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  • 1
    Electronic Resource
    Electronic Resource
    Influence of O2 availability on NO and N2O release by nitrification and denitrification in soils (1998)
    Oxford, UK : Blackwell Science, Ltd
    Global change biology 4 (1998), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The availability of O2 is believed to be one of the main factors regulating nitrification and denitrification and the release of NO and N2O. The availability of O2 in soil is controlled by the O2 partial pressure in the gas phase and by the moisture content in the soil. Therefore, we investigated the influence of O2 partial pressures and soil moisture contents on the NO and N2O release in a sandy and a loamy silt and differentiated between nitrification and denitrification by selective inhibition of nitrification with 10 Pa acetylene. At 60% whc (maximum water holding capacity) NO and N2O release by denitrification increased with decreasing O2 partial pressure and reached a maximum under anoxic conditions. Under anoxic conditions NO and N2O were only released by denitrification. NO and N2O release by nitrification also increased with decreasing O2 partial pressure, but reached a maximum at 0.1–0.5% O2 and then decreased again. Nitrification was the main source of NO and N2O at O2 partial pressures higher than 0.1–0.5% O2. At lower O2 partial pressures denitrification was the main source of NO and N2O. With decreasing O2 partial pressure N2O release increased more than NO release, indicating that the N2O release was more sensitive against O2 than the NO release. At ambient O2 partial pressure (20.5% O2) NO and N2O release by denitrification increased with increasing soil moisture content. The maximum NO and N2O release was observed at soil moisture contents of 65–80% whc and 100% whc, respectively. NO and N2O release by nitrification also increased with increasing soil moisture content with a maximum at 45–55% whc and 90% whc, respectively. Nitrification was the main source of NO and N2O at soil moisture contents lower than 90% whc and 80% whc, respectively. Higher soil moisture contents favoured NO and N2O release by denitrification. Soil texture had also an effect on the release of NO and N2O. The coarse-textured sandy silt released more NO than N2O compared with the fine-textured loamy silt. At high soil moisture contents (80–100% whc) the fine-textured soil showed a higher N2O release by denitrification than the coarse-textured soil. We assume that the fine-textured soil became anoxic at a lower soil moisture content than the coarse-textured soil. In conclusion, the effects of O2 partial pressure, soil moisture and soil texture were consistent with the theory that denitrification increasingly contributes to the release of NO and in particular N2O when conditions for soil microorganisms become increasingly anoxic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1998.00161.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of short-term drainage and aeration on the production of methane in submerged rice soil (1998)
    Oxford, UK : Blackwell Science, Ltd
    Global change biology 4 (1998), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Emission rates of CH4 were measured in microcosms of submerged soil which were planted with rice. Drainage of the rice microcosms for 48 h resulted in drastically decreased CH4 emission rates which only slowly recovered to the rates of the undrained controls. Drainage also resulted in drastically increased sulphate concentrations which only slowly decreased to nearly zero background values after the microcosms were submerged again. The mechanisms responsible for the decrease of CH4 production by aeration were investigated in slurries of a loamy and a sandy Italian rice soil. Incubation of the soil slurries under anoxic conditions resulted first in the reduction of nitrate, sulphate and ferric iron before CH4 production started. Incubation of the soil slurries for 48 h under air resulted in immediate and complete inhibition of CH4 production. Although the soil slurries were then again incubated under anoxic conditions (N2 atmosphere), the inhibition of CH4 production persisted for more than 30 days. The redox potential of the soil increased after the aeration but returned within 15 days to the low values typical for CH4 production. However, the concentrations of sulphate and of ferric iron increased dramatically after the aeration and stayed at elevated levels for the period during which CH4 production was inhibited. These observations show that even brief exposure of the soil to O2 allowed the production of sulphate and ferric iron from their reduced precursors. Elevated sulphate and ferric iron concentrations allowed sulphate-reducing and ferric iron-reducing bacteria to outcompete methanogenic bacteria on H2 as common substrate. Indeed, concentrations of H2 were decreased as long as sulphate and ferric iron were high so that the Gibbs free energy of CH4 production from H2/CO2 was also increased (less exergonic). On the other hand, concentrations of acetate, the more important precursor for CH4, were not much affected by the short aeration of the soil slurries, and the Gibbs free energy of CH4 production from acetate was highly exergonic suggesting that acetotrophic methanogens were not outcompeted but were otherwise inhibited. Aeration also resulted in increased rates of CO2 production and in a short-term increase of N2O production. However, these increases were 〈 10% of the decreased production of CH4 and did not represent a trade-off in terms of CO2 equivalents. Hence, short-term drainage and aeration of submerged paddy fields may be a useful mitigation option for decreasing the emission of greenhouse gases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1998.00162.x
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  • 3
    Electronic Resource
    Electronic Resource
    Oxidative consumption of nitric oxide by heterotrophic bacteria in soil (1996)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 19 (1996), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: Uptake rate constants for nitric oxide were measured in a neutral calcic cambisol (KBE) and an acidic luvisol (PBE). The NO uptake was higher under oxic than under anoxic incubation conditions by a factor of about three. Gassing the soils with air containing 10 ppmv NO resulted in the accumulation of nitrate which accounted for 57–94% of the NO consumed. Aerobic heterotrophic bacteria were isolated on glucose-yeast extract medium from soil dilutions corresponding to a most probable number of 108–109 bacteria per gram dry weight soil. One of the isolates (strain PS88, a Pseudomonas sp.) exhibited NO consumption activity that was much higher under oxic than anoxic incubation conditions. When sterile KBE amended with strain PS88 was gassed with air containing 10 ppmv NO, 88% of the consumed NO was recovered as nitrate and nitrite. A screening of various bacteria obtained from culture collections showed a widespread ability for consumption of low NO concentrations. Our results indicate that NO consumption in soil is not only possible by reductive denitrification, but also by oxidation due to aerobic heterotrophic bacteria such as strain PS88.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1996.tb00209.x
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  • 4
    Electronic Resource
    Electronic Resource
    Intermediary metabolism in methanogenic paddy soil and the influence of temperature (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 18 (1995), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: The intermediary metabolism in methanogenic rice paddy soil was studied by slurry incubation experiments at low (15°C) and high (30°C) temperatures. A shift to a low temperature, inhibition of methanogenesis by the addition of CHCl3, or inhibition of H2-producing syntrophic bacteria by increased partial pressures of H2 (0.2 bar) all resulted in the accumulation of metabolic intermediates. The temperature shift to 15°C resulted in a decrease of the CH4 production rate and of the H2 and CO2 partial pressures, and resulted in the transient accumulation of acetate, propionate, caproate, lactate, and iso-propanol. Chloroform inhibited methanogenesis and resulted in the accumulation of acetate, H2, propionate, caproate, lactate, and iso-propanol at both 15°C and 30°C. Addition of H2 resulted in the accumulation of propionate, caproate, lactate, formate and iso-propanol at both temperatures. The added H2 was consumed, together with CO2, mainly by methanogenesis at 30°C, but mainly by homoacetogenesis at 15°C. A decrease in temperature caused an increase (less exergonic) of the Gibbs free energy of the H2-producing reactions that was larger than that of the H2-consuming reactions. Addition of chloroform, and even more so of H2, also resulted in increased Gibbs free energies of H2-producing reactions, thus explaining why the intermediates detected did accumulate. The metabolites that accumulated when methanogenesis was inhibited by chloroform largely (76–108%) accounted for the missing CH4. Carbon flow through acetate contributed 79–83% of the total carbon flow to CH4. Comparison of the relative amounts of accumulated intermediates indicates that the H2-producing reactions (presumably syntrophic bacteria) were more sensitive to low temperature than the H2-consuming reactions, and that H2 consumption by methanogenesis was more sensitive than H2 consumption by homoacetogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1995.tb00166.x
