Environmental factors and survival strategies of annual plant species in the Negev Desert, Israel

Abstract

Several environmental factors have pronounced influences on the complementary sets of survival strategies, at different stages of the plant life cycle, of some of the most common annual plants in the Negev Desert, Israel. Plasticity of seed germination may spread germination over time and thus reduce the risk to species survival. This plasticity may be affected by day length during seed development and maturation and by position of seeds on mother plants. Post-seed maturation dry storage temperatures may affect the duration of after-ripening. The tiny, dust-like seeds produced by some plants that are dispersed by wind after maturation may escape massive seed predation and remain in large seed banks in the soil. Seeds of other species are protected in lignified structures in aerial seed banks on dead, dry, lignified mother plants. Seed dispersal strategies from these aerial seed banks by rain may also prevent massive seed collection by animals. The 'cautious' or 'opportunistic' germination strategy and seedling drought tolerance may increase seedling survival in many of the plant species under the unpredictable amounts and distribution of rain in these desert areas. Factors such as amount of rain, temperature, relative humidity, time of the beginning of soil wetting (day or night), seed size and history and the depth of seeds in the soil may affect germination percentages. Day length and soil water content during plant development may have a pronounced influence on plant age at first flowering, seed yield and plant life span.