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| Titel |
A dual isotope approach to isolate soil carbon pools of different turnover times |
| VerfasserIn |
M. S. Torn, M. Kleber, E. S. Zavaleta, B. Zhu, C. B. Field, S. E. Trumbore |
| 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 ; 10, no. 12 ; Nr. 10, no. 12 (2013-12-10), S.8067-8081 |
| Datensatznummer |
250085466
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| Publikation (Nr.) |
 copernicus.org/bg-10-8067-2013.pdf |
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| Zusammenfassung |
| Soils are globally significant sources and sinks of atmospheric CO2.
Increasing the resolution of soil carbon turnover estimates is important for
predicting the response of soil carbon cycling to environmental change. We
show that soil carbon turnover times can be more finely resolved using a
dual isotope label like the one provided by elevated CO2 experiments
that use fossil CO2. We modeled each soil physical fraction as two
pools with different turnover times using the atmospheric 14C bomb
spike in combination with the label in 14C and 13C provided by an
elevated CO2 experiment in a California annual grassland.
In sandstone and serpentine soils, the light fraction carbon was 21–54%
fast cycling with 2–9 yr turnover, and 36–79% slow cycling with
turnover slower than 100 yr. This validates model treatment of the light
fraction as active and intermediate cycling carbon. The dense,
mineral-associated fraction also had a very dynamic component, consisting of
∼7% fast-cycling carbon and ∼93% very slow cycling
carbon. Similarly, half the microbial biomass carbon in the sandstone soil
was more than 5 yr old, and 40% of the carbon respired by microbes had
been fixed more than 5 yr ago.
Resolving each density fraction into two pools revealed that only a small
component of total soil carbon is responsible for most CO2 efflux from
these soils. In the sandstone soil, 11% of soil carbon contributes more
than 90% of the annual CO2 efflux. The fact that soil physical
fractions, designed to isolate organic material of roughly homogeneous
physico-chemical state, contain material of dramatically different turnover
times is consistent with recent observations of rapid isotope incorporation
into seemingly stable fractions and with emerging evidence for hot spots or
micro-site variation of decomposition within the soil matrix. Predictions of
soil carbon storage using a turnover time estimated with the assumption of a
single pool per density fraction would greatly overestimate the near-term
response to changes in productivity or decomposition rates. Therefore, these
results suggest a slower initial change in soil carbon storage due to
environmental change than has been assumed by simpler (one-pool) mass
balance calculations. |
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