Methanotrophs In Soils Research Articles

Methane oxidation coupling with heavy metal and microplastic transformations for biochar-mediated landfill cover soil

The impact of co-occurring heavy metal (HM) and microplastic (MP) pollution on methane (CH4) oxidation by methanotrophs (MOB) in landfill cover soil (LCS) and the role of biochar in mediating these collaborative transformations remains unclear. This study conducted batch-scale experiments using LCS treated with individual or combined HMs and MPs, with or without biochar amendment. Differentiation in methanotrophic activities, HM transformations, MP aging, soil properties, microbial communities, and functional genes across the groups were analyzed. Biochar proved essential in sustaining efficient CH4 oxidation under HM and MP stress, mainly by diversifying MOB, and enhancing polysaccharide secretion to mitigate environmental stress. While low levels of HMs slightly inhibited CH4 oxidation, high HM concentration enhanced methanotrophic activities by promoting electron transfer process. MPs consistently stimulated CH4 oxidation, exerting a stronger influence than HMs. Notably, the simultaneous presence of low levels of HMs and MPs synergistically boosted CH4 oxidation, linked to distinct microbial evolution and adaptation. Methanotrophic activities were demonstrated to affect the fate of HMs and MPs. Complete passivation of Cu was readily achieved, whereas Zn stabilization was negatively influenced by biochar and MPs. The aging of MPs was also partially suppressed by biochar and HM adsorption.

Lindane degradation potential of methanotrophs and soil microbial biomass from HCH contaminated sites

In the present study, soil physico-chemical properties, hexachlorocyclohexane (HCH) isomers, lindane degrading soil methanotrophs and soil microbial biomass-C, N and P were investigated by selecting 6 study sites in Lucknow and Renukoot region of Uttar Pradesh, Northern India. The ANOVA revealed significant variations soil physico-chemical properties (P<0.001), HCH residues concentrations (P<0.001) and lindane degradation by soil methanotrophs (P<0.001), across different study sites. The GC and GC-MS/MS analysis revealed soil contamination by α, β-, γ-, and δ-HCH, along with organochlorine pesticides (OCPs) including aldrin, β-endosulphan, and dichlorodiphenyltrichloroethane (DDT). The concentration of soil HCH isomers (0.43-310.97 μg g−1) was higher in the soil samples of Lucknow region, compared to the Renukoot (0.12–194.44 μg g−1) region. These results depict that methanotrophic isolates SBRJS01, SBIJS02 and SBJS03 compared to control, showed better growth at selected environmental parameters. During lindane degradation the maximum Cl− release among the methanotrophic isolates showed the trend as SBJS03> SBRJS01> SBIJS02> ControlURRH3. A positive linear relationship (R2=0.7951) was noted between lindane degradation and Cl− release during the methanotrophic isolates incubation period. A greater SMB–C, –N and –P values (365.2, 65.5, and 26.8 μg g−1 soil, respectively), having higher HCH residues were, recorded in the soil samples of Renukoot region, compared to the soils of Lucknow region.The negative correlation between SMB–C, –N, and –P values and different soil HCH isomers suggests that higher concentrations of lethal HCH residues persisting in soils negatively impacts the quantity of soil microbial biomass. Therefore, on-site monitoring and methanotrophic mediated bioremediation of HCH soil residues might be a viable and eco-friendly option in removal of this particular persistent soil pesticide from the contaminated area.

Fiddler crab bioturbation stimulates methane emissions in mangroves: Insights into microbial mechanisms

Mangrove ecosystems are pivotal in blue carbon capture, yet they can also release varying levels of methane (CH4). Fiddler crabs are known players in carbon (C) cycling within mangrove ecosystems, but their precise contributions to CH4 emissions and microbially-driven processes are not yet well understood. We compared CH4 emissions, soil physicochemical properties, and methanogenic and methanotrophic communities in non-bioturbated and bioturbated soils within two mangrove communities: Sonneratia apetala (SA) and Pongamia pinnata (PP). The presence of fiddler crabs led to an increase in CH4 emission rates in the bioturbated soil, ranging from 86% to 430% compared to un-bioturbated soil. The bioturbated soil also exhibited higher levels of ammonium, pH, and dissolved organic carbon (DOC) but with lower concentrations of nitrate, sulfate, salinity, and total nitrogen. Moreover, an increase was observed in the abundance methanogenic communities, but the abundance and diversity of methanotrophic communities was reduced in the bioturbated soil. The increased abundance of Methanosarcina and reduced abundance of type II methanotrophs in the bioturbated soil could result in an overall increase in CH4 emissions. This study result highlights that bioturbation can greatly influence CH4 emissions in mangroves and emphasizes the importance of considering the ecological role of fiddler crabs in the evaluation of coastal blue carbon sequestration.

