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Titel |
Low vertical transfer rates of carbon inferred from radiocarbon analysis in an Amazon podzol |
VerfasserIn |
Carlos Sierra, Eliana Jimenez, Björn Reu, Angelika Thuille |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250078234
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Zusammenfassung |
Hydromorphic podzol soils in the Amazon basin generally support low-stature forests with
some of the lowest amounts of aboveground net primary production (NPP) in the
region. However, they can also exhibit large values of belowground NPP that can
contribute significantly to the total annual inputs of organic matter into the soil. These
hydromorphic podzol soils also exhibit a horizon rich in organic matter at around
1 m depth, presumably as a result of elluviation of dissolved organic matter and
sesquixides of Fe and Al. Therefore, it is likely that these ecosystems store large
quantities of carbon by a) large amounts of C inputs to soils dominated by their high
levels of fine-root production, b) stabilization of organic matter in an illuviation
horizon due to significant vertical transfers of C. To assess these ideas we studied soil
carbon dynamics using radiocarbon in two adjacent Amazon forests growing on
contrasting soils, a hydromorphic podzol and a well-drained alisol supporting a
high-stature terra-firme forest. Our measurements showed similar concentrations of C and
radiocarbon in the litter layer and the first 5 cm of the mineral soil for both sites.
This result is consistent with the idea that the hydromorphic podzol soil has similar
soil C storage and cycling rates than the well-drained alisol that supports a more
opulent vegetation. However, we found important differences in carbon dynamics and
transfers along the vertical profile. At both soils, we found similar radiocarbon
concentrations in the subsoil, but the carbon released after incubating soil samples
presented radiocarbon concentrations of recent origin in the alisol, but not in the
podzol. There were no indications of incorporation of C fixed after 1950 in the
illuvial horizon of the podzol. With the aid of a simulation model, we predicted
that only a minor fraction (1.7%) of the labile carbon decomposed in the topsoil is
transferred to the subsoil of the podzol, while this proportional transfer is about
90% in the alisol. Furthermore, our estimates were 8 times lower than previous
estimations of vertical C transfers in Amazon podzols, and question the validity of these
previous estimations for all podzols within the Amazon basin. Our results also
challenge previous ideas about the genesis of these soils and suggest that either
these soils are not true podzols or the podzolization processes had already stopped. |
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