CH4 Oxidation Potential Research Articles

Microbial mechanism for rice variety control on methane emission from rice field soil

AbstractRice variety is one of the key factors regulating methane (CH4) production and emission from the paddy fields. However, the relationships between rice varieties and populations of microorganisms involved in CH4 dynamics are poorly understood. Here we investigated CH4 dynamics and the composition and abundance of CH4‐producing archaea and CH4‐oxidizing bacteria in a Chinese rice field soil planted with three types of rice. Hybrid rice produced 50–60% more of shoot biomass than Indica and Japonica cultivars. However, the emission rate of CH4 was similar to Japonica and lower than Indica. Furthermore, the dissolved CH4 concentration in the rhizosphere of hybrid rice was markedly lower than Indica and Japonica cultivars. The rhizosphere soil of hybrid rice showed a similar CH4 production potential but a higher CH4 oxidation potential compared with the conventional varieties. Terminal restriction fragment length polymorphism analysis of the archaeal 16S rRNA genes showed that the hydrogenotrophic methanogens dominated in the rhizosphere whereas acetoclastic methanogens mainly inhabited the bulk soil. The abundance of total archaea as determined by quantitative (real‐time) PCR increased in the later stage of rice growth. However, rice variety did not significantly influence the structure and abundance of methanogenic archaea. The analysis of pmoA gene fragments (encoding the α‐subunit of particulate methane monooxygenase) revealed that rice variety also did not influence the structure of methanotrophic proteobacteria, though variable effects of soil layer and sampling time were observed. However, the total copy number of pmoA genes in the rhizosphere of hybrid rice was approximately one order of magnitude greater than the two conventional cultivars. The results suggest that hybrid rice stimulates the growth of methanotrophs in the rice rhizosphere, and hence enhances CH4 oxidation which attenuates CH4 emissions from the paddy soil. Hybrid rice is becoming more and more popular in Asian countries. The present study demonstrated that planting of hybrid rice will not enhance CH4 emissions albeit a higher grain production than the conventional varieties.

Methane and nitrous oxide fluxes, and carbon dioxide production in boreal forest soil fertilized with wood ash and nitrogen

AbstractWood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N2O emission and suppress CH4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO2 emission. The fluxes of CH4, N2O and CO2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH4 oxidation potential, CO2 production, net nitrification and N2O production were studied in laboratory incubations. The mean in situ N2O emissions and in situ CO2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μg N2O m−2 h−1 and from 533 to 611 mg CO2 m−2 h−1. However, ash increased the CH4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH4 uptake rates in situ. The mean in situ CH4 uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μg m−2 h−1, respectively.

Soil Moisture between Rice-Growing Seasons Affects Methane Emission, Production, and Oxidation

Methane (CH4) emissions from rice (Oryza sativa L.) fields are believed to contribute to the greenhouse effect. Earlier studies on CH4 emission were mostly focused on the rice-growing season. The objective of this study was to determine the effects of soil moisture during the non-rice growing season on CH4 emission, production, and oxidation within the subsequent rice-growing season. Five moisture levels ranging from air-dryness to flooding were established in pots during the non-rice growing season. The CH4 fluxes from rice soils in the pots were monitored in a closed chamber and dark incubation was performed to determine CH4 production and oxidation potentials. Both CH4 emission and production increased significantly as the soil got wetter except when it was air-dried. The CH4 oxidation potential was also stimulated by the previous higher soil water content, which therefore buffered emission of the gas as its production increased. Soil water content considerably affected the seasonal variation pattern of CH4 flux and soil redox potential (EH). The higher the soil water content, the quicker soil EH declined and the earlier CH4 emission initiated after rice transplantation. Previous soil water content significantly affected soil organic C content before rice transplantation. Within the rice-growing season both the mean CH4 flux and its production rate were significantly correlated with soil organic C content. Thus water-history-induced change of soil organic C content may have affected soil reduction rate, and then CH4 production and emission within the rice-growing season. The results demonstrate how water management between rice crops can regulate CH4 emission, production, and oxidation during the rice-growing season.

