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要旨

We investigated the merits of radiocarbon measurements for estimating soil organic matter
(SOM) turnover and vertical transport for a temperate deciduous forest in Germany. Eleven parameters,
defining decomposition and transport in the soil carbon model SOMPROF, were estimated using a Bayesian
approach based on organic carbon measurements and radiocarbon concentration of SOM and
heterotrophic respiration. The addition of radiocarbon data had strong effects on the parameters, most
importantly a reduction of the decomposition and production rate of the slowest SOM pool by an order
of magnitude, and a similar reduction in advective SOM transport. The modified parameters further led
to changes in the partitioning of SOM over the different model pools. The calibration results were
subsequently used to perform transient soil carbon projections for the period 1901–2100. These simulations
were run with parameter sets from calibrations both with and without radiocarbon. The results show an
increase over time of topsoil carbon and a decrease in the subsoil, adding to a net gain overall. Near the
end of the 21st century, total carbon stocks stabilize and—for the radiocarbon-constrained model—start
to decrease. However, the changes are small compared to the total stocks. The model results for the
calibrations with and without radiocarbon are in general quite similar, but the latter shows notably higher
heterotrophic respiration fluxes. Constraining the model with radiocarbon yielded only a small reduction
of uncertainty for the total carbon stocks, while for the individual depth compartments, the uncertainty was increased.