Methane Oxidation Potential Research Articles

Methane Oxidation Potentials of Rice-associated Plant Growth Promoting Methylobacterium Species

Methane Oxidation Potentials of Rice-associated Plant Growth Promoting <italic>Methylobacterium</italic> Species-Methane,Methane oxidation,Methanotrophs,<italic>Methylobacterium</italic> spp.,Soluble methane monooxygenase

Enhanced Methane Oxidation Potential of Landfill Cover Soil Modified with Aged Refuse

Aged refuse with a landfill age of 1.5 years was collected from a municipal solid waste landfill with high kitchen waste content and mixed with soil as biocover material for landfill. A series of laboratory batch tests was performed to determine the methane oxidation potential and optimal mixing ratio of landfill cover soil modified with aged refuse, and the effects of water content, temperature, CO2/CH4, and O2/CH4 ratios on its methane oxidation capacity were analyzed. The microbial community analysis of aged refuse showed that the proportions of type I and type II methane-oxidizing bacteria were 56.27% and 43.73%, respectively. Aged refuse could significantly enhance the methane oxidation potential of cover soil, and the optimal mixing ratio was approximately 1:1. The optimal temperature and water content were about 25 °C and 30%, respectively. Under the conditions of an initial methane concentration of 15% and an O2/CH4 ratio of 0.8–1.2, the measured methane oxidation rate was negatively correlated with the O2/CH4 ratio. The maximum methane oxidation capacity measured in the test reached 308.5 (μg CH4/g)/h, indicating that the low-age refuse in the landfill with high kitchen waste content is a biocover material with great application potential.

Revisiting the passive biocover system at Klintholm landfill, six years after construction

A biocover system was established at Klintholm landfill in Denmark in 2009 to mitigate methane emissions, and the system exhibited high mitigation efficiency during the first year after implementation. The biocover system was revisited in 2016/2017, and a series of field and laboratory tests were carried out to evaluate functionality about six years after establishment. Three field campaigns were executed in three different barometric pressure conditions, namely increasing, stable and decreasing. Local surface flux measurements and gas concentration profiles in the methane oxidation layer showed that barometric pressure changes had a significant effect on gas emission and methane oxidation. Elevated concentrations of oxygen were observed in the gas distribution layer, and field data showed that significant methane oxidation took place in this location. This finding was verified in laboratory-based methane oxidation incubation tests. Temperatures higher than ambient temperature were observed throughout the methane oxidation layer, with average temperatures ranging between 13 and 27 °C, even in the coldest month of the year. Field measurements showed that total methane emissions from the whole landfill cell were at the same level or lower than measurements performed in 2009/2010 after implementation of the biocover system, and laboratory tests showed methane oxidation potential approximately equal to former tests. In spite of an inhomogeneous distribution of landfill gas load to the methane oxidation layer, the performance of the biocover system had not declined over the 6–7 years since its establishment, even though no maintenance had been carried out in the intervening years.

Field study on the effect of vegetation on the performance of soil methanotrophy-based engineered systems – Column experiments

Current literature provides conflicting information on the role vegetation plays when considering methane (CH4) oxidation potential of engineered Biosystems, such as landfill biocovers (LBCs), bio-windows and methane biofilters. The primary objective of this study was to determine whether the impact of vegetation on biological CH4 oxidation was positive or negative and to explain the reasons for the observations using a variety of experiments. A total of eight flow-through columns (two alfalfa, two native grass, two canola and two bare-soil replicates) were set up outdoors to simulate field operation in cold climatic conditions. Each column was layered with 18 cm of topsoil and 32 cm of compost mixture (compost 30%: topsoil 70% v/v) as packing material and treated with CH4 fluxes ranging from 180 to 815 g CH4 m−2 d−1. The bare-soil columns exhibited the highest CH4 oxidation rate of 455 g CH4 m−2 d−1, while the maximum CH4 oxidation rates for the vegetated columns ranged between 147 and 171 g CH4 m−2 d−1 with the alfalfa column showing the lowest. Gas profiles of vegetated columns showed high concentrations of nitrogen (N2) and oxygen (O2) at all depths, possibly due to increased permeability created by the plant root systems. Quantitative Polymerase Chain Reaction (q-PCR) assessment showed that pmoA gene copy numbers, indicative of methanotrophic population levels, were higher in bare-soil columns than in vegetated columns. The Illumina based sequencing of 16S rRNA gene showed that Type I methanotrophs dominated both vegetated and bare-soil columns. Soil incubation experiments conducted to determine oxidation kinetic parameters also indicated greater methanotrophic activity in the bare-soil columns than in vegetated columns. The plant data collected at the end of the column experiments provided clear evidence of CH4 escape due to preferential pathways created by plant roots (reaching 38 cm, 31.5 cm and 26.5 cm by alfalfa, canola and native grass, respectively) that resulted in decreased CH4 oxidation in vegetated columns. The study results clearly demonstrate that vegetation decreases CH4 oxidation at high loading rates, notwithstanding the type of vegetation.

Finding the pieces for the anaerobic methane oxidation jigsaw puzzle in mangrove wetlands

Estuarine mangrove wetlands are generally considered a major source of methane (CH4) emissions. Anaerobic methane oxidation (AMO) is an important pathway for reducing CH4 emissions and is known to be tightly linked to carbon, nitrogen, sulfur and metal cycling processes largely driven by microorganisms. However, these coupled processes and their contributions to mitigating global warming remain unclear in mangrove wetlands. In this study, the depth-specific potential methane oxidation rates of nitrate-, nitrite- and nitrous oxide-dependent anaerobic methane oxidation (nitrate-, nitrite- and N2O-AMO) and sulfate-dependent anaerobic methane oxidation (sulfate-AMO) processes were investigated using stable isotope tracing along with an assessment of the vertical nutrient and CH4 content profiles in mangrove sediments. The results indicated that nitrite-AMO, nitrate-AMO, N2O-AMO and sulfate-AMO were active and exhibited methane oxidation rates varying from 24.1 to 1077.4, 14.1 to 66.1, 14.3 to 40.9 and 4.2–36.7 nmol CO2 g−1 dry soil d−1, respectively. Furthermore, nitrite-AMO and N2O-AMO tended to be more active in the upper sediment layers, while nitrate-AMO and sulfate-AMO displayed higher rates in the deeper layers. The contribution rate of nitrite-AMO to the total of the 4 AMO processes examined in the mangrove sediments reached 28.90–95.80%, followed by nitrate-AMO (2.73–46.46%), sulfate-AMO (1.46–24.65%) and N2O-AMO (1.70–4.47%), suggesting that the nitrite-AMO process is a significant methane sink in mangrove wetland ecosystems. The temporal and spatial variations in the nitrite-AMO bacterial depth and genus-specific distribution, abundance, activity and sensitivity to environmental factors were then investigated. The absolute abundances of the nitrite-AMO bacterial 16S rRNA and pmoA genes were 0.51–6.55 × 107 and 0.79–8.43 × 106 copies g−1 ds, respectively, and these values decreased with sediment depth; most of the samples were characterized as belonging to Group B of NC10. In addition, NO2− is the limiting factor for nitrite-AMO bacteria in mangrove wetlands.

Long-term incorporation of wheat straw changes the methane oxidation potential, abundance and community composition of methanotrophs in a paddy ecosystem

A recent study showed that the Intergovernmental Panel on Climate Change (IPCC) methodologies overestimated the effect of long-term (>5 years) straw incorporation on CH4 emissions from paddy ecosystems. It was suggested that the IPCC methodologies underestimated the active role of methanotrophs in regulating CH4 emissions under long-term straw incorporation; however, direct evidence has not yet been provided. Herein, the methane oxidation potential, abundance and community composition of methanotrophs were investigated in paddy fields under three long-term (32 years) fertilization treatments, including unfertilized control (CK), mineral fertilizers (NPK), and wheat straw incorporation with mineral fertilizers (SNPK). The results showed that the methane oxidation potential in the SNPK treatment was significantly (p < 0.05) higher than those in the NPK and CK treatments. Furthermore, the pmoA gene abundance of methanotrophs was also significantly (p < 0.05) higher in the SNPK treatment than that in the NPK and CK treatments. It was calculated that the overall methane oxidation potential in the SNPK treatment was increased by 67.0% and 62.5% in comparison to the CK and NPK treatments, respectively. Similarly, the pmoA gene abundance in the SNPK treatment was increased by 87.1% and 59.1% as compared to other two treatments, respectively. In addition, the SNPK treatment significantly increased the relative abundance of type II methanotrophs (Methylocystis). The changes in soil organic carbon (OrgC) content, nitrate content, and aeration status under the SNPK treatment were the key factors affecting the methane oxidation potential and communities of methanotrophs. Taken together, we provide the first direct evidence that methanotrophs responded positively to long-term straw incorporation in paddy ecosystems, which could partly explain the overestimation by the IPCC methodologies of CH4 emissions induced due to straw incorporation.

Identification of functionally active aerobic methanotrophs and their methane oxidation potential in sediments from the Shenhu Area, South China Sea

Large amounts of gas hydrate are distributed in the northern slope of the South China Sea, which is a potential threat of methane leakage. Aerobic methane oxidation by methanotrophs, significant methane biotransformation that occurs in sediment surface and water column, can effectively reduce atmospheric emission of hydrate-decomposed methane. To identify active aerobic methanotrophs and their methane oxidation potential in sediments from the Shenhu area in the South China Sea, multi-day enrichment incubations were conducted in this study. The results show that the methane oxidation rates in the studied sediments were 2.03‒2.36 μmol/gdw/d, which were higher than those obtained by sediment incubations from other areas in marine ecosystems. Thus we suspect that the methane oxidation potential of methanotrophs was relatively higher in sediments from the Shenhu area. After the incubations family <i>Methylococcaea</i> (type I methanotrophs) mainly consisted of<i> genus Methylobacter and Methylococcaea_Other</i> were predominant with an increased proportion of 70.3%, whereas <i>Methylocaldum</i> decreased simultaneously in the incubated sediments. Collectively, this study may help to gain a better understanding of the methane biotransformation in the Shenhu area.

Nitrite-dependent anaerobic methane oxidation bacteria and potential in permafrost region of Daxing'an Mountains.

Nitrite-dependent anaerobic methane oxidation (n-damo) acts as a crucial link between biogeochemical carbon and nitrogen cycles. Nevertheless, very few studies have characterized n-damo microorganisms in high-latitude permafrost regions. Therefore, this study investigated the vertical distribution and diversity of n-damo bacterial communities in soil from three forest types in the permafrost regions of the Daxing'an Mountains. A total of 11 and 8 operational taxonomic units (OTUs) of n-damo 16S rRNA and pmoA genes were observed, respectively. Remarkable spatial variations in n-damo bacteria community richness, diversity, and structure were observed at different soil depths. Moreover, the abundances of n-damo bacteria (16S rRNA and pmoA genes) varied between 1.55 × 104 to 1.47 × 105 and 1.31 × 103 to 3.11 × 104 copies g-1 dry soil (ds), as demonstrated by quantitative PCR analyses. 13CH4 stable isotope tracer assays indicated that the potential n-damo rates varied from 0 to 1.26nmolg-1day-1, with the middle layers (20-40cm and 40-60cm) exhibiting significantly higher values than the upper (0-20cm) and deeper layers (80-100cm) in all three forest types. Redundancy analyses (RDA) indicated that total organic carbon (TOC), nitrate (NO3--N), and nitrite (NO2--N) were key modulators of the distribution of n-damo bacterial communities. This study thus demonstrated the widespread occurrence of n-damo bacteria in cold and high-latitude regions of forest ecosystems and provided important insights into the global distribution of these bacteria. KEY POINTS: • This study detected n-damo bacteria in soil samples obtained from the permafrost region of three forest types in the Daxing'an Mountains. • The community composition of n-damo bacteria was mainly affected by soil depth and not forest type. • The abundances of n-damo bacteria first increased and then decreased at higher soil depths.

Amsterdam urban canals contain novel niches for methane-cycling microorganisms.

SummaryUrbanised environments have been identified as hotspots of anthropogenic methane emissions. Especially urban aquatic ecosystems are increasingly recognised as important sources of methane. However, the microbiology behind these emissions remains unexplored. Here, we applied microcosm incubations and molecular analyses to investigate the methane‐cycling community of the Amsterdam canal system in the Netherlands. The sediment methanogenic communities were dominated by Methanoregulaceae and Methanosaetaceae, with co‐occurring methanotrophic Methanoperedenaceae and Methylomirabilaceae indicating the potential for anaerobic methane oxidation. Methane was readily produced after substrate amendment, suggesting an active but substrate‐limited methanogenic community. Bacterial 16S rRNA gene amplicon sequencing of the sediment revealed a high relative abundance of Thermodesulfovibrionia. Canal wall biofilms showed the highest initial methanotrophic potential under oxic conditions compared to the sediment. During prolonged incubations the maximum methanotrophic rate increased to 8.08 mmol gDW −1 d−1 that was concomitant with an enrichment of Methylomonadaceae bacteria. Metagenomic analysis of the canal wall biofilm lead to the recovery of a single methanotroph metagenome‐assembled genome. Taxonomic analysis showed that this methanotroph belongs to the genus Methyloglobulus. Our results underline the importance of previously unidentified and specialised environmental niches at the nexus of the natural and human‐impacted carbon cycle.

Effect of elevated atmospheric CO2 concentration on the activity, abundance and community composition of aerobic methanotrophs in paddy soils

The elevated atmospheric CO2 concentration (eCO2) has a great impact on soil microbial communities and their functions; however, how the activity and communities of methanotrophs respond to eCO2 in paddy ecosystem is poorly known. Here, we examined the effects of a 4-year exposure to eCO2 (EC; ambient + 200 ppm) in open top chambers on the potential activity, abundance and community composition of methanotrophs in paddy fields in Nanjing City, China. The potential activity was measured in a slurry incubation under aerobic condition, and the community composition and abundance of methanotrophs were analyzed through Illumina Miseq sequencing and quantitative PCR of pmoA genes. The results demonstrated that EC significantly increased (p < 0.05) the methane oxidation potential and pmoA gene abundance of methanotrophs by 52.9%–56.7% and 83.5%–213.6%, respectively, during late rice growth stages as compared with ambient condition (CK). Further, the community composition of methanotrophs in soil changed significantly (p < 0.05), with the dominant methanotrophs shifting from type II under CK to type I under EC. The variation of soil dissolved organic carbon and inorganic nitrogen levels caused by eCO2 had an important impact on the methane oxidation potential and methanotrophic community structure. Taken together, our results indicate that eCO2 can have an important impact on the activity, abundance and community composition of methanotrophs, adding new insights into the effects of rising CO2 on methane cycling in paddy ecosystems.

Revealing the community and metabolic potential of active methanotrophs by targeted metagenomics in the Zoige wetland of the Tibetan Plateau.

The Zoige wetland of the Tibetan Plateau is one of the largest alpine wetlands in the world and a major emission source of methane. Methane oxidation by methanotrophs can counteract the global warming effect of methane released in the wetlands. Understanding methanotroph activity, diversity and metabolism at the molecular level can guide the isolation of the uncultured microorganisms and inform strategy-making decisions and policies to counteract global warming in this unique ecosystem. Here we applied DNA stable isotope probing using 13 C-labelled methane to label the genomes of active methanotrophs, examine the methane oxidation potential and recover metagenome-assembled genomes (MAGs) of active methanotrophs. We found that gammaproteobacteria of type I methanotrophs are responsible for methane oxidation in the wetland. We recovered two phylogenetically novel methanotroph MAGs distantly related to extant Methylobacter and Methylovulum. They belong to type I methanotrophs of gammaproteobacteria, contain both mxaF and xoxF types of methanol dehydrogenase coding genes, and participate in methane oxidation via H4 MPT and RuMP pathways. Overall, the community structure of active methanotrophs and their methanotrophic pathways revealed by DNA-SIP metagenomics and retrieved methanotroph MAGs highlight the importance of methanotrophs in suppressing methane emission in the wetland under the scenario of global warming.

