mg C-CH₄ g⁻1 dry soil). Principal Component Analysis illustrated that PC1, named as diet quality, explained 61.9% of the variance, was positively correlated with N₂O and negatively correlated with fiber content and C/N ratio, while PC2, named as acetrophic and hydrogenotrophic methanogenesis, explained 19.6% of the variance, linking VS to reduced CH₄ emissions. This study establishes relationships between manure chemical composition and GHG emissions, filling a fundamental knowledge gap and supporting the development of cause-and-effect models.

Assessment of Greenhouse Gas Emissions and Carbon Sequestration in Dairy Goat Farming Systems in Northern Extremadura, Spain.

Livestock farming is an activity closely linked to the environment, directly affecting its surrounding ecosystem while utilizing the natural resources it provides. Accordingly, it is essential to study these production systems in order to implement more sustainable models that allow for a balance between socioeconomic and environmental factors. The main objective of this study was to analyze the environmental impact of nine different dairy goat production systems located in northern Extremadura, Spain. The selected farms ranged from extensive and organic production models to more intensive ones. The methodology used was a life cycle assessment (LCA) to calculate the carbon footprint, following the IPCC (Intergovernmental Panel on Climate Change) guidelines. A comprehensive evaluation of emissions was conducted, considering the different global warming potentials (GWPs) established by the IPCC for the main gases associated with livestock farming. In addition, carbon sequestration (Cseq) was incorporated into the analysis to assess the contribution of goat farming to climate change mitigation based on its production management. CH4 emissions were the main source (44-67%) of GHGs, followed by CO2 from inputs (20-48%), and finally N2O (7-13%). A trend was observed linking increased CH4 emissions to more extensive and less productive livestock systems. However, the significant role of soil as a carbon sink was highlighted, as it greatly offsets the emissions produced, demonstrating its potential mitigation due to Cseq, particularly in more extensive models. The importance of this factor suggests that it should be taken into account in such studies to provide a realistic view of the final impact of each production system.

Diversity of primary vegetation species of lake shore impacts largely carbon emissions in thermokarst lakes on the Qinghai-Tibet plateau.

Terrestrial organic matter from surrounding primary vegetation is critical for carbon cycling in thermokarst lakes. However, the characteristics and contribution of this vegetation in shaping microbial community and affecting carbon emissions in thermokarst lakes remain poorly understood. This study quantifies the influence of lakeshore primary vegetation characteristics on microbial community and carbon emissions across lakes with different vegetation types on the Qinghai-Tibet Plateau (QTP). Our findings indicate that methane (CH4) diffusion and ebullition emissions increase significantly from alpine desert (AD), alpine steppe (AS), alpine meadow (AM) to swamp meadow (SM). Specifically, diffusion fluxes in lakes averaged 1.7 mmol m‌‌-2 d-1 (ranging from 0.04 to 5.7 mmol m-2 d-1), and ebullition fluxes in lakes averaged 14.5 mmol m-2 d-1 (ranging from 0.18 to 99.1 mmol m-2 d-1). Carbon dioxide (CO2) diffusive emissions in SM, AM, AS were significantly higher than AD, with fluxes ranging from -14.12 mmol m-2 d-1 to 51.33 mmol m-2 d-1. The primary vegetation diversity also showed a significant increase from AD (3.17 ± 1.33), AS (5.33 ± 1.63), AM (4.5 ± 1.05) to SM (9.2 ± 1.40). Lake shore primary vegetation diversity indirectly enhances CH4 and CO2 emissions by altering water pH. Additionally, it influences methane-cycling microorganisms through pH regulation, further promoting CH4 emissions. Greater vegetation diversity also increases CH4 emissions by affecting sediment microbial carbon. These results underscore the importance of integrating vegetation diversity and microbial community patterns into carbon cycling models to improve the predictions of thermokarst lake carbon emissions in a warming and greening future, emphasizing the urgent requirement to protect the pristine environments of permafrost regions.

