Methanotrophic Activity Research Articles

Influence of temperature on the δ13C values and distribution of methanotroph‐related hopanoids in Sphagnum‐dominated peat bogs

Methane emissions from peat bogs are mitigated by methanotrophs, which live in symbiosis with peat moss (e.g. Sphagnum). Here, we investigate the influence of temperature and resultant changes in methane fluxes on Sphagnum and methanotroph‐related biomarkers, evaluating their potential as proxies in ancient bogs. A pulse‐chase experiment using 13C‐labelled methane in the field clearly showed label uptake in diploptene, a biomarker for methanotrophs, demonstrating in situ methanotrophic activity in Sphagnum under natural conditions. Peat cores containing live Sphagnum were incubated at 5, 10, 15, 20 and 25°C for two months, causing differences in net methane fluxes. The natural δ13C values of diploptene extracted from Sphagnum showed a strong correlation with temperature and methane production. The δ13C values ranged from −34‰ at 5°C to −41‰ at 25°C. These results are best explained by enhanced expression of the methanotrophic enzymatic isotope effect at higher methane concentrations. Hence, δ13C values of diploptene, or its diagenetic products, potentially provide a useful tool to assess methanotrophic activity in past environments. Increased methane fluxes towards Sphagnum did not affect δ13C values of bulk Sphagnum and its specific marker, the C23 n‐alkane. The concentration of methanotroph‐specific bacteriohopanepolyols (BHPs), aminobacteriohopanetetrol (aminotetrol, characteristic for type II and to a lesser extent type I methanotrophs) and aminobacteriohopanepentol (aminopentol, a marker for type I methanotrophs) showed a non‐linear response to increased methane fluxes, with relatively high abundances at 25°C compared to those at 20°C or below. Aminotetrol was more abundant than aminopentol, in contrast to similar abundances of aminotetrol and aminopentol in fresh Sphagnum. This probably indicates that type II methanotrophs became prevalent under the experimental conditions relative to type I methanotrophs. Even though BHP concentrations may not directly reflect bacterial activity, they may provide insight into the presence of different types of methanotrophs.

Diversity of active root-associated methanotrophs of\xa0three\xa0emergent\xa0plants in\xa0a eutrophic wetland in northern China

Root-associated aerobic methanotrophs play an important role in regulating methane emissions from the wetlands. However, the influences of the plant genotype on root-associated methanotrophic structures, especially on active flora, remain poorly understood. Transcription of the pmoA gene, encoding particulate methane monooxygenase in methanotrophs, was analyzed by reverse transcription PCR (RT-PCR) of mRNA isolated from root samples of three emergent macrophytes, including Phragmites australis, Typha angustifolia, and Schoenoplectus triqueter (syn. Scirpus triqueter L.) from a eutrophic wetland. High-throughput sequencing of pmoA based on DNA and cDNA was used to analyze the methanotrophic community. Sequencing of cDNA pmoA amplicons confirmed that the structure of active methanotrophic was not always consistent with DNA. A type I methanotroph, Methylomonas, was the most active group in P. australis, whereas Methylocystis, a type II methanotroph, was the dominant group in S. triqueter. In T. angustifolia, these two types of methanotroph existed in similar proportions. However, at the DNA level, Methylomonas was predominant in the roots of all three plants. In addition, vegetation type could have a profound impact on root-associated methanotrophic community at both DNA and cDNA levels. These results indicate that members of the genera Methylomonas (type I) and Methylocystis (type II) can significantly contribute to aerobic methane oxidation in a eutrophic wetland.

Effect of phosphorus amendments on rice rhizospheric methanogens and methanotrophs in a phosphorus deficient soil

