XVI International Botanical Congess

Seed germination of an annual plant species is the first step towards seasonal re-appearance in the plant community. The seed germinability and distribution, of at least some plant species are affected by the soil substrate. The Negev landscape includes microphytic patches with soil crust and macrophytic patches with raised soil mound and litter below perennial shrubs. The thickness of the soil crust and microphytic community changes from 1 to 15 mm along the rainfall gradient. Seeds of the two annual plant species were germinated on the soil samples and crusts, in constant temperature and light. Both species showed negative correlation between seed germination rate on soil crusts and precipitation in the source site. On soils collected from the macrophytic patches Plantago coronopus showed the same correlation while Carrichtera annua seeds showed the opposite: a positive correlation with the annual precipitation. Similar germination trends of both species on the soil crusts may be explained by competition with the microphytic plants.