Guanidinoacetic acid effects on ruminal fermentation, digestibility and methane production in sheep liquor: Dose-response analysis

Guanidinoacetic acid (GAA), a precursor of creatine, is partially degraded in the rumen when unprotected. While GAA has shown promise as a feed additive, its optimal dose for ruminants remains unclear. This study investigated the dose-response effects of GAA on in vitro ruminal fermentation and greenhouse gas production in fattened sheep. Rumen inoculum from two Pelibuey sheep (30 kg ± 2 kg) fed a 50:50 forage: concentrate diet was used to test seven GAA doses: 0 (GAA0, control), 500 (GAA0.5), 1000 (GAA1), 1500 (GAA1.5), 2000 (GAA2), 2500 (GAA2.5), and 3000 (GAA3) mg/kg DM (dry matter). A completely randomized design was employed. GAA0.5 produced significantly higher total gas than GAA2. The CH4 production was similar across doses, except for GAA2.5, which was significantly higher than GAA0 and GAA0.5. GAA exhibited quadratic relationships with total gas production and linear relationships with CH4 and CO production but no significant effect on H2S. GAA linearly increased DM digestibility without significantly affecting ruminal fermentation profiles. GAA inclusion strongly influenced crude protein (CP) digestibility and degradability kinetics, with varying effects at different time points. The rate constant for degradation of the insoluble but potentially degradable CP fraction was highest with GAA1. In conclusion, GAA supplementation at GAA0.5 improved total gas production without increasing CH4 emissions, implying enhanced fermentation efficiency and improved performance. GAA's impact on CP digestibility varied with incubation time. These findings provide insights into developing optimal GAA dose/level supplementation that is effective in fattening sheep, though further in vivo studies are warranted to validate these effects and explore long-term impacts on rumen microbial populations and protein utilization.

Effects of Straw and Green Manure Addition on Crop Yield, Soil Properties and CH4 Emissions: A Meta-Analysis

The incorporation of organic amendments is widely acknowledged for its capacity to enhance soil fertility and boost crop productivity. However, whether the addition of organic amendments can improve soil quality and crop production, simultaneously causing methane emissions in paddy fields, deserves further investigation. In this meta-analysis, the effects of different organic amendments on soil nutrient levels, rice yield and CH4 emissions were evaluated in paddy fields based on 328 observations from 77 field trial studies. Our results revealed that the addition of organic amendments significantly increased soil organic carbon (9.47%), microbial biomass carbon (21.13%), microbial biomass nitrogen (28.91%), urease (25.07%) and β-glucosidase (24.41%). Moreover, straw addition significantly increased the CH4 emissions by 152.68% and rice yield by 7.16%; green manure addition significantly increased CH4 emissions by 71.62% and rice yield by 10.09%, respectively. Although both increased the CH4 emissions, green manure had the ability to improve the availability of N, which could improve rice uptake. The regression results showed that the variation in crop yield, soil nutrients and CH4 emissions are influenced through the types and quality of organic amendments. Overall, this study suggests that organic amendments are beneficial in maintaining soil quality and improving rice yield, whereas it also increased the CH4 emissions. These meta-analysis results may provide some references for optimizing organic amendments incorporated into the soil to sustain soil fertility and crop production while mitigating soil constraints and methane emissions.

Ebullition mediated transport dominates methane emission from open water area of the floating national park in Indo Burma hotspot.

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH4 emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH4 emissions and understand the factors influencing CH4 ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH4 flux ranged from 220.24 to 1889.35mgm-2 d-1, while the overall CH4 fluxes varied widely ranging from 345.81 to 2240.56mgm-2 d-1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO2 comprising 8.82% of the total sediment gas in the wetland. This suggests that CH4 emission through ebullition plays an important role in transporting biogenic CH4 to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH4 emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH4 production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH4 ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research.

Extreme rainfall events eliminate the response of greenhouse gas fluxes to hydrological alterations and fertilization in a riparian ecosystem

Riparian ecosystems are essential carbon dioxide (CO2) sources, which considerably promotes climate warming. However, the other greenhouse gas fluxes (GHGs), such as methane (CH4) and nitrous oxide (N2O), in the riparian ecosystems have not been well studied, and it remains unclear whether and how these GHG fluxes respond to extreme weather, fertilization and hydrological alterations associated with reservoir management. Here, we assessed the impacts of hydrological alterations (i.e., flooding frequency) and fertilization (nitrogen and/or phosphorus) induced by human activities (hydroengineering construction and agricultural activities) on GHG fluxes, and further investigated the underlying mechanisms in two contrasting years (normal vs. extreme rainfall years) in a reservoir riparian zone dominated by grasses. The significant combined effects of extreme rainfall events and human activities (hydrological alterations and fertilization) on the GHGs were observed. Continuous flooding reduced CO2 emissions by 24% but increased CH4 emissions by ∼4 times in a normal rainfall year. In addition, nitrogen fertilization promoted CO2 emissions by 37%. However, these phenomena were not observed in the year with extreme rainfall events, which made the flooding levels homogeneous across the treatments. Furthermore, we found that CO2 fluxes were driven by the soil moisture, nutrient content, aboveground biomass, and root carbon content, while CH4 and N2O fluxes were merely driven by the soil properties (pH, moisture, and nutrient content). This study provides valuable insights into the crucial role of extreme rainfall events, hydrological alteration, and fertilization in regulating GHG fluxes in riparian ecosystems, as well as supports the integration of these changes in GHG emission models.

