Seasonal variation in dormancy and light sensitivity in buried seeds of eight annual weed species

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Abstract
We recorded germination in three different light environments (light, dark, and after a short light exposure) in eight annual weed species. Seeds were buried outdoors at the end of November 1994 and exhumed monthly from March 1995 to April 1996. All species exhibited substantial seasonal changes in dormancy level, and the patterns suggest that seeds of Papaver rhoeas germinate strictly in the autumn; Capsella bursa-pastoris, Descurainia sophia, Spergula arvensis, and Urtica urens mainly in the autumn; Chenopodium suecicum strictly in the spring; and Matricaria perforata mainly in the spring. Lapsana communis showed inconsistent dormancy changes over the year. All species had acquired a light requirement for germination after being in the soil, and in many cases the short light exposure (1050 μmol∙m−2) was enough to fulfil this requirement. The demonstrated seasonal changes in light sensitivity in several of the species will have to be taken into account in attempts to photocontrol weeds. By using the short-light treatment, we were able to detect seasonal dormancy changes that would not have been obvious by testing for germination in only light and darkness. Hence, light is not a simple dichotomous factor in its effect on germination. Key words: dormancy, germination, light, seed, Sweden, weed.