Germination ecology of the grassland biennial Linum catharticum

The germination ecology of the short-lived grassland biennial Linum catharticum L. was studied. Its seeds had a primary dormancy that was overcome by cold-treatment. Seeds buried in the soil became germinative in midwinter (December), but since the seeds germinate only at relatively high temperatures, autumn-sown seeds did not germinate in the field until late spring, at which time the average soil temperature was 20°C. During the first half of the summer, buried seeds re-entered dormancy, but by August this secondary dormancy had already been broken. In the following summer some of the seeds became dormant again. Hence, buried L. catharticum seeds exhibited an annual dormancy cycle. Most exhumed seeds needed light to germinate, which is probably why L. catharticum accumulates a persistent soil seed bank. After 25 months, 96% of the seeds buried were still ungerminated and alive.