Agricultural fertilization near marshes impacts the potential for greenhouse gas emissions from wetland ecosystems by modifying microbial communities

Ensuring agricultural security and preserving the health of wetland ecosystems are crucial concerns facing northeast China. However, the adverse effects of environmental pollution, especially nitrogen (N), caused by prolonged agricultural development on the health of marsh wetlands cannot be systematically recognized. To address this issue, an 18-year trial with four different levels of N application was carried out in a typical area of the Northeast region: 0, 6, 12, and 24 gN·m−2·a−1 (referred to as CK, N6, N12, and N24, respectively) to investigate changes in wetland ecological functioning. The results showed that long-term N input significantly enhanced soil N availability. High-level of N addition (N24) significantly reduced soil bacterial richness in October, while fungal diversity was significantly higher in June than in October for both control and N6 treatments. The main environmental factors affecting microorganisms in June were TN, NH4+, and EC, while bacterial and fungal communities were influenced by TN and Leaf Area Index (LAI), respectively, in October. It was found that the AN16S gene was significantly higher in June than in October, indicating that summer is the critical time for N removal in the wetland. N addition significantly reduced the abundance of the NIFH gene and decreased the N fixation potential of the wetland. In June, low and medium levels of N inputs promoted denitrification processes in the wetland and elevated the wetland N2O emission potential. The abundance of NARG, NIRK, and NOSZ genes decreased significantly in October compared to June, indicating a decrease in the wetland N2O emission potential. Additionally, it was observed that soil methanotrophs were positively affected by NH4+ and TN in October, thereby reducing the wetland CH4 emission potential. Our research provides a systematic understanding of the impact of agricultural N pollution on marsh wetlands, which can inform strategies to protect wetland health.

Resilience of aerobic methanotrophs in soils; spotlight on the methane sink under agriculture.

Aerobic methanotrophs are a specialized microbial group, catalyzing the oxidation of methane. Disturbance-induced loss of methanotroph diversity/abundance, thus results in the loss of this biological methane sink. Here, we synthesized and conceptualized the resilience of the methanotrophs to sporadic, recurring, and compounded disturbances in soils. The methanotrophs showed remarkable resilience to sporadic disturbances, recovering in activity and population size. However, activity was severely compromised when disturbance persisted or reoccurred at increasing frequency, and was significantly impaired following change in land use. Next, we consolidated the impact of agricultural practices after land conversion on the soil methane sink. The effects of key interventions (tillage, organic matter input, and cover cropping) where much knowledge has been gathered were considered. Pairwise comparisons of these interventions to nontreated agricultural soils indicate that the agriculture-induced impact on the methane sink depends on the cropping system, which can be associated to the physiology of the methanotrophs. The impact of agriculture is more evident in upland soils, where the methanotrophs play a more prominent role than the methanogens in modulating overall methane flux. Although resilient to sporadic disturbances, the methanotrophs are vulnerable to compounded disturbances induced by anthropogenic activities, significantly affecting the methane sink function.

Variations of activity and community structure of nitrite-driven anaerobic methanotrophs in soils between native and invasive species in China's coastal wetlands

Nitrite-driven anaerobic oxidation of methane (nitrite-driven AOM), mediated by ‘Candidatus Methylomirabilis oxyfera’ (M. oxyfera)-related bacteria, is a newly-discovered CH4 consumption process in coastal wetlands. Although Spartina alterniflora invasion significantly affects CH4 emissions from coastal wetlands, its impact on the nitrite-driven AOM process and the underlying mechanisms remain unknown. Here, we examined nitrite-driven AOM activity and M. oxyfera-related bacterial community in four coastal wetlands along the southeastern coast of China, under invasive Spartina alterniflora and native plants, including Kandelia candel, Avicennia marina or Phragmites australis. Linear mixed-effects models indicated that the Spartina alterniflora invasion stimulated the overall nitrite-driven AOM activity by an average of 61.5% in coastal wetlands (p < 0.05), but had no impact on the M. oxyfera-related bacterial abundance (p > 0.05). The nitrite-driven AOM activity was 7.1 times higher under Spartina alterniflora than under native species in Yueqing Bay (p < 0.05), and was 34.7%, 8.9% and 15.1% higher under Spartina alterniflora than under native species in Hengsha Island, Jiulong River and Zhanjiang, respectively (p > 0.05). Spartina alterniflora invasion increased the bacterial abundance in Yueqing Bay and Jiulong River Estuary by 6.8 and 7.6 times, respectively, while decreased the abundance by 34.4% and 51.4%, respectively, in Hengsha Island and Zhanjiang (p > 0.05). The partial least squares path model indicated an indirect impact of Spartina alterniflora invasion on the nitrite-driven AOM activity through its effect on soil properties, primarily including dissolved organic carbon content and nitrate content. The Spartina alterniflora invasion did not greatly alter M. oxyfera-related bacterial community. Overall, we shed new light on the potential impact of Spartina alterniflora invasion on CH4 cycling in coastal wetlands.

Extreme drought alters methane uptake but not methane sink in semi-arid steppes of Inner Mongolia

Global climate change, particularly drought, is expected to alter grassland methane (CH4) oxidation, a key natural process against atmospheric greenhouse gas accumulation, yet the extent of this effect and its interaction with future atmospheric CH4 concentrations increases remains uncertain. To address this research gap, we measured CH4 flux during an imposed three-month rain-free period corresponding to a 100-year recurrence drought in soil mesocosms collected from 16 different Eurasian steppe sites. We also investigated the abundance and composition of methanotrophs. Additionally, we conducted a laboratory experiment to explore the impact of elevated CH4 concentration on the CH4 uptake capacity of grassland soil under drought conditions. We found that regardless of the type of grassland, CH4 flux was still being absorbed at its peak, meaning that all grasslands functioned as persistent CH4 sinks even when the soil water content (SWC) was <5 %. A bell-shaped relationship between SWC and CH4 uptake was observed in the soils. The average maximum CH4 oxidation rate in the meadow steppe was higher than that in the typical and desert steppe soils during extreme drought. The experimental elevation of atmospheric CH4 concentration counteracted the anticipated reduction in CH4 uptake related to physiological water stress on methanotrophic soil microbes under the drought stress. On the contrary, we found that across the regional scale, nitrogen, phosphorous, and total soil organic content played a crucial role in moderating the duration and magnitude of CH4 uptake with respect to SWC. USC-γ (Upland Soil Cluster γ) and JR-3 (Jasper Ridge Cluster) were the dominant group of soil methanotrophic bacteria in three types of grassland. However, the methanotrophic abundance, rather than the methanotrophic community composition, was the dominant microbiological factor governing CH4 uptake during the drought.

Reduction of soil methane emissions from croplands with 20–40 years of cultivation mediated by methane-metabolizing microorganisms

Reducing carbon emissions from cropland ecosystems is an important measure to achieve early carbon neutrality. However, how methane-metabolizing microorganisms affect methane emissions from cropland soils of different planting years is not known. In this study, we determined methane emissions from cropland soils of different tobacco-rice rotation years after rice harvesting. By mean of functional gene sequencing, we analyzed the relationship between methane-metabolizing microorganisms and methane emissions, and revealed the microbial mechanism of action for methane emissions from cropland soils. The results showed that the soil organic carbon content was higher (P < 0.05) and methane emissions were lower (P < 0.05) in cropland cultivated for 20–40 years (PY20). Soil methane emissions from PY20 cropland were reduced by 30.11% and 14.58% (P < 0.05) compared to cropland planted for 10–20 years and more than 40 years. The alpha diversity of methanogens communities was significantly lower in PY20 cropland soils, whereas the methanotrophs communities alpha diversity did not differ significantly between planting years. The methanogenic genus Methanocorpusculum was significantly and positively correlated with methane emissions. The relative abundance of Methanocorpusculum in PY20 cropland soil was lower (P < 0.05), and the relative abundance of Methylocystis, a type II methanotrophs with greater oxidizing capacity for methane, was higher (P < 0.05). Reducing PY20 cropland soil methane emissions by reducing methane production and enhancing methane oxidation. At the same time, more methanotrophs in PY20 cropland soil formed a molecular interactions network with methanogens. Planting years altered the diversity and composition of methane-metabolizing microbial communities and the interactions of different taxa, which in turn affected methane emissions. Cropland soils that have been cultivated for 20–40 years have lower methane production capacity and higher methane oxidation capacity, resulting in lower methane emissions. This study provides a scientific reference for the microbial action mechanism of soil methane emission from cropland under different planting years, with a view to contributing to carbon neutralization in cropland ecosystems.

