CH4 Oxidation In Soils Research Articles

Elevated [CO2] reduces CH4 emissions from rice paddies under in situ straw incorporation

Rice paddies contribute to ∼48% of greenhouse gas emissions from cropland, with ∼94% from methane (CH4). Elevated atmospheric CO2 concentrations (eCO2) due to human activities, generally stimulate the rice growth, and in turn affect CH4 emissions from rice paddies. However, the effects of eCO2 on CH4 emissions from rice paddies are still unclear under in situ straw incorporation, the popular agricultural practice. Therefore, we conducted a 3-yr field experiment to investigate the effects of eCO2 on CH4 emissions under in situ straw incorporation in the rice-wheat cropping system, using the open-top chamber technology. We found that eCO2 reduced the CH4 emissions from rice paddies by 10.9–23.8%, but increased rice plant biomass by 4.2–35.6%. The eCO2 reduced the soil NH4+ and NO3- concentrations, but did not affect the soil dissolved organic C. The eCO2 did not affect the abundance of methanogens and CH4 production potential, whereas it stimulated the abundance of methanotrophs and CH4 oxidation potential by 102.5% and 15.1%, respectively. The eCO2 also shifted the community composition of methanotrophs and reduced the relative abundance of type Ⅱ methanotrophs by 8.5%. The random forest analysis identified that soil CH4 oxidation potential is the most important factor affecting CH4 emissions. Our findings indicate that eCO2 can reduce the CH4 emissions from rice paddies under in situ straw incorporation mainly through increasing the soil CH4 oxidation potential. Our study suggests the effects of eCO2 on CH4 emissions from global paddies may be overestimated and underline the need for smart agricultural management to reduce CH4 emissions.

Large, sustained soil CO2 efflux but rapid recovery of CH4 oxidation in post-harvest and post-fire stands in a mixedwood boreal forest

The net effect of forest disturbances, such as fires and harvesting, on soil greenhouse gas fluxes is determined by their impacts on both biological and physical factors, as well as the temporal dynamics of these effects post-disturbance. Although harvesting and fire may have distinct effects on soil carbon (C) dynamics, the temporal patterns in soil CO2 and CH4 fluxes and the potential differences between types of disturbances, remain poorly characterized in boreal forests. In this study, we measured soil CO2 and CH4 fluxes using a off-axis integrated cavity output spectroscopy system in snow-free seasons over two years in post-harvest and post-fire chronosequence sites within a mixedwood boreal forest in northwestern Ontario, Canada. Soil CO2 efflux showed a post-disturbance peak, with differing dynamics depending on the disturbance type: post-harvest stands exhibited a nearly tenfold increase (from ∼1 to ∼11 μmol CO2.m-2.s−1) from 1 to 9–10 years post-disturbance, followed by a steep decline; post-fire stands showed a more gradual increase, peaking at ∼6–7.2 μmol CO2.m-2.s−1 after ∼12–15 years. The youngest post-harvest stands were net sources of CH4,whereas post-fire stands were never net CH4 sources. In both disturbance types, the strength of the CH4 sink increased with stand age, approaching ∼2.4 nmol.m-2.s−1 by 15 years post-disturbance. Volumetric water content, bulk density, litter depth, and pH were significant predictors of CO2 fluxes; for CH4 fluxes, litter depth, pH, and the interaction of VWC and soil temperature were significant predictors in both disturbance types, with EC also showing a relationship in post-harvest stands. Our findings indicate that while soil CH4 oxidation rapidly recovers following disturbance, both post-harvest and post-fire stands show a multi-decade release of soil CO2 that is too large to be offset by C gains over this period.

Application of nitrogen-rich sunflower husks biochar promotes methane oxidation and increases abundance of Methylobacter in nitrogen-poor soil

The area of sunflower crops is steadily increasing. A beneficial way of managing sunflower waste biomass could be its use as a feedstock for biochar production. Biochar is currently being considered as an additive for improving soil parameters, including the ability to oxidise methane (CH4) – one of the key greenhouse gases (GHG). Despite the high production of sunflower husk, there is still insufficient information on the impact of sunflower husk biochar on the soil environment, especially on the methanotrophy process. To fill this knowledge gap, an experiment was designed to evaluate the effects of addition of sunflower husk biochar (produced at 450–550 °C) at a wide range of doses (1–100 Mg ha−1) to Haplic Luvisol. In the presented study, the CH4 oxidation potential of soil with and without sunflower husk biochar was investigated at 60 and 100% water holding capacity (WHC), and with the addition of 1% CH4 (v/v). The comprehensive study included GHG exchange (CH4 and CO2), physicochemical properties of soil (pH, soil organic carbon (SOC), dissolved organic carbon (DOC), nitrate nitrogen (NO3−-N), WHC), and the structure of soil microbial communities. That study showed that even low biochar doses (5 and 10 Mg ha−1) were sufficient to enhance pH, SOC, DOC and NO3−-N content. Importantly, sunflower husk biochar was significant source of NO3−-N, which soil concentration increased from 9.40 ± 0.09 mg NO3−-N kg−1 for the control to even 19.40 ± 0.26 mg NO3−-N kg−1 (for 100 Mg ha−1). Significant improvement of WHC (by 11.0–12.4%) was observed after biochar addition at doses of 60 Mg ha−1 and higher. At 60% WHC, application of biochar at a dose of 40 Mg ha−1 brought significant improvements in CH4 oxidation rate, which was 4.89 ± 0.37 mg CH4–C kg−1 d−1. Higher biochar doses were correlated with further improvement of CH4 oxidation rates, which at 100 Mg ha−1 was seventeen-fold higher (8.36 ± 0.84 mg CH4–C kg−1 d−1) than in the biochar-free control (0.48 ± 0.28 mg CH4–C kg−1 d−1). CO2 emissions were not proportional to biochar doses and only grew circa (ca.) twofold from 3.16 to 6.90 mg CO2–C kg−1 d−1 at 100 Mg ha−1. Above 60 Mg ha−1, the diversity of methanotrophic communities increased, with Methylobacter becoming the most abundant genus, which was as high as 7.45%. This is the first, such advanced and multifaceted study of the wide range of sunflower husk biochar doses on Haplic Luvisol. The positive correlation between soil conditions, methanotroph abundance and CH4 oxidation confirmed the multifaceted, positive effect of sunflower husk biochar on Haplic Luvisol. Sunflower husk biochar can be successfully used for Haplic Luvisol supplementation. This additive facilitates soil protection against degradation and has the potential to mitigate GHG emissions.

Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO2, CH4 fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO2 and CH4 exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO2 from grassland and the city park was two times higher than from the arable land. The calculated CH4 oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.The estimated Q10 values ranged between 1.68 and 1.79 for CO2 and from 1.26 to 1.49 for CH4, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO2 fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH4 oxidation. This indicates that with ongoing warming, the higher Q10 of CO2 production vs. CH4 oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.

Dynamics of Functional Genes and Bacterial Community during Bioremediation of Diesel-Contaminated Soil Amended with Compost.

Compost is widely used as an organic additive to improve the bioremediation of dieselcontaminated soil. In this study, the effects of compost amendment on the remediation performance, functional genes, and bacterial community are evaluated during the bioremediation of diesel-contaminated soils with various ratios of compost (0-20%, w/w). The study reveals that the diesel removal efficiency, soil enzyme (dehydrogenase and urease) activity, soil CH4 oxidation potential, and soil N2O reduction potential have a positive correlation with the compost amendment (p < 0.05). The ratios of denitrifying genes (nosZI, cnorB and qnorB) to 16S rRNA genes each show a positive correlation with compost amendment, whereas the ratio of the CH4-oxidizing gene (pmoA) to the 16S rRNA genes shows a negative correlation. Interestingly, the genera Acidibacter, Blastochloris, Erythrobacter, Hyphomicrobium, Marinobacter, Parvibaculum, Pseudoxanthomonas, and Terrimonas are strongly associated with diesel degradation, and have a strong positive correlation with soil CH4 oxidation potential. Meanwhile, the genera Atopostipes, Bacillus, Halomonas, Oblitimonas, Pusillimonas, Truepera, and Wenahouziangella are found to be strongly associated with soil N2O reduction potential. These results provide useful data for developing technologies that improve diesel removal efficiency while minimizing greenhouse gas emissions in the bioremediation process of diesel-contaminated soil.

