Epsilon Archive for Student Projects

Abstract

Aerated soils are the largest sinks of atmospheric methane on the Earth’s surface. Methane
removal from the atmosphere is performed through oxidation by microorganisms (methaneoxidising
bacteria) in the soil. Methanotrophic bacteria utilise methane (single-carbon
compound) as their main carbon and energy source, but some groups have been found to grow
on different multi-carbon compounds. This thesis investigated the influence of soil
methanotrophs on the kinetics of methane oxidation in Swedish forest soils and the effect of
the tree species Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula
pendula) on methane consumption rates. Soil samples were collected from the study area
Vipängen (Ultuna), which is classified as a Dystrocryept with its O horizon between 0-5 cm,
A horizon 5-20 cm and B horizon 20-40 cm. The potential effect of other multi-carbon
substrates (acetate, vanillic acid and guaiacol) that could be expected to enhance the oxidation
rate of atmospheric methane was also examined. The results showed that the methanotrophs at
the study site were high-affinity species with Vmax values ranging between 4.3 and 11.0 nmol
CH4 g-1d.w. hr-1 and Km ranging between 7.4 and 185.5 nmol g-1d.w. Type of tree species
which is proposed to have a strong influence on the methane sink, clearly did so in this
incubation experiment. Consumption in soil samples from a birch stand displayed the highest
consumption rate, followed by spruce and pine for all four different initial concentrations of
methane tested (4.5, 7, 14.1 and 45.1 ppmv). Evaluation of the effects of acetate, vanillic acid
and guaiacol on methane consumption rates in the Swedish forest soils studied showed that
only addition of acetate yielded a substantial effect, demonstrating that methanotrophs are not
just limited to single-carbon bonds. Further studies on the effects of different multi-carbon
compounds on the growth of some methanotrophic species (increased oxidation) will provide
in-depth knowledge of the factors governing methane fluxes between the atmosphere and the
soil.