HR: 1340h
AN: B13B-1191    [Abstracts]
TI: Diurnal patterns of CO₂ concentrations and stable isotopes in subalpine forest soils
AU: * Schaeffer, S M
EM: schaeffer@biology.utah.edu
AF: University of Utah, Department of Biology 257 S. 1400 E. University of Utah, Salt Lake City, UT 84112, United States
AU: Bowling, D
EM: bowling@biology.utah.edu
AF: University of Utah, Department of Biology 257 S. 1400 E. University of Utah, Salt Lake City, UT 84112, United States
AB: Respiration of carbon dioxide (CO₂) from soils contributes significantly to the carbon balance of ecosystems. Measurement of the stable isotopic composition (δ¹³C) of soil and soil-respired CO₂ can provide insight into the physical and biological mechanisms controlling respiration. Very few studies examine diurnal variations in the isotopic composition of CO₂ in soils because of the difficulty in making such measurements. We measured [CO₂] and δ¹³C in and above soils in a subalpine forest near Niwot Ridge Colorado. Profile measurements were made every two hours of CO₂ in air below the soil surface (-3 cm), on the soil surface, and up to 40 cm above the soil surface. Over the course of 20 days in July of 2007, the δ¹³C of respired CO₂ (δ_R-soil) measured using these vertical profiles varied from -25.42 to -21.10‰ with a mean of -23.48 ± 1.11‰. Measurements in the air near the ground (δ_R-ground, 0.1 to 2 m) varied from -26.71 to -23.96‰ with a mean of - 25.49 ± 0.63‰. Values of δ_R-soil were enriched relative to δ_R-ground,. Diurnal patterns in δ¹³C of respired CO₂ were not apparent even though soil temperatures varied by as much as 15°C over a 24 hour period. Soil moisture is also likely important as it affects the diffusion rate of CO₂ soil and may stimulate microbial activity. Improved knowledge of the controls on soil respiration have the potential to increase process-level understanding of ecosystem respiratory fluxes and may also help better constrain terrestrial carbon cycling models.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting