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| Titel |
Bayesian calibration of a soil organic carbon model using Δ14C measurements of soil organic carbon and heterotrophic respiration as joint constraints |
| VerfasserIn |
B. Ahrens, M. Reichstein, W. Borken, J. Muhr, S. E. Trumbore, T. Wutzler |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 8 ; Nr. 11, no. 8 (2014-04-17), S.2147-2168 |
| Datensatznummer |
250117366
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| Publikation (Nr.) |
 copernicus.org/bg-11-2147-2014.pdf |
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| Zusammenfassung |
| Soils of temperate forests store significant amounts of organic matter and
are considered to be net sinks of atmospheric CO2. Soil organic carbon
(SOC) turnover has been studied using the Δ14C values of bulk SOC
or different SOC fractions as observational constraints in SOC models.
Further, the Δ14C values of CO2 that evolved during the
incubation of soil and roots have been widely used together with
Δ14C of total soil respiration to partition soil respiration into
heterotrophic respiration (HR) and rhizosphere respiration. However, these
data have not been used as joint observational constraints to determine SOC
turnover times. Thus, we focus on (1) how different combinations of
observational constraints help to narrow estimates of turnover times and
other parameters of a simple two-pool model, the Introductory Carbon Balance
Model (ICBM); (2) whether relaxing the steady-state assumption in a multiple
constraints approach allows the source/sink strength of the soil to be
determined while estimating turnover times at the same time. To this end ICBM
was adapted to model SOC and SO14C in parallel with
litterfall and the Δ14C of litterfall as driving variables. The
Δ14C of the atmosphere with its prominent bomb peak was used as a
proxy for the Δ14C of litterfall. Data from three spruce-dominated
temperate forests in Germany and the USA (Coulissenhieb II, Solling D0 and
Howland Tower site) were used to estimate the parameters of ICBM via Bayesian
calibration. Key findings are as follows: (1) the joint use of all four
observational constraints (SOC stock and its Δ14C, HR flux and its
Δ14C) helped to considerably narrow turnover times of the young
pool (primarily by Δ14C of HR) and the old pool (primarily by
Δ14C of SOC). Furthermore, the joint use of all observational
constraints made it possible to constrain the humification factor in ICBM,
which describes the fraction of the annual outflux from the young pool that
enters the old pool. The Bayesian parameter estimation yielded the following
turnover times (mean ± standard deviation) for SOC in the young pool:
Coulissenhieb II 1.1 ± 0.5 years, Solling D0 5.7 ± 0.8 years and
Howland Tower 0.8 ± 0.4 years. Turnover times for the old pool were
377 ± 61 years (Coulissenhieb II), 313 ± 66 years (Solling D0)
and 184 ± 42 years (Howland Tower), respectively. (2) At all three
sites the multiple constraints approach was not able to determine if the soil
has been losing or storing carbon. Nevertheless, the relaxed steady-state
assumption hardly introduced any additional uncertainty for the other
parameter estimates. Overall the results suggest that using Δ14C
data from more than one carbon pool or flux helps to better constrain SOC
models. |
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