Dynamics of epicotyl emergence of Quercus robur from different climatic regions is strongly driven by post-germination temperature and humidity conditions

Pedunculate oak (Quercus robur L.) is an important component of temperate forests in the northern hemisphere. It occurs naturally across Europe and in parts of North Africa, the Balkans, the Urals and the Caucasus. In Poland, it predominantly grows on the plains at ≤700 m a.s.l. The main objective of this study was to determine how different temperature-humidity growth conditions influence dormancy breakage and epicotyl emergence in Q. robur, using growth curve models. We also investigated whether these differences result from changes in the climatic conditions under which the oak populations grow naturally. In this study, we selected four pedunculate oak stands in western and eastern Poland. These sites were characterised by oceanic and continental climates, respectively. Mature acorns were collected in the autumn of 2016 and pretreated for two weeks in the cold (4 °C). The acorns were then sown in plastic pots filled with a peat/sand substrate. Four climatic variants (cold-dry, cold-wet, warm-dry and warm-wet) and a control (average conditions) were used. Epicotyl emergence was monitored daily for 74 days. Epicotyl emergence dynamics (maximum absolute growth rate, lag time, T50), number of days to epicotyl emergence, and cumulative epicotyl emergence were measured or calculated. The acorns from oceanic climates required more intense warm humid conditions for epicotyl emergence than those from continental climates. In contrast, acorns from continental climates had an evolutionary advantage in that their epicotyl emergence occurred both in cold-dry and warm-wet seasons. This indicated that each population was adapted to its local environment.