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| Titel |
Short term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 pulse labelling of boreal pine forest |
| VerfasserIn |
J.-A. Subke, H. W. Vallack, T. Magnusson, S. G. Keel, D. B. Metcalfe, P. Högberg, P. Ineson |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023600
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| Zusammenfassung |
| Physical diffusion of isotopic tracers into soil pores and back to the atmosphere constitutes a
considerable uncertainty for the timing and magnitude of plant belowground allocation in
pulse-chase experiments. Experiments that do not account for physical tracer diffusion into
soil pores are prone over-estimate the amount of biological tracer allocation below ground,
and under-estimate the time for this allocation to occur. We present results obtained during
the 13CO2 labelling of a Swedish Pinus sylvestris forest stand. Using a field deployed
mass spectrometer, we monitored the soil CO2 efflux and its isotopic composition
from a combination of deep and surface soil collars. These are used to partition soil
CO2 isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux and
autotrophic flux contributions. Additionally, 13C of CO2 within the soil profile was
monitored. Physical (abiotic) efflux of 13CO2 from soil pore spaces was found to
be significant for up to 48 hours after pulse labelling, and equalled the amount of
biotic label flux over 6 days. Changes in 13CO2 concentration within soil pore
spaces at different depths corroborated these results. Total soil CO2 efflux showed
significant variation between collar treatments. In particular, diurnal maxima observed
on surface collars (i.e. with plant-derived C input through roots and mycorrhizal
hyphae) were consistently shifted back in time by about 4 hours compared to deep
collars (heterotrophic flux only). The variation in biotic 13CO2 flux from surface
collars was considerable, and showed a significant correlation with the proxomity of
surrounding trees. Our results show for the first time the significance of the confounding
influence of physical isotopic tracer return from the soil matrix, calling for the
inclusion of meaningful control treatments in future pulse chase experiments. They
further point to complex interactions between plant C input and CO2 flux from
bith autotrophic and heterotrophic sources, which warrant further investigation. |
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