Soil samples, collected to a depth of 15 cm from 24 plots at six UK deciduous woodland sites in 1971 and 2002, were analysed for C-14, and total soil carbon pools (gC m(-2)) were estimated. The results, together with data from a further woodland site, were interpreted using steady-state models, driven by the C-14 content of atmospheric CO2. The average soil pool is 6700 (+/- 1100)gC m(-2), where the error term is the standard deviation. Application of a single soil pool model yielded a mean residence time (MRT) of 87 (+/-82)years, with an input of 113 (+/- 52) gC m(-2) a(-1). This implies that the remainder of the total litter production, about 300 gC m(-2) a(-1), passes through a fast pool with a short MRT (i.e. rapid mineralisation occurs). Slightly better fits, with less bias, were obtained using a model that has two soil C pools with fixed MRTs of 15 (slow pool) and 350 (passive pool), based on the findings of DD Harkness, AF Harrison and PJ Bacon (Radiocarbon 28, 328-337, 1986). From the 21 soils that gave similar results with the two C pool model, it is calculated that, on average, the soil contains 3300 gC m(-2) in the slow pool (input 215 gC m(-2) a(-1)) and 3400 gC m(-2) in the passive pool (10 gC m(-2) a(-1)); about 200 gC m(-2) a(-1) of the litter input is rapidly mineralised. The slow pool is approximately constant for all the soils, variations in total soil C being due to the range of passive pools (1800 to 5900 gC m(-2)). Equally good fits of the bulk soil C-14 data were obtained with different assumptions about the MRTs of the slow and passive pools; therefore additional information about soil fractions is needed for more exact characterisation of soil organic matter cycling on timescales of decades to millennia.
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