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Title: Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration

Recent studies have examined temporal fluctuations in the amount and carbon isotope content (δ 13C) of CO 2 produced by the respiration of roots and soil organisms. These changes have been correlated with diel cycles of environmental forcing (e.g., sunlight and soil temperature) and with synoptic-scale atmospheric motion (e.g., rain events and pressure-induced ventilation). We used an extensive suite of measurements to examine soil respiration over 2 months in a subalpine forest in Colorado, USA (the Niwot Ridge AmeriFlux forest). Observations included automated measurements of CO 2 and δ 13C of CO 2 in the soil efflux, the soil gas profile, and forest air. There was strong diel variability in soil efflux but no diel change in the δ 13C of the soil efflux (δ R) or the CO 2 produced by biological activity in the soil (δ J). Following rain, soil efflux increased significantly, but δ R and δ J did not change. Temporal variation in the δ 13C of the soil efflux was unrelated to measured environmental variables, and we failed to find an explanation for this unexpected result. Measurements of the δ 13C of the soil efflux with chambers agreed closely with independent observations of the isotopicmore » composition of soil CO 2 production derived from soil gas well measurements. Deeper in the soil profile and at the soil surface, results confirmed established theory regarding diffusive soil gas transport and isotopic fractionation. Deviation from best-fit diffusion model results at the shallower depths illuminated a pump-induced ventilation artifact that should be anticipated and avoided in future studies. There was no evidence of natural pressure-induced ventilation of the deep soil. However, higher variability in δ 13C of the soil efflux relative to δ 13C of production derived from soil profile measurements was likely caused by transient pressure-induced transport with small horizontal length scales.« less
 [1] ;  [2] ;  [1] ;  [3]
  1. Univ. of Utah, Salt Lake City, UT (United States)
  2. Dalhousie Univ., Halifax, NS (Canada)
  3. St. Francis Xavier Univ., Antigonish, NS (Canada)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Biogeosciences (Online)
Additional Journal Information:
Journal Name: Biogeosciences (Online); Journal Volume: 12; Journal Issue: 16; Journal ID: ISSN 1726-4189
European Geosciences Union
Research Org:
Univ. of Utah, Salt Lake City, UT (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23). Climate and Environmental Sciences Division
Country of Publication:
United States
OSTI Identifier: