Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    Production, oxidation and emission of methane in rice paddies
    ( 1985)
    Holzapfel-Pschorn, A.
    ;
    Seiler, W.
    ;
    Conrad, R.
    Production and emission of methane from submerged paddy soil was studied in laboratory rice cultures and in Italian paddy fields. Up to 80% of the CH4 produced in the paddy soil did not reach the atmosphere but was apparently oxidized in the rhizosphere. CH4 emission through the rice plants was inhibited by an atmosphere of pure O2 but was stimulated by an atmosphere of pure N2 or an atmosphere containing 5% acetylene. Gas bubbles taken from the submerged soil contained up to 60% CH4 but only smaller than 1% CH4 after the bubbles had passed the soil-water interface or had entered the intercellular gas space system of the rice plants. CH4 oxidation activities were detected in the oxic surface layer of the submerged paddy soil. Flooding the paddy soil with water containing greater than 0.15% sea salt (0.01% sulfate) resulted in a strong inhibition of the rates of methanogenesis and a decrease in the rates of CH4 emission. This result explains the observation of relatively low CH4 emissio n rates in rice paddy areas flooded with brackish water. (IFU)
  • Publication
    Production and consumption of hydrogen in a eutrophic lake
    ( 1983)
    Seiler, W.
    ;
    Conrad, R.
    ;
    Aragno, M.
    The vertical distribution of hydrogen was measured in the Loclat, an eutrophic and holomictic lake near Neuchatel, Switzerland, before and during summer stratification. H2 concentrations decreased with depth in the anaerobic hypolimnion and were often below the detection limit (2.5 nl of H2 liter E-1) in the water adjacent to the lake sediment. The highest H2 concentrations (bigger than 4 myl of H2 liter E-1) were observed in the aerobic water of the epilimnion and metalimnion. There, the H2 concentrations changed with time, indicating a turnover of H2. The possible role of cyanobacteria and algae for H2 production is discussed. Aerobic or anaerobic H2 consumption activities were observed at all depths of the water column, with highest activities in the hypolimnion. Aerobic H2 consumption activity was insensitive to azide inhibition, but sensitive to heat, mercuric chloride, or cyanide. It was restricted to a particle fraction of 0.2 to 3.0 mym in size, so that it must be due to single bacterial cells. Aerobic hydrogen bacteria, on the other hand, occured in clusters of bigger than 3.0 mym. Therefore, the hydrogen bacteria could not have caused the H2 consumption in lake water. The aerobic H2 consumption activity followed Michaelis-Menten kinetics, with a K sub m of 67 nM H2. This is an exceptionally low value compared with K sub m values of hydrogenases in hydrogen bacteria and other species, but is similar to that for H2-decomposing abiontic soil hydrogenases. (IFU)
  • Publication
    Utilization of traces of carbon monoxide by aerobic oligotrophic microorganisms in ocean, lake and soil
    ( 1982)
    Seiler, W.
    ;
    Conrad, R.
    Carbon monoxide at trace concentrations (equal or smaller than 1 nM) was utilized in ocean water, lake water and soil. By boiling or by poisoning the water with HgCl2, NaCN or NaN3 must read CO consumption was switched off; this demonstrated that CO utilization was due to metabolic processes. Since CO consumption activity was removed by filtration through 0.2 mym filters, but not by filtration through 3.0 mym filters, CO consumption was most probably due to single bacterial cells. CO consumption followed Michaelis-Menten kinetics with K sub m-values of 7-9 nM CO. Enrichment experiments were carried out by gassing lake water and soil suspensions with ambient pressurized air containing 0.5-1.0 ppmv CO. After a total supply of approximately 2 ml CO, utilization of CO became detectable. Then, the CO consumption rates of the suspensions increased steadily with incubation time indicating the growth of a specific CO-utilizing microbial population. No CO consumption activity was detectable in control suspensions, which were gassed with CO-free air. The high affinity of soil and water for CO as well as the increase of CO consumption activity upon incubation under ambient atmospheric CO is indicative for the oligotrophic nature of a specific CO-utilizing microflora. (IFU)