Effect of temperature on dormancy and germination of Eupatorium cannabinum L. achenes

Abstract

This study investigated the effects of various temperature regimes on dormancy and germination inEupatorium cannabinum, a common wetland species in Central Europe. Germination of dry-stored achenes was tested at increasing amplitudes of temperature fluctuations, and stratified achenes were germinated at constant temperatures. Dormancy release was examined in the laboratory at constant temperatures of 3, 8, 12, 15 and 18°C. The effect of an increase in temperature during stratification from 5°C to 15, 18 or 20/10°C on dormancy was tested. Moreover, achenes were exposed to yearly seasonal temperature cycles in the soil in an experimental garden. Germination of dry-stored achenes was not promoted by fluctuating temperatures, while stratified achenes germinated (>5%) over a range of constant temperatures between 9 and 36°C. Dormancy was relieved at all stratification temperatures, but temperatures ≤12°C were more effective than higher temperatures, since germination occurred over a wider range of test conditions after these pretreatments. An induction of secondary dormancy occurred only if the temperature was increased during stratification. Annual dormancy cycles were apparent when achenes were germinated at 15°C, while at 25 and 15/5°C germination was always >60%. The germination behaviour ofEupatoriumis that of a typical wetland species. Thus, non-dormant achenes germinated at relatively high temperatures, and germination was promoted by fluctuating temperatures. The annual course of dormancy revealed that achenes can germinate throughout the growing season under favourable conditions. Achenes sown in an experimental garden germinated in spring, when daily mean temperatures were around 14°C. A decline in viability of achenes after 19 months' burial indicated thatEupatoriumdoes not form a long-term persistent seed bank.