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Soil moisture effects on the carbon isotope composition of soil respiration
Author(s) -
Phillips Claire L.,
Nickerson Nick,
Risk David,
Kayler Zachary E.,
Andersen Chris,
Mix Alan,
Bond Barbara J.
Publication year - 2010
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4511
Subject(s) - soil respiration , chemistry , water content , environmental chemistry , moisture , soil water , respiration , soil carbon , humidity , delta , soil science , environmental science , botany , geology , geotechnical engineering , physics , organic chemistry , aerospace engineering , engineering , thermodynamics , biology
The carbon isotopic composition ( δ 13 C) of recently assimilated plant carbon is known to depend on water‐stress, caused either by low soil moisture or by low atmospheric humidity. Air humidity has also been shown to correlate with the δ 13 C of soil respiration, which suggests indirectly that recently fixed photosynthates comprise a substantial component of substrates consumed by soil respiration. However, there are other reasons why the δ 13 CO 2 of soil efflux may change with moisture conditions, which have not received as much attention. Using a combination of greenhouse experiments and modeling, we examined whether moisture can cause changes in fractionation associated with (1) non‐steady‐state soil CO 2 transport, and (2) heterotrophic soil‐respired δ 13 CO 2 . In a first experiment, we examined the effects of soil moisture on total respired δ 13 CO 2 by growing Douglas fir seedlings under high and low soil moisture conditions. The measured δ 13 C of soil respiration was 4.7‰ more enriched in the low‐moisture treatment; however, subsequent investigation with an isotopologue‐based gas diffusion model suggested that this result was probably influenced by gas transport effects. A second experiment examined the heterotrophic component of soil respiration by incubating plant‐free soils, and showed no change in microbial‐respired δ 13 CO 2 across a large moisture range. Our results do not rule out the potential influence of recent photosynthates on soil‐respired δ 13 CO 2 , but they indicate that the expected impacts of photosynthetic discrimination may be similar in direction and magnitude to those from gas transport‐related fractionation. Gas transport‐related fractionation may operate as an alternative or an additional factor to photosynthetic discrimination to explain moisture‐related variation in soil‐respired δ 13 CO 2 . Copyright © 2010 John Wiley & Sons, Ltd.