HR: 1340h
AN: B13B-1203 [Abstracts]
TI: Carbon isotope ratios of soil respiration from soil CO2 profiles and surface chamber measurements using a tunable diode laser spectrometer
AU: * Moyes, A B
EM: moyes@biology.utah.edu
AF: University of Utah, Department of Biology
257 South 1400 East, Salt Lake City, UT 84112, United States
AU: Schaeffer, S M
EM: schaeffer@biology.utah.edu
AF: University of Utah, Department of Biology
257 South 1400 East, Salt Lake City, UT 84112, United States
AU: Schauer, A
EM: schauer@biology.utah.edu
AF: University of Utah, Department of Biology
257 South 1400 East, Salt Lake City, UT 84112, United States
AU: Bowling, D R
EM: bowling@biology.utah.edu
AF: University of Utah, Department of Biology
257 South 1400 East, Salt Lake City, UT 84112, United States
AB:
A method was developed to measure δ13C of soil CO2 from soil gas samples injected directly
into the sample air stream of a tunable diode laser (TDL) spectrometer. Measurement precision was
±0.2‰, and each measurement required two minutes. An open chamber design was also evaluated
for use with the TDL. Comparison of Keeling plot intercepts from CO2 profiles generated in a laboratory
soil medium and δ13C of surface fluxes showed a 4.4‰ diffusive enrichment, as predicted by
theory. Surface CO2 flux rates were measured accurately by the TDL, but the precision of chamber isotope
measurements with the TDL was lower than would be predicted from instrument uncertainty (RMS error
>0.4‰). This may be due to small pressure fluctuations caused by flow through the chamber or
variations in background air. Soil respiration δ13C signatures were calculated from soil CO2
profiles from garden plots with and without (trenched) tree (boxelder, Acer negundo) roots for a growing season.
Respiration in plots containing roots was 2‰ enriched relative to trenched plots during the active leaf
period of the deciduous trees. This trend was contrary to expectations and potentially caused by enriched
respiration from roots, or a priming effect from root exudates, resulting in increased decomposition of enriched
soil organic matter.
DE: 0428 Carbon cycling (4806)
DE: 0486 Soils/pedology (1865)
DE: 1694 Instruments and techniques
SC: Biogeosciences [B]
MN: 2007 Fall Meeting