Global assessment of soil methanotroph abundances across biomes and climatic zones: The role of climate and soil properties

The pmoA gene serves as a biomarker of the methane-oxidizing communities in soils. Therefore, much effort has been directed at quantifying the pmoA gene to quantify the abundances of methanotrophs at the local or regional scale, however, the abundances of methane-oxidizing bacteria as well as factors shaping the abundance of methane-oxidizing bacteria at the global scale remains poorly understood. To fill this knowledge gap, we performed a quantitative analysis of peer-reviewed publications to assess the distribution of the pmoA gene abundances across various biomes, climatic zones, land use, and between forest and grassland biomes, with 114 observations collected from 27 peer-reviewed articles. Results showed that the abundance of pmoA genes increased significantly with latitude, whereas a higher pmoA gene abundance was observed in the boreal forest than in cold grassland, dry grassland, temperate forest, and temperate grassland, while tropical grassland and the tropical forest did not differ significantly from other biomes in pmoA gene abundance. The PCA indicated that pmoA abundance was positively correlated with MAT and MAP but negatively correlated with pH. The TOC was as a key driver of pmoA gene abundance at a global scale. The abundance of the pmoA gene in tropical and boreal forests increased with TOC, while the pmoA gene abundance in temperate forests and grasslands decreased with TOC. The pmoA gene abundance in the tropical and subtropical zones increased with TOC while pmoA gene abundance in the temperate climatic zones decreased with TOC. The path model revealed a direct effect of vegetation cover on the pmoA gene abundance, but indirect effect of climate and soil properties on pmoA gene abundance via their direct effect on vegetation cover. We suggest that the changes of TOC and C:N ratio due changes of vegetation and climate across biomes may serve as a possible mechanism underlying the idiosyncratic effects of TOC on the abundance of methanotrophs in soils.

Depth-dependent patterns of activity and abundance of atmospheric methane-oxidizing bacteria in semiarid grassland on the Loess Plateau of China

High-affinity methanotrophs in upland soils are responsible for the well-known biological sink of atmospheric methane. However, the vertical distribution pattern of their abundance and activity remains largely unknown. Here, we collected soil samples in 2 cm intervals from the surface to a depth of 40 cm in a typical semiarid steppe in the Loess Plateau of China. We found a bell-shaped distribution of the atmospheric methane-oxidizing potential (atmMOP) along the soil depth, and its peak appeared in the 10–20 cm soil layers. The abundance of methanotrophs (dominated by the upland soil cluster gamma, USCγ) showed a similar vertical distribution pattern and was well correlated with the atmMOP (P < 0.01). Pearson correlation analysis and the structural equation model showed that pH and inorganic nitrogen concentration were the main environmental factors that affecting atmMOP and USCγ abundance.

Temporal and environmental factors drive community structure and function of methanotrophs in volcanic forest soils

Temporal and environmental factors drive community structure and function of methanotrophs in volcanic forest soils

Effects of fir-wood biochar on CH4 oxidation rates and methanotrophs in landfill cover soils packed at three different proctor compaction levels

Application of biochar to landfill cover soils can purportedly improve methane (CH4) oxidation rates, but understanding the combined effects of soil texture, compaction, and biochar on the activity and composition of the methanotrophs is limited. The amendment of wood biochar on two differently textured landfill cover soils at three compaction levels of the Proctor density was explored by analyzing changes in soil physical properties relevant to methane oxidation, the effects on CH4 oxidation rates, and the composition of the methanotrophic community. Loose soils with and without biochar were pre-incubated to equally elevate the CH4 oxidation rates. Hereafter, soils were compacted and re-incubated. Methane oxidation rates, gas diffusivity, water retention characteristics, and pore size distribution were analyzed on the compacted soils. The relative abundance of methanotrophic bacteria (MOB) was determined at the end of both the pre-incubation and incubation tests of the packed samples. Biochar significantly increased porosity at all compaction levels, enhancing diffusion coefficients. Also, a re-distribution in pore sizes was observed. Increased gas diffusivity from low compaction and amendment of biochar, though, did not reflect higher methane oxidation rates due to high diffusive oxygen fluxes over the limited height of the compacted soil specimens. All soils, with and without biochar, were strongly dominated by Type II methanotrophs. In the sandy soil, biochar amendment strongly increased MOB abundance, which could be attributed to a corresponding increase in the relative abundance of Methylocystis species, while no such response was observed in the clayey soil. Compaction did not change the community composition in either soil. Fir-wood biochar addition to landfill cover soils may not always enhance methanotrophic activity and hence reduce fugitive methane emissions, with the effect being soil-specific. However, especially in finer and more compacted soils, biochar amendment can maintain soil diffusivity above a critical level, preventing the collapse of methanotrophy.

