Artikkelit kirjoittajalta Ingvar Sundh

The anaerobic production and potential aerobic oxidation of methane were assessed in a Sphagnum-dominated peatland in Sweden. Peat from four depths in the 0-40 cm (below the vegetation surface) layer was collected in three different plant communities. The rate measurements were made with peat slurries in flasks. The ratio between the mean production and mean oxidation activities was more than ten-fold higher in the two wetter than in the driest community. The within profiles depth distributions of methanogenic and methane-oxidizing activity were similar, showing that a particular level may act as a net source or a net sink for methane, depending on prevailing environmental conditions (primarily the oxygen distribution). The results also suggest that methane production and consumption processes can occur in anaerobic and aerobic micro-zones in very close proximity to each other. Key words: Carbon flow, methane oxidation, methane production, peatlands

• Sundh, Department of Microbiology, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden Sähköposti: ei.tietoa@nn.oo
• Nilsson, Sähköposti: ei.tietoa@nn.oo
• Svensson, Sähköposti: ei.tietoa@nn.oo

Two main factors control the rates of methane production in peat (in senso microbial formation of methane): the water table level and the chemical characteristics of the peat material. The water table restricts oxygen penetration into the peat because of the much slower diffusion of gases in water compared to gaseous phases. The oxygen distribution will govern the location of the strictly anaerobic, methanogenic bacteria in the peat profile. The degree of waterlogging will also influence the availability of the peat plant material for microbial decomposition, when it reaches the anaerobic zone. In waterlogged environments, the surface litter will quickly enter anoxic conditions. In such environments, high methane formation potentials are often found in the uppermost peat layers. Where the water table is positioned further down in the peat profile, a higher proportion of the easily degradable compounds are degraded under oxic conditions and therefore gone by the time the litter enters the anoxic layers. Lignified organic matter reaching the anaerobic zone will be little further degraded. This effect is most likely to be compounded if the nitrogen content of the litter is low. The net flux of methane from peat surfaces is highly dependent on the extent of microbial methane oxidation in the peat profile. Methane oxidizing bacteria need oxygen for the primary oxidation of methane and for their oxygen dependent respiration. The oxygen distribution, and hence the water table position, will therefore also affect the activity of the methanotrophic bacteria. Typically, highest methane oxidation activity is found around the most frequent position of the water table. At this level, high concentrations of methane meet oxygen diffusing down from the peat surface. Methane oxidation potentials in peat have been observed to correlate with the level of the water table, the concentration of methane just below this level, and in some sub-habitats, with the emissions of methane. Field studies have also shown that comparatively dry environments with fluctuating water table levels may act as sinks as well as sources for atmospheric methane. Some habitats show diurnal rhythms, with higher emissions during night. This is probably due to temperature limitation of the methanotrophic bacteria during the night. Keywords: Carbon flow, methanogenic bacteria, methanotrophic bacteria, mire ecology

• Svensson, Department of Microbiology, Swedish University of Agricultural Sciences, Box 7025, S-750 07 Uppsala, Sweden Sähköposti: ei.tietoa@nn.oo
• Sundh, Sähköposti: ei.tietoa@nn.oo