Methane oxidation activity inhibition via high amount aged biochar application in paddy soil

Fresh biochar application has been recommended as an effective strategy to mitigate methane emissions from paddy soil due to its role in promoting potential methane oxidation (PMO). However, little is known about the effect of biochar on PMO after long-term aging. Here, a laboratory incubation experiment was performed to gain insight into the combined effects of biochar characteristics on soil PMO during the biochar aging process. Biochar samples aged with an HNO3/H2SO4 mixture (1:3) were prepared and added at 22.5 and 2.8 t ha-1 to paddy soil. Mixed acid with a dilution of 10– 40% indicated the aging process in paddy field properly. Smaller biochar particles, smoother surface, higher surface area and porosity were observed with the increase of mixed acid ratio. Carboxylic functional groups (COOR) on biochar surface increased accompanied with biochar aging process. Aged biochar application at 22.5 t ha-1 inhibited paddy soil PMO, which mainly caused from the increased COOR groups induced NH4+-N inhibition for PMO. Increased soil NH4+-N inhibited PMO by limiting the growth of methanotrophs and nitrifiers due to decreased soil pH. In contrast, 2.8 t aged biochar ha-1 application showed no significant difference on PMO compared with control. Our results indicated that aged biochar exerted in paddy soil have limited effect on mitigating methane emissions from paddy soil in the long term.

Methane production and oxidation potentials along a fen-bog gradient from southern boreal to subarctic peatlands in Finland.

Methane (CH4 ) emissions from northern peatlands are projected to increase due to climate change, primarily because of projected increases in soil temperature. Yet, the rates and temperature responses of the two CH4 emission-related microbial processes (CH4 production by methanogens and oxidation by methanotrophs) are poorly known. Further, peatland sites within a fen-bog gradient are known to differ in the variables that regulate these two mechanisms, yet the interaction between peatland type and temperature lacks quantitative understanding. Here, we investigated potential CH4 production and oxidation rates for 14 peatlands in Finland located between c. 60 and 70°N latitude, representing bogs, poor fens, and rich fens. Potentials were measured at three different temperatures (5, 17.5, and 30℃) using the laboratory incubation method. We linked CH4 production and oxidation patterns to their methanogen and methanotroph abundance, peat properties, and plant functional types. We found that the rich fen-bog gradient-related nutrient availability and methanogen abundance increased the temperature response of CH4 production, with rich fens exhibiting the greatest production potentials. Oxidation potential showed a steeper temperature response than production, which was explained by aerenchymous plant cover, peat water holding capacity, peat nitrogen, and sulfate content. The steeper temperature response of oxidation suggests that, at higher temperatures, CH4 oxidation might balance increased CH4 production. Predicting net CH4 fluxes as an outcome of the two mechanisms is complicated due to their different controls and temperature responses. The lack of correlation between field CH4 fluxes and production/oxidation potentials, and the positive correlation with aerenchymous plants points toward the essential role of CH4 transport for emissions. The scenario of drying peatlands under climate change, which is likely to promote Sphagnum establishment over brown mosses in many places, will potentially reduce the predicted warming-related increase in CH4 emissions by shifting rich fens to Sphagnum-dominated systems.

Slow recovery of soil methane oxidation potential after cessation of N addition in a typical steppe

Atmospheric nitrogen (N) deposition can profoundly affect methane (CH4) oxidation; however, how it responds to the cessation of N addition has rarely been reported. An incubation experiment was conducted using soils from plots treated with long-term N addition to estimate the soil CH4 oxidation potential. The results showed a unimodal relationship between the levels of soil CH4 consumption and N addition and a slow recovery of CH4 oxidation potential after the cessation of N addition. CH4 consumption was stimulated only at low levels of N addition, and this stimulatory effect quickly diminished with increasing N addition, possibly resulting from the decoupled relationship between the potential for CH4 consumption and the abundance of pmoA-carrying bacteria.

