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1

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Hydrogen consumption and carbon monoxide production in soils with different properties (2000)

Gödde, Monika ; Meuser, Katja ; Conrad, R.

Springer

Biology and fertility of soils 32 (2000), S. 129-134

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ISSN: 1432-0789

Keywords: Key words Atmospheric hydrogen ; Atmospheric carbon monoxide ; Soil organic carbon ; Substrate-induced respiration ; Multiple regression

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Soils are the dominant sink in the global budget of atmospheric H2, and can be an important local source of atmospheric CO. In order to understand which soil characteristics affect the rates of H2 consumption and CO production, we measured these activities in 16 different soils at 30% and 60% of their maximum water holding capacity (whc). The soils were obtained from forests, meadows and agricultural fields in Germany and exhibited different characteristics with respect to texture, pH, total C, substrate-induced respiration (SIR), respiration, total and inorganic N, N mineralization, nitrification, N2O production and NO turnover. The H2 consumption rate constants were generally lower at 60% than at 30% whc, whereas the CO production rates were not influenced by the whc. Spearman correlation analysis showed that H2 consumption correlated significantly (r〉0.5, P〈0.05) at both water contents only with SIR and potential nitrification. The correlation with these variables that are largely dominated by soil microorganisms is consistent with our understanding that atmospheric H2 is oxidized by soil hydrogenases. Multiple regression analysis and factor analysis gave similar results. Production of CO, on the other hand, was significantly correlated to soil total C, respiration, total N and NH4 +. The correlation with these variables that are largely dominated by a soil's chemical composition is consistent with our understanding that CO is produced by chemical oxidation of soil organic C. CO production was also influenced by soil usage, with rates increasing in the order: arable〈meadow〈forest. H2 consumption was not influenced by soil usage.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003740000226

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2

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Electron balance during steady-state production of CH4 and CO2 in anoxic rice soil (2000)

Yao, H. ; Conrad, R.

Oxford, UK : Blackwell Science Ltd

European journal of soil science 51 (2000), S. 0

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ISSN: 1365-2389

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: In methanogenic rice-field soil, organic matter (SOM) is anaerobically fermented to acetate, CO2 and H2 which then serve as substrates for methanogenesis. The whole process is a disproportionation reaction in which part of the SOM is oxidized to CO2 and part is reduced to CH4. We were interested in the electron balance during this process. The rates VCO2 and VCH4 at which CO2 and CH4 are produced by anaerobic degradation of SOM, and the fraction RH2 of the CH4 produced by reduction of CO2 with H2 (as opposed to acetotrophic methanogenesis), depend on (i) the presence or absence of inorganic oxidants and (ii) the electron balance ΔZ. Under pseudo steady-state conditions, where inorganic oxidants are exhausted and the rate of SOM degradation is small compared with the size of the pool, VCO2, VCH4 and RH2 are constrained by ΔZ. Conversely, ΔZ may be determined from VCO2, VCH4 and RH2, all of which may be independently measured. We measured VCO2 (0.149–0.308 μmol g−1 day−1), VCH4 (0.169–0.466 μmol g−1 day−1) and RH2 (0.19–0.35) in eight soils and obtained values of ΔZ ranging from −0.918 to 0.035 μmol g−1 day−1. The majority (six) were negative, indicating a decrease in the oxidation state of the SOM carbon on degradation. This could be caused by humic acids acting as an electron acceptor and allowing more of the SOM to be oxidized to CO2 rather than reduced to CH4. Direct measurement of SOM carbon oxidation state Z produced values around zero (−0.1 ± 0.1), but is too insensitive to reveal changes of the magnitude of ΔZ.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2389.2000.00330.x

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Effect of soil aggregate size on methanogenesis and archaeal community structure in anoxic rice field soil (2000)

Ramakrishnan, B ; Lueders, T ; Conrad, R ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology ecology 32 (2000), S. 0

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ISSN: 1574-6941

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: In anoxically incubated slurries of Italian rice field soil, CH4 production is initiated after a lag phase during which ferric iron and sulfate are reduced. The production of CH4 was affected by the size of soil aggregates used for the preparation of the soil slurry. Rates of CH4 production were lowest with small aggregates (〈50 and 50–100 μm), were highest with aggregates of 200–2000 μm size and were intermediate with aggregates of 2000–15 000 μm size. The different amounts of CH4 accumulated were positively correlated to the concentrations of acetate, propionate and caproate that transiently accumulated in the slurries prepared from different aggregate sizes and also to the organic carbon content. The addition of organic debris that was collected from large-size aggregates to the aggregate size fractions 〈200 and 〈50 μm resulted in an increase of CH4 production to amounts that were comparable to those measured in unamended aggregates of 200–2000 μm size, indicating that CH4 production in the different aggregate size fractions was limited by substrate. The distribution of archaeal small-subunit rRNA genes in the different soil aggregate fractions was analyzed by terminal restriction fragment length polymorphism which allowed seven different archaeal ribotypes to be distinguished. Ribotype-182 (consisting of members of the Methanosarcinaceae and rice cluster VI), ribotype-389 (rice cluster I and II) and ribotype-820 (undigested DNA, rice cluster IV and members of the Methanosarcinaceae) accounted for 〉20, 〉30 and 〉10% of the total, respectively. The other ribotypes accounted for 〈10% of the total. The relative quantity of the individual ribotypes changed only slightly with incubation time and was almost the same among the different soil aggregate fractions. Ribotype-389, for example, slightly decreased with time, whereas ribotype-182 slightly increased. At the end of incubation, the relative quantity of ribotype-182 seemed to be slightly higher in soil fractions with larger than with smaller aggregates, whereas it was the opposite with ribotype-80 (Methanomicrobiaceae) and ribotype-88 (Methanobacteriaceae). Ribotype-280 (Methanosaetaceae and rice cluster V), ribotype-375 (rice cluster III), ribotype-389 and ribotype-820, on the other hand, were not much different among the different soil aggregate size fractions. However, the differences were not significant relative to the errors encountered during the extraction of polymerase chain reaction (PCR)-amplifiable DNA from soil. In conclusion, soil aggregate size and incubation time showed a strong effect on the function but only a small effect on the structure of the methanogenic microbial community.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1574-6941.2000.tb00719.x

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Effect of 2-bromo-ethane sulfonate, molybdate and chloroform on acetate consumption by methanogenic and sulfate-reducing populations in freshwater sediment (2000)

Scholten, Johannes C.M. ; Conrad, R. ; Stams, Alfons J.M.

Oxford, UK : Blackwell Publishing Ltd

FEMS microbiology ecology 32 (2000), S. 0

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ISSN: 1574-6941

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The relative importance of methanogenesis and sulfate reduction in freshwater sediment supplemented with acetate was investigated. Addition of acetate stimulated both methane formation and sulfate reduction, indicating that an active aceticlastic population of methanogens and sulfate reducers was present in the sediment. Sulfate reducers were most important in the consumption of acetate. However, when sulfate reducers were inhibited, acetate was metabolised at a similar rate by methanogens. Acetate, propionate and valerate accumulated only when both processes were inhibited by the combined addition of 2-bromo-ethane sulfonate and molybdate. The relative amounts of acetate, propionate and valerate were 93, 6 and 1 mol%, respectively. These results demonstrate the role of acetate as a key intermediate in the terminal step of organic matter mineralisation in the sediment. Addition of chloroform inhibited both methanogenesis and sulfate reduction. We studied the inhibitory effect of CHCl3 on homoacetogenic bacteria, sulfate-reducing bacteria and methanogens. The results showed that inhibition by CHCl3 correlates with microorganisms, which operate the acetyl-CoA cleavage pathway. We propose that chloroform can be used to elucidate the role of different metabolic types of sulfate reducers to sulfate reduction in natural environments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1574-6941.2000.tb00696.x

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5

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Influence of soil properties on the turnover of nitric oxide and nitrous oxide by nitrification and denitrification at constant temperature and moisture (2000)

Gödde, Monika ; Conrad, R.

Springer

Biology and fertility of soils 32 (2000), S. 120-128

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ISSN: 1432-0789

Keywords: Key words Nitric oxide production ; Nitric acid uptake ; Nitrous oxide release ; Factor analysis ; Multiple regression

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Soils are a major source of atmospheric NO and N2O. Since the soil properties that regulate the production and consumption of NO and N2O are still largely unknown, we studied N trace gas turnover by nitrification and denitrification in 20 soils as a function of various soil variables. Since fertilizer treatment, temperature and moisture are already known to affect N trace gas turnover, we avoided the masking effect of these soil variables by conducting the experiments in non-fertilized soils at constant temperature and moisture. In all soils nitrification was the dominant process of NO production, and in 50% of the soils nitrification was also the dominant process of N2O production. Factor analysis extracted three factors which together explained 71% of the variance and identified three different soil groups. Group I contained acidic soils, which showed only low rates of microbial respiration and low contents of total and inorganic nitrogen. Group II mainly contained acidic forest soils, which showed relatively high respiration rates and high contents of total N and NH4 +. Group III mainly contained neutral agricultural soils with high potential rates of nitrification. The soils of group I produced the lowest amounts of NO and N2O. The results of linear multiple regression conducted separately for each soil group explained between 44–100% of the variance. The soil variables that regulated consumption of NO, total production of NO and N2O, and production of NO and N2O by either nitrification or denitrification differed among the different soil groups. The soil pH, the contents of NH4 +, NO2 – and NO3 –, the texture, and the rates of microbial respiration and nitrification were among the important variables.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003740000247

