Postphotosynthetic Fractionation in Leaves, Phloem and Stem
Arthur Geßler, Juan Pedro Ferrio
Abstract
Abstract Stable carbon isotope ratios (δ 13 C) in organic matter convey important integrated and (if assessed in the tree ring archive) dateable information on plant physiology and related environmental drivers. While the generation of the δ 13 C signal in the primary assimilates in the leaves via photosynthetic carbon isotope fractionation is well understood, we still lack detailed knowledge of the processes that determine the isotopic fractionation in downstream processes in the leaves and during the transport in the stem, which in turn affect δ 13 C in the tree-ring archive. We here provide an update on processes that drive post-carboxylationcarbon isotope fractionation in the leaves, on potential changes in δ 13 C related to phloem loading and transport and we also discuss the role of stem CO 2 fluxes (bark photosynthesis, stem respiration and CO 2 fixation by phosphoenol pyruvate carboxylase). Moreover, we address the impact of carbon storage and remobilization on the intra-annual variation of δ 13 C in tree rings. Finally, we point to the potential importance of the intra-molecularcarbon isotope distribution in carbohydrates for tree ring δ 13 C and its relation to shifts in metabolic pathways.