Minor stable carbon isotope fractionation between respired carbon dioxide and bulk soil organic matter during laboratory incubation of topsoil

Breecker, D.O., Bergel, S., Nadel, M., Tremblay, M.M. , Osuna-Orozco, R., Larson, T.E. and Sharp, Z.D. (2015) Minor stable carbon isotope fractionation between respired carbon dioxide and bulk soil organic matter during laboratory incubation of topsoil. Biogeochemistry, 123(1-2), pp. 83-98. (doi:10.1007/s10533-014-0054-3)

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Abstract

A common assumption in paleoenvironmental reconstructions using soils is that the carbon isotope composition of soil-respired CO2 is equivalent to the carbon isotope composition of bulk soil organic matter (SOM). However, the occurrence of a non-zero per mil carbon isotope enrichment factor between CO2 and SOM ( εCO2−SOMεCO2−SOM) during soil respiration is the most widely accepted explanation for the down-profile increase in SOM δ13C values commonly observed in well-drained soils. In order to shed light on this apparent discrepancy, we incubated soil samples collected from the top 2 cm of soils with pure C3 vegetation and compared the δ13C values of soil-respired CO2 to the δ13C values of bulk SOM. Our results show near-zero εCO2−SOMεCO2−SOM values (−0.3 to 0.4 ‰), supporting the use of paleosol organic matter as a proxy for paleo soil-respired CO2. Significantly more negative εCO2−SOMεCO2−SOM values are required to explain the typical δ13C profiles of SOM in well-drained soils. Therefore our results also suggest that typical SOM δ13C profiles result from either (1) a process other than carbon isotope fractionation between CO2 and SOM during soil respiration or (2) εCO2−SOMεCO2−SOM values that become increasingly negative as SOM matures.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Tremblay, Dr Marissa
Authors: Breecker, D.O., Bergel, S., Nadel, M., Tremblay, M.M., Osuna-Orozco, R., Larson, T.E., and Sharp, Z.D.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Biogeochemistry
Publisher:Springer
ISSN:0168-2563
ISSN (Online):1573-515X
Published Online:27 November 2014
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