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| Titel |
Biological and physical influences on soil 14CO2 seasonal dynamics in a temperate hardwood forest |
| VerfasserIn |
C. L. Phillips, K. J. McFarlane, D. Risk, A. R. Desai |
| 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 (2013-12-09), S.7999-8012 |
| Datensatznummer |
250085463
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| Publikation (Nr.) |
 copernicus.org/bg-10-7999-2013.pdf |
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| Zusammenfassung |
| While radiocarbon (14C) abundances in standing stocks of soil carbon
have been used to evaluate rates of soil carbon turnover on timescales of
several years to centuries, soil-respired 14CO2 measurements are an
important tool for identifying more immediate responses to disturbance and
climate change. Soil Δ14CO2 data, however, are often
temporally sparse and could be interpreted better with more context for
typical seasonal ranges and trends. We report on a semi-high-frequency
sampling campaign to distinguish physical and biological drivers of soil
Δ14CO2 at a temperate forest site in northern Wisconsin, USA.
We sampled 14CO2 profiles every three weeks during snow-free months
through 2012 in three intact plots and one trenched plot that excluded roots.
Respired Δ14CO2 declined through the summer in intact plots,
shifting from an older C composition that contained more bomb 14C to a
younger composition more closely resembling present 14C levels in the
atmosphere. In the trenched plot, respired Δ14CO2 was
variable but remained comparatively higher than in intact plots, reflecting
older bomb-enriched 14C sources. Although respired Δ14CO2
from intact plots correlated with soil moisture, related analyses did not
support a clear cause-and-effect relationship with moisture. The initial
decrease in Δ14CO2 from spring to midsummer could be explained
by increases in 14C-deplete root respiration; however,
Δ14CO2 continued to decline in late summer after root activity
decreased. We also investigated whether soil moisture impacted vertical
partitioning of CO2 production, but found this had little effect on
respired Δ14CO2 because CO2 contained modern bomb C at
depth, even in the trenched plot. This surprising result contrasted with
decades to centuries-old pre-bomb CO2 produced in lab incubations of the
same soils. Our results suggest that root-derived C and other recent C
sources had dominant impacts on respired Δ14CO2 in situ, even
at depth. We propose that Δ14CO2 may have declined through
late summer in intact plots because of continued microbial turnover of
root-derived C, following declines in root respiration. Our results agree
with other studies showing declines in the 14C content of soil
respiration over the growing season, and suggest inputs of new photosynthates
through roots are an important driver. |
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