Seed dormancy and germination of northern red oak
Northern red oak (Quercus rubra l.), a valuable timber in species in the eastern United States, has a delayed growth in the early years of establishment. Freshly harvested northern red oak seed exhibit dormancy that may be broken by stratification or pericarp removal. In this research, germination, seedling growth and adenylate energy metabolism of northern red oak with pericarp removed and intact was measured during stratification (5C) for two consecutive years. Two seed moisture levels (50% and 70% d.w.) during stratification were tested on intact acorns, pericarp removed seeds and acorns intact during stratification and then the pericarp removed prior to germination. Pericarp removal increased germination five-fold at harvest (from 10% to 55%), but almost half the naked seeds were still dormant. There was a deepening of dormancy during the first 4 weeks of stratification; but, stratification for 6 to 8 weeks significantly increased germination and germination rate. Etiolated seedlings grew taller and faster from acorns that had been stratified 8 to 12 weeks than from acorns with no or only 4 weeks of stratification. Significant increases in root, shoot, and axial dry weight and lengths, and root/shoot ratios were observed as early as 14 days after germination. Pericarp removal had no significant effect on seedling growth. Relative growth rates of seedlings were compared by pericarp treatment and stratification time. There were no significant differences in germination or seedling growth between 50% and 70% seed moisture content. Adenylate (ATP, ADP, AMP) levels were measured using the luciferin-luciferase assay). Energy charge (EC) increased during stratification at 2 weeks when germination was low. Thereafter EC decreased before increasing at 8 weeks of stratification. This second rise in EC was concurrent with an increase in germinability. ATP concentrations during the 28 day growth time appeared to be associated with surges in relative growth rates of roots and shoots.