Methane emission can be affected by soil fertility, but little is known about the influence of soil phosphorus (P) nutrition on methane production and oxidation processes. In this study, a pot experiment was conducted to explore the effects of P amendments on activity, abundance and community composition of soil methanogens and methanotrophs using P deficient paddy soil. The abundance and community composition of methanogens and methanotrophs, methane production and oxidation potentials were investigated by real-time quantitative PCR, Miseq high-throughput sequencing and biochemical assays, respectively. The results showed that although P amendments induced increases of both methanogenic and methanotrophic abundances and potential activities within bulk soils, the increases were relatively small. In contrast, P applications resulted in large and significant increases in the copy numbers and potential activity of methanogens within rhizosphere soils, whereas, this phenomenon was not detected for methanotrophs. Moreover, the methanogenic community structure remained similar amongst the P amendment treatments for both rhizosphere and bulk soils. For methanotrophs, P application induced clear shifts in the community composition within rhizosphere soils but not in bulk soils, where the relative abundance of type I methanotrophs increased whilst type II decreased. Our data indicate that the application of phosphate to P deficient paddy soils could preferentially stimulate the abundance and activity of methanogens over methanotrophs within the rice rhizosphere. Ultimately, improving plant growth by P input may accelerate methane emissions through stimulating rhizosphere methanogenic populations without a concomitant increase in the methanotrophic compartment.

The link between Soil Methane Oxidation Rate and Abundance of Methanotrophs Estimated by Quantitative PCR

The pmoA gene number is considered as a soil microbiological parameter indicating abundance and potential activity of methanotrophic bacteria. The efficiency of this parameter for prediction and modeling of the real soil methane consumption rates remains an open issue. In the current study rate of methane oxidation by soil at its ambient concentration and the number of the pmoA genes determined by quantitative polymerase chain reaction were compared. Soil samples were collected in May, July, and September 2018 in the middle taiga subzone forest ecosystems near Khanty-Mansiysk, Russia. Soil methane oxidation rate varied from 0.01 to 8 ng СН4/g dry weight per hour. The pmoA gene numbers per g of dry weight varied from 107 to 109. The correlation between these two parameters became smaller as the scale changed from the soil profile level to ecosystem and interseasonal levels. Methane oxidation rate increased significantly above the threshold methanotroph abundance of 2 × 108pmoA genes/g. Within the intervals below and above this threshold value, no significant changes in methane oxidation rate occurred while methanotroph abundance increased. Thus, quantification of methanotroph abundance alone is insufficient for assessment of methanotrophic activity in upland soils, and the effect of other factors should be considered.

Methanotrophy in geothermal soils, an overlooked process: The example of Nisyros island (Greece)

A multidisciplinary field campaign was carried out at Nisyros Island (Greece). Hydrothermal gases were sampled and analysed, and CH4 and CO2 fluxes from the soils were measured with the accumulation chamber method. The sampling area (Lakki plain) covers an area of about 0.08 km2, and includes the main fumarolic areas of Kaminakia, Stefanos, Ramos, Lofos and Phlegeton. Flux values measured at 130 sites range from −3.4 to 1420 mg m−2 d−1 for CH4 and from 0.1 to 383 g m−2 d−1 for CO2. The fumarolic areas show very different CH4 degassing patterns, Kaminakia showing the highest CH4 output values (about 0.8 t a−1 from an area of about 30,000 m2) and Phlegeton the lowest (about 0.01 t a−1 from an area of about 2500 m2). The total output from the entire geothermal system of Nisyros should not exceed 2 t a−1. Previous indirect estimates of the CH4 output at Nisyros, based on soil CO2 output and CH4/CO2 ratios in fumarolic gases, were more than one order of magnitude higher. The present work further underscores the utmost importance of direct CH4 flux data because indirect methods totally disregard methanotrophic activity within the soil. Ten soil samples were collected for CH4 consumption experiments and for metagenomic analysis. Seven of the soil samples showed small but significant CH4 consumption (up to 39.7 ng g−1 h−1) and were positive for the methanotrophs-specific gene (pmoA) confirming microbial CH4 oxidation in the soil, notwithstanding the harsh environmental conditions (high temperature and H2S concentrations and low pH).

Methane emissions and associated microbial activities from paddy salt-affected soil as influenced by biochar and cow manure addition

Although previous studies showed that biochar can mitigate methane emissions through microbial activities from paddy fields, little is known about its effects on salt-affected soil. The current study aims to examine the interactive effect of biochar and cow manure (CM) on (1) methane emissions from salt-affected soil and (2) methanogenic and methanotrophic activities to identify potential mechanisms for the emissions. A two-factor pot experiment was set up, following a randomized complete block design with four replicates. Paddy rice (Oryza sativa L.) was grown on six treatments (no CM + no biochar; no CM + rice husk biochar; no CM + rice straw biochar; CM + no biochar; CM + rice husk biochar; CM + rice straw biochar). Methane emissions from salt-affected soil were relatively low and CM addition significantly increased CH4 emissions (by 801%). For the CM treatments, biochar addition significantly reduced methane emissions (by 28 to 680%), but for the non-CM treatments, biochar addition showed no clear effect. The increase in methane emissions by CM could be involved in the improved relative abundance of methanogenic and methanotrophic genes. In contrast, the reduction of methane emissions by biochar was likely related to the reduced abundance of methanogenic and increased that of methanotrophic genes. In brief, low methane emissions from salt-affected soil were increased by CM addition and biochar addition could mitigate the CM's effect. Balancing methanogenic and methanotrophic activities could serve as a major mechanism in determining methane emissions from salt-affected soil added with cow manure and biochar.

Effects of oxygen tension on the microbial community and functional gene expression of aerobic methane oxidation coupled to denitrification systems.

Aerobic CH4 oxidation coupled to denitrification (AME-D) can not only mitigate the emission of greenhouse gas (e.g., CH4) to the atmosphere, but also reduce NO3- and/or NO2- and alleviate nitrogen pollution. The effects of O2 tension on the community and functional gene expression of methanotrophs and denitrifiers were investigated in this study. Although higher CH4 oxidation occurred in the AME-D system with an initial O2 concentration of 21% (i.e., the O2-sufficient condition), more NO3--N was removed at the initial O2 concentration of 10% (i.e., the O2-limited environment). Type I methanotrophs, including Methylocaldum, Methylobacter, Methylococcus, Methylomonas, and Methylomicrobium, and type II methanotrophs, including Methylocystis and Methylosinus, dominated in the AME-D systems. Compared with type II methanotrophs, type I methanotrophs were more abundant in the AME-D systems. Proteobacteria and Actinobacteria were the main denitrifiers in the AME-D systems, and their compositions varied with the O2 tension. Quantitative PCR of the pmoA, nirS, and 16S rRNA genes showed that methanotrophs and denitrifiers were the main microorganisms in the AME-D systems, accounting for 46.4% and 24.1% in the O2-limited environment, respectively. However, the relative transcripts of the functional genes including pmoA, mmoX, nirK, nirS, and norZ were all less than 1%, especially the functional genes involved in denitrification under the O2-sufficient condition, likely due to the majority of the denitrifiers being dormant or even nonviable. These findings indicated that an optimal O2 concentration should be used to optimize the activity and functional gene expression of aerobic methanotrophs and denitrifiers in AME-D systems.

Methane emission and methanotrophic activity in groundwater-fed drinking water treatment plants

Abstract Groundwater for drinking water production may contain dissolved methane (CH4) at variable concentrations. Most of this important greenhouse gas is often vented to the atmosphere during primary aeration and gas stripping processes at drinking water treatment plants (DWTPs). However, limited information exists regarding emission and fate of methane at many groundwater-fed DWTPs. This study estimates emission of methane from 1,004 DWTPs in Denmark and includes data from 3,068 groundwater wells. The fate of methane and occurrence of methane oxidizing bacteria in DWTPs was examined, including the potential role in ammonia removal. Methane emission from Danish DWTPs was estimated to be 1.38–2.95 × 10−4 Tg CH4/y which corresponds to 0.05–0.11% of the national anthropogenic methane emission. Trace levels of methane remained in the drinking water after primary aeration and entered the sand filters as a potential microbial substrate. Methanotrophic bacteria and active methane oxidation was always detected in the sand filters at groundwater-fed DWTPs. Methanotrophic consortia isolated from DWTP sandfilters were inoculated into laboratory-scale sand filters and the activity confirmed that methanotrophic consortia can play a role in the removal of ammonia via assimilation and co-oxidation. This suggests a potential for facilitating the removal of inorganic constituents from drinking water using methane as a co-substrate.

