Salinity is a worldwide phenomenon engulfing large chunks of good arable lands while secondary salinization is creeping into fertile lands making production of many crops redundant. Water, the fountain of life, is present in abundance on earth; almost 3/4th of planet earth is water albeit of poor quality not suited for crop growth. The underground water quality is generally dependent on surface soil; if it is saline, the salts trickle down to pollute. Fresh water, required for irrigating field crops, is available only in limited quantity and is decreasing with time and the above trends are unlikely to revert at least in the near future. The effects of reduced crop yields under these conditions are further compounded by burgeoning world population, more so in the less developed countries of arid and semi arid regions.
This however, is not a doomsday scenario as salinity and plant growth are not entirely inimical; plants can be found growing in saline soils inland, a large number of species thrives along the seacoast inundated occasionally by seawater and a wealth of flora exists in the sea itself. These plants called halophytes occupy saline habitats; many require a certain concentration of salts for optimum growth which may be inhibitory or even fatal for many field crops. There is a need to explore the potential of these plants for the benefit of mankind through mobilization of salty water and saline land resources. Research has indicated that halophytes can be put to an array of uses like food, fodder/ forage, fiber, fuel wood, biofuel, oilseed, medicine, chemicals, landscaping, ornamentals, environmental conservation through carbon sequestration etc. Taking cue from here, the concept of cash crop halophytes developed.
There is an understandable reluctance on part of the stake holders to come to terms with the idea because of its novelty but the looming crisis of diminishing land and water resources makes its acceptance inevitable. A survey shows that out of a total 410 reported from Pakistan, some 100 halophytes are found on the coast of Sindh and Balochistan. From these, about 51 could be used for extracting medicine, 48 as forage, 47 as fodder, 38 as food, 34 as ornaments, and others as fibers, timber and other usages of wood, and various chemicals.
Food yielding halophytes
The seed bearing species, which are used as food, include among others, Salvadora oleoides, S. persica, Trianthema portulacastrum, Oxystelma esculentum and Zizyphus nummularia. The young leaves, shoots, radicles of Rhizophora mucronata, Ceriops tagal, Thespesia populnea, Hibiscus tiliaceus, Salicornia bigelovii, S. brachiata, Sesuvium portulacastrum, Chenopodium album, Atriplex hortensis, Triglochin maritima, Arundo donax, Rumex vesicarius, Apium graveolens, Portulaca oleracea, and Suaeda maritima have been used for vegetables, salads and pickles in Indo-Pakistan. Additional uses include Aster tripolium as vegetable in Netherlands, Belgium and Portugal; Salicornia species and Tripolium vulgare as food in W. Siberia, Avicennia marina and A. germinans as food in Columbia; Zizania aquatica as a catch crop in western USA and Canada, Distichlis species for making bread, biscuits etc. in many parts of the world.
Forage and fodder
There are about 95 halophytic species that could be used as either forage or fodder and most prominent among them are mangroves- Avicennia marina, Aegiceras corniculata, Ceriops tagal, and Rhizophora mucronata. Among trees, species of Acacia, Prosopis, Salvadora and Zizyphus are traditional fodder of arid regions. Many species of Alhagi, Salicornia, Chenopodium, Atriplex, Salsola, Suaeda and Kochia are common fodder shrubs. Among grasses Leptochloa fusca, Lasarius scindicus, Panicum turgidum, Dactyloctenium sindicum, Cynodon dactylon, Paspalum vaginatum, Sporobolus marginatus, Chloris gayana, C. virgata, Echinochloa turnerana, E. colonum and Puccinellia distans are commonly found in saline and alkaline areas.
In face of energy crisis, search for suitable halophytes for biofuel production attains significance. These may include species having high biomass yield, low lignin with high cellulose/hemi-cellulose which can easily be extracted, converted into sugars and subsequently fermented to alcohol.
Seeds of various halophytes, such as Suaeda fruticosa, Arthrocnemum macrostachyum, Salicornia bigelovii, S. brachiata, Halogeton glomeratus, Kochia scoparia, and Haloxylon stocksii possess a sufficient quantity of high quality edible oil with unsaturation ranging from 70-80 %. Seeds of Salvadora oleoides and S. persica contain 40 50% fat and are a good source of lauric acid- a potential substitute for coconut oil.
Fuel wood and timber
More than a billion people in developing countries rely on wood for cooking and heating. Quite often fuel wood is obtained from salt-tolerant trees and shrubs, which may include species of Prosopis, Tamarix, Salsola, Acacia, Suaeda, Kochia, Capparis, Casuarina, Pithecellobium, Parkinsonia, and Salvadora. In addition species like Dalbergia sisso, Pongamia pinnata, Populus euphratica, Tamarix spp. could provide good-quality wood. In coastal areas the mangroves species of Rhizophora, Ceriops, Avicennia and Aegiceras are good fuel woods and also contribute to charcoal production.
Halophytic plants are known to provide relief in the following diseases: Cold, flu and cough (Achillea mellifolium, Microcephala lamellate, Phylla nodiflora, Caesalpinea bonduc, Plantago lanceolata, Portulaca quadrifida, Portulaca oleracea, Solanum surrattense, Withania sominifera, Tribulus terrestris, Capparis decidua, Zygophyllum simplex, Salvadora persica & S. oleoides): vermifuge (Artimesia scoparia, Portulaca quadrifida, Seriphidium brevifolium, S. quetenses, Cocos nucifera, Portulaca oleracea, Evolvulous alsinoides, Salsola imbricata, S. tetrandra, Zygophyllum propinqum, Z. simplex): stomach ailments (Juncus rigidus, Seriphidium quetenses, Thespesia populnea, Zaleya pentandra): pain killer (Artemesia scoparia, Solanum surratense): diuretic (Plantago major, Portulaca quadrifida, P. oleracea, Withania sominifera,Tribulus terrestris, Juncus rigidus): snake bite (Rumex vesicarius, Verbena officinalis, Zaleya pentandra): gonorrhea (Portulaca oleracea, Corchorus depressus): sedative (Withania somnifera): ulcer (Ceriops tagal, Withania sominifera): pneumonia (Corchorus depressus): heart disease (Ammi visnaga, Tribulus terrestris, Capparis decidua, Kochia indica, Zygophyllum simplex): skin diseases (Centella asiatica, Salsola imbricata): laxative (Capparis deciduas): eyes (Zygophyllum simplex): ear pain (Artemesia scoparia): asthma (Evolvulous alsinoides, Solanum incanum): wound healing (Plantago lanceolata) and stimulant (Kochia indica).
Source of chemicals
Most of the mangroves are rich in tannin, also present in Acacia and some other species. A kind of soda is obtained in large quantities from Suaeda, Salicornia, Salsola, and Haloxylon species, used in soap making and in glass industry. Seeds of Annona glabra are source of insecticide. Rotenon, an insect and fish/arrow poison is extracted from the roots of Derris trifoliata.
Paspalum vaginatum and Sporobolus virginicus may be suitable candidates for lawns and golf courses etc. Avicennia germinan,Atriplex halimus, Sesuvium portulacastrum, Batis maritime, Casuarina stricta, Salicornia stricta, Spartina species are used for dune stabilization.
Many halophytes are useful ornamentals; these include among others Aster tripolium, Limoniastrum monopetalum, Batis maritima, Tamarix nilotica, Tamarix amnicola, Cistanche fistulosum, Atriplex halimus, Sesuvium portulacastrum, Noronhia emarginata.
Accumulation of carbon dioxide (CO2) in the atmosphere is a major environmental concern of modern times as evidenced by the increase in atmospheric CO2 and subsequent global warming. This trend can partly be reversed through the removal of CO2 from the atmosphere and sequestration into long lived pools of carbon in soil and plant e.g. wood, leaf litter, root debris etc.
It has been estimated that about 130 million ha of highly saline lands around the world may immediately be available to grow suitable halophytes with a capacity to assimilate 0.6-1.2 gig tons of C per year. These may include trees (Prosopis, Acacia spp.), grasses (Panicum) etc.
Parts of the seeds of Calotropis procera are filled in pillows; many Acacia produce gums and the stem and leaves of Juncus maritimus, Kochia scoparia, Aristida adscenscoinis, Imperata cylindrica, Phragmites australis and Typha domingensis have been used since ancient times for the manufacture of mats, baskets thatching and cordage. Pyrus betulaefolia and Malus sieversii rootstocks are used for propagating pears and apples respectively and rootstock of Annona glabra is used for producing high quality Annona clones. Suaeda esteroa, Salicornia bigelovii, Atriplex barclayana have been successfully grown using saline wastewater discharged from aquaculture projects. This also opens the possibility of utilizing urban and industrial wastes similarly.