Application of crop straw with different C/N ratio affects CH4 emission and Cd accumulation in rice (Oryza sativa L.) in Cd polluted paddy soils

Return straw to field is a common practice for straw utilization. However, effects of crop straw with different C/N ratio incorporation on the CH4 emission and Cd phytoavailaility in Cd-contaminated paddy soils have not been simultanously evaluated. Here, we investigated the impacts of rice straw (RS) and pea straw (PS) incorporation on CH4 emission and rice Cd available in heavily Cd polluted soil (HP) and lightly polluted soil (LP) through a pot experiment. Results showed that RS and PS significantly increased CH4 emission in the two soils (p ​< ​0.05). CH4 emission in PS treatment were greater than that in RS treatment. PS with lower C/N ratio favored to increase soil DOC and SOM (p ​< ​0.05), and promote dominant methanogens of Methanobacterium uliginosum and uncultured Methanocellales archeaon growth (p ​< ​0.05), which mainly contributed to higher CH4 emisison. The significant influences of straw application on soil chemical parmeters subsequently affected soil different Cd fractions (p ​< ​0.05). Specifically, straw significantly decreased water soluble ​+ ​exchangeable Cd and manganese oxides Cd, but significantly increased other Cd fractions in HP soil (p ​< ​0.05); whereas there were nearly opposite trendancies in LP soil. Thus, roots Cd was mainly determined by soil soluble ​+ ​changeable Cd in HP soil, while it was more likely affected by other Cd fractions except for the soluble ​+ ​exchangeable Cd in LP soil, thereby reduced Cd transport from roots to stems in both soils. Greater effects of PS were displayed in inhibiting rice growth and reducing organs Cd than RS in HP soil, while higher efficiency of RS treatment on improving rice growth than that of PS was found in LP soil (p ​< ​0.05). The results can provide a basis for scientific straw returning in Cd contaminated paddy field, achieving safe rice production and reducing carbon emission.

The biological mechanism of a lower carbon/nitrogen ratio increases methane emissions during vegetable waste composting

The initial carbon/nitrogen (C/N) ratio is one of the most important factors impacting composting processes, such as methane (CH4) emissions. However, the effects of the C/N ratio on CH4 emissions and the associated biological mechanisms during vegetable waste composting are largely unknown. In this study, a lab-scale experiment was conducted to investigate the effects of different C/N ratios on CH4 emissions and the mechanisms associated with methane-metabolizing microorganisms (methanogens and methanotrophs) during capsicum straw composting. The initial C/N ratios were set to 18, 30 and 50 to simulate the low (L), medium (M) and high (H) C/N ratios, respectively. The results showed that CH4 emissions were mainly concentrated in the thermophilic phase and that the cumulative CH4 emissions were significantly greater in the L treatment than in the M and H treatments by 10.8 and 15.4 times, respectively. During the methanogenic process, the relative abundance of the dominant genus Methanoculleus (47.59 % ∼ 76.92 %) was higher than in the L treatment than in the M and H treatments at the thermophilic and maturation stages, and the Chao1 index and the mcrA gene abundance followed the order of L > M > H at each composting stage. During the methanotrophic process, the dominant genus unclassified_d_bacteria (51.3 % ∼ 91.87 %), Chao1 index, pmoA gene abundance and CO2 emissions were in the order of L > M > H at each composting stage. This pattern suggests that a lower C/N ratio simultaneously enhanced CH4 production and oxidation. A structural equation model further revealed that the methanogenic community, which was driven directly by the relative contents of hemicellulose and cellulose in the substrates, as indicated by the C/N ratio, made greater contributions to CH4 emissions than did the methanotrophic community. In conclusion, a lower C/N ratio increased CH4 emissions mainly by regulating the population and composition of methanogen community.

