Physical and chemical factors associated with the reduction or delay of seed germination and seedling emergence of bull thistle, Cirsium vulgare (Savi) Ten. under leaf litter

Leaf litter can affect seed germination and seedling emergence by altering both the physical and chemical environment. A series of experiments were conducted to investigate litter effects on germination and emergence of Cirsium vulgare seeds and seedlings. Thin (2 layers) and thick (5 layers) of leaf litter of Acer saccharum, Quercus alba, and Juglans nigra reduced and delayed seedling emergence of bull thistle (C. vulgare) in two greenhouse experiments. Leaves of J. nigra were less effective than those of the other two species. In one experiment, removal of the litter after seedling emergence had ceased was followed by a second flush of emergence, but no further emergence occurred in the non-litter control. However, in a second experiment no further emergence was recorded after litter removal. Artificial litter, chemical-free cotton paper cut in leaf shapes, reduced and delayed seedling emergence but to a lesser extent than natural leaf litter. Germination in distilled water in Petri dishes was not affected within a pH range of 3-10. However, black walnut leaf extract reduced seed germination, and extracts of all three species slowed germination rates. There was no effect of leaf extracts on rates or percent emergence from soil in the greenhouse. We concluded that leaf litter can have an important role in determining patterns of seedling emergence of C vulgare, possibly because of physical effects on the dormancy status of its seeds. bull thistle, Cirsium vulgare, seedling emergence, intermittent germination, leaf litter, induced dormancy.