Germination characteristics and emergence time of annual Bromus species of differing weediness in Sweden

The germination ecology of four annual Bromus species, which differ in weediness on arable land in southern Sweden, was investigated. The most problematic species is Bromus sterilis, while Bromus hordeaceus frequently occurs on arable land. In contrast, Bromus arvensis is a rare weed, and Bromus tectorum is found infrequently in fields despite being a widespread ruderal species, Five experiments were conducted to identify germination characteristics that could explain differences in habitat and abundance: (i) intraspecific variation in dormancy level; (ii) germination response to different light conditions; (iii) light and temperature interactions at germination; (iv) timing of seedling emergence; and (v) seed persistence in soil. Bromus sterilis and B. tectorum behaved similarly in all tests. For both these species, there were large differences in dormancy level among populations and strong inhibition of germination by light. In addition, emergence from seeds sown on the soil surface was both delayed and reduced compared with buried seeds. In contrast, B. hordeaceus and B. arvensis showed generally weak dormancy, and germination was only slightly inhibited by light. It was concluded that germination characteristics alone do not explain the differences in weediness between these four species.