Methane oxidation potential of the arctic wetland soils of a taiga-tundra ecotone in northeastern Siberia

ABSTRACT Arctic wetlands are significant sources of atmospheric methane and the observed accelerated climate changes in the arctic could cause a change in methane dynamics. Methane oxidation would be the key process to control methane emission from wetlands. In this study, we determined the potential methane oxidation rate of the wetland soils of a taiga–tundra transition zone in northeastern Siberia. Peat soil samples were collected in summer from depressions covered with tussocks of sedges and Sphagnum spp. and from mounds vegetated with moss and larch trees. An aerobic bottle incubation experiment demonstrated that the soil samples collected from depressions in the moss- and sedge-dominated zones exhibited active methane oxidation with no time lag, while the mound soils showed no methane oxidation under the given conditions. The potential methane oxidation rates of the soils at 15°C ranged from 94 to 496 nmol h−1 g−1 dw. The immediate and active methane oxidation was observed over the depths studied (0–40 cm) including the water-saturated anoxic layers; the maximum methane oxidation rate was recorded in the layer above the water-saturated layer. The methane oxidation rate was temperature-dependent, but substantial methane oxidation was observed even at 0°C particularly for the moss soil samples. Soil samples collected from the frozen layer of Sphagnum peat also showed immediate methane consumption when incubated at 15°C. The present results suggest that the methane oxidizing bacteria in the wetland soils could survive under anoxic and frozen conditions keeping their potential activities and immediately utilize methane when the conditions become favorable. On the other hand, the inhibitor of methane oxidation (difluoromethane) did not affect the methane flux from the sedge and moss zones in situ, which suggested the minor role of plant-associated methane oxidation.

Niche differentiation of denitrifying anaerobic methane oxidizing bacteria and archaea leads to effective methane filtration in a Tibetan alpine wetland

Denitrifying anaerobic methane oxidation (DAMO) is a vital methane sink in wetlands. However, the interactions and niche partitioning of DAMO bacteria and archaea in freshwater wetland soils, in addition to the interactions among microorganisms that couple methane and nitrogen cycling is still unclear, despite that these factors may govern the fate of methane and nitrogen in wetlands. Here, we evaluated the vertical distribution of DAMO bacteria and archaea in soil layers along with the potential interactions among populations in the methane-coupled nitrogen cycling microbial community of Tibetan freshwater wetlands. A combination of molecular biology, stable isotope tracer technology, and microbial bioinformatics was used to evaluate these interrelated dynamics. The abundances and potential methane oxidation rates indicated that DAMO bacteria and archaea differentially occupy surface and subsurface soil layers, respectively. The inferred interactions between DAMO bacteria and nitrogen cycling microorganisms within their communities are complex, DAMO bacteria apparently achieve an advantage in the highly competitive environment of surface soils layers and occupy a specific niche in those environments. Conversely, the apparent relationships between DAMO archaea and nitrogen cycling microorganisms are relatively simple, wherein high levels of cooperation are inferred between DAMO archaea and nitrate-producing organisms in subsurface soils layers. These results suggest that the vertical distribution patterns of DAMO bacteria and archaea enable them to play significant roles in the methane oxidation activity of different soil layers and collectively form an effective methane filtration consortium.

Ammonium Impacts Methane Oxidation and Methanotrophic Community in Freshwater Sediment.

