Current address: Department of Forest Ecology & Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
Rapid mixing between old and new C pools in the canopy of mature forest trees
Article first published online: 25 JUN 2007
Plant, Cell & Environment
Volume 30, Issue 8, pages 963–972, August 2007
How to Cite
KEEL, S. G., SIEGWOLF, R. T.W., JÄGGI, M. and KÖRNER, C. (2007), Rapid mixing between old and new C pools in the canopy of mature forest trees. Plant, Cell & Environment, 30: 963–972. doi: 10.1111/j.1365-3040.2007.01688.x
- Issue published online: 25 JUN 2007
- Article first published online: 25 JUN 2007
- Received 28 November 2006; received in revised form 22 May 2007; accepted for publication 23 May 2007
- stable isotopes;
- climate reconstruction
Stable C isotope signals in plant tissues became a key tool in explaining growth responses to the environment. The technique is based on the fundamental assumption that the isotopic composition of a given unit of tissue (e.g. a tree ring) reflects the specific C uptake conditions in the leaf at a given time. Beyond the methodological implications of any deviation from this assumption, it is of physiological interest whether new C is transferred directly from sources (a photosynthesizing leaf) to structural sinks (e.g. adjacent stem tissue), or inherently passes through existing (mobile) C pools, which may be of variable (older) age. Here, we explore the fate of 13C-labelled photosynthates in the crowns of a 30–35 m tall, mixed forest using a canopy crane. In all nine study species labelled C reached woody tissue within 2–9 h after labelling. Four months later, very small signals were left in branch wood of Tilia suggesting that low mixing of new, labelled C with old C had taken place. In contrast, signals in Fagus and Quercus had increased, indicating more intense mixing. This species-specific mixing of new with old C pools is likely to mask year- or season-specific linkages between tree ring formation and climate and has considerable implications for climate reconstruction using stable isotopes as proxies for past climatic conditions.