Seed survival and periodicity of seedling emergence in ten species of annual weeds

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Abstract
SUMMARY: Seeds or fruits of 10 species of annual weeds were collected in each of 3 years and mixed with the top 7 · 5 cm of sterilised soil (confined in cylinders sunk in the ground outdoors and cultivated three times yearly. The numbers of seedlings emerging were recorded for 5 yr and the numbers of viable seeds remaining then determined. Emergence of Anagallis arvensis, Anchusa arvensis, Chaenorrhinum minus and Euphorbia peplus was mainly in spring; Lamium amplexicaule and Myosotis arvensis also had a spring peak but emergence continued in summer and autumn. Seedlings of Aphanes arvensis appeared almost entirely in autumn and those of Lamium purpureum between May and October. Veronica arvensis had spring and autumn peaks, while Fumaria densiflora showed no definite pattern. Except for Anagallis arvensis and F. densiflora, in which there was apparent innate dormancy due to the seed coat, most seedlings appeared in the first year with a decrease, usually exponential, from year to year. This was most rapid in C. minus and E. peplus, of which few viable seeds remained after 5 yr. Seed survival for the other species ranged from 2·6% of those sown for Anchusa arvensis to 14·8% for F. densiflora.