STRATEGIES OF SEED DISPERSAL AND GERMINATION IN PLANTS INHABITING DESERTS

Massive seed consumption is typical in many deserts. The ''escape'' or ''protection'' strategies of seed dispersal are important, as they prevent massive seed consumption. The more extreme the desert, the more unpredictable the low amounts and distribution of the rains as well as the beginning and length of the season or seasons with rains. Seeds, which have the highest resistance to extreme environmental conditions, develop during germination into seedlings, which are the most sensitive. Therefore, germination of parts of the seed population at their respective proper times spreads the risk over time and is thus very important for plant survival, especially in those plants inhabiting the more extreme deserts. Each of the plant species studied was found to have its own survival strategies of seed dispersal and germination. At least two extreme seed-dispersal and -germination strategies have been observed: 1) the ''escape'' seed dispersal and ''opportunistic'' portioned seed-germination strategies, such as in Schismus arabicus and Spergularia diandra, and 2) the ''cautious'' portioned dispersal by rain of the protected seeds, such as in Asteriscus hierochunticus and portioned dispersal and rapid germination strategies such as in Blepharis spp. The fate of future generations, as far as the germinability of seeds of some species is concerned, depends on the influences of maternal and environmental factors when the seeds are still on the mother plant, mostly during the final stage of seed maturation, as in Trigonella arabica. It may even depend on the position of the caryopsis from which the mother plant originated, as in Aegilops geniculata. The dry post-maturation conditions and the environmental factors during seed wetting and germination may also affect the percentage of seed germination, as in Schismus arabicus.