CARBOHYDRATE CYCLING IN EVERGREEN AND DECIDUOUS TREES OF SE WISCONSIN: IMPLICATIONS FOR HIGH-RESOLUTION ISOTOPE ANALYSES OF GROWTH RINGS OF MODERN AND FOSSIL WOOD

The stable carbon isotope geochemistry of tree rings is a powerful tool for the reconstruction of paleoclimate from well-correlated dendrochronologic records. However, it has been recognized for over two decades that there is an intra annual variation in carbon isotopes of annually grown wood, such that the traditional theory governing carbon isotope fractionation in leaves does not fully explain the carbon isotope variation in wood of deciduous trees. Here, we conduct a high-resolution monitoring study of seasonal carbon isotope variation in evergreen and deciduous gymnosperms in Wisconsin to evaluate possible controls on the anomalous isotope effect preserved in tree rings. Our hypothesis is that the reservoir of glucose in starches has a major control on the carbon isotope composition of earlywood in deciduous trees. In contrast to our hypothesis, the seasonal starch effect was synchronized in evergreen and deciduous trees in this forest. Indicating that another mechanism is required to explain the different carbon isotope trends in rings of evergreen and deciduous trees. Thus, we include a new application of carbon isotope heterogeneity in glucose as a tracer to document where isotope fractionation takes place in the tree and the relative importance of sucrose and starch as sources of glucose used in the production of new wood. Our results also have direct implications for carbon isotope analysis in fossil wood material for interpretations of leaf longevity and plant physiology in response to environmental variation.