Dynamics of Functional Genes and Bacterial Community during Bioremediation of Diesel-Contaminated Soil Amended with Compost.

Compost is widely used as an organic additive to improve the bioremediation of diesel-contaminated soil. In this study, the effects of compost amendment on the remediation performance, functional genes, and bacterial community are evaluated during the bioremediation of diesel-contaminated soils with various ratios of compost (0-20%, w/w). The study reveals that the diesel removal efficiency, soil enzyme (dehydrogenase and urease) activity, soil CH4 oxidation potential, and soil N2O reduction potential have a positive correlation with the compost amendment (p < 0.05). The ratios of denitrifying genes (nosZI, cnorB and qnorB) to 16S rRNA genes each show a positive correlation with compost amendment, whereas the ratio of the CH4-oxidizing gene (pmoA) to the 16S rRNA genes shows a negative correlation. Interestingly, the genera Acidibacter, Blastochloris, Erythrobacter, Hyphomicrobium, Marinobacter, Parvibaculum, Pseudoxanthomonas, and Terrimonas are strongly associated with diesel degradation, and have a strong positive correlation with soil CH4 oxidation potential. Meanwhile, the genera Atopostipes, Bacillus, Halomonas, Oblitimonas, Pusillimonas, Truepera, and Wenahouziangella are found to be strongly associated with soil N2O reduction potential. These results provide useful data for developing technologies that improve diesel removal efficiency while minimizing greenhouse gas emissions in the bioremediation process of diesel-contaminated soil.

Attenuation of Methane Oxidation by Nitrogen Availability in Arctic Tundra Soils.

CH4 emission in the Arctic has large uncertainty due to the lack of mechanistic understanding of the processes. CH4 oxidation in Arctic soil plays a critical role in the process, whereby removal of up to 90% of CH4 produced in soils by methanotrophs can occur before it reaches the atmosphere. Previous studies have reported on the importance of rising temperatures in CH4 oxidation, but because the Arctic is typically an N-limited system, fewer studies on the effects of inorganic nitrogen (N) have been reported. However, climate change and an increase of available N caused by anthropogenic activities have recently been reported, which may cause a drastic change in CH4 oxidation in Arctic soils. In this study, we demonstrate that excessive levels of available N in soil cause an increase in net CH4 emissions via the reduction of CH4 oxidation in surface soil in the Arctic tundra. In vitro experiments suggested that N in the form of NO3- is responsible for the decrease in CH4 oxidation via influencing soil bacterial and methanotrophic communities. The findings of our meta-analysis suggest that CH4 oxidation in the boreal biome is more susceptible to the addition of N than in other biomes. We provide evidence that CH4 emissions in Arctic tundra can be enhanced by an increase of available N, with profound implications for modeling CH4 dynamics in Arctic regions.

Great and fast increase in soil CH4 uptake after reforestation in karst cropland area is linked to the environmental and microbial factors

Karst environments are an important but often overlooked global sink of atmospheric CH4. Little is known about methanotrophic bacterial communities in karst soils; consequently, the effects of land use change (LUC) and soil management practices on them and how they function as part of the soil CH4 sink are unclear. In this study, we compared net soil CH4 fluxes, kinetic parameters (Km and Vmax) of CH4 oxidation, and the pmoA gene of CH4 oxidizers at five test soil plots in karst areas that have different soil types and land use types. The maximum atmospheric CH4 uptake rate (−5.62 ± 3.14 kg ha-1 y-1) occurred in reverting scrublands just 10 years after they had been utilized for crop cultivation; followed by natural forest (−4.30 ± 4.02 kg ha-1 y-1) in limestone soils. The cultivated soils in the cropland emitted CH4 into the atmosphere. The difference in net CH4 fluxes (−8.21 kg ha–1 y–1) between soils in cropland and soils in reverting scrubland from cropland was 4–8 times higher than the global average values, suggesting that reforestation on limestone soils in karst cropland areas has much greater potential to enhance soil CH4 oxidation than in non-karst areas. Soil moisture is the most likely environmental factor to trigger the enhancement effect of reforestation. The remarkable corresponding relationships between Km, net soil CH4 fluxes, and methanotrophic compositions in these plots suggest that bacteria play an essential role in regulating the effects of LUC on soil CH4 oxidation rates. It is type Ⅰ methanotroph USCγ and JR3 (USCγ sensu lato), not type II methanotrophs USCα as in previous studies, that dominate in enhancing soil oxidation of atmospheric CH4 since reforestation on limestone soils. The specific unstable habitats in karst settings favor USCγ who, as r-strategists, can change rapidly to adapt to new conditions formed from LUC and then grow presumably at an exponential rate. This coupling of environmental and microbial factors can well explain the great and fast response of CH4 oxidation in limestone soils. Our study provides new insights that reforestation of cropland in karst areas may be a noticeably more efficient way to potentially mitigate atmospheric CH4 build-up and thus should be strongly encouraged.

Enhanced soil methane oxidation in both organic layer and topsoil during the succession of subtropical forests

Although (sub)tropical forests account for 10–20% of the atmospheric methane (CH4) uptake by soils, the study of soil CH4 oxidation rates and the controlling factors during the chronosequences of forest succession remains poorly understood. The objectives of this study were to characterize the vertical distribution patterns and dynamics of CH4 oxidation among the early-, mid-, and late-successional stages of subtropical forests, and to investigate the main drivers of soil CH4 fluxes. Three successional forests soils were collected and the ambient and potential CH4 oxidation rates, the related enzymes as well as the key soil parameters were determined in the laboratory. The soils at mid- and late-successional stages functioned exclusively as a CH4 sink while the soil at early-succesional stage was either a CH4 source or sink. Soil CH4 oxidations showed significant vertical distributions along with the successional gradients. The highest rate of ambient CH4 oxidation was observed in the A-horizon of the mid-successional stage (forest age ∼ 100 years), increased by 26-fold compared to the early successional stage, while the highest rate of potential CH4 oxidation was detected in the O-horizon of the late-successional stages (forest age > 300 years), which increased the CH4 oxidation by 29% and 21% respectively compared to the early- and mid-successional stages. Soil CH4 oxidation enhanced with decreasing of soil nitrite and nitrate content but weakened with declining of soil moisture at the successional chronosequence. Collectively, subtropical forests have the potential to increase the soil sink capacity for CH4 oxidation along the successional gradient, and thereby providing the negative feedbacks to ecosystems under climate changing.

Plant community mediated methane uptake in response to increasing nitrogen addition level in a saline-alkaline grassland by rhizospheric effects

Methane (CH4) uptake in dryland ecosystems is a pathway in mitigating atmospheric CH4 concentrations. A number of studies have demonstrated that nitrogen availability is a key regulator of the CH4 oxidation process. However, how plants mediate soil CH4 oxidation in response to N addition, particularly in saline-alkaline grasslands in the vast regions of the northern China, has received little attention. We conducted a 3-yr (2017–2019) in-situ experiment with eight N addition levels to examine the effect of N on soil CH4 oxidation, and to explore the linkages between the N-induced changes of plant community and the seasonal dynamics of CH4 in a saline-alkaline grassland.We found that the saline-alkaline grassland was a weak CH4 sink displaying nonlinear CH4 uptake levels in response to N additions, possibly due to the nonlinear changes in the abundance of key functional genes (pmoA) that were responsible for CH4 oxidation. The changes in plant productivity and diversity that were induced by N additions explained 21 % of the variations in CH4 uptake. The N-induced increase in productivity indirectly enhanced CH4 uptake at N addition rates of <10 g m−2 yr−1, while the decrease in biodiversity indirectly inhibited CH4 uptake when N addition exceeded 10 g m−2 yr−1. The N-induced changes in the plant community can affect CH4 uptake, mainly through the rhizospheric effects of plants. In conclusion, our findings underscore the importance of rhizosphere when assessing the CH4 uptake in saline-alkaline grassland ecosystems.

Diversity and Composition of Methanotroph Communities in Caves.

ABSTRACTMethane oxidizing microorganisms (methanotrophs) are ubiquitous in the environment and represent a major sink for the greenhouse gas methane (CH4). Recent studies have demonstrated methanotrophs are abundant and contribute to CH4 dynamics in caves. However, very little is known about what controls the distribution and abundance of methanotrophs in subterranean ecosystems. Here, we report a survey of soils collected from > 20 caves in North America to elucidate the factors shaping cave methanotroph communities. Using 16S rRNA sequencing, we recovered methanotrophs from nearly all (98%) of the samples, including cave sites where CH4 concentrations were at or below detection limits (≤0.3 ppmv). We identified a core methanotroph community among caves comprised of high-affinity methanotrophs. Although associated with local-scale mineralogy, methanotroph composition did not systematically vary between the entrances and interior of caves, where CH4 concentrations varied. We also observed methanotrophs are able to disperse readily between cave systems showing these organisms have low barriers to dispersal. Lastly, the relative abundance of methanotrophs was positively correlated with cave-air CH4 concentrations, suggesting these microorganisms contribute to CH4 flux in subterranean ecosystems.IMPORTANCE Recent observations have shown the atmospheric greenhouse gas methane (CH4) is consumed by microorganisms (methanotrophs) in caves at rates comparable to CH4 oxidation in surface soils. Caves are abundant in karst landscapes that comprise 14% of Earth’s land surface area, and therefore may represent a potentially important, but overlooked, CH4 sink. We sampled cave soils to gain a better understand the community composition and structure of cave methanotrophs. Our results show the members of the USC-γ clade are dominant in cave communities and can easily disperse through the environment, methanotroph relative abundance was correlated with local scale mineralogy of soils, and the relative abundance of methanotrophs was positively correlated with CH4 concentrations in cave air.

Potential soil methane oxidation in naturally regenerated oak-dominated temperate deciduous forest stands responds to soil water status regardless of their age—an intact core incubation study

Key messagePotential CH4 oxidation in the top soil layer increased with decreasing soil water content in spring but was inhibited during severe summer drought in naturally-regenerated oak-dominated temperate deciduous forest stands regardless of their age. No direct effect of mineral nitrogen on soil CH4 oxidation was found. Soil CH4 oxidation in temperate forests could be reduced by extreme climatic events.ContextThe oxidation of atmospheric methane (CH4) by methanotrophic bacteria in forest soils is an important but overlooked ecosystem service.AimOur objective was to determine which factors drive variations in soil CH4 oxidation in oak-dominated temperate deciduous forest stands of different ages.MethodsSoil samples were collected in 16 stands aged 20 to 143 years in periods of high and low soil water content (SWC). The potential rate of soil CH4 oxidation was measured by incubating the first five centimetres of intact soil cores at 20 °C.ResultsSWC was the main driver accounting for variations in CH4 oxidation. In spring, a two-fold reduction in SWC greatly increased CH4 oxidation. But when the soil was dry in late summer, a further reduction in SWC led to a decrease in CH4 oxidation in the top soil layer. No direct effect of mineral nitrogen on soil CH4 oxidation was found.ConclusionsWith regard to soil CH4 oxidation, naturally regenerated forest stands contribute equally to climate change mitigation regardless of their age. Considering future climate scenarios for Europe, soil CH4 sink in temperate forests could be reduced, due to both an increase in the number of flooding episodes in spring and drier summers.

Positron-emitting radiotracers spatially resolve unexpected biogeochemical relationships linked with methane oxidation in Arctic soils.

