Germination ecology of Sison amomum (Apiaceae) at the northern edge of its distribution range on the European mainland

Abstract

Background and aims Sison amomum reaches the north-western limit of its distribution on the European mainland as a rare species in a very small area in western Belgium. For conservation management it is important to know different aspects of life history such as seed longevity, phenology of germination and survival of seedlings. Methods Germination requirements in field and laboratory conditions were analyzed in detail. Survival of seedlings in winter conditions was recorded. Key results Most seeds germinated soon after dispersal in autumn. Eighty percent of the autumn seedlings survived winter conditions and grew up to flowering plants in the 2nd and 3rd calendar year. Buried seeds survived till next spring, but later on very few seeds were able to germinate after exhumation, thus no persistent seed bank was formed. In fresh seeds, the underdeveloped embryo (embryo to seed ratio = c. 0.35) immediately started to grow in light conditions at low temperatures (5, 10°C and alternating 20/10°C); when the critical E:S ratio of 0.82 was reached after two to four weeks, the radicle protruded. In darkness and at 20 or 23°C growth of the embryo was very slow and very few seeds germinated. Conclusions The small seeds of S. amomum are morphologically dormant, and germinate very soon in light at lower temperatures. No persistent seed bank is formed. Based on life history characteristics revealed in this study, we propose a mowing of the grasslands in late autumn to protect this threatened plant. Well timed mowing reduces the biomass and decreases the competition, while still allowing seed set and dispersal of S. amomum.