Elevated and atmospheric‐level methane consumption by soil methanotrophs of three grasslands in China

AbstractBackgroundMethane (CH4) oxidation driven by soil aerobic methanotrophs demonstrates the capacity of grassland as a CH4 sink.MethodsIn this study, we compared the oxidation characteristics of atmospheric‐level and elevated concentration (10%) CH4 in a typical grassland (steppe) on the Loess Plateau, an alpine meadow (meadow) on the Qinghai‐Tibet Plateau, and an inland arid‐area artificial grassland (pasture) in northwest China and investigated the communities of active methanotrophs and their contribution to CH4 oxidation using DNA‐based stable‐isotope probing and Illumina Miseq sequencing.ResultsThe results showed that the oxidation of atmospheric CH4 only occurred in steppe and meadow soils where the USCγ group of methanotrophs was numerically dominant in the methanotroph community. Pasture soils, with their very low relative abundance of USCγ, did not show atmospheric CH4 oxidation. However, a DNA‐stable isotope probing experiment with 10% CH4 indicated that conventional CH4 oxidizers (Methylocaldum and Methylocystis) rather than USCγ communities assimilated significant amounts of 13CH4 for growth.ConclusionsThe CH4 oxidation mechanisms in the three experimental grassland soils varied significantly. The USCγ group may be obligate oligotrophic microorganisms or their growth requires specific unknown conditions.

The diversity of plant communities in different habitats can lead to distinct methanotrophic communities

Methanotrophic communities are susceptible to environmental interference in natural ecosystems. However, little is known about methanotrophs and their drivers in the riparian zone ecosystem. Therefore, the soil methanotrophic community structure, assembly process, and their driving factors were examined in five habitats in the riparian zone ecosystem of Three Gorges Reservoir in China. Soil samples were collected from the woody plant community, perennial plant community, annual plant community, perennial mixed annual plant community, and bare land in the riparian zone areas. We assessed plant community diversity, analyzed soil physiochemical properties, and measured enzyme activities to find the driving factors for the methanotrophic community. The findings revealed that Methylosarcina, Methylocystis, and rice paddy clusters dominated habitats. They preferred different pH levels and plant diversity. The diversity of the soil methanotrophic community was greater in vegetation-covered areas than on bare land. Likewise, the co-occurrence network of soil methanotrophs was more complex in vegetation-covered areas than in bare land, indicating a more stable community structure. Soil nitrogen, catalase, and plant diversity influence stability and diversity. During the transformation from bare land to plant community, the assembly process of the soil methanotrophic community converted from stochastic to deterministic processes, in which dispersal limitation and homogenous selection played prominent roles and were primarily influenced by soil pH and plant diversity. This research helps us understand the evolution of methanotrophs during vegetation restoration. It can also help us find plant communities that can effectively sequester carbon pools and plant them in riparian zones around reservoir systems to maintain soil and water quality.

Characterization of methanotrophic community and activity in landfill cover soils under dimethyl sulfide stress

Landfill cover soil is the environmental interface between landfills and the atmosphere and plays an important role in mitigating CH4 emission from landfills. Here, stable isotope probing microcosms with CH4 or CH4 and dimethyl sulfide (DMS) were carried out to characterize activity and community structure of methanotrophs in landfill cover soils under DMS stress. The CH4 oxidation activity in the landfill cover soils was not obviously influenced at the DMS concentration of 0.05%, while it was inhibited at the DMS concentrations of 0.1% and 0.2%. DMS-S was mainly oxidized to sulfate (SO42-) in the landfill cover soils. In the landfill cover soils, DMS could inhibit the expression of bacteria and decrease the abundances of pmoA and mmoX genes, while it could prompt the expression of pmoA and mmoX genes. γ-Proteobacteria methanotrophs including Methylocaldum, Methylobacter, Crenothrix and unclassified Methylococcaceae and α-Proteobacteria methanotrophs Methylocystis dominated in assimilating CH4 in the landfill cover soils. Of them, Methylobacter and Crenothrix had strong tolerance to DMS or DMS could promote the growth and activity of Methylobacter and Crenothrix, while Methylocaldum had weak tolerance to DMS and showed an inhibitory effect. Metagenomic analyses showed that methanotrophs had the genes of methanethiol oxidation and could metabolize CH4 and methanethiol simultaneously in the landfill cover soils. These findings suggested that methanotrophs might metabolize sulfur compounds in the landfill cover soils, which may provide the potential application in engineering for co-removal of CH4 and sulfur compounds.

Effects of abrupt and gradual increase of atmospheric CO2 concentration on methanotrophs in paddy fields

The simulation of abrupt atmospheric CO2 increase is a common way to examine the response of soil methanotrophs to future climate change. However, atmosphere is undergoing a gradual CO2 increase, and it is unknown whether the previously reported response of methanotrophs to abrupt CO2 increase can well represent their response to the gradual increase. To improve the understanding of the effect of elevated CO2 (eCO2) on methanotrophs in paddy ecosystems, the methane oxidation potential and communities of methanotrophs were examined via open top chambers under the three following CO2 treatments: an ambient CO2 concentration (AC); an abrupt CO2 increase by 200 ppm above AC (AI); a gradual CO2 increase by 40 ppm each year until 200 ppm above AC (GI). Relative to AC treatment, AI and GI treatments significantly (p < 0.05) increased the methane oxidation rate by 43.8% and 36.7%, respectively, during rice growth period. Furthermore, the abundance of pmoA genes was significantly (p < 0.05) increased by 62.4% and 32.5%, respectively, under AI and GI treatments. However, there were no significant variations in oxidation rate or gene abundance between the two eCO2 treatments. In addition, no obvious change of overall community composition of methanotrophs was observed among treatments, while the proportions of Methylosarcina and Methylocystis significantly (p < 0.05) changed. Taken together, our results indicate similar response of methanotrophs to abrupt and gradual CO2 increase, although the magnitude of response under gradual increase was smaller and the abrupt increase may somewhat overestimate the response.

Aerobic and denitrifying methanotrophs: Dual wheels driving soil methane emission reduction

The greenhouse gas methane in soils has been considered to be consumed mainly by aerobic methane-oxidizing bacteria for a long time. In the last decades, the discovery of anaerobic methanotrophs greatly complemented the methane cycle, but their contribution rates and ecological significance in soils remain undescribed. In this work, the soil samples from forest, grassland and cropland in four different climatic regions were collected to investigate these conventional and novel methanotrophs. A dual-core microbial methane sink, responsible for over 80 % of soil methane emission reduction, was unveiled. The aerobic core was performed by aerobic methanotrophic bacteria in topsoil, who played important roles in stabilizing bacterial communities. The anaerobic core was denitrifying methanotrophs in anoxic soils, including denitrifying methanotrophic bacteria from NC10 phylum and denitrifying methanotrophic archaea from ANME-2d clade. They were ubiquitous in terrestrial soils and potentially led to around 50 % of the total methane removal. Human activities such as livestock farming and rice cultivation further promoted the contribution rates of these denitrifying methanotrophs. This work elucidated the emission reduction contribution of different methanotrophs in the continental setting, which would help to reduce uncertainties in the estimations of the soil methane emission.

Mining the landfill soil metagenome for denitrifying methanotrophic taxa and validation of methane oxidation in microcosm

In the present study, the microbial community residing at different depths of the landfill was characterized to assess their roles in serving as a methane sink. Physico-chemical characterization revealed the characteristic signatures of anaerobic degradation of organic matter in the bottom soil (50–60 cm) and, active process of aerobic denitrification in the top soil (0–10 cm). This was also reflected from the higher abundance of bacterial domain in the top soil metagenome represented by dominant phyla Proteobacteria and Actinobacteria which are prime decomposers of organic matter in landfill soils. The multiple fold higher relative abundances of the two most abundant genera; Streptomyces and Intrasporangium in the top soil depicted greater denitrifying taxa in top soil than the bottom soil. Amongst the aerobic methanotrophs, the genera Methylomonas, Methylococcus, Methylocella, and Methylacidiphilum were abundantly found in the top soil metagenome that were essential for oxidizing methane generated in the landfill. On the other hand, the dominance of archaeal domain represented by Methanosarcina and Methanoculleus in the bottom soil highlighted the complete anaerobic digestion of organic components via acetoclasty, carboxydotrophy, hydrogenotrophy, methylotrophy. Functional characterization revealed a higher abundance of methane monooxygenase gene in the top soil and methyl coenzyme M reductase gene in the bottom soil that correlated with the higher relative abundance of aerobic methanotrophs in the top soil while methane generation being the active process in the highly anaerobic bottom soil in the landfill. The activity dependent abundance of endogenous microbial communities in the different zones of the landfill was further validated by microcosm studies in serum bottles which established the ability of the methanotrophic community for methane metabolism in the top soil and their potential to serve as sink for methane. The study provides a better understanding about the methanotrophs in correlation with their endogenous environment, so that these bacteria can be used in resolving the environmental issues related to methane and nitrogen management at landfill site.

Atmospheric methane oxidation is affected by grassland type and grazing and negatively correlated to total soil respiration in arid and semiarid grasslands in Inner Mongolia

Methane (CH4) is an important trace greenhouse gas and atmospheric CH4 uptake by high-affinity methanotrophs in grassland soil accounts for an important proportion of the terrestrial CH4 sink. However, our understanding of the comprehensive effects of grassland type and grazing treatment on active soil methanotrophs and atmospheric CH4 uptake is still under debate. This study investigates the impact of grazing on CH4 oxidation rate and active atmospheric CH4 oxidizing methanotroph communities in two arid and semiarid grassland ecosystems (meadow and desert) by detecting transcripts of methane monooxygenase (pmoA) genes. Atmospheric CH4 oxidation rates differed according to grassland type and grazing treatment. The highest activity was found in desert grasslands with moderate grazing and the lowest activity in meadow grasslands with exclosures. The differences in activities were linked with changes in abundance, composition and co-occurrence network patterns of active methanotrophs and CO2 production rate. Redundancy, correlation and random forest analyses indicated that pmoA transcripts, available phosphorus (AP), NO3−-N, and CO2 production rate were the most important factors predicting active methanotroph community composition and atmospheric CH4 oxidation activity in these grassland ecosystems. A glucose amendment incubation experiment showed that addition of glucose increased heterotrophic microbial respiration and inhibited atmospheric CH4 oxidation. This study provides evidence that CO2 production rate is an important factor associated with atmospheric CH4 oxidation activity in arid and semiarid grassland ecosystems and suggests that interactions between methanotrophs and other heterotrophs influence methanotroph activity in grassland ecosystems.

Sheep grazing impacts on soil methanotrophs and their activity in typical steppe in the Loess Plateau China

Soil methanotrophs are the only biological sink for atmospheric methane (CH4). The activity and the diversity of methanotrophic communities in grassland soils can be impacted by animal grazing. In this study, soils were collected from a 17-year running grazing intensity trial in a typical steppe in the Loess Plateau, China to examine the responses of CH4 oxidation rate and active methanotroph composition and abundance to different levels of sheep grazing. Soils were collected from summer grazed pastures at no (0 sheep ha−1), low (2.67 sheep ha−1), moderate (5.33 sheep ha−1) and high (8.67 sheep ha−1) levels of grazing. We found that all soils were able to oxidize atmospheric and high concentration (10%) CH4 through soil methanotrophs. Compared to ungrazed soils, the atmospheric CH4 oxidation rate and methanotroph abundance were higher in low and high grazed soils but lower in moderately grazed soils. Across all soils, the in-situ methanotroph community was dominated by upland soil cluster gamma methanotrophs and potentially contributed to the atmospheric concentration CH4 oxidation. Soil methanotroph community responses to the high 13CH4 concentration revealed an increase in methanotroph abundance and a transition of the active methanotroph community to traditional Type I (Methylocaldum and Methylobacter) and Type II (Methylocystis) methanotrophs. Methylocaldum responses to the high CH4 concentration were greater in highly grazed soil than in ungrazed soil. The activity of Methylobacter and Methylocystis under high CH4 concentrations was reduced by high grazing intensity. This study provides evidence that recent intensifications of animal grazing can result in particular community assembly of microbial methane oxidizers responsible for CH4 sink capabilities of grassland soils.