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  • 5
    Electronic Resource
    Electronic Resource
    Role of interspecies H2 transfer to sulfate and ferric iron-reducing bacteria in acetate consumption in anoxic paddy soil (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 16 (1995), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Addition of sulfate resulted in complete inhibition of methanogenesis in anoxic paddy soil. About 20% of the CH4 was produced from H2/14CO2, the rest from acetate. Inhibition of H2-dependent methanogenesis was explained by successful competition by sulfate reducers for H2, as the H2 partial pressures decreased upon addition of sulfate. However, acetate concentrations did not decrease. Sulfate reduction was stimulated by H2, but not by acetate. Counts of acetate-utilizing sulfate reducers were relatively low both in fresh and pasteurized soil indicating that the bacteria were only present as spores. Inhibition of methanogenesis by chloroform resulted in accumulation of both H2 and acetate. When sulfate was added in addition, H2 accumulation stopped, but acetate still accumulated indicating that the activity of the methanogens was necessary for acetate conversion and that acetate could not be utilized by the sulfate reducers directly. Conversion of [2-14C]acetate resulted in formation of relatively more 14CO2, when sulfate was added, indicating that the methyl group of acetate was now being oxidized instead of reduced. Addition of chloroform strongly inhibited the conversion of [2-14C]acetate, even in the presence of sulfate. A conceivable explanation is sulfate-dependent interspecies H2 transfer between acetate-utilizing methanogens and H2-utilizing sulfate reducers, changing the electron flow from CH4 production to sulfate reduction. Addition of ferrihydrite resulted only in incomplete inhibition of methanogenesis which could be explained by successful competition of ferric iron reducers for H2. The ferric iron reducers were able to use acetate directly, but did not outcompete the methanogens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1995.tb00269.x
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  • 6
    Electronic Resource
    Electronic Resource
    Methane emission from hypersaline microbial mats: Lack of aerobic methane oxidation activity (1995)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 16 (1995), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Methane emission was measured in intact cores of microbial mats taken from hypersaline Solar Lake (Sinai) and from salterns of the city of Eilat at salinities of 9% and 13%, respectively. The CH4 emission rates were 0.4–2.2 nmol cm−2 h−1 irrespectively of the incubation conditions, i.e. incubation in the light versus dark, with air versus argon headspace. CH4 emission rates did not increase under anaerobic conditions in the dark. The rate of CH4 emission also did not increase in the presence of potential inhibitors of CH4 oxidation, i.e. acetylene (≤ 8%), methyl fluoride (1.5%), or dimethyl ether (≤ 10%) indicating that the CH4 flux was not affected by CH4 oxidation. However, addition of 20% acetylene inhibited CH4 production and resulted in zero emission. Aerobic incubation of mat pieces in the presence of 0.1 to 10% CH4 did not result in uptake of CH4. Attempts to obtain enrichment cultures of methanotrophic bacteria from the microbial mats at 9% salinity failed. Measurement of O2 microprofiles using a poiarographic O2 electrode showed that O2 was available in darkness to at least 0.5 mm depth. in the light, O2 was produced by oxygenic photosynthesis, reached supersaturation at about 1.5 mm depth, and penetrated to at least 2.5 mm depth. Measurement of CH4 microprofiles using a gas diffusion probe showed that CH4 concentrations increased linearly from the surface down to 〉 20 mm depth. The CH4 flux calculated from the CH4 gradient was the same as the flux that was actually measured. All these experiments indicate that hypersaiine microbial mats contain no aerobic CH4 oxidation activity, and probably no methanotrophic bacteria, although both O2 and CH4 are available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1995.tb00294.x
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  • 7
    Electronic Resource
    Electronic Resource
