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<sup>13</sup>C) of CO<sub>2</sub> produced by the respiration of roots and soil organisms. These changes have been correlated with diel cycles of environmental forcing (e.g., sunligh...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-08-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/5143/2015/bg-12-5143-2015.pdf |
| _version_ | 1818031672565694464 |
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| author | D. R. Bowling J. E. Egan S. J. Hall D. A. Risk |
| author_facet | D. R. Bowling J. E. Egan S. J. Hall D. A. Risk |
| author_sort | D. R. Bowling |
| collection | DOAJ |
| description | Recent studies have examined temporal fluctuations in the amount and carbon
isotope content (δ<sup>13</sup>C) of CO<sub>2</sub> 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<sub>2</sub> and δ<sup>13</sup>C of CO<sub>2</sub> 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<sup>13</sup>C of the soil efflux (δ<sub>R</sub>)
or the CO<sub>2</sub> produced by biological activity in the soil
(δ<sub>J</sub>). Following rain, soil efflux increased significantly,
but δ<sub>R</sub> and δ<sub>J</sub> did not change. Temporal
variation in the δ<sup>13</sup>C 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<sup>13</sup>C of the soil efflux
with chambers agreed closely with independent observations of the isotopic
composition of soil CO<sub>2</sub> 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<sup>13</sup>C of the soil efflux relative to δ<sup>13</sup>C
of production derived from soil profile measurements was likely caused by
transient pressure-induced transport with small horizontal length scales. |
| first_indexed | 2024-12-10T05:55:12Z |
| format | Article |
| id | doaj.art-11f8b10a2643470a8f911960cee72952 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-10T05:55:12Z |
| publishDate | 2015-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-11f8b10a2643470a8f911960cee729522022-12-22T01:59:56ZengCopernicus PublicationsBiogeosciences1726-41701726-41892015-08-0112165143516010.5194/bg-12-5143-2015Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respirationD. R. Bowling0J. E. Egan1S. J. Hall2D. A. Risk3Department of Biology, University of Utah, Salt Lake City, Utah, USADepartment of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, CanadaGlobal Change and Sustainability Center, Univ. of Utah, Salt Lake City, Utah, USADepartment of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, CanadaRecent studies have examined temporal fluctuations in the amount and carbon isotope content (δ<sup>13</sup>C) of CO<sub>2</sub> 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<sub>2</sub> and δ<sup>13</sup>C of CO<sub>2</sub> 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<sup>13</sup>C of the soil efflux (δ<sub>R</sub>) or the CO<sub>2</sub> produced by biological activity in the soil (δ<sub>J</sub>). Following rain, soil efflux increased significantly, but δ<sub>R</sub> and δ<sub>J</sub> did not change. Temporal variation in the δ<sup>13</sup>C 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<sup>13</sup>C of the soil efflux with chambers agreed closely with independent observations of the isotopic composition of soil CO<sub>2</sub> 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<sup>13</sup>C of the soil efflux relative to δ<sup>13</sup>C of production derived from soil profile measurements was likely caused by transient pressure-induced transport with small horizontal length scales.http://www.biogeosciences.net/12/5143/2015/bg-12-5143-2015.pdf |
| spellingShingle | D. R. Bowling J. E. Egan S. J. Hall D. A. Risk Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration Biogeosciences |
| title | Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| title_full | Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| title_fullStr | Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| title_full_unstemmed | Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| title_short | Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| title_sort | environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration |
| url | http://www.biogeosciences.net/12/5143/2015/bg-12-5143-2015.pdf |
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