Does the lag time between radicle and epicotyl emergences in acorns of pedunculate oak (Quercus robur L.) depend on the duration of cold stratification and post-stratification temperatures? Modelling with the sigmoidal growth curves approach

The objective of this study was to determine how the current (10-16 weeks) and predicted future (2-8 weeks) length of cold stratification and current and predicted future post-stratification temperatures influence radicle and epicotyl emergence in acorns of Quercus robur. We tested radicle and epicotyl emergence at two temperatures corresponding to the current (15/6 degrees C) and predicted future early autumn and spring temperatures (25/15 degrees C) in Poland. We fitted models to describe and derive parameters for radicle and epicotyl emergences over time. The parameters included maximum percentage, rate of emergences, time to achieve the maximum emergence rate, emergence delay and time to 50% emergence. In most cases, the Gompertz model was the best fit, but in a few cases, the logistic model was the best. Richard's model for most of the cases did not converge. This model, according to both information criteria values, was the best fit for epicotyl emergence at 15/6 degrees C following 8 weeks of cold stratification. Richard's model was also the best fit for epicotyl emergence at 25/15 degrees C following 14 weeks of stratification.. Our results indicate that at temperatures typical for early autumn (15/6 degrees C), the time necessary for radicle emergence from 50% of acorns was longer than that from acorns placed at 25/15 degrees C. Four weeks of cold stratification extended 50% radicle emergence at 15/6 degrees C to 70 d, whereas 12 weeks of stratification shortened the time to 11 d. When the acorns were incubated at 25/15 degrees C, radicle emergence occurred faster than at 15/6 degrees C and the time lag between radicle and epicotyl was shorter.