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| Titel |
An isotopic investigation of the temperature response of young and old soil organic matter respiration |
| VerfasserIn |
Nancy Burns, Joanna Cloy, Mark Garnett, David Reay, Keith Smith, Wilfred Otten |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040846
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| Zusammenfassung |
| The effect of temperature on rates of soil respiration is critical to our understanding of the
terrestrial carbon cycle and potential feedbacks to climate change. The relative
temperature sensitivity of labile and recalcitrant soil organic matter (SOM) is still
controversial; different studies have produced contrasting results, indicating limited
understanding of the underlying relationships between stabilisation processes and
temperature. Current global carbon cycle models still rely on the assumption that SOM
pools with different decay rates have the same temperature response, yet small
differences in temperature response between pools could lead to very different climate
feedbacks.
This study examined the temperature response of soil respiration and the age of soil
carbon respired from radiocarbon dated fractions of SOM (free, intra-aggregate and
mineral-bound) and whole soils (organic and mineral layers). Samples were collected from a
peaty gley soil from Harwood Forest, Northumberland, UK.Â
SOM fractions were isolated from organic layer (5 - 17 cm) material using high
density flotation and ultrasonic disaggregation - designated as free (< 1.8 g cm-3),
intra-aggregate (< 1.8 g cm-3 within aggregates > 1.8 g cm-3) and mineral-bound (>
1.8 g cm-3) SOM. Fractions were analysed for chemical composition (FTIR,
CHN analysis, ICP-OES), 14C (AMS), δ13C and δ15N (MS) and thermal properties
(DSC).
SOM fractions and bulk soil from the organic layer and the mineral layer (20 – 30 cm)
were incubated in sealed vessels at 30 Ë C and 10 Ë C for 3 or 9 months to allow
accumulation of CO2 sufficient for sampling. Accumulated respired CO2 samples were
collected on zeolite molecular sieve cartridges and used for AMS radiocarbon dating. In
parallel, material from the same fractions and layers were incubated at 10 Ë C, 15 Ë C, 25 Ë C
and 30 Ë C for 6 months and sampled weekly for CO2 flux measurements using GC
chromatography.Â
Initial data have shown radiocarbon ages ranging from modern to 219 y BP in bulk soil
from the organic layer (5 – 17 cm depth), while free OM ranged from modern to 74 y BP,
intra-aggregate OM 413 – 657 y BP and mineral-bound material 562 - 646 y BP. Bulk soil
from the mineral layer (20 – 30 cm) was considerably older, at 2142 – 2216 y BP. These
results indicate that within the upper layer of soil, mineral-bound OM represents a
slow-cycling or recalcitrant pool of SOM; intra-aggregate OM is slightly less recalcitrant than
mineral-bound OM, while free OM represents a fast-cycling, labile pool of SOM. Bulk soil
from the mineral layer (20 – 30 cm) is much older than mineral-bound OM in the
upper layers, suggesting the involvement of other stabilising factors associated
with depth besides mineral interactions. The link between age and recalcitrance is
corroborated by measured CO2 flux rates, which increase with decreasing age of
fractions.
Results for the 14C contents and calculated ages of isolated SOM fractions, bulk organic
and mineral soils and their respired CO2 at different temperatures will be discussed and
compared with long term trends in soil/SOM fraction CO2 fluxes and their temperature
sensitivity. Data on soil chemical characteristics and δ13C values will also be presented. |
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