    How specific is the inhibition by methyl fluoride of acetoclastic methanogenesis in anoxic rice field soil? (1999)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 30 (1999), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Acetoclastic methanogens have been described to be inhibited at much lower concentrations of methyl fluoride, CH3F, than H2/CO2-utilizing methanogens. Therefore, we tested whether CH3F inhibition may be used to determine, in anoxic rice field soil, the contribution of H2/CO2-dependent methanogenesis to the total CH4 production by comparing this technique with the incorporation of 14CO2 into CH4. In general, addition of 0.01–1% CH3F to the gas phase resulted in an immediate partial inhibition of the total CH4 production which lasted for at least 200 h. Inhibition increased with the logarithm of the initial CH3F concentration up to about 0.2–0.6%. The initial CH3F concentration slowly decreased with time, probably due to decomposition. CH4 production sometimes completely recovered during the course of the experiment. The presence of CH3F resulted in the accumulation of acetate, the final concentration of which was usually stoichiometrically related to the deficit in CH4 production and increased with the initial CH3F concentration. In some experiments, acetate accumulation was larger than expected from the CH4 deficit and a substantial incorporation of 14CO2 into acetate was observed. Hydrogen, on the other hand, was only slightly elevated in the presence of CH3F. Addition of increasing CH3F resulted in an increase of the percentage of H2-dependent methanogenesis (measured by conversion of 14CO2 to 14CH4) demonstrating that acetoclastic methanogenesis was preferentially inhibited by CH3F. However, the conversion of 14CO2 to 14CH4 was also slightly inhibited by CH3F. Apparently, CH3F inhibited the H2-dependent methanogenesis to some extent, depending on the concentration of CH3F applied. Indeed, the ratio between the residual CH4 production rate and the fraction of CH4 produced from 14CO2 decreased with an increasing CH3F concentration. A ratio of unity was obtained at initial CH3F concentrations of 0.2–0.6% (58–174 μM). Both methods, i.e. inhibition using 0.5% CH3F and conversion of 14CO2 to 14CH4, were applied to determine the temporal change of the contribution of H2/CO2-dependent methanogenesis to the total CH4 production in two different batches of Italian rice field soil during a 120-days anoxic incubation period. The results of the two methods agreed well within the error of the methods and showed a relatively constant contribution of H2/CO2-dependent methanogenesis of about 25–30% as soon as CH4 was produced at a steady rate and H2 partial pressures had stabilized at about 1.5–2.5 Pa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1999.tb00634.x
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  • 8
    Electronic Resource
    Electronic Resource
    Inhibitory effects of nitrate, nitrite, NO and N2O on methanogenesis by Methanosarcina barkeri and Methanobacterium bryantii (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 25 (1998), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In order to elucidate the mechanism of the inhibitory effect of nitrate and its denitrification intermediates nitrite, NO and N2O on methanogenesis in anoxic environments, we tested possible toxic effects of these N-compounds on the methanogenic bacteria Methanosarcina barkeri and Methanobacterium bryantii which are ubiquitous in methanogenic rice field soils. The different N-compounds inhibited H2-dependent methanogenesis by these bacteria to different extents. Nitrate showed the weakest inhibition of methanogenesis in both bacteria, followed by N2O and nitrite for Ms. barkeri, and nitrite and N2O for Mb. bryantii, respectively. In both bacteria, the strongest inhibition was caused by NO. Concentrations of 30 mM nitrate still enabled a CH4 production rate of 25–40% of that before the addition of the N-compound, whereas NO completely inhibited methanogenesis at concentrations ≥0.8–1.7 μM (equivalent to 50–100 Pa NO partial pressure). Removal of NO by replacing the atmosphere with H2/CO2 (8:2) resulted in resumption of methanogenesis only if the bacteria had been treated with NO concentrations ≤0.8 μM (50 Pa). Removal of N2O from the cultures resulted in resumption of methanogenesis if Mb. bryantii had been treated with ≤95 μM N2O (500 Pa) or Ms. barkeri with ≤950 μM N2O (5 kPa). These results show that the denitrification products of nitrate can inhibit CH4 production both reversibly and irreversibly depending on the type of methanogenic bacterium and the applied concentration of the N-compound. In a separate experiment with methanogenic rice field slurries addition of nitrate resulted in immediate inhibition of CH4 production. Nitrate was consumed resulting in the sequential accumulation of nitrite, NO and N2O which were subsequently utilized. Nitrite and N2O reached maximum concentrations that would have been inhibitory in the methanogenic bacterial cultures examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1998.tb00484.x
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  • 9
    Electronic Resource
    Electronic Resource
    Detection in soil of aerobic hydrogen-oxidizing bacteria related to Alcaligenes eutrophus by PCR and hybridization assays targeting the gene of the membrane-bound (NiFe) hydrogenase (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 22 (1997), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The presence and abundance of the aerobic, chemolithoautotrophic Alcaligenes eutrophus, and related hydrogen-oxidizing bacteria, in soil samples were determined by using a hydrogenase gene probe and two different PCR primer sets that were derived from the alignment of (NiFe) hydrogenase gene sequences available in the EMBL data bank. The specificity of both the gene probe and the primer sets was tested on the genomic DNAs of 19 hydrogenase-containing, or hydrogenase-lacking, bacteria. The hydrogenase gene probe detected hydrogenase-containing Knallgas bacteria, N2-fixing bacteria, and enterobacteria, belonging to the alpha, beta, and gamma subclasses of the Proteobacteria. Hydrogenase-containing sulfate reducers (delta subclass) were not detected. One primer set was degenerated and resulted in the amplification of gene fragments of Knallgas bacteria and N2-fixing bacteria. The other primer set was specifically designed for the gene of the small subunit of the membrane-bound hydrogenase of A. eutrophus. In addition to the target organism, only Variovorax (Alcaligenes) paradoxus gave a gene product of the expected length. A. eutrophus-related bacteria were detected in soil by using two different strategies. The first strategy required cultivation and isolation of soil bacteria on complex media. Colonies were isolated from six different soils and tested by colony hybridization with the hydrogenase gene probe. Fifteen of the positive colonies were chosen for further characterization with the PCR primers. Two of the isolates gave amplification products with the A. eutrophus-specific PCR primers, which were sequenced and found to be 89–90% identical on a nucleotide level to the hydrogenase gene of A. eutrophus H16. The second strategy avoided a cultivation step. Total DNA was isolated from the rhizosphere of rice plants and tested in PCR amplification experiments with the A. eutrophus-specific PCR primers. Two different types of hydrogenase fragments were cloned and partially sequenced. The gene fragment sequences showed 73 and 75% identity to the A. eutrophus hydrogenase sequence. In quantitative PCR amplification assays, the number (about 2.6×107 g−1 fresh roots) of these two species of hydrogenase-containing bacteria was determined in the rice rhizosphere and was found to be similar to the number (about 7.4×106 g−1 fresh roots) of Knallgas bacteria that were determined by enumeration on selective media. Thus, it was apparently possible to detect and enumerate A. eutrophus-related bacteria in soil samples by molecular techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1997.tb00371.x
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  • 10
    Electronic Resource
    Electronic Resource
    Agitation of anoxic paddy soil slurries affects the performance of the methanogenic microbial community (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 22 (1997), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rates of CH4 production in slurries of anoxic Italian paddy soils were higher when incubated without agitation than with shaking or stirring. Stirring resulted in a drastically reduced transformation of [2-14C]acetate to 14CH4 and increased the relative contribution of CH4 production from H14CO3− to total methanogenesis. Numbers of acetotrophic methanogens were low (103 g−1 dry soil) in stirred slurries. An anoxic suspension of sterile sand which was amended with Methanosarcina barkeri and acetate produced only CH4 if it was not stirred. In stirred anoxic paddy soil, acetate accumulated to very high concentrations (〈10 mM). Propionate, butyrate and/or isopropanol also increased in stirred slurries. Hydrogen partial pressures, on the other hand, reached in all treatments a similar value of about 3–5 Pa. However, H2 production was apparently inhibited by stirring, since H2 accumulated only if slurries in which methanogenesis was inhibited by chloroform were not stirred. Our results indicate that measurements of metabolic rates in anoxic paddy soil are better conducted in non-agitated incubations to avoid the potential destruction of acetotrophic methanogens, syntrophic microbial associations and other microorganisms that are sensitive to mechanical forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6941.1997.tb00378.x
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