The carbon isotope composition of CO₂ respired by trunks: comparison of four sampling methods

Abstract

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 delta(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 delta(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 per thousand. 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.

Seasonal, daily and diurnal variations in the stable carbon isotope composition of carbon dioxide respired by tree trunks in a deciduous oak forest

“…The high CO 2 d 13 C values occurring in winter were also observed for beech and oak trunks by Damesin et al (2005), and also at the forest level for hardwood species by Knohl et al (2005) and Mortazavi et al (2005). However, high values in winter are not always found (e.g.…”

“…On the same day or the following day, the contents of the syringes were analysed in the laboratory with a mass spectrometer to determine the isotope signature of trunk-respired CO 2 . This method has been tested by Damesin et al (2005) and gave the same results as a Keeling plot method applied to the same chambers. Ambient air was also collected monthly in syringes at a height of 2 m near the measured trees in the forest.…”

“…Indeed, as for leaves when the major structural material is fixed, there are only minor temporal changes in the C isotope composition of the tissue (see Damesin et al 1998;Fessenden and Ehleringer 2003). For Q. petraea, the phloem is depleted in 13 C by about 1& relative to the sapwood (see Damesin et al 2005). As a consequence, the 13 C enrichment of respired CO 2 observed relatively to phloem (1-5&) remains valid when considering the xylem.…”

“…We called this efflux ''trunk respiration'', keeping in mind that the CO 2 released in the chamber could also come from CO 2 transported by the xylem, as suggested in several studies (Hari et al 1991;Martin et al 1994;Meir et al 1999;Teskey and McGuire 2002). At breast height, the chambers (described in Damesin et al 2005) were fixed on the trunk with a malleable rubber sealant (Terostat-7; Teroson, Ludwisburg, Germany) and straps. The installation was considered to be satisfactory if blowing along the seals caused no increase in the CO 2 level inside the chamber.…”

Stable Isotopes Reveal the Contribution of Corticular Photosynthesis to Growth in Branches of Eucalyptus miniata

“…The d 13 C of this CO 2 source, therefore, could potentially be affected by processes such as variation in the d 13 C of CO 2 produced by respiration within woody tissues (Damesin et al, 2005;Maunoury et al, 2007;Kodama et al, 2008) or uptake by roots of CO 2 dissolved in soil water (Levy et al, 1999;Moore et al, 2008;Teskey et al, 2008;Ubierna et al, 2009a). Table III.…”