SPECIAL ISSUE ON LEARNING FROM EXTREMOPHYTES: XEROPHYTES AND HALOPHYTES
Stresses in plants caused by salt, drought, temperature, radical oxygen species, and toxic substances such as heavy metals are the major reasons for reduction in crop yield. For example, around 1000 million ha of land is affected by soil salinity. It can be calculated from FAO reports that current irrigation practices lead to annual losses of about 1.6 million ha of arable land just due to salting.This destruction of farmland stands in contradistinction to the demand for food. The world population is predicted to reach nine billion people by the year 2050, and although crop production has significantly increased during the period 1950?2010, populations in developing countries are growing so quickly that the land and water are unable to sustain them because farmlandand fresh water are already fully utilized. Furthermore, the increasing tendency of diverting farmland or crops for biofuels production to the detriment of the food supply enhances this dilemma. Consequently, improvement of food crop production no longer keeps up with population growth.Therefore, we have to consider new concepts when discussing how to improve agricultural productivity worldwide in order to feed the growing population.Obviously, improving fertilization and irrigation technology, as well as breeding common crops does not result in the enhancement of the annual crop yield at a rate needed to meet the demand. Extending the cropping areas is also challenging, as the land in question is located in arid regions where water is scarce. Although irrigation can be employed to bring land in arid areas into production, it often leads to no sustainable conditions and in many cases to increasing desertification and/or salinization if conventional crops are used. In some countries, the amount of newly irrigated land is equalled by salinized (desertified) irrigated land going out of production.Salt- resistant plants (haloophytes) may provide one of the alternatives for many developing countries to ensure sustainable growth conditions by using groundwater too saline for irrigating conventional mainly halophobous crops. Halophytes can be also used for the successful rehabilitation of degraded or salinized farmland land or for processing industrial waters without costly remedial measures. In terms of resource conservation they have the potential to increase the area of arable land by opening wasteland. In addition, unconventional irrigation water such as saline groundwater can be used to grow these representatives of extremophytes under sustainable conditions. Even coastal deserts may serve as new agricultural land, with the use of seawater water - unsuitable for conventional crops - for irrigation of salt-resistant plants to produce food, fodder, fuel, fiber, essential oils, and pharmaceutical feedstocks. Beside this they can also serve for more ecological purposes such as to build better sea defences.Halophytes are not the only source for the enhancement of crop production. There are extremophytes available showing an extended range for drought, temperature, oxidative stress or heavy metal resistance jointly or severally. This issue brings together contributions from laboratories around the world in order to discuss and compare the current and potential uses and the current knowledge about representatives of these extremophytes, to create greater awareness of this fascinating underrated group of experts. It will be shown that much progress has been made in the identification and characterization of the mechanisms that allow plants to tolerate abiotic stresses.