GERMINATION ECOLOGY OF THE POLYCARPIC GRASSLAND PERENNIALS PRIMULA-VERIS AND TROLLIUS-EUROPAEUS

The seed germination behaviour of Primula veris and Trollius europaeus, both perennial, polycarpic grassland plants was compared. The species have similar-sized seeds that are dormant at dispersal. Seeds buried in soil and exhumed at regular intervals showed that for both species, primary seed dormancy was overcome by cold-stratification. Hence, their germination in the field should occur in spring, following dispersal, or later. Seeds of P. veris became dormant again in the late spring/early summer, and dormancy was broken again in the second winter. Seeds of T. europaeus did not exhibit such changes in dormancy. Seeds of P. veris did not germinate in darkness. This suggests that P. veris can accumulate a persistent seed bank because buried seeds are prevented from germinating. Trollius europaeus, on the other hand, germinated equally well in darkness and in light which suggests that seeds might germinate even when they are too deep in the soil for seedlings to emerge. Two lines of evidence confirm this difference in seed bank behaviour: (i) Primula veris was detected in the persistent seed bank of a grassland site, whereas T. europaeus was not. (ii) After 16 months burial, 85% of the P. veris seeds but only 8% of the T. europaeus seeds remained viable.