Germination strategies of halophyte seeds under salinity. (Special Issue: Sustainable cultivation and exploitation of halophyte crops in a salinizing world.)

摘要

Halophytes are plants of saline habitats that grow under conditions that may vary in extremes of temperatures (freezing to very hot), water availability (drought to water logging) and salinity (mild to almost saturation). Halophytes may also face sudden micro-environmental variations within their habitats. In this review we examine some of the factors that determine the ability of seeds of halophytes to germinate when conditions are optimal for seedling growth and survival. Seed dormancy (innate, induced or acquired) is an important means of initiating growth under appropriate conditions. Saline environments are often wet and so the seeds of halophytes may remain un-germinated over extended periods even after imbibition if the external environment does not favour germination and seedling survival. Many perennial halophytes, however, do not possess elaborate dormancy systems because they propagate largely through ramets and have no ecological compulsions for seed germination. The seeds of halophytes also have the capacity to recover from a salinity shock and start germination once salinity is reduced, which may happen following rain. In some cases, imbibition in a low-salt solution may help in osmo-priming and improve germination. Seed heteromorphism is yet another strategy adopted by some halophytes, whereby seeds of different size and colour are produced that germinate consecutively at suitable intervals. Light-dependent germination may also help if the seed is under a dense canopy or buried in debris; germination only occurs once these restraints are removed thus increasing the chances of seedling survival.