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6

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Effect of temperature on reduction of iron and production of carbon dioxide and methane in anoxic wetland rice soils (2000)

Yao, H. ; Conrad, R.

Springer

Biology and fertility of soils 32 (2000), S. 135-141

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ISSN: 1432-0789

Keywords: Key words Methane ; Sequential reduction ; Thermophile ; Activation energy ; Iron reduction

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Wetland rice soils from Italy (Pavia) and the Philippines (Bugallon, Luisiana, Maligaya) were incubated under anoxic conditions at 31 different temperatures ranging from 4.7 °C to 49.5 °C. Production of CO2 was most intensive at the beginning of the incubation (0–4 days) and was predominantly coupled to the reduction of free Fe(III). The optimum temperature for these processes was between 32 °C and 41 °C. After 9–16 days, CO2 production rates had decreased and the available Fe(III) had been completely reduced at the optimum temperatures. However, Fe(III) was still available at temperatures below and above the optimum. Maximum CH4 production rates were observed after 4–16 days (except in soil from Maligaya) with temperature optima between 32 °C and 41 °C, similar to those for CO2 production and Fe reduction. Since ongoing Fe reduction is known to suppress CH4 production, the temperature range of optimum CH4 production was restricted to those temperatures at which Fe(III) had already been depleted. Nevertheless, the temperature characteristics of both CO2 and CH4 production often exhibited two temperature optima at some time during the incubation, suggesting a complex pattern of adaptation of the methanogenic microbial community to temperature. When available Fe(III) was completely depleted by anoxic pre-incubation at 30 °C, CH4 was produced at a constant rate (steady state conditions) which increased with increasing temperature. Steady state CH4 production reached a first maximum at about 40 °C, but increased further up to at least 50 °C, suggesting the presence of thermophilic microorganisms whose activity was apparently masked when Fe had not been completely reduced. The apparent activation energy of CH4 production at steady state ranged between 48 kJ mol–1 and 65 kJ mol–1.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003740000227

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Air Monitoring Data Reveal Previously Unknown Contamination at Radioactive Waste Disposal Area, Los Alamos National Laboratory (2000)

Kraig, D. H. ; Conrad, R. C.

Springer

Journal of radioanalytical and nuclear chemistry 243 (2000), S. 353-359

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ISSN: 1588-2780

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering

Notes: Abstract Air monitoring at Area G, the low-level radioactive waste disposal area at Los Alamos National Laboratory, revealed increased air concentrations of 239Pu and 241Am at one location along the north boundary. This air monitoring location is a couple of meters north of a dirt road used to access the easternmost part of Area G. Air concentrations of 238Pu were essentially unaffected, which was puzzling because both 238Pu and 239Pu are present in the local, slightly contaminated soils. Air concentrations of these radionuclides increased about a factor of ten in early 1995 and remained at those levels until the first quarter of 1996. During the spring of 1996 air concentrations again increased by a factor of about ten. No other radionuclides were elevated, and no other Area G stations showed elevations of these radionuclides. After several formal meetings did not provide an adequate explanation for the elevations, a gamma-survey was performed and showed a small area of significant contamination just south of the monitor location. We found that in February 1995, a trench for a water line had been dug within a meter or so of the air stations. Then, during early 1996, the dirt road was rerouted such that its new path was directly over the unknown contamination. It appears that the trenching brought contaminated material to the surface and caused the first rise in air concentrations and then the rerouting of the road over the contamination caused the second rise, during 1996. We also found that during 1976 and 1977 contaminated soils from the clean-up of an old processing facility had been spread over the filled pits in the vicinity of the air monitors. These soils, which were probably the source of the air contamination, were very low in 238Pu which explains why we saw very little 238Pu in the increased air concentrations. A layer of gravel and sand was spread over the contaminated area. Although air concentrations of 239Pu and 241Am dropped considerably, they have not returned to pre-1995 levels.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1016049308340

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