Carbon and Oxygen Isotopes in Trees: Tools to Study Assimilate Transport and Partitioning and to Assess Physiological Responses Towards the Environment

Abstract

At present, there is lack of knowledge on how plant physiological processes, the transfer of carbon within the plant, carbon storage, and remobiliza- tion in the plant tissues as well as the release of carbon from the roots to the soil interact with ecosystem-scale processes. On the background of global climate change, we need to mechanistically link plant physiology, CO2 net exchange between ecosystems and the atmosphere and plant biomass accumulation. This is the basis for predicting productivity of forests as well as their carbon sequestration potential in future. This chapter will give an overview on how stable isotope studies can give insights into the fate of newly assimilated carbon transported within trees and transferred to the soil and atmosphere. The review includes studies either characterizing temporal and spatial variation in the natural abundance of carbon and oxygen isotopes or applying isotopically enriched tracers. In addition, it high- lights the fact that the stable isotope composition of assimilates transported within the plant contains important time integrated information on environmental condi- tions, leaf physiology, and postphotosynthetic metabolism. This review will on the one hand focus on the fast turn over carbon pools, which fuel plant respiration and soil microbial activity and on the other hand explore the transfer of the isotope information to long-lived compounds in the tree-ring archive.