The Temporal Distribution of ‘Bomb’ 14 C in a Forest Soil

Abstract

Patterns of 14 C 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 based on the recorded changes in atmospheric 14 C concentration since AD 1900. Leaf litter and decomposing plant debris are characterized by steady-state turnover values of ca 2 and ca 8 years, respectively. A two-component system of ‘fast’ (≤20 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’ 14 C to the soil carbon pool.