Disentangling abiotic and biotic controls of aerobic methane oxidation during re-colonization

Aerobic methane oxidation is driven by both abiotic and biotic factors, which are often confounded in the soil environment. Using a laboratory-scale reciprocal inoculation experiment with two native soils (paddy and upland agricultural soils) and the gamma-irradiated fraction of these soils, we aim to disentangle and determine the relative contribution of abiotic (i.e., soil edaphic properties) and biotic (i.e., initial methanotrophic community composition) controls of methane oxidation during re-colonization. Methane uptake was appreciably higher in incubations containing gamma-irradiated paddy than upland soil despite the initial difference in the methanotrophic community composition. This suggested an overriding effect of the soil edaphic properties, which positively regulated methane oxidation. Community composition was similar in incubations with the same starting inoculum, based on quantitative and qualitative pmoA gene analyses. Thus, results suggested that the initial community composition affects the trajectory of community succession to an extent, but not at the expense of the methanotrophic activity under high methane availability. Still, methane oxidation was affected more by soil edaphic properties than by the initial composition of the methanotrophic community.

Water reservoirs are important sinks for greenhouse gases

Water reservoirs are considered as important sources and sinks for greenhouse gases (GHG). There are limited studies that have investigated potential sinks in water reservoirs and this has led to the production of the unreal GHG budgets for water reservoirs. This study discusses the possible GHG sinks in water reservoirs, including carbon deposition in sediments, primary production in aqueous environments, induced vegetation growth in riparian zones and alternation in soil methanotrophic activity along the shoreline. Organic carbon deposition in water reservoirs is an important anthropogenic carbon sink and a substantial portion of carbon deposition is stored in sediment. The primary production of reservoirs as an important carbon sink is not well understood. Damming increases the water table and in riparian zones extends vegetation into new areas. Vegetation growth in areas that had limited plant cover may lead to higher carbon sequestration in soils. These changes in the carbon content of soils along shorelines should be considered as carbon sinks for water reservoirs. The improved methanotrophic activity in soils can be found in dry regions where severe soil moisture stress inhibits methanotrophic activity. Generally, to generate a real estimation of the GHG budget of water reservoirs, all sinks should be included in model development in future studies.

Microbial consortia including methanotrophs: some benefits of living together.

With the progress of biotechnological research and improvements made in bioprocessing with pure cultures, microbial consortia have gained recognition for accomplishing biological processes with improved effectiveness. Microbes are indispensable tool in developing bioprocesses for the production of bioenergy and biochemicals while utilizing renewable resources due to technical, economic and environmental advantages. They communicate with specific cohorts in close proximity to promote metabolic cooperation. Use of positive microbial associations has been recognized widely, especially in food industries and bioremediation of toxic compounds and waste materials. Role of microbial associations in developing sustainable energy sources and substitutes for conventional fuels is highly promising with many commercial prospects. Detoxification of chemical contaminants sourced from domestic, agricultural and industrial wastes has also been achieved through microbial catalysis in pure and co-culture systems. Methanotrophs, the sole biological sink of greenhouse gas methane, catalyze the methane monooxygenasemediated oxidation of methane to methanol, a high energy density liquid and key platform chemical to produce commodity chemical compounds and their derivatives. Constructed microbial consortia have positive effects, such as improved biomass, biocatalytic potential, stability etc. In a methanotroph-heterotroph consortium, non-methanotrophs provide key nutrient factors and alleviate the toxicity from the culture. Non-methanotrophic organisms biologically stimulate the growth and activity of methanotrophs via production of growth stimulators. However, methanotrophs in association with co-cultured microorganisms are in need of further exploration and thorough investigation to study their interaction mode and application with improved effectiveness.

Novel facultative Methylocella strains are active methane consumers at terrestrial natural gas seeps

BackgroundNatural gas seeps contribute to global climate change by releasing substantial amounts of the potent greenhouse gas methane and other climate-active gases including ethane and propane to the atmosphere. However, methanotrophs, bacteria capable of utilising methane as the sole source of carbon and energy, play a significant role in reducing the emissions of methane from many environments. Methylocella-like facultative methanotrophs are a unique group of bacteria that grow on other components of natural gas (i.e. ethane and propane) in addition to methane but a little is known about the distribution and activity of Methylocella in the environment. The purposes of this study were to identify bacteria involved in cycling methane emitted from natural gas seeps and, most importantly, to investigate if Methylocella-like facultative methanotrophs were active utilisers of natural gas at seep sites.ResultsThe community structure of active methane-consuming bacteria in samples from natural gas seeps from Andreiasu Everlasting Fire (Romania) and Pipe Creek (NY, USA) was investigated by DNA stable isotope probing (DNA-SIP) using 13C-labelled methane. The 16S rRNA gene sequences retrieved from DNA-SIP experiments revealed that of various active methanotrophs, Methylocella was the only active methanotrophic genus common to both natural gas seep environments. We also isolated novel facultative methanotrophs, Methylocella sp. PC1 and PC4 from Pipe Creek, able to utilise methane, ethane, propane and various non-gaseous multicarbon compounds. Functional and comparative genomics of these new isolates revealed genomic and physiological divergence from already known methanotrophs, in particular, the absence of mxa genes encoding calcium-containing methanol dehydrogenase. Methylocella sp. PC1 and PC4 had only the soluble methane monooxygenase (sMMO) and lanthanide-dependent methanol dehydrogenase (XoxF). These are the first Alphaproteobacteria methanotrophs discovered with this reduced functional redundancy for C-1 metabolism (i.e. sMMO only and XoxF only).ConclusionsHere, we provide evidence, using culture-dependent and culture-independent methods, that Methylocella are abundant and active at terrestrial natural gas seeps, suggesting that they play a significant role in the biogeochemical cycling of these gaseous alkanes. This might also be significant for the design of biotechnological strategies for controlling natural gas emissions, which are increasing globally due to unconventional exploitation of oil and gas.

Thermophilic methanotrophs: in hot pursuit

Methane is a potent greenhouse gas responsible for 20-30% of global climate change effects. The global methane budget is ∼500-600 Tg y-1, with the majority of methane produced via microbial processes, including anthropogenic-mediated sources such as ruminant animals, rice fields, sewage treatment facilities and landfills. It is estimated that microbially mediated methane oxidation (methanotrophy) consumes >50% of global methane flux each year. Methanotrophy research has primarily focused on mesophilic methanotrophic representatives and cooler environments such as freshwater, wetlands or marine habitats from which they are sourced. Nevertheless, geothermal emissions of geological methane, produced from magma and lithosphere degassing micro-seepages, mud volcanoes and other geological sources, contribute an estimated 33-75 Tg y-1 to the global methane budget. The aim of this review is to summarise current literature pertaining to the activity of thermophilic and thermotolerant methanotrophs, both proteobacterial (Methylocaldum, Methylococcus, Methylothermus) and verrucomicrobial (Methylacidiphilum). We assert, on the basis of recently reported molecular and geochemical data, that geothermal ecosystems host hitherto unidentified species capable of methane oxidation at higher temperatures.

Comparison of the methane-oxidizing capacity of landfill cover soil amended with biochar produced using different pyrolysis temperatures

The in-situ mitigation of methane (CH4) in landfill gas using landfill cover soil (LCS) is a cost-effective approach, but its efficiency needs to be enhanced. In this study, we incorporated an enriched methane-oxidizing bacteria (MOB) consortium into LCS and established four biochar-amended LCS groups with biochar produced at 300 °C (BC300), 400 °C (BC400), 500 °C (BC500), and 600 °C (BC600). The purpose was to evaluate the CH4 oxidation capacity of biochar-amended LCS after inoculation with MOB and to investigate how the physicochemical properties of biochar that are influenced by the pyrolysis temperature affect the performance and microbial activity of biochar-amended LCS. It was found that a 15% volume ratio (representing a mass ratio of 2.49%–2.78%) for biochar amendment in LCS enhanced CH4 removal efficiency, with the highest removal observed to be 46% for BC400-amended LCS compared to 30% for the original LCS. In addition, CH4 adsorption by the biochar was not observed, and a 15% mass ratio for biochar in the LCS had no or a negative impact. Besides improving the water-holding capacity and gas permeability of LCS, other possible advantages of biochar amendment in terms of CH4 oxidization include greater retention of nutrients, electron acceptors, and exchangeable cations, as well as introducing iron ions. It was also found that CH4 oxidation capacity and the methanotroph activity of biochar-amended LCS did not continue to increase with higher pyrolysis temperatures, even though higher micropore volumes and surface areas were obtained at higher pyrolysis temperatures. From this study, BC400 was identified as the optimal choice for the best performance in terms of enhancing both the CH4 oxidation capacity of the amended LCS and the growth of type II methanotroph Methylocystaceae, which can possibly be attributed to having the highest cation exchange capacity of the four biochars.

Coupled steel slag and biochar amendment correlated with higher methanotrophic abundance and lower CH4 emission in subtropical paddies.

