Seed Germination Strategies of Mediterranean Halophytes Under Saline Condition

The study of the ecological strategies adopted by seed plants to ensure their success in different environments is closely related to germination ecology. This implies a careful knowledge of ecophysiology of seeds and, therefore, also of interaction between plants and the complexity of external factors. In particular, the environmental conditions of the area where a plant grows and produces seeds represent the main factors that influence successful seedling establishment. The physical-chemical features of habitats, and therefore their heterogeneity, affect the behavior of seeds in different ways. In addition to the timing of seed production, they can induce or terminate dormancy and/or germination and influence the germination pattern of different seeds in the same plant and so the composition and dispersal of soil seed banks. Salinity is a major abiotic stress affecting growth and plant productivity worldwide, constituting one of the main topics of study in the field of plant physiology. Halophytes are the plants that have the availability to survive and develop in different types of saline habitats. In this chapter, we consider some examples to illustrate the main adaptive strategies used by the seeds of halophytes on ecophysiological perspectives to survive in habitats affected by high levels of salinity. The focus is on the species that live in the brackish or salt coastal areas of the Mediterranean Basin. On these environments, the salt stress may act synergistically with intense anthropic pressure, generating profound alterations in the ecosystem and threatening the survival of the plant species very sensitive to the effects of climate change also. The results show the main diverse strategies, such as dormancy cycling, seed heteromorphism, and recovery capacity, from saline shock, favoring the chances of seed survival. The interaction between temperature and salinity during germination was also discussed assessing its crucial role as an ecological strategy

Plants of Sabkha Ecosystems of the Arabian Peninsula.

Sabkhas are unique ecosystems that are highly saline and where specially adapted plants are able to grow, flower, and fruit. In general, saline environments are poor in species – for the Arabian Peninsula about 120 taxa are recorded as halophytes which constitute about 4% of the total flora of the Arabian Peninsula. Key halophytes of Arabia are nearly always perennial; predominant life-forms are somewhat succulent, semiwoody dwarf shrubs belonging to the families Amaranthaceae, Zygophyllaceae, and Plumbaginaceae and hemicryptophytes belonging to the Poaceae, Cyperaceae, and Juncaceae; annuals are exceptions. Coastal species are either obligate halophytes or salt-tolerant genera from unspecialized families, such as Sporobolus and Aeluropus (Poaceae), or salt-secreting species such as Avicennia (Acanthaceae) and Limonium (Plumbaginaceae). The submerged coastal vegetation, e.g., seagrasses, is one of the most important vegetation types of the Gulf coast and is of great importance to marine fauna. The north-south distribution of coastal species is more distinct on the Red Sea coast, with the border lying near Jeddah, than on the Persian Gulf coast where there is a broad transitional zone between Qatar and northern Oman. The east-west distribution of coastal species is not as distinct. The eastern elements are either restricted to the coasts around the Arabian Gulf or are Irano-Turanian species extending into the Gulf region. Several vicariant species groups of halophytes are represented in the Arabian Peninsula. Halophytes have developed strategies for seed germination such as high germination levels and fast germination speed. These traits are found in the sabkha plants of the Arabian Peninsula. Some halophytes have been investigated for their potential for phytoremediation in their ability to survive weathered oil-contaminated soils. They have been found to have a set of micoorganisms around their root system that are related to the degradation of oil in contaminated soils. Sabkha ecosystems are being degraded and altered throughout the Gulf countries as they appear to be nonproductive. Over the last two decades, there has been a growing concern in protecting and restoring mangroves, and programs do to so have seen promising results. But, on the whole, coastal and inland sabkhas are neglected, and these unique ecosystems require urgent protection