Arctic soils are marked by cryoturbic features, which impact soil-atmosphere methane (CH4 ) dynamics vital to global climate regulation. Cryoturbic diapirism alters C/N chemistry within frost boils by introducing soluble organic carbon and nutrients, potentially influencing microbial CH4 oxidation. CH4 oxidation in soils, however, requires a spatio-temporal convergence of ecological factors to occur. Spatial delineation of microbial activity with respect to these key microbial and biogeochemical factors at relevant scales is experimentally challenging in inherently complex and heterogeneous natural soil matrices. This work aims to overcome this barrier by spatially linking microbial CH4 oxidation with C/N chemistry and metagenomic characteristics. This is achieved by using positron-emitting radiotracers to visualize millimeter-scale active CH4 uptake areas in Arctic soils with and without diapirism. X-ray absorption spectroscopic speciation of active and inactive areas shows CH4 uptake spatially associates with greater proportions of inorganic N in diapiric frost boils. Metagenomic analyses reveal Ralstonia pickettii associates with CH4 uptake across soils along with pertinent CH4 and inorganic N metabolism associated genes. This study highlights the critical relationship between CH4 and N cycles in Arctic soils, with potential implications for better understanding future climate. Furthermore, our experimental framework presents a novel, widely applicable strategy for unraveling ecological relationships underlying greenhouse gas dynamics under global change.

Post-harvest recovery of soil methane oxidation on skid trails and landings in a managed northern hardwood forest

Skid trails and landings are features within managed forest landscapes where soils are moderately to extremely disturbed by forestry vehicles. They have been found to exhibit reduced methane (CH4) oxidation or CH4 emissions six months to a year after a harvest has ended, but little is known about when these changes begin to occur (either during or after harvests) or how they recover over a longer timeframe. We took periodic measurements of soil CH4 flux from skid trails and landings during a harvest, and also quantified CH4 flux rates from sites that had been harvested up to 15 years prior to form a replicated chronosequence of soil recovery. In the thirteen-week period of active harvesting soil CH4 oxidation steadily declined, with small emissions occurring by the end of the measurement period. The chronosequence measurements revealed high rates of CH4 emissions the first year after harvest followed by a decrease in the following years. Emissions were particularly strong from landings and skid trails that had experienced high amounts of traffic and were located on lower slopes. By the end of the 15-year chronosequence landing and skid trail soils had returned to acting as CH4 sinks; however, the rates of oxidation remained lower than undisturbed forest soils. Further, integration of models created to predict CH4 flux over time indicates that CH4 flux from these soils are unlikely to reach a full recovery within a 20-year period - the average length of time of a harvest cycle in this region. On landings the change from emissions back to oxidation was correlated with soil temperatures, which decreased over time. On some skid trails CH4 flux was correlated with soil moisture content, which initially increased from buried wood’s increased water holding capacity and then decreased over time. The results suggest that remediation measures ought to be implemented immediately after harvest to avoid the high emissions that occur in the following few years and should prioritize the removal or prevention of incorporation of wood fragments.

Soil Properties Interacting With Microbial Metagenome in Decreasing CH4 Emission From Seasonally Flooded Marshland Following Different Stages of Afforestation.

Wetlands are the largest natural source of terrestrial CH4 emissions. Afforestation can enhance soil CH4 oxidation and decrease methanogenesis, yet the driving mechanisms leading to these effects remain unclear. We analyzed the structures of communities of methanogenic and methanotrophic microbes, quantification of mcrA and pmoA genes, the soil microbial metagenome, soil properties and CH4 fluxes in afforested and non-afforested areas in the marshland of the Yangtze River. Compared to the non-afforested land use types, net CH4 emission decreased from bare land, natural vegetation and 5-year forest plantation and transitioned to net CH4 sinks in the 10- and 20-year forest plantations. Both abundances of mcrA and pmoA genes decreased significantly with increasing plantation age. By combining random forest analysis and structural equation modeling, our results provide evidence for an important role of the abundance of functional genes related to methane production in explaining the net CH4 flux in this ecosystem. The structures of methanogenic and methanotrophic microbial communities were of lower importance as explanatory factors than functional genes in terms of in situ CH4 flux. We also found a substantial interaction between functional genes and soil properties in the control of CH4 flux, particularly soil particle size. Our study provides empirical evidence that microbial community function has more explanatory power than taxonomic microbial community structure with respect to in situ CH4 fluxes. This suggests that focusing on gene abundances obtained, e.g., through metagenomics or quantitative/digital PCR could be more effective than community profiling in predicting CH4 fluxes, and such data should be considered for ecosystem modeling.

