Germination Ecology of the Facultative Biennial Arabis laevigata variety laevigata

Abstract

-As a contribution to understanding the diversity of seed dormancy types with respect to habitat, life cycles and phylogenetic relationships, the dormancy type and germination ecology of seeds of Arabis laevigata var. laevigata (Brassicaceae) were investigated. This facultative biennial grows mostly in rocky woodlands in eastern North America, and its seeds have non-deep physiological dormancy (PD) (sensu Nikolaeva, 1977). Seeds mature in June, and dispersal lasts for up to 19 mo. Seeds collected in July, October and January and stored in mesh bags on the soil surface were nondormant in March. In the field, germination occurs in March and April, and seeds that fail to germinate in spring become part of a persistent seed bank. Seeds sown under leaf litter in October did not germinate until the litter was removed 16 mo later. Freshly matured seeds were either dormant or conditionally dormant; they germinated to a maximum of 38%, at 30/15 C in light. Seeds became nondormant during stratification at 5 C. Freshly matured, dormant seeds buried in soil in a nonheated greenhouse became nondormant during winter and re-entered dormancy or conditional dormancy during summer, which was broken the following winter. Although the facultative biennial life cycle is rare in deciduous forests, non-deep PD is not, since it occurs in woodland species with various types of life cycles. Arabis laevigata is similar to weedy facultative biennials in a number of plant families in that non-deep PD is broken by cold stratification. Of the 16 species of Brassicaceae whose seed dormancy we previously have investigated, all have non-deep PD; one of these is a strict biennial and the other 15 are winter annuals.