MINIREVIEW: Survival adaptations and strategies of annuals occurring in the Judean and Negev Deserts of Israel

Abstract

The more extreme the desert and the smaller and more unpredictable the annual precipitation and its distribution during the rainy season, the more important the sets of complementary adaptations and survival strategies during the different stages of the life cycle of winter annuals. The history of each seed, from seed development and maturation to seed wetting and germination, may affect the phenotypic plasticity of seed germination. This may be affected by environmental factors such as day length during seed development and maturation. Also involved are maternal influences and the influence of the position of the seeds in the plant inflorescences or capsules, even 30 years after seed maturation. Post-maturation primary or secondary seed dormancy mechanisms and strategies may also be involved. In addition, environmental factors during seed wetting, such as the amount of rain, relative humidity, temperature, light, soil salinity, and germination inhibitors, may play a role in the regulation of the percentage of seeds that are ready to germinate after a particular rainfall. Adaptations and survival strategies in desert annual plant species have also evolved during the stages of seedling development, flowering, and seed dispersal. These include escape or protection mechanisms and strategies of seed dispersal that may decrease seed collection and contribute to the large and long-lasting living aerial or soil seed banks of the species. Many of the common plant species occurring in the Negev, where the average annual rainfall gradient ranges from 25 to 200 mm, produce large quantities of tiny, dust-like seeds. These plant species have developed escape strategies of seed dispersal as well as opportunistic strategies of seed germination. In contrast, other plant species that produce relatively larger seeds in much smaller quantities, have protection strategies of seed dispersal as well as cautious germination strategies. All these adaptations of mechanisms and strategies may affect the chances of these plant species to survive in their desert locations and habitats. The greater the fitness of a plant genotype to its habitat, the greater the chance for the seeds that germinate to complete their life cycles by producing new mature seeds and retaining a large and long-lasting seed bank in such arid areas and extreme deserts.