Short-term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 pulse labelling of a boreal pine forest.
Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in pulse-labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after pulse labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future pulse-chase experiments.
Subke
Jens-Arne
JA
Stockholm Environment Institute, Department of Biology, University of York, York YO10 5DD, UK.
Vallack
Harry W
HW
Stockholm Environment Institute, Department of Biology, University of York, York YO10 5DD, UK.
Magnusson
Tord
T
Section of Soil Science, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
Keel
Sonja G
SG
Section of Soil Science, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
Metcalfe
Daniel B
DB
Section of Soil Science, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
Högberg
Peter
P
Section of Soil Science, Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
Ineson
Phil
P
Stockholm Environment Institute, Department of Biology, University of York, York YO10 5DD, UK.
D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes; D002940:Circadian Rhythm; D028223:Pinus / Q000378:metabolism*; D012987:Soil; D013696:Temperature; D013997:Time Factors; D014197:Trees / Q000378:metabolism*
D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide