Diurnal photosynthetic performance of two oak species from two provenances in a Mediterranean and a central European common garden

Abbreviations : DOY – day of the year; g s – stomatal conductance; OLY – Olympiada/Greece; PI abs – performance index on absorption basis; P Nmax – light-saturated net photosynthetic rate; RC/ABS – active reaction centers on absorption base; SWA – Schwanheim/ Germany; WUE – water-use efficiency; φP 0 – F v /F m – maximum quantum efficiency of the reduction of Q A ; ψE 0 – the probability that an absorbed photon leads to a reduction further than Q A . Acknowledgments : The authors are thankful to F. Lyrou, F. Süßel, and S. Ströll for their assistance in the field campaigns. We acknowledge the City of Frankfurt, especially H. Scheel, for the support in the establishment and management of the German common garden and Hellas Gold SA, especially D. Ballas, for the provision of climate data. Finally, we thank Li-cor Biosciences GmbH (Bad Homburg, Germany) and particularly D. Facius and O. Marx for the kind provision of technical support during the gas-exchange measurements in Germany. This study was financially supported by the project IKYDA-FUTUREOAKS Oaks may contribute to the stabilization of European forests under climate change. We utilized two common gardens established in contrasting growth regimes, in Greece (Olympiada) and Germany (Schwanheim), to compare the diurnal photosynthetic performance of a Greek and an Italian provenance of two Mediterranean oaks ( Quercus pubescens and Q. frainetto ) during the 2019 growing season. Although the higher radiation in the southern common garden led to a strong midday depression of chlorophyll a fluorescence parameters (maximum quantum efficiency of PSII, performance index on absorption basis), comparable light-saturated net photosynthetic rates were achieved in both study areas. Moreover, both species and provenances exhibited analogous responses. Q. pubescens had enhanced chlorophyll a fluorescence traits but similar photosynthetic rates compared to Q. frainetto , whereas the provenances did not differ. These findings indicate the high photosynthetic efficiency of both oaks under the current climate in Central Europe and their suitability for assisted migration schemes.