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Halophyte

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Title: Halophyte  
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Halophyte

A halophyte is a plant that grows in waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. An example of a halophyte is the salt marsh grass Spartina alterniflora (smooth cordgrass). Relatively few plant species are halophytes - perhaps only 2% of all plant species.

The large majority of plant species are glycophytes, which are not salt-tolerant and are damaged fairly easily by high salinity.[1]

Salt tolerance

One quantitative measure of salt tolerance (halotolerance) is the total dissolved solids in irrigation water that a plant can tolerate. Seawater typically contains 40 grams per litre (g/l) of dissolved salts (mostly sodium chloride). Beans and rice can tolerate about 1-3 g/l, and are considered glycophytes (as are most crop plants). At the other extreme, Salicornia bigelovii (dwarf glasswort) grows well at 70 g/l of dissolved solids, and is a promising halophyte for use as a crop. [2] Plants such as barley (Hordeum vulgare) and the date palm (Phoenix dactylifera) can tolerate about 5 g/l, and can be considered as marginal halophytes.[1]

Adaptation to saline environments by halophytes may take the form of salt tolerance or salt avoidance. Plants that avoid the effects of high salt even though they live in a saline environment may be referred to as facultative halophytes rather than 'true', or obligatory, halophytes.

For example, a short-lived plant species that completes its reproductive life cycle during periods (such as a rainy season) when the salt concentration is low would be avoiding salt rather than tolerating it. Or a plant species may maintain a 'normal' internal salt concentration by excreting excess salts through its leaves, by way of a hydathode, or by concentrating salts in leaves that later die and drop off.

Examples

Some halophytes are:

As biofuel

Some halophytes are being studied for use as "3rd-generation" biofuel precursors. Halophytes such as Salicornia bigelovii can be grown in harsh environments[3] and typically do not compete with food crops for resources, making them promising sources of biodiesel[4] or bioalcohol.

References

  1. ^ a b Glenn, E. P., et al. (1999). Salt tolerance and crop potential of halophytes. Critical Review in Plant Sciences 18(2), 227-55. doi:10.1080/07352689991309207
  2. ^ Glenn, E. P.; Brown, J. J.; O'Leary, J. W. (1998). "Irrigating Crops with Seawater", Scientific American, Vol. 279, no. 8, Aug. 1998, pp. 56-61.
  3. ^ "Fact Sheet: Alternative Fuels".  
  4. ^ Glenn, Edward P.; Brown, J. Jed; O'Leary, James W. (August 1998). "Irrigating Crops with Seawater" (PDF).  
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