Estimating wetland CH4 emissions on the Qinghai-Tibetan Plateau based on a processed model coupled with inundation dynamics between 1960 and 2100

Quantifying the impacts of climate change and wetland area dynamics on methane (CH4) emissions in the Qinghai-Tibetan Plateau (QTP) is crucial for enhancing our understanding of regional and global CH4 budgets. However, a major source of uncertainty in estimating wetland methane emissions stems from the limited delineation of wetland area dynamics. In this study, we integrated dynamic wetland inundation schemes into a process-based model to quantify the contributions of wetland area variations to natural wetland CH4 emissions on the QTP, both historically and in the future. The results revealed that climate change significantly influenced the spatiotemporal distribution of wetland CH4 emissions, with wetland inundation dynamics contributing between 21.84 % and 27.18 % of the increase in CH4 emissions from 1960 to 2020. Under future climate change scenarios, wetland CH4 emissions are projected to exhibit a more pronounced increasing trend, with wetland inundation dynamics projected to contribute 18.94 % to 21.80 % of the increase in CH4 emissions in the QTP under seven Shared Socioeconomic Pathways scenarios.

Assessing the Impact of Climate Change on Methane Emissions from Rice Production Systems in Southern India

The impact of climate change on methane (CH4) emissions from rice production systems in the Coimbatore region (Tamil Nadu, India) was studied by leveraging field experiments across two main treatments and four sub-treatments in a split-plot design. Utilizing the closed-chamber method for gas collection and gas chromatography analysis, this study identified significant differences in CH4 emissions between conventional cultivation methods and the system of rice intensification (henceforth SRI). Over two growing seasons, conventional cultivation methods reported higher CH4 emissions (range: from 36.9 to 59.3 kg CH4 ha−1 season−1) compared with SRI (range: from 2.2 to 12.8 kg CH4 ha−1 season−1). Experimental data were subsequently used to guide parametrization and validation of the DeNitrification–DeComposition (DNDC) model. The validation of the model showed good agreement between the measured and modeled data, as denoted by the statistical tests performed, which included CRM (0.09), D-index (0.99), RMSE (7.16), EF (0.96), and R2 (0.92). The validated model was then used to develop future CH4 emissions projections under various shared socio-economic pathways (henceforth SSPs) for the mid- (2021–2050) and late (2051–2080) century. The analysis revealed a potential increase in CH4 emissions for the simulated scenarios, which was dependent on specific soil and irrigation management practices. Conventional cultivation produced the highest CH4 emissions, but it was shown that they could be reduced if the current practice was replaced by minimal flooding or through irrigation with alternating wetting and drying cycles. Emissions were predicted to rise until SSP 370, with a marginal increase in SSP 585 thereafter. The findings of this work underscored an urgency to develop climate-smart location-specific mitigation strategies focused on simultaneously improving current water and nutrient management practices. The use of methanotrophs to reduce CH4 production from rice systems should be considered in future work. This research also highlighted the critical interaction that exists between agricultural practices and climate change, and emphasized the need to implement adaptive crop management strategies that can sustain productivity and mitigate the environmental impacts of rice-based systems in southern India.

Responses of yield, CH4 and N2O emissions to ratoon rice cropping and different management practices

Context or problemConversion from single rice (SR) or double rice (DR) to ratoon rice (RR) is gaining growing popularity in China. Yet, a quantitative synthesis of their impact on greenhouse gas (GHG, including methane (CH4) and nitrous oxide (N2O)) emissions and grain yield has not been conducted. Objective or research questionThe objective was to evaluate the effects of conversion from SR or DR to RR on CH4 and N2O emissions, grain yield, global warming potential (GWP), and greenhouse gas intensity (GHGI) and to investigate the potential responses to different operating practices [alternate wetting-drying irrigation, nitrogen management, rice variety selection, and their multiple treatments (multiple measures)] in RR fields (oRR). MethodsIn this study, a comprehensive meta-analysis of 571-paired measurements from ratoon rice fields was conducted. ResultsOur results showed that the conversion from SR to RR significantly increased CH4 emissions, grain yield, and GWP by 35.4 %, 30.6 %, and 43.3 %, respectively. In contrast, the conversion from DR to RR decreased CH4 emissions, grain yield, and GWP by 23.2 %, 7.4 %, and 30.0 %, respectively. Interestingly, both conversions from SR or DR to RR did not affect N2O emissions but reduced GHGI in paddy fields, suggesting that RR provided an economically and ecologically sustainable rice planting model. Furthermore, on average, oRR further decreased CH4 and N2O emissions and GHGI from RR fields but did not affect grain yield. Among the existing management practices, the overall effect of multiple measures was better than that of alternate wetting-drying irrigation, nitrogen management, and rice variety selection. ConclusionsOverall, ratoon rice cropping decreased CH4 emissions and maintained rice grain yield. However, it is also necessary to further implement comprehensive cultivation strategies in the future to maximize the benefits of grain yield and GHG emissions reduction.

