XVI International Botanical Congess

The main factors affecting the evolution of germination survival strategies of annuals in the Negev Desert are the unpredictable low amounts and distribution of rain, and seed consumption. Annuals have developed various survival strategies affecting: 1) seed dispersal, to escape or be protected from consumption, 2) the number of seeds that are 'ready to germinate' after one rainfall 3) seedling drought tolerance. Pheno- and genotypic plasticity of seed germination are affected by pre- and post-maturation and germination environmental conditions. This plasticity increases survival, as a small percentage of the seed bank germinates after one rainfall. Seed germination may be regulated by local desert soils chemically, biologically and mechanically, according to the annual average rainfall gradient which affects the soil flora and soil crust depth. Duration of seedling drought tolerance and delayed point of no return, which may enable germinating seedlings to survive periods of drought between the rains, are important survival strategies in extreme desert conditions.