Seed dormancy in Trillium camschatcense (Melanthiaceae) and the possible roles of light and temperature requirements for seed germination in forests

Abstract

Seeds of some temperate plants require multiple treatments to break complex forms of dormancy, such as deep simple double morphophysiological dormancy (MPD), but embryo growth and radicle and cotyledon emergence have not been studied in depth for this level of MPD. Here we studied Trillium camschatcense, a species that is purported to have this MPD and that is sensitive to habitat fragmentation with decreased recruitment at forest edges. Trillium camschatcense seeds were collected and experiments conducted in Hokkaido, Japan over 5 years. Growth of embryos and emergence of radicles and cotyledons were tracked in relation to field temperature to determine specific temperature and light requirements for these stages under laboratory conditions. Low (winter) temperatures overcame dormancy in the underdeveloped embryos, and embryo growth and radicle emergence occurred between July and September, ca. 1 year after seed dispersal. Radicles emerged optimally over a narrow temperature range (20-25°C), in darkness, and at constant temperatures. Roots developed during the second autumn. Cotyledons needed a second low temperature (second winter) to emerge from seeds with roots, doing so in April, slightly over 1.5 years after dispersal. Seeds of T. camschatcense have deep simple double MPD and requirements for radicle emergence: darkness and constant temperatures. Ecologically, edges of forests may be deleterious for germination of the species due to increased light and to higher temperature fluctuations as compared to the interiors of forests. Thus, these specific requirements may play an important role in reducing seed germination of this plant at forest edges.