Lacustrine ecosystems are regarded as one of the important natural sources of greenhouse gas methane. Aerobic methane oxidation, carried out by methane-oxidizing bacteria, is a key process regulating methane emission. And ammonium is believed to greatly influence aerobic methane oxidation activity. To date, disagreement exists in the threshold of ammonium effect. Moreover, knowledge about how aerobic methanotrophic community composition and functional gene transcription respond to ammonium is still lacking. In the present study, microcosms with freshwater lake sediment were constructed to explore the effect of ammonium level on aerobic methanotrophs. Methane oxidation potential, and the density, diversity and composition of pmoA gene and its transcripts were examined during 2-week incubation. A negative impact of ammonium on aerobic methane oxidation potential and a positive impact on pmoA gene density were observed only at a very high level of ammonium. However, pmoA gene transcription increased notably at all ammonium levels. The composition of functional pmoA gene and transcripts were also influenced by ammonium. But a great shift was only observed in pmoA transcripts at the highest ammonium level.

Changes in &lt;i&gt;pmoA&lt;/i&gt; Gene Containing Methanotrophic Population and Methane Oxidation Potential of Dry Deciduous Tropical Forest Soils

In natural ecosystems such as forests topographical gradients, species composition variability and seasonality, are the potential drivers of methane (CH 4 ) metabolism, and thus, of the population size and activities of methane oxidizing bacteria (MOB). To test the hypothesis that topography, tree species and seasonal variability influence MOB population and soil methane oxidation potential (MOP), we conducted two consecutive years of study selecting three sites in a dry deciduous tropical forest in Chandauli district of eastern Uttar Pradesh, India. The qPCR results showed a large variation in MOB population size (copies g −1 dws), ranging from 1.0 × 10 6 to 2.1 × 10 7 and 9.0 × 10 5 to 2.2 × 10 7 during 2016 and 2017 respectively. The distribution of MOB population revealed the trend: hilltop > middle > hillbase with its maxima in the winter and minima in the rainy season. Laboratory incubation study revealed a similar trend in soil MOP (ng CH 4 g −1 h −1 dws), it varied from 10.6 to 20.6 and 10.5 to 20.7 during 2016 and 2017 respectively. The outer canopy soils showed lower MOB population and MOP compared to under canopy soils of tree species Butea monosperma, Madhuca indica and Tectona grandis during both years of study. The topography, season and tree species significantly influenced the MOB population size and MOP. Soil MOP showed a highly significant correlation (r = 0.89; p < 0.01) with MOB population, and a negative correlation was found with soil moisture (r = 0.76; p < 0.01). The results indicate that the dry deciduous tropical forest soils are potential sinks of atmospheric CH 4 wherein, the MOB population characteristically responds to topographical changes, tree species and seasonal shifts driving collectively the overall MOP of forest soils.

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.

Temporal shift in methanotrophic community and methane oxidation potential in forest soils of dry tropics: high-throughput metagenomic approach

Forest soil contributes to global methane (CH4) cycle as the natural sink for atmospheric CH4 by methane-oxidizing bacteria (MOB). In this study, high-throughput sequencing of pmoA gene amplicons based approach was used to investigate temporal variations in molecular diversity of MOB in soil of tropical dry forest. Quantitative PCR (qPCR) analysis revealed pmoA and 16S rRNA gene copy numbers (copies g−1 dws) ranging from 2.23 × 106 to 14.62 × 106 and from 0.92 × 109 to 14.99 × 109, respectively, in the year 2016. In 2017, the respective values varied from 1.96 × 106 to 13.62 × 106 and from 2.55 × 109 to 20.15 × 109, respectively. The sequence analysis revealed the existence of both type I and type II methanotrophs in soils. The average observed OTUs were about 800/sample, and Shannon diversity index ranged between 4.24 and 6.22 being highest in winter season. The rice paddy clusters (RPCs), Methylocystis, Methlylocystis-Methylosinus and JR2 and JR3, dominated the methanotrophic community with relative abundance of 32.7–50.2, 15.4–34.2, 0.45–15.8, 0.0–17.8 and 1.6–19.2%, respectively. Relatively, higher CH4 oxidation potential (MOP) (ng CH4 g−1 h−1 dws) was observed in winter (14.12) compared with rainy (2.10) and summer (3.72) coinciding with high methanotrophic diversity and abundance. Overall, the study suggests that tropical dry deciduous forest soils favour considerable range of methanotrophic diversity and abundance that positively correlates with MOP of soils across season.