Effects of N‐fertilisation on CH4 oxidation and production, and consequences for CH4 emissions from microcosms and rice fields

AbstractThe world's growing human population causes an increasing demand for food, of which rice is one of the most important sources. In rice production nitrogen is often a limiting factor. As a consequence increasing amounts of fertiliser will have to be applied to maximise yields. There is an ongoing discussion on the possible effects of fertilisation on CH4 emissions. We therefore investigated the effects of N‐fertiliser (urea) on CH4 emission, production and oxidation in rice microcosms and field experiments. In the microcosms, a substantial but short‐lived reduction of CH4 emission was observed after N‐addition to 43‐d‐old rice plants. Methane oxidation increased by 45%, demonstrated with inhibitor measurements and model calculations based on stable carbon isotope data (δ13CH4). A second fertilisation applied to 92‐d‐old plants had no effect on CH4 emission rates.The positive effect of additional N on methanotrophic bacteria was also found in vitro for potential CH4 oxidation rates in soil and root samples from the microcosm and field experiments, indicated by elevated initial oxidation rates and reduced lag‐phases. Fertilisation did not affect methane production in the microcosms. In the field, the effects were diverse: methane production was inhibited in the topsoil, but stimulated instead in the bulk soil. Stimulation occurred probably in the anaerobic food chain at the level of hydrolytic or fermenting bacteria, because acetate, a methanogenic precursor, increased simultaneously.Combining field, microcosm and laboratory experiments we conclude that any agricultural treatment improving the N‐supply to the rice plants will also be favourable for the CH4 oxidising bacteria. However, N‐fertilisation had only a transient influence and was counter‐balanced in the field by an elevated CH4 production. A negative effect of the fertilisation was a transient increase of N2O emissions from the microcosms. However, integrating over the season the global warming potential (GWP) of N2O emitted after fertilisation was still negligible compared to the GWP of emitted CH4.

Methane‐limited methanotrophy in tidal freshwater swamps

We investigated the relationship between CH4 production and oxidation in two tidal freshwater wetland forests in order to determine whether CH4 oxidation efficiency was limited by O2 or CH4. Methane oxidation was measured in situ over a 16‐month period with bi‐monthly applications of the inhibitor CH3F. Oxidation consumed 52 ± 10 and 81 ± 9% of diffusive CH4 emissions on the two sites. Methane oxidation rates were linearly related to gross CH4 emissions on both sites (r2 = 0.96), demonstrating the process was CH4‐limited. This interpretation is consistent with the fact that the apparent activation energies for the potential CH4 production and oxidation differed by <4 kJ mol−1. Apparent activation energies calculated from field emissions data were also similar for the two processes. The high CH4 oxidation efficiency on these sites may be attributed to relatively low rates of methane production, a deep oxidizing zone (5–10 cm), and low cover of understory vegetation capable of CH4 transport. If our results are typical of forested wetlands, CH4 oxidation efficiency in forested wetlands will not change in response to soil warming.

Methane cycling in the sediment and water column of mid-boreal hyper-eutrophic Lake Kevätön, Finland

Methane (CH 4 ) dynamics were studied in the sediments and the water column of mid-boreal, hyper-eutrophic Lake Kevaton, Finland. We determined the CH 4 production and oxidation potentials in deep and shallow profundal sediments, water column CH4 oxidation potentials, and seasonal variation in CH 4 oxidation in water column in situ. The sediment CH 4 production and oxidation potentials were greater in summer than in winter. In the shallow profundal, the CH 4 oxidation potential of the surface sediment was equal to or higher than the sediment CH4 production potential, whereas in the deep profundal sediment, CH 4 production potential exceeded the CH 4 oxidation potential. The entire water column had the potential to oxidize CH 4 . The CH 4 oxidation rates (shown as negative values) in the water column in situ, ranged from 0 to -27 mmol m -3 d -1 , and were lower than the potential CH4 oxidation rates, which ranged from -9 to -160 mmol m -3 d -1 . The supply of CH 4 regulated its oxidation rate in water in situ, resulting in a clear seasonal variation in the level of CH 4 oxidation. The highest oxidation rates occurred in the hypolimnion during summer and winter stratifications when there were the highest CH 4 concentrations. During these stratifications, the CH 4 oxidation contributed significantly to the hypolimnetic O 2 consumption. In winter, there was CH 4 oxidation both in the aerobic and anaerobic water column. The depth integrated CH 4 oxidation in the water column was highest during stratification, in winter -31 and in summer -15 mmol m -2 d -1 . During the autumn overturn, the water column oxidized some CH 4 , but in spring, after the ice melt, the water column had a very low CH 4 production. Oxidation of CH 4 both in the sediments and water column reduced the emissions of CH 4 to the atmosphere.

Seasonal variation in pathways of CH4 production and in CH4 oxidation in rice fields determined by stable carbon isotopes and specific inhibitors

AbstractFlooded rice fields, which are an important source of the atmospheric methane, have become a model system for the study of interactions between various microbial processes. We used a combination of stable carbon isotope measurements and application of specific inhibitors in order to investigate the importance of various methanogenic pathways and of CH4 oxidation for controlling CH4 emission. The fraction of CH4 produced from acetate and H2/CO2 was calculated from the isotopic signatures of acetate, carbon dioxide (CO2) and methane (CH4) measured in porewater, gas bubbles, in the aerenchyma of the plants and/or in incubation experiments. The calculated ratio between both pathways reflected well the ratio determined by application of methyl fluoride (CH3F) as specific inhibitor of acetate‐dependent methanogenesis. Only at the end of the season, the theoretical ratio of acetate: H2 = 2 : 1 was reached, whereas at the beginning H2/CO2‐dependent methanogenesis dominated. The isotope discrimination was different between rooted surface soil and unrooted deep soil. Root‐associated CH4 production was mainly driven by H2/CO2. Porewater CH4 was found to be a poor proxy for produced CH4.The fraction of CH4 oxidised was calculated from the isotopic signature of CH4 produced in vitro compared to CH4 emitted in situ, corrected for the fractionation during the passage from the aerenchyma to the atmosphere. Isotope mass balances and in situ inhibition experiments with difluoromethane (CH2F2) as specific inhibitor of methanotrophic bacteria agreed that CH4 oxidation was quantitatively important at the beginning of the season, but decreased later. The seasonal pattern was consistent with the change of potential CH4 oxidation rates measured in vitro. At the end of the season, isotope techniques detected an increase of oxidation activity that was too small to be measured with the flux‐based inhibitor technique. If porewater CH4 was used as a proxy of produced CH4, neither magnitude nor seasonal pattern of in situ CH4 oxidation could be reproduced. An oxidation signal was also found in the isotopic signature of CH4 from gas bubbles that were released by natural ebullition. In contrast, bubbles stirred up from the bulk soil had preserved the isotopic signature of the originally produced CH4.

Effect of experimental nitrogen load on methane and nitrous oxide fluxes on ombrotrophic boreal peatland

Methane (CH4) and nitrous oxide (N2O) dynamics were studied in a boreal Sphagnum fuscum pine bog receiving annually (from 1991 to 1996) 30 or 100 kg NH4NO3-N ha−1. The gas emissions were measured during the last three growing seasons of the experiment. Nitrogen treatment did not affect the CH4 fluxes in the microsites where S. fuscum and S. angustifolium dominated. However, addition of 100 kg NH4NO3-N ha−1 yr−1 increased the CH4 emission from those microsites dominated by S. fuscum. This increase was associated with the increase in coverage of cotton grass (Eriophorum vaginatum) induced by the nitrogen treatment. The differences in the CH4 emissions were not related to the CH4 oxidation and production potentials in the peat profiles. The N2O fluxes were negligible from all microsites. Only minor short-term increases occurred after the nitrogen addition.

Methane Oxidation in Three Alberta Soils: Influence of Soil Parameters and Methane Flux Rates

Current concern over the potentially negative impacts of climate change has brought attention to anthropogenic sources of methane, a primary greenhouse gas. Two such emission sources are methane leakage at heavy oil wells and sanitary landfills. At both of these sources, substantial quantities of methane could potentially be oxidised by methanotrophic microbes living in soils. Optimisation of this phenomenon may serve as an inexpensive technique for reducing methane emissions. Soil column and batch incubation experiments were performed on a landfill loam, an agricultural loam and a sedge peat to gain a better quantitative understanding of the biological and physical processes limiting CH4 oxidation in soils that undergo the freeze-thaw cycles associated with northern climates. Moisture content emerged as a critical variable that can limit a soil's CH4 oxidation potential. For example, the oxidation rate of the agricultural soil was seen to increase by an order of magnitude after increasing its moisture content from 6% to 10% of its dry weight.

Methane emission from rice fields at Cuttack, India.

Methane (CH4) emission from rice fields at Cuttack (State of Orissa, eastern India) has been recorded using an automatic measurement system (closed chamber method) from 1995–1998. Experiments were laid out to test the impact of water regime, organic amendment, inorganic amendment and rice cultivars. Organic amendments in conjunction with chemical N (urea) effected higher CH4 flux over that of chemical N alone. Application of Sesbania, Azolla and compost resulted in 132, 65 and 68 kg CH4 ha−1 in the wet season of 1996 when pure urea application resulted in 42 kg CH4 ha−1. Intermittent irrigation reduced emissions by 15% as compared to continuous flooding in the dry season of 1996. In the wet season of 1995, four cultivars were tested under rainfed conditions resulting in a range of emissions from 20 to 44 kg CH4 ha−1. Application of nitrification inhibitor dicyandiamide (DCD) inhibited while Nimin stimulated CH4 flux from flooded rice compared to that of urea N alone. Wide variation in CH4 production and oxidation potentials was observed in rice soils tested. Methane oxidation decreased with soil depth, fertilizer-N and nitrification inhibitors while organic amendment stimulated it. The results indicate that CH4 emission from the representative rainfed ecosystem at the experimental site averaged to 32 kg CH4 ha−1 yr−1.

Effects of increased CO2 and N on CH4 efflux from a boreal mire: a growth chamber experiment.

Increases in the supply of atmospheric CO2 and N are expected to alter the carbon cycle, including CH4 emissions, in boreal peatlands. These effects were studied in a glasshouse experiment with peat monoliths cored from an oligotrophic pine fen. The cores with living plants were kept in 720 ppmv and 360 ppmv CO2 atmospheres for about 6 months under imitated natural temperature cycle. Fertilisation with NH4NO3 (3 g m-2 for 25 weeks) was applied to 18 of the 36 monoliths. The rate of CH4 flux was non-linearly dependent on the number of Eriophorum vaginatum shoots growing in the monoliths, probably due to the gas transport properties of the aerenchyma. The average CH4 efflux rate, standardised by the number of shoots, was increased by a maximum of 10-20% in response to the raised CO2 level. In the raised-NH4NO3 treatment, the increase in CH4 release was lower. The effect of combined CO2+NH4NO3 on CH4 release was negligible and even lower than in the single treatments. Both potential CH4 production and oxidation rates at 5, 15 and 25°C were higher near the surface than at the bottom of the core. As expected, the rates clearly depended on the incubation temperature, but the different treatments did not cause any consistent differences in either CH4 production or oxidation. The determination of potential CH4 production and oxidation in the laboratory is evidently too crude a method of differentiating substrate-induced differences in CH4 production and oxidation in vivo. These results indicate that an increase in atmospheric CO2 or N supply alone, at least in the short term, slightly enhances CH4 effluxes from boreal peatlands; but together their effect may even be restrictive.

Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire

1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment. 2 The vascular cores (‘Sedge’) consisted of a moss layer with sedges, and the moss cores (‘Sphagnum’) of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C). 4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.

Seasonal variation in CH 4 emissions and production and oxidation potentials at microsites on an oligotrophic pine fen

Temporal and spatial variation in CH4 emissions was studied at hummock, Eriophorum lawn, flark and Carex lawn microsites in an oligotrophic pine fen over the growing season using a static chamber method, and CH4 production and oxidation potentials in peat profiles from hummock and flark were determined in laboratory incubation experiments. Emissions were lowest in the hummocks, and decreased with increasing hummock height, while in the lawns and flarks they increased with increasing sedge cover. Statistical response functions with water table and peat temperature as independent variables were calculated in order to reconstruct seasonal CH4 emissions by reference to the time series for peat temperature and water table specific to each microsite type. Mean CH4 emissions in the whole area in the snow-free period of 1993, weighted in terms of the proportions of the microsites, were 1.7 mol CH4 m-2. Potential CH4 production and oxidation rates were very low in the hummocks rising above the groundwater table, but were relatively similar when expressed per dry weight of peat both in the hummocks and flarks below the water table. The CH4 production potential increased in autumn at both microsites and CH4 oxidation potential seemed to decrease. The decrease in temperature in autumn certainly reduced in situ decomposition processes, possibly leaving unused substrates in the peat, which would explain the increase in CH4 production potential.

Depth distribution of microbial production and oxidation of methane in northern boreal peatlands

The depth distributions of anaerobic microbial methane production and potential aerobic microbial methane oxidation were assessed at several sites in both Sphagnum- and sedge-dominated boreal peatlands in Sweden, and compared with net methane emissions from the same sites. Production and oxidation of methane were measured in peat slurries, and emissions were measured with the closed-chamber technique. Over all eleven sites sampled, production was, on average, highest 12 cm below the depth of the average water table. On the other hand, highest potential oxidation of methane coincided with the depth of the average water table. The integrated production rate in the 0-60 cm interval ranged between 0.05 and 1.7 g CH4 m (-2) day(-) and was negatively correlated with the depth of the average water table (linear regression: r (2) = 0.50, P = 0.015). The depth-integrated potential CH4-oxidation rate ranged between 3.0 and 22.1 g CH4 m(-2) day(-1) and was unrelated to the depth of the average water table. A larger fraction of the methane was oxidized at sites with low average water tables; hence, our results show that low net emission rates in these environments are caused not only by lower methane production rates, but also by conditions more favorable for the development of CH4-oxidizing bacteria in these environments.