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Evaluating high time‐resolved changes in carbon isotope ratio of respired CO 2 by a rapid in‐tube incubation technique
Author(s) -
Werner Christiane,
Hasenbein Nils,
Maia Rodrigo,
Beyschlag Wolfram,
Máguas Cristina
Publication year - 2007
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.2970
Subject(s) - chemistry , isotopes of carbon , carbon dioxide , analytical chemistry (journal) , isotope , incubation , chromatography , radiochemistry , environmental chemistry , total organic carbon , biochemistry , physics , organic chemistry , quantum mechanics
Recent insights into fractionation during dark respiration and rapid dynamics in isotope signatures of leaf‐ and ecosystem‐respired CO 2 indicate the need for new methods for high time‐resolved measurements of the isotopic signature of respired CO 2 ( δ 13 C res ). We present a rapid and simple method to analyse δ 13 C res using an in‐tube incubation technique and an autosampler for small septum‐capped vials. The effect of storage on the δ 18 O and δ 13 C ratios of ambient CO 2 concentrations was tested with different humidity and temperatures. δ 13 C ratios remained stable over 72 h, whereas δ 18 O ratios decreased after 24 h. Storage at 4°C improved the storage time for δ 18 O. Leaves or leaf discs were incubated in the vials, flushed with CO 2 ‐free air and respired CO 2 was automatically sampled within 5 min on a µGas autosampler interfaced to a GV‐Isoprime isotope ratio mass spectrometer. Results were validated by simultaneous on‐line gas‐exchange measurements of δ 13 C res of attached leaves. This method was used to evaluate the short‐term (5–60 min) and diurnal dynamics of δ 13 C res in an evergreen oak ( Quercus ilex ) and a herb ( Tolpis barbata ). An immediate depletion of 2–4‰ from the initial δ 13 C res value occurred during the first 30 min of darkening. Q . ilex exhibited further a substantial diurnal enrichment in δ 13 C res of 8‰, followed by a progressive depletion during the night. In contrast, T. barbata did not exhibit a distinct diurnal pattern. This is in accordance with recent theory on fractionation in metabolic pathways and may be related to the different utilisation of the respiratory substrate in the fast‐growing herb and the evergreen oak. These data indicate substantial and rapid dynamics (within minutes to hours) in δ 13 C res , which differed between species and probably the growth status of the plant. The in‐tube incubation method enables both high time‐resolved analysis and extensive sampling across different organs, species and functional types. Copyright © 2007 John Wiley & Sons, Ltd.