There exists a global challenge of feeding the growing human population of the world and supplying its energy needs without exhausting global resources. This challenge includes the competition for biomass between food and fuel production. The aim of this paper is to review to what extent the biomass of plants growing under hostile conditions and on marginal lands could ease that competition. Biomass from salt-tolerant algae and halophytes has shown potential for bioenergy production on salt-affected soils. Halophytes and algae could provide a bio-based source for lignoceelusic biomass and fatty acids or an alternative for edible biomass currently produced using fresh water and agricultural lands. The present paper provides an overview of the opportunities and challenges in the development of alternative fuels from halophytes and algae. Halophytes grown on marginal and degraded lands using saline water offer an additional material for commercial-scale biofuel production, especially bioethanol. At the same time, suitable strains of microalgae cultured under saline conditions can be a particularly good source of biodiesel, although the efficiency of their mass-scale biomass production is still a concern in relation to environmental protection. This review summaries the pitfalls and precautions for producing biomass in a way that limits environmental hazards and harms for coastal ecosystems. Some new algal and halophytic species with great potential as sources of bioenergy are highlighted.

Haloxylon stocksii is a perennial halophytic shrub found in saline arid habitats. Ecophysiology of this xerohalophyte was studied to better understand its adaptations to survive under saline conditions (0-300 mM NaCl). Growth parameters remained unaffected at 100 mM NaCl compared to non-saline control and declined at 300 mM; root biomass however, increased in 100 mM NaCl. Shoot water potential, osmotic potential and turgor decreased under saline conditions. Gas exchange parameters such as rate of photosynthesis, rate of transpiration and stomatal conductance decreased in 300 mM NaCl with a decline in intercellular carbon dioxide concentration suggesting stomatal limitation of photosynthesis. Water use efficiency increased significantly in 300 mM NaCl compared to 0 and 100 mM NaCl. Chlorophyll content decreased progressively with increasing salinity while chlorophyll a/b ratio remained unaffected. Potential photochemical quantum yield of PSII (Fv/Fm) and the effective quantum yield [Y (II)] were not affected by salinity; however, there was a constitutive increase in non-photochemical quenching under saline conditions (100 and 300 mM) and decrease in relative electron transport rate in 300 mM NaCl as a protective measure to reduce oxidative stress at cellular level. Total soluble sugars increased by approximate to 25% in 300 mM NaCl possibly indicating a lower energy demand for growth. Anti-nutritive secondary metabolites such as polyphenols, tannins, flavonoids, saponins and nitrates decreased under saline conditions except for some increase in oxalates in 100 mM NaCl. This study indicates that Haloxylon stocksii is a moderately salt tolerant plant with adaptations to down-regulate its photosynthetic machinery to avoid oxidative stress and could be a palatable animal feed.

Based on biomass composition of plants collected from saline habitats, Phragmites karka (Retz.) Trin. ex Steud. has emerged as a suitable feedstock for biofuel. In the present study, plant growth, eco-physiological responses and bioenergy characteristics of P. karka grown under conditions ranging from non-saline to ~80% seawater salinity are reported. Moderate salinity (NaCl at 100 mol m–3) increased plant fresh weight (20%), number of leaves (25%) and specific plant length, which were directly linked with increased net photosynthetic rate (25%) and stomatal conductance (25%) compared with the non-saline control. Higher photosynthetic efficiency was achieved by increasing electron transport rate (ETR, 20%), effective quantum yield (YII, 21%) and maximum efficiency of photosystem II (Fv/Fm, 20%). Decreased non-photochemical quenching (Y(NPQ)) and malondialdehyde content (18%) indicated an oxidative balance, which was also reflected in total carotenoids and chlorophylls. These eco-physiological parameters worked together to increase cellulose (34%) and hemicellulose (70%) at NaCl concentrations up to 200 mol m–3. Decreased growth under higher salinity could be linked with photosynthesis inhibition, due to stomatal closure and co-occurring reduction in CO2 uptake. Lower stomatal conductance increased water-use efficiency but led to over-production of reactive oxygen species, which disturbed oxidative stability (increasing ETR/PN) and imposed membrane leakage. Consequently, plants accumulated more carotenoids and soluble carbohydrates to stabilise PSII machinery (Fv/Fm, YII and Y(NPQ)), and to survive under high salinity. Such adaptations, however, led to growth penalty and reduced quality of lignocellulosic biomass. The above findings suggest that P. karka qualifies as a suitable raw material for biofuel under moderate salinity.

Zaleya pentandra is a moderately salt resistant xero-halophyte, used locally as cattle fodder and as a source of medicine for various ailments. The present study deals with the effect of salinity on growth, leaf water relations, photosynthesis and antinutritive chemicals of this plant. Plants were grown in plastic pots containing sandy loam soil irrigated with Hoagland's nutrient solution under various salt (0, 75 and 150 mM NaCl) treatments in an open netted green house. Shoot and root length and biomass, number of leaves and nodes, remained unchanged at 75 mM NaCl treatment compared to non-saline controls. Shoot dry weight decreased by about 70% at 150 mM NaCl treatment, while root dry weight remained unaffected by salinity. Leaf osmotic potential also was unaffected at 75 Mm NaCl but decreased at 150 mM NaCl. Leaf water potential decreased progressively with increasing salinity treatments. Calculated turgor pressure decreased with increase in salinity. Rate of photosynthesis was unaffected under 75 mM NaCl treatment but decreased by about 50% at high NaCl treatment (i.e. 150 mM NaCl). Similar trends were observed for stomatal conductance and rate of transpiration with concomitant increase in water use efficiency (WUE) at 150 mM NaCl. There was no change in the intrinsic photochemical efficiency of PSII (Fv/Fm) (no photoinhibition) under saline conditions. However, the effective photochemical efficiency of PSII (Fv'/Fm') was generally low particularly at 150 mM NaCl. Among anti-nutrient chemicals, saponin and nitrate decreased significantly under saline conditions, tannins increased whereas, oxalates, phenols and flavonoids were unaffected. However, all these chemicals were within acceptable limits for cattle feed except for oxalates, which were marginally higher.

This study is based on the assumptions that annual grasses express more complex seed dormancy than perennials, while dormancy regulating chemicals (DRCs) help in recovering seeds from dormancy. The role of six such chemicals, viz. plant hormones - Kinetin, Fusicoccin; organic osmotica - Proline, Betaine; nitrogenous compounds - Nitrate, Thiourea, in alleviating effects of salinity and light on seed germination of three subtropical grasses (perennials: Phragmites karka, Dichanthium annulatum; and annual: Eragrostis ciliaris) was hence investigated. All seeds of P. karka and D. annulatum germinated in non-saline condition while in E. ciliaris, 60% seeds germinated in absence of salts, 10% were dead and 30% were dormant. Salinity reduced germination of the test species to following levels (% of non-saline control) under highest NaCl concentration used: P. karka (30% at 500 mM), D. annulatum (25% at 400 mM) and E. ciliaris (10% at 125 mM). The application of all DRCs alleviated conditional dormancy associated with salinity more in P. karka than D. annulatum but negligibly in the case of E. ciliaris. Absence of light inhibited seed germination of P. karka (partially) and E. ciliaris (completely) but under these conditions the application of DRCs increased germination of P. karka only. Nitrate was generally more effective than other DRCs in increasing seed germination both in salinity as well as in complete darkness. Seed germination was synergistically inhibited by salinity under dark conditions compared to their individual effects and was completely alleviated in P. karka and D. annulatum seeds by DRCs. In conclusion, the annual grass (E. ciliaris) used both innate and induced type of seed dormancy along with absolute light demand for successful seedling establishment while perennials (P. karka and D. annulatum) depended on enforced dormancy. Moreover, seed dormancy could be alleviated by DRCs in perennial grasses but not in the annual species. (C) 2017 Elsevier GmbH. All rights reserved.

Rampant salinity coupled with population explosion necessitates search for suitable alternatives to conventional sources of food both for human and animal consumption. While it may be difficult to change our culinary preferences, training animals to adopt a changed diet of nonconventional salt tolerant plants is easier. Using these wild plants however, requires estimation of undesirable secondary metabolites (SMs) produced during stressful conditions, which may be harmful for health of animals. Some of these anti-nutritional components (total phenols, flavonoids, tannins, nitrates, saponins and oxalates) were determined in 22 halophytes locally used as fodder/forage. Most of the species were perennial shrubs and herbs of an area where environmental conditions like high mean annual temperature (similar to 35 degrees C), low rainfall (< 250mm) with soil mostly dry (average 2% moisture) and saline (average EC 13 dSm(-1)) supported the growth of halophytes and xerophytes. Values of SMs in the studied plants ranged from 0.13-4.05% for total phenols, 0.38-6.99% for tannins, 0.15-1.50% for flavonoids, 0.10-1.15% for nitrates, 0.45-8.68% for saponins and 0.36-2.34% for oxalates. Most of the species (19) contained low to moderate amount of individual as well as total SMs which were within the non-toxic ranges. However, three species distributed in coastal habitats where average soil salinity (27.67 dSm(- 1)) was considerably higher than inland ones (7.09 dSm(-1)) had SMs contents above the safe limits. It is evident from these results that most of these plants contained moderate to low levels of anti-nutritional factors, which lies under the safe limits and hence, could be used as a potential feed source to raise animals, particularly in arid/semiarid areas. Additionally, these plants represents a viable choice as they can be grown without encroaching on agricultural lands and fresh water resources and could promote livestock production which may improve socio-economic conditions of poor farmers in a sustainable and eco-friendly manner.

Good quality water and arable land are needed to grow conventional crops to provide food for human and animal population. However, burgeoning world population leading to wide spread urbanization and industrialization is aggressively sharing these resources. A solution may be found in using saline water and salinized lands to produce quality animal feed from salt tolerant plants. In this study, two halophytic grasses (Panicum antidotale and Desmostachya bipinnata) were tested for their potential to replace conventional cattle fodder in the diet of cattle. Four trials were conducted in which cow calves were fed diets containing above mentioned halophytes alone or in combination with conventional fodders (wheat and maize). Weight gain in animals fed diets supplemented with halophytes were generally at par with or in few cases marginally better than those on conventional fodder. For instance, P. antidotale increased the calf weight around 15% when used as green and 8% in case of hay. Feeding Berseem (Trifolium alexandrinum, 15% crude protein) as the only source of concentrate in a diet containing D. bipinnata sustained weight only for about 6-7 weeks after which it started to decrease. Supplementing the diet with a regular concentrate was subsequently needed to restore weight gain. Halophytes as green/hay/concentrate were as good as conventional fodder regarding dressed meat. The protein content of meat was showing increasing trend when replacing conventional fodders with halophytes, particularly 20% protein was higher in meat when Prosopis juliflora pods and Manilkara zapota were used as concentrate and P. antidotale as hay in diet.

The financial and technical aspects of using edible plants as a biodiesel source have been studied extensively, but research on the potential use of salt resistant, non-edible plants for this purpose remains relatively underexplored. Data available on salt tolerance range, seed oil content, composition of fatty acid methyl esters (FAME) and engine performance parameters – Iodine Value (IV), Cetane Number (CN) and Saponification Number (SN) – of 20 salt-resistant plants were examined to assess their suitability for use as diesel engine fuel. Most of the test species were perennial from family Amaranthaceae, exhibiting high salt tolerance. The quantity of their seed oil ranged from 10–30% while nine species contained >25% oil. The SN, IV and CN values varied from 130–206, 29–156 and 38–81, respectively. Based on the above mentioned parameters, seven halophytic plant species – Salicornia fruticosa, Cressa cretica, Arthrocnemum macrostachyum, Alhagi maurorum, Halogeton glomeratus, Kosteletzkya virginica and Atriplex rosea – appear to be promising biodiesel candidates. These non-food plants which can grow using saline resources and have an oil composition suitable for engine efficiency are more salt resistant than Jatropha or other glycophytic feedstock to serve in a bioenergy farming system. Cultivation of such plants for biodiesel production has the additional advantage of reclaiming degraded lands with the environmental benefit of carbon sequestration.

Freshwater resources will become limited in near future and it is necessary to develop sustainable biological production systems, which can tolerate hyper-osmotic and hyper-ionic salinity. Plants growing in saline conditions primarily have to cope with osmotic stress followed by specific ion effects, their toxicities, ion disequilibrium and related ramifications such as oxidative burst. This is an exclusion criterion for the majority of our common crops. In order to survive under such conditions, suitable adjustments are necessary. Beside the control of the entrance on root level, the ability to secrete ions (excreter) or to dilute ions (succulents) helps to preserve a vital ion balance inside the tissues. Sadly, traditional approaches of breeding crop plants with improved abiotic stress resistance have met limited success so far. Failures were due to two problem areas, lack of easy to detect traits and too many genes that had to be transferred at a time. These arguments underline the advantage of utilizing suited halophytes as crops on saline lands and to improve their individual crop potential. Because of their diversity, halophytes have been regarded as a rich source of potential germplasm. A variety of halophytic plant species already has been utilized as nonconventional cash-crops. Lieth H, Mochtchenko M (Cash crop halophytes: recent studies. Tasks for vegetation science, vol 38. Kluwer, Dordrecht, 2003) described the utilization of halophytic species for the improvement of sustainable agriculture as well as sources of income. However, knowing that saline irrigation always comprises the risk of increasing salinity up to levels where no plants (even no halophytes) can exist anymore, it is important to achieve sustainable conditions. Therefore it is essential to study the interaction among soil salinity, individual species (to study heterogeneity within the halophytes and plant diversity), biotic interactions, and atmosphere at distinct conditions before application. The heterogeneity within halophytes (biotic factor) is often ignored but biotic interactions can be in this context an ideal accessory to stabilize sustainable populations on saline lands. The aspect, that dicotyledonous halophytes, when grown in saline soils, generally accumulate more NaCl in shoot tissues than monocotyledonous halophytes (especially grasses) has several consequences on their suitability as crops and their culture conditions (procedure to apply salinity). The implementation of an intercropping system (halophyte culture) is such a way to use saline land and brackish water for producing an economically viable and environmentally sound agriculture. It was estimated that 15 % of undeveloped land in the world's coastal and inland salt deserts could be suitable for growing crops using saltwater agriculture. This amounts to 130 million hectares of new cropland that could be brought into human or animal food production chain - without cutting down forests or consuming more scarce freshwater for irrigation.

Panicum antidotale is a promising grass species for use as fodder and forage using non-conventional agricultural practices. It was therefore grown using brackish water irrigation to determine the optimal spacing and fertilizer treatment required for sustainable growth, ion relations and photosynthesis. Planting distance of 1.5 ft 2 resulted in higher biomass yield. Composite NPK fertilizer (NPK120) @ 120 kg ha -1 supported better plant growth rather than N, P, K individually or their various combinations (NP, NK, PK, NPK). Addition of fermented farmyard manure (NPK120+FM) improved ion regulation (lower Na + uptake, higher K + /Na + ratio), photosynthetic rates and water use efficiency but did not improve biomass production compared to NPK120. However, higher Na + uptake with NPK120 would result in lower ion accumulation in the root zone and delayed soil degradation. We conclude that NPK120 could support sustainable growth of Panicum antidotale in our cropping system by keeping leaf Na + within safe limits for CO2 assimilation and reducing the need for frequent re-planting of salinized root stock.

Muhammad Qasim, Zainul Abideen, Muhammad Yousuf Adnan, Raziuddin Ansari, Bilquees Gul*, Muhammad Ajmal Khan Institute of Sustainable Halophyte Utilization, University of Karachi-75270, Karachi, Pakistan Qatar Shell Professorial Chair of Sustainable Development, Department of International Affairs, College of Arts and Sciences, Qatar University, PO Box 2713, Doha, Qatar Journal of Coastal Life Medicine 2014; 2(1): 22-30

Increasing human population demands more fuel supply causing the release of hazardous greenhouse gases that could be compensated by supplementing with renewable and environment-friendly alternatives such as biofuels. The argument against the use of food crops for biofuel production that it may cause food shortages can be countered by using feedstock outside the human food chain. This opens up the possibility of using halophytes, algae and photosynthetic bacteria as sources of the carbon neutral biofuel which can be produced sustainably without compromising conventional agriculture. In this review we assess the suitability of these non-food resources as bio-fuel alternates.

Degraded land area is increasing in many arid and semi arid countries (UNEP, 2010). Additionally, fresh water resources are becoming limited and routine irrigation practices in conventional agriculture are causing a steady increase in soil salinity. This will lead to further desertification of affected areas in the future with concomitant reduction in the yield of crops known for human and animal consumption. Consequently it has become imperative to search for suitable alternatives and develop ecologically sustainable and economically sound biological systems that can use low quality water and drought affected saline lands to produce plants of economic importance. A large number of halophytes could be used as animal forage/fodder without encroaching upon arable lands and irrigation water. This paper emphasizes the agricultural importance of these salt tolerant plants in a world where most of the water is saline at any given moment. However, the economic use should be in accordance with the ecological demands suited to particular biomes. Pakistan for example, is spread over an area of 800,000 square kilometers with varied climatic conditions ranging from temperate to sub-tropical desert, eventually displaying a high biodiversity in local flora including halophytes. About 16% of the world halophytic flora is distributed in Pakistan with more than 410 species and among them >100 have potential economic usages as cattle feed. A number of these species are also distributed in the regions between the Atlantic coasts of Africa to western India. The Sindh/Balochistan coast of Pakistan extending from Seer Creek to Jiwani and from coast to mountains including Indus basin are rich sanctuaries for many of these plants. There is a need to conduct systematic survey of this flora, ascertain their chemical characteristics for nutritive value and subsequently identify the species suited to particular conditions through animal feeding trials. Some of these trials have already indicated a promise for ecologically sustainable use of perennial grasses such as Panicum antidotale, formerly identified as Panicum turgidum and Desmostachya bipinnata that may be taken to commercial scale. The system that was developed in Pakistan may serve as a model to other semi-arid subtropical countries of the region.

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.

Effect of several concentrations of NaCl or sea salt was studied on seeds germination of two halophytic grasses- an annual (Eragrostis ciliaris) and a perennial (Dichanthium annulatum) in controlled growth chambers maintained at 10:20, 15:25, 20:30 and 25:35 o C (12 h dark: light) and 24 h dark photoperiods. Sea salt and NaCl both inhibited seed germination but NaCl prevented more seed from germination. Optimal germination was obtained at temperature regime of 25:35 o C for both grasses. Seeds of D. annulatum had similar germination both in light and dark at cooler temperatures in distilled water while addition of salinity in dark inhibited more seed germination compared to light treated seeds. No seeds of E. ciliaris germinated in dark and this positive photoblastic response was associated with temperature irrespective of salinity treatment. All seeds recovered from salts stress when returned to distilled water. Most of the un-germinated seeds were dormant and viable at the end of experiment indicating that they could form a viable seed bank to ensure the continuity of the population in saline habitat.

High salinity, high temperature and absence of light may disturb the balance in endogenous growth regulators. This may put constraint on seed germination of halophytic grasses forcing them to adopt necessary measure like going into dormancy. Germination regulating chemicals may release dormancy imposed by such factors hence effect of Thiourea (10 mM), Nitrate (20 mM), Proline (0.1 mM), Betaine (0.1 mM), GA(3) (3 mM), Kinetin (0.05 mM) and Fusicoccin (5 mu M) was studied in alleviating the inhibitory effect of a range of NaCl and temperature on seed germination of the halophytic grass Phragmites karka. Six NaCl concentrations (0, 100, 200, 300, 400 & 500 mM) were used in 12h light: 12h dark photoperiod and in complete darkness, at different temperature regimes (10/20 degrees C, 15/25 degrees C, 20/30 degrees C and 25/35 degrees C, the lower temperature corresponding to dark and the higher to light photoperiod). Highest number of seeds germinated in non-saline control and the seed germination decreased with increase in salinity at all temperature regimes. All growth regulators significantly promoted seed germination in saline and also in non-saline conditions at all thermoperiods, except at 25-35 degrees C. Only GA(3) and fusicoccin successfully alleviated salinity enforced dormancy of seeds at this thermoperiod. Growth regulators promoted germination in darkness at all temperature regimes. Rate of germination was also significantly affected by the application of these chemicals. Salt induced dormancy of P. karka seeds was broken by the application of different growth regulators. These chemicals also alleviated the temperature (GA3 and fusicoccin) and light (Nitrate) enforced dormancy from seeds of P. karka. It is concluded that germination regulating chemicals have differential effect on the seed germination of P karka. Some of them may alleviate the dormancy while others have no effect.

The effect of chloride and sulfate salts of Na + , K + and Mg 2+ on seed germination of a halophytic grass Phragmites karka was studied under different dark/light conditions and a range of temperature regimes. Seeds germinated better at 20/30oC and their germination decreased with increases in salinity. This reduction in germination could be attributed to specific ion toxicity as well as variable osmotic stress due to the composition of salts. Among cations, K + was generally most toxic followed by