The carbon isotope composition of CO 2 respired by trunks: comparison of four sampling methods

• Published in: Rapid communications in mass spectrometry 2005-02, Vol.19 (3), p.369-374
• Main Authors: Damesin, C., Barbaroux, C., Berveiller, D., Lelarge, C., Chaves, M., Maguas, C., Maia, R., Pontailler, J.‐Y.
• Format: Article
• Language: English
• ISSN: 0951-4198; 1097-0231
• DOI: 10.1002/rcm.1799

The 13 C natural abundance of CO 2 respired by plants has been used in the laboratory to examine the discrimination processes that occur during respiration. Currently, field measurements are being expanded to interpret the respiration δ 13 C signature measured at ecosystem and global levels. In this context, forests are particularly important to consider as they represent 80% of the continental biomass. The objective of this investigation was to compare four methods of sampling the CO 2 respired by trunks for the determination of its carbon isotope composition: three in situ methods using chambers placed on the trunk, and one destructive method using cores of woody tissues. The in situ methods were based either on a Keeling plot approach applied at the tissue level or on an initial flush of the chamber with nitrogen or with CO 2 ‐free air. In parallel, we investigated the possibility of an apparent discrimination during tissue respiration by comparing the δ 13 C signature of the respired CO 2 and that of the organic matter. The study was performed on six tree species widely distributed in temperate and mediterranean areas. The four methods were not significantly different when overall means were considered. However, considering the individual data, the Keeling plot approach and the nitrogen flush methods gave fairly homogeneous results, whereas the CO 2 ‐free air method produced more variable results. The core method was not correlated with any of the chamber methods. Regardless of the methodology, the respired CO 2 generally was enriched in 13 C relative to the total organic matter. This apparent enrichment during respiration was variable, reaching as much as 3–5‰. This study showed that, on the whole, the different sampling techniques gave similar results, but one should be aware of the variability associated with each method. Copyright © 2005 John Wiley & Sons, Ltd.