Warming increases CH4 emissions from rice paddies through shifts in methanogenic and methanotrophic communities

Warming often stimulates methane (CH4) emissions from rice paddies, one of the largest anthropogenic sources of CH4 emissions. However, the responses of methanogenic and methanotrophic communities to warming, particularly within active communities, remain unclear. Therefore, based on a field warming experiment in a rice-wheat system, we investigated the effects of warming on methanogenic and methanotrophic communities, using the DNA stable-isotope probing technology. Our results indicated that warming increased CH4 emissions by 27–49% over two rice growing seasons compared to ambient conditions. Warming significantly increased the abundance of methanogens by 53%, whereas did not affect activities of methanogens and active methanogenic community. Conversely, warming did not influence the abundance of methanotrophs, but reduced activities of methanotrophs by 44%. Notably, warming led to a significant rise in the relative abundance of the active type II methanotrophic community, which exhibits lower CH4 oxidation efficiency. These findings suggest that the observed increase in CH4 emissions under warming conditions is primarily driven by the enhanced abundance of methanogens and the increased presence of less efficient active type II methanotrophs. This study underscores the critical role of active microbial communities in understanding and managing CH4 emissions from rice paddies in a warming world.

Glacier melting promotes methane emission via increased methanogenic activity in the foreland alpine meadow

Annual glacier melting alters hydrothermal conditions of the foreland alpine meadows, and causes significant fluctuations in methane (CH4) flux. Previously we found that Tibetan glacier foreland alpine meadow shifts to CH4 source from sink during the melting season, but the potential mechanisms remain unclear. This study, via combination of in-situ measurement of seasonal CH4 flux and survey of microbial species that may involve in CH4 metabolism, explores the causes of glacier melting on CH4 flux in a glacier foreland alpine meadow on Tibetan Plateau. We determined a pronounced CH4 emission (13.95 μg·m−2·h−1) in August (melting season) but CH4 uptake in June (−3.76 μg·m−2·h−1) and October (−17.77 μg·m−2·h−1), and 1.4-fold higher soil moisture in August than the other two months. This showed a direct correlation of CH4 flux with glacier melting increased soil water. Additionally, glacier melting caused more CH4 fluxes increase in hollows than in hummocks. Amplicon sequencing determined 126-fold higher abundance of mcrA, the methanogenic marker gene, in August than in June and October, and a higher relative abundance of a fungal phylum Mortierellomycota and syntrophic bacteria that convert the fatty acids, the degradation intermediates of organic complexes to CO2 and acetate, the methanogenic substrates like in August. However, no seasonal variation of pmoA, the marker gene of aerobic methanotrophs, was observed. It appears that glacier melting promotes the CH4 producing but not the consuming microorganisms, thus leading to increased CH4 emission. The findings of this work indicate that global warming resulted glacier melting would increase global CH4 emissions, and in turn worsens global warming, so an alarming positive feedback loop.

Effects of aged biochar additions at different addition ratios on soil greenhouse gas emissions

Biochar addition is effective in reducing soil greenhouse gas (GHG) emissions, but it's essential to evaluate whether aged biochar retains this capability as its properties change over time. However, research comparing the effects of fresh and aged biochar on soil GHG emissions is limited. Moreover, exploring the priming effect of biochar on native soil organic carbon (SOC) mineralization is crucial for revealing the effect mechanism on soil CO2 emission. However, research investigating the priming effects of aged biochar is limited. In this study, the effects of aged biochar addition on soil physicochemical properties, GHG emissions, and global warming potential (GWP) were examined through an incubation experiment with three treatments: (1) soil only (CK), (2) 1 % aged maize straw biochar addition (HBC1) and (3) 4 % aged maize straw biochar addition (HBC4), and then their effects were compared with those of fresh biochar from our previous research. 13C tracer technology was used to assess the priming effect of aged biochar on native SOC mineralization. Results showed that aged biochar improved soil physicochemical properties. Compared to CK, HBC1 and HBC4 reduced CO2 emissions by 28.02 % and 20.15 %, respectively, and reduced N2O emissions by 61.54 % and 66.39 %. HBC4 significantly increased CH4 emission, whereas HBC1 reduced it. HBC1 and HBC4 reduced GWP by 29.01 % and 21.41 %, respectively. Overall, aged biochar demonstrated a greater reduction effect compared to fresh biochar at the 1 % addition ratio. The CO2 reduction is attributed to the negative priming effect of aged biochar on native SOC mineralization. The reduction in N2O emissions is attributed to aged biochar promoting microbial nitrogen fixation and reducing the ratio of denitrification to nitrification. The variation in CH4 emissions reflects differing dominant factors influencing CH4 emission across varying addition ratios. In conclusion, 1 % aged biochar addition demonstrates a more favorable long-term effect on mitigating GHG emissions.

Crystalline iron oxide mineral (magnetite) accelerates methane production from petroleum hydrocarbon biodegradation

Methane (CH4) emissions are a factor in climate change; in addition, CH4 production may affect reclamation of fluid fine tailings (FFT) in tailings ponds, and end-pit lakes (EPLs). In laboratory cultures, we investigated the effect of crystalline iron mineral (magnetite) on CH4 production from the biodegradation of hydrocarbons added to FFT collected from methanogenically more and less active sites in a demonstration EPL. Magnetite enhanced CH4 production from both sites, having a greater effect in more active FFT, where it increased the CH4 production rate as much as 48% (from 6.67 μmol d−1 to 9.87 μmol d−1) compared to FFT without magnetite. Correspondingly, magnetite hastened biodegradation of hydrocarbons (monoaromatics, n-alkanes and iso-alkanes), with a pronounced effect on o-xylene, ethylbenzene, m/p-xylenes, n-octane, n-nonane, and 2-methyloctane, where biodegradation rates increased by 46, 117, 11, 45, 28 and 37%, respectively, compared to FFT without magnetite. Little FeII was produced, suggesting that magnetite is not being used as an electron acceptor but rather functions as a conduit for electron transfer. Thus, magnetite may be a suitable amendment to enhance bioremediation of anaerobic environments contaminated with hydrocarbons. Importantly, our observations imply that magnetite may increase CH4 emissions from terrestrial ecosystems, thus affecting carbon budget estimations.

Meta-analysis of GHG emissions stimulated by crop residue return in paddy fields: Strategies for mitigation

The stimulating impact of crop residue return on greenhouse gas (GHG) emissions from paddy fields have been widely accepted, while the influence of site environmental and human factors on the simulating degree remains unclear. Here, we performed a meta-analysis to assess the GHG emissions affected by residue return, and its mitigation potential combined with key factors in paddy fields. Drawing upon 1047 observation sets of CH4 and N2O emissions from 155 peer-reviewed publications we found that residue return to paddy fields caused an average increase of 73% CH4 emissions and 14% in N2O emissions. Utilizing meta-analytical models, we identified pH as the most significant driver modulating GHG emissions, followed by soil organic matter (SOC) and total nitrogen. In alkaline soils, combining straw return with intermittent irrigation (285.2%) or mid-season drainage (118.9%) significantly reduced CH4 emissions compared to continuous flooding (1201.9%). Additionally, pairing straw return with higher nitrogen inputs (above 150 kg N ha−1) improved soil N2O uptake by −11.5%. In acid and neutral soils, straw carbonization achieved soil CH4 negative emissions (from −2.9% to −39.3%), but the long-term effects remained unclear. Reduced drainage frequency mitigates N2O emissions but may increase CH4 emissions. To efficiently mitigate GHG emissions, we proposed low-carbon schemes for acid or neutral soils based on specific SOC content: For soils with SOC content <10 g kg−1, prioritize nitrogen input control with rates not exceeding 174 kg N ha−1. For soils with SOC content >10 g kg−1, prioritize adjusting the type of straw. Our study underscores the significance of site-specific factors in modulating GHG emissions. Efficient GHG mitigation can be achieved by combining residue return with other agronomic measures tailored to different soil conditions.