Results of laboratory experiments show that C-14-labeled methane added to s
oil was consumed faster than atmospheric C-12 methane. This implies a sourc
e of methane, presumably through methanogenesis, in a soil that is a net co
nsumer of atmospheric methane. The soil was well-drained forest soil from I
spra, Italy. An undisturbed sample was taken with a steel corer and incubat
ed under oxic conditions in a jar. Headspace samples were taken at time int
ervals and analyzed for total methane by gas chromatography and analyzed fo
r C-14 methane by liquid scintillation counting. Fluxes calculated from the
decreasing headspace mixing ratios were, for example, -6.5 and -7.1 mu mol
m(-2) hr(-1) for C-12 methane and C-14 methane, respectively. A simple mod
el is considered which reproduces reasonably well the observed mixing ratio
s as function of time.