Seasonal changes in germination responses of buried seeds of Verbascum thapsus and V. blattaria and ecological implications

Abstract

In a 2-year study buried seeds of Verbascum thapsus and V. blattaria were exposed to natural seasonal temperature cycles, and at monthly intervals they were exhumed and tested in light and darkness over a range of alternating temperatures simulating those in the habitat throughout the growing season. At any time from spring to early autumn, seeds of both species germinated in light at prevailing habitat temperatures. Seeds of V. blattaria germinated in darkness in spring at spring temperatures but did not germinate in darkness at any temperature in summer or autumn. Unlike V. blattaria, seeds of V. thapsus germinated to 25–85% in darkness in summer at summer temperatures. In the second spring of burial, seeds of both species showed a reduction in ability to germinate in darkness at spring temperatures. Only 5% of the V. blattaria and 16% of the V. thapsus seeds germinated while they were buried. The germination characteristics are discussed in relation to the ecology of these two early successional species.