No evidence for carryover effect in tree rings based on a pulse-labelling experiment on Juniperus communis in South Germany

摘要

Key message A clear carryover effect of tree-ring formation was not detected based on a pulse-labelling experiment conducted on Juniperus communis in South Germany. The inherent linkage between photosynthesis and the formation of wood is important for the understanding of relationships between tree-ring series and climate/environmental data in dendroclimatology studies. However, it is impossible to reach a mechanistic procedure of tree stem radial growth depending on its carbon balance from a traditional statistical point of view alone. Pulse labelling experiment with stable carbon isotope ((CO2)-C-13) has provided innovative insights into the fate of recently assimilated carbon in organs and carbon-containing compounds. In this study, we conducted an in situ pulse labelling experiment on 27 July 2016 to examine the response of tree ring and different-aged needles to short-term elevated (CO2)-C-13 of a juniper shrub growing on a heathland in South Germany. New and old needles from four expositions were sampled before and after the experiment. A wood segment was taken from the main branch and stable carbon isotope composition (delta C-13) was analysed at an intra-annual time scale. Before the experiment, the mean delta C-13 was - 26.8 +/- 0.4 parts per thousand (mean +/- standard deviation) for both needle ages, while woody tissue showed about 3 parts per thousand higher delta C-13 compared to needles. Substantial enriched C-13 was detected in the needles after the experiment. New needles showed significant higher delta C-13 than the old ones 1-7 days after the experiment. Significant enriched delta C-13 was detected in the wood from 35 to 61% of the annual tree ring in 2016, indicating that the short-term enrichment of C-13 can affect wood formation for a large section. No enhancement in C-13 signal appeared in the tree ring of the subsequent year 2017, suggesting the absence of a carryover effect. Wood formation did not reply on the carbohydrates stored even 1 year before and thus tree-ring ecophysiological modelling as well as dendrochronological studies should therefore benefit from such result.