Aerobic methanotrophs in paddies serve as methane (CH4) filters and thereby reduce CH4 emissions. Amending soil with waste products can mitigate CH4 emissions in crops, but little is known about the impacts of amendments with steel slag and biochar on the populations and activities of aerobic methanotrophs in rice cropland. We used real-time quantitative PCR detecting system and high-throughput sequencing to determine the effects of slag and biochar amendments on CH4 emission, abundance, and community structure of methanotrophs, and the relationships between soil properties and the abundance and community composition of methanotrophs during the rice growing season in both early and late paddies. Soil salinity and pH were significantly higher for an amendment with both slag and biochar than the control in both the early and late paddies, and pH was significantly higher for a slag amendment in the late paddy. Cumulative CH4 emission was lower for the slag and slag + biochar amendments than the control in early paddy by-34.1%. Methanotrophic abundance was three- and sixfold higher for the slag + biochar amendment than the control in the early and late paddies (p < 0.05), respectively. The abundance of different groups of methanotrophs varied among the treatments. The relative abundance of Methylosarcina was higher for the slag amendment than the control, and the relative abundance of Methylomonas was lower for biochar, and slag + biochar amendments than the control. The relative abundance of Methylocystis was higher for the slag and slag + biochar amendments than the control in the early paddy, and the relative abundance of Methylocystis was higher for the slag, biochar, and slag + biochar amendments in the late paddy. Univariate and multivariate analyses indicated that the higher abundance of methanotrophic bacteria for the slag and slag + biochar amendments was correlated with soil pH, salinity, soil organic carbon, and C/N ratio, and the relative abundances of Methylocystis, Methylomonas, and Methylosarcina were associated with the effective mitigation of CH4 emission in the paddies. A discriminant general analysis indicated that the total population of methanotrophs was larger for the slag + biochar amendment than the control, and that this effect was only weakly correlated with changes in the soil properties, demonstrating that this effect on the size and species composition of methanotrophic soil populations was mostly associated with a direct effect of the slag + biochar amendment.

Anaerobic methane oxidation coupled to chromate reduction in a methane-based membrane biofilm batch reactor.

Chromate can be reduced by methanotrophs in a membrane biofilm reactor (MBfR). In this study, we cultivated a Cr(VI)-reducing biofilm in a methane (CH4)-based membrane biofilm batch reactor (MBBR) under anaerobic conditions. The Cr(VI) reduction rate increased to 0.28 mg/L day when the chromate concentration was ≤ 2.2 mg/L but declined sharply to 0.01 mg/L day when the Cr(VI) concentration increased to 6 mg/L. Isotope tracing experiments showed that part of the 13C-labeled CH4 was transformed to 13CO2, suggesting that the biofilm may reduce Cr(VI) by anaerobic methane oxidation (AnMO). Microbial community analysis showed that a methanogen, i.e., Methanobacterium, dominated in the biofilm, suggesting that this genus is probably capable of carrying out AnMO. The abundance of Methylomonas, an aerobic methanotroph, decreased significantly, while Meiothermus, a potential chromate-reducing bacterium, was enriched in the biofilm. Overall, the results showed that the anaerobic environment inhibited the activity of aerobic methanotrophs while promoting AnMO bacterial enrichment, and high Cr(VI) loading reduced Cr(VI) flux by inhibiting the methane oxidation process.

Methane sources and sinks in karst systems: The Nerja cave and its vadose environment (Spain)

Karst caves are considered a natural sink of atmospheric methane (CH4). Studies generally focus on measuring CH4 within the cave environment, and little information is available about the factors influencing CH4 abundance, such as the surrounding vadose and saturated zones of the aquifer, inputs of carbon dioxide (CO2) – a potential precursor of CH4 – and methanotrophic bacteria, which is likely the main cause of CH4 consumption. In this paper we report the first study of CH4 budget in Nerja, one of the main karst caves in Spain, based on seasonal monitoring of CH4 and CO2 concentration and stable C isotopic ratio in the cave system, integrated with analogue data from the underlying and overlying saturated/vadose zone, and methanotrophic bacteria activity (rDNA and Polymerase Chain Reaction analyses) in cave sediments and water. The results show that the cave environment consumes, via methanotrophic activity and through γ- and α–Proteobacteria, CH4 coming from both the atmosphere and the vadose/saturated zones of the aquifer, where it is produced microbially. However, vadose zone methanogenesis may seasonally exceed the methanotrophy capacity of the cave, resulting in a net CH4 increase in it. This competition process may be an important factor limiting the sink potential of karst caves.

Potential methane production and oxidation along the soil chronosequence of the Rotmoos glacier forefield

Summary Five differently developed soils aged 6, 35, 80, 150, and &gt;5000 years with the same bedrock and the same (current) climate conditions were chosen to assess abiotic and enzymatic properties as well as methanogenic and methanotrophic activities. Most abiotic properties (dry weight, pH, soil organic matter, and ammonium content), enzyme activities (dehydrogenase [DH] activity, ammonification [AM] rate, dimethylsulfoxide reduction), and potential methane oxidation (PoMO) per gram of dry weight (DW) increased with soil age. In contrast, potential methane production (PoMP) as well as the nitrate content per gram of DW and most enzymatic properties per gram of soil organic matter (SOM) did not increase with soil age but reached its maximum in the middle-aged soils (80–150 years). Our results show that (i) microbial activity does not consequently increase with SOM content/soil age; (ii) methane production can be measured in undeveloped soils, whereas methane oxidation is more restricted to fully developed soils; and (iii) certain soil modifications (change in water content, ammonium addition) could influence potential methane production/oxidation. When considering the concurrent release of raw soil because of the melting of perpetual ice, these data could help to better understand and assess the consequences of global change.

The response of methanotrophs to additions of either ammonium, nitrate or urea in alpine swamp meadow soil as revealed by stable isotope probing.

Different forms of nitrogen (N) are deposited on the Qinghai-Tibetan plateau (QTP), while their differential effects on soil methanotrophs and their activity remain elusive. We constructed microcosms amended with different N fertilizers (ammonia, nitrate and urea) using the soils sampled from a swamp meadow on the QTP. The responses of active methanotrophs to different forms of nitrogen were determined by stable isotope probing with 5% 13C-methane. At the early stage of incubation, all N fertilizers, especially urea, suppressed methane oxidation compared with the control. The methane oxidation rate increased during the incubation, suggesting an adaptation and stimulation of some methanotrophs to elevated methane. At the onset of the incubation, the type II methanotrophs Methylocystis were most abundant, but decreased during the incubation and were replaced by the type Ia methanotrophs Methylomonas. Ammonia and urea had similar effects on the methanotroph communities, both characterized by an elevation in the proportion of Methylobacter and more diverse methanotroph communities. Nitrate had less effect on the methanotroph community. Our results uncovered the active methanotrophs responding to different nitrogen forms, and suggested that urea-N might have large effects on methanotroph diversity and activity in swamp meadow soils on the QTP.

Microbial mechanisms in the reduction of CH4 emission from double rice cropping system amended by biochar: A four-year study

Biochar amendment can reduce CH4 emissions from paddy soils. However, little is known about how the soil microbial communities associated with paddy soil CH4 emissions respond to biochar aging after biochar amendment. In this study, we examined the effects of biochar on CH4 emissions, soil properties, and abundance/community composition of methanogens and methanotrophs in a double rice cropping system from 2012 to 2016. Straw-derived biochar was applied once in 2012 at 24 and 48 t ha−1. Biochar application decreased the annual CH4 emissions by 20–51%. Biochar increased the abundances of both methanogens and methanotrophs, with a larger increase of methanotrophs than methanogens in the first year, mainly caused by the increases in soil dissolved organic carbon, NH4+-N, and porosity. Biochar suppressed the abundance of methanogens and had little effect on the methanotrophs in the following three years, probably due to the increased soil porosity. Eventually, the ratios of abundance of methanogens to methanotrophs decreased by 11–31% in each of the four years and were positively correlated to CH4 emissions. Biochar addition increased the relative abundances of Methanocella and Methanospirillum and reduced those of Methanoregula and Methanosaeta for methanogens, while it increased the proportion of the basophilic methanotrophs Methylomicrobium and decreased that of Methylocaldum in the growing season 2014. Our results demonstrate that biochar aging greatly alters the responses of abundances and community compositions of soil methanogens and methanotrophs to biochar addition. The reduction of CH4 emissions owing to biochar in the long run was probably mainly due to the lesser suppression of abundance and activity of methanotrophs compared with methanogens.