The temporal distribution of bomb 14C in a forest soil.

Patterns of 14C enrichment in the superficial plant debris and mineral soil horizons of an established woodland have been monitored at regular intervals during the past 15 years. These data are compared with a model evaluation of carbon turnover recorded based on the changes in atmospheric 14C concentration since AD 1900. Leaf litter and decomposing plant debris are characterized by steady-state turnover val- ues of ca 2 and ca 8 years, respectively. A two-component system of `fast' (s20 yr) and `slow' (ca 350 yr) cycling carbon is indicated for the surface (0-5cm) soil humus; below 10cm, the `fast' component is rare (<5%). Selective microbal humification of leaf litter, branch, and root debris is proposed to explain a delay of several years in the peak transfer of `bomb' 14C to the soil carbon pool.