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Borken, Werner ; Brumme, Rainer:
Methane uptake by temperate forest soils.
In:
Brumme, Rainer ; Khanna, Partap K. (Hrsg.): Functioning and Management of European Beech Ecosystems. -
Berlin
: Springer
,
2009
. - S. 369-385
. - (Ecological Studies
; 208
)
ISBN 978-3-642-00339-4
Abstract
Net uptake of atmospheric methane by methanotrophic bacteria in forest soils isgenerally less than 20 kg CH4 ha1 per year and therefore has almost no impact onthe carbon budget of forest ecosystems. However, terrestrial soils are the mostimportant biological sink for atmospheric methane, consuming between 20 and 45Tg CH4 per year (Smith et al. 2000; Dutaur and Verchot 2007). The methaneconcentration in the atmosphere increased from about 700 to 1,774 ppb (by volume)during the last 150 years, though the concentration has possibly stabilised duringthe past decade (IPCC 2007). Methane currently contributes approximately 18% tothe anthropogenic greenhouse effect and has a global warming potential 25 timeshigher than that of CO2 based on a time horizon of 100 years (IPCC 2007).Human activities have reduced the soil sink for atmospheric methane by convertingnatural forests and grasslands to coniferous plantations, agricultural andurban land (Ojima et al. 1993; Dobbie et al. 1996; Smith et al. 2000; Borken et al.2003; Borken and Beese 2006) and by causing acid deposition in temperate forests(Brumme and Borken 1999). Undisturbed forest soils generally consume muchhigher rates of atmospheric methane than agricultural and urban soils, although themethane uptake rates may vary considerably within and among forests over allclimatic regions. Comparisons of adjacent forest and agricultural soils showed thatconverting forest land to agricultural use reduced methane uptake rates by twothirdsin both temperate and tropical regions (Smith et al. 2000). The mechanismsfor long-term reduction in methane uptake are not completely understood. Disturbancesof the soil structure as well as changes in vegetation, micro-climate, andnutrient status may have diminished the population of methane-utilising bacteria inseveral ways after land conversion to agricultural use. It is believed that these stillunidentified bacteria have an extremely slow growth rate due to the small atmosphericmethane concentration. Methanotrophs have a high affinity for methane asindicated by low Km values and low threshold concentrations (Bender and Conrad1993).