Methane emissions from Icelandic landfills – A comparison between measured and modelled emissions

This study compares methane (CH4) emissions from five Icelandic landfills, quantified using tracer gas dispersion to modelled emission rates using the IPCC FOD model. The average CH4 emission rates measured from the investigated landfills were 475.4 kg CH4 h−1 (Álfsnes landfill), 32.5 kg CH4 h−1 (Fíflholt), 40.8 kg CH4 h−1 (Gufunes), 9.8 kg CH4 h−1 (Kirkjuferjuhjáleiga) and 78.4 kg CH4 h−1 (Stekkjarvík). At three of the landfills (Álfsnes, Fíflholt and Kirkjuferjuhjáleiga), the modelled emission was higher than the measured emission by factors ranging from 1.1 to 4.8, neglecting any CH4 oxidation in the cover soils. Even though CH4 oxidation might play a role at some of the investigated landfills, and thus reduce the gap between modelled and measured emissions, it is likely that the model overestimated CH4 generation due to uncertainties in input model parameters. Assuming that the measured emissions at the five landfills are representative of all the waste disposed in Iceland from 2007 to 2016, the measured emission should be extrapolated to 817 kg CH4 h−1, which is relatively close to the modelled national emission of 936 kg CH4 h−1 in 2017. This study showed that the application of the IPCC FOD model at national level is appropriate for estimating landfill CH4 emissions in Iceland. CH4 emissions from landfills in Iceland can be reduced by expanding or implementing gas collection or biocover systems for optimised microbial oxidation.

Influences of phosphorus and potassium deficiencies on the methanotrophic communities in rice rhizosphere

Soil methanotrophs can modulate net methane (CH4) emissions in rice paddy fields, but their growth and development depend, to a great extent, upon the soil nutrient status. In this study, a pot experiment was conducted to explore how deficiencies in soil phosphorus (P) or potassium (K) affect the methanotrophic abundance (based on pmoA q-PCR), community composition (based on MiSeq high-throughput sequencing) and CH4 oxidation potential using historically severe P and K deficient paddy soils, respectively. The results showed that P deficiency induced a significant decrease in methanotrophic abundance and potential activity in both rhizosphere and bulk soils. Additionally, P deficiency also caused clear shifts in the methanotrophic community composition within the rhizosphere, where the relative abundance of type II methanotrophs (e.g., Methylocystis and Methylosinus) increased while type I (e.g., Methylomonas, Methylobacter and Unclassified_typeIb) decreased. In contrast, K deficiency did not significantly affect the methanotrophic potential activity and community composition in both rhizosphere and bulk soils. More interestingly, P or K deficiency, particularly P deficiency, narrowed the differences in the abundance and community composition between rhizosphere and bulk soils, implying that P and K deficiencies could attenuate the rhizosphere effects on methanotrophic communities by limiting rice plant growth. Collectively, our results indicated that soil P deficiency, would inhibit soil CH4 oxidation directly or indirectly through restricting rice plant growth, while K deficiency have slight effects on the activity and community composition of soil methanotrophs.

Impact of Spartina alterniflora invasion on soil bacterial community and associated greenhouse gas emission in the Jiuduansha wetland of China

Coastal wetlands are essential sources of greenhouse gases (GHGs) emission, and lots of them are invaded by Spartina alterniflora across different climate zones. We chose Jiuduansha wetland as a typical wetland ecosystem with minimal human activities to study the impacts and interactions between S. alterniflora invasion, soil functional microorganisms, and GHGs emission. Our findings indicated that in comparison to the mudflat and S. mariqueter habitat, the S. alterniflora invasion increased soil carbon dioxide (CO2) emission, which was highly positively related to aboveground biomass, soil organic carbon (SOC), and the ammonium‑nitrogen (NH4+-N) concentration, but negatively related to the nitrate‑nitrogen (NO3–-N) concentration. The relative abundances of soil C-decomposing bacteria increased in S. alterniflora habitat compared with S. mariqueter habitat. Compared with the P. australis habitat, S. alterniflora invasion reduced soil CO2 emission, which was negatively related to salinity. The relative abundances of soil C-fixing bacteria (phylum Chloroflexi) and functional genes (acsA-F and rbcL) decreased in S. alterniflora habitat. Moreover, the S. alterniflora invasion increased soil methane (CH4) emission compared with the S. mariqueter and P. australis habitats, which was positively related to aboveground biomass, SOC and NH4+-N concentration, and negatively related to the NO3–-N concentration. Besides, the relative abundances of CH4 oxidation functional genes were decreased in S. alterniflora habitat compared with the S. mariqueter and P. australis habitats. Meanwhile, the oxidation of CH4 to methanol was mainly regulated by mmoX gene at our study site. Thus, the soil CO2 and CH4 emissions after S. alterniflora invasion were regulated by soil environmental factors and soil C-fixing, C-decomposing, and CH4 oxidation functional microorganisms. Our results are helpful to better understand the mechanisms involved in the impacts of S. alterniflora invasions on GHG emissions in coastal wetlands.

Winter CH4 oxidation in cold-temperate grassland soils of northern Japan: 222Rn as a proxy for the validation of CH4 diffusivity

Amidst changing seasonal snow-covered periods and extents in northern high latitude regions, winter CH4 oxidation is susceptible to drastic climate change, all of which modulates an accurate assessment of regional carbon balance. The importance of winter CH4 oxidation to the soils in these regions has previously been recognized; in this study, concentrations of CH4 and 222Rn were observed in the snowpack and underlying cold temperate soils during the winters of 1995/96 and 1996/97. These observations were carried out in order to 1) validate the 222Rn tracer as a proxy for variations in CH4 diffusivity within a snowpack containing many seasonal ice lenses, and to 2) estimate winter CH4 oxidation through the snowpack to the soils. Winter CH4 oxidations estimated by snow density (method 1); using the 222Rn tracer under steady (method 2) and non-steady (method 3) conditions; and using a static chamber (method 4) during the winter of 1996/97 yielded 16.7 ± 6.3; 8.2 ± 2.9; 9.8 ± 7.4; and 4.5 ± 2.5 mg CH4–C m−2, respectively. These results suggest that contributions from average CH4 oxidation represent 23.3% (range: 12.7–35.1%) of the annual CH4 oxidation into cold temperate soils. Wintertime CH4 oxidation significantly reflects temporal variation in the snowpack, demonstrating that soil temperature depends on snow cover, and that a threshold snow depth of 40 cm does not prevent, but rather promotes, atmospheric CH4 oxidation through snowpack to the soils. These findings demonstrate that the 222Rn tracer was useful for estimating winter CH4 diffusivity and oxidation, using a one-dimensional vertical diffusion box model in cold temperate soils in Japan during multiple snow-covered seasons.

Nitrogen addition decreases methane uptake caused by methanotroph and methanogen imbalances in a Moso bamboo forest

Forest soils play an important role in controlling global warming by reducing atmospheric methane (CH4) concentrations. However, little attention has been paid to how nitrogen (N) deposition may alter microorganism communities that are related to the CH4 cycle or CH4 oxidation in subtropical forest soils. We investigated the effects of N addition (0, 30, 60, or 90 kg N ha−1 yr−1) on soil CH4 flux and methanotroph and methanogen abundance, diversity, and community structure in a Moso bamboo (Phyllostachys edulis) forest in subtropical China. N addition significantly increased methanogen abundance but reduced both methanotroph and methanogen diversity. Methanotroph and methanogen community structures under the N deposition treatments were significantly different from those of the control. In N deposition treatments, the relative abundance of Methanoculleus was significantly lower than that in the control. Soil pH was the key factor regulating the changes in methanotroph and methanogen diversity and community structure. The CH4 emission rate increased with N addition and was negatively correlated with both methanotroph and methanogen diversity but positively correlated with methanogen abundance. Overall, our results suggested that N deposition can suppress CH4 uptake by altering methanotroph and methanogen abundance, diversity, and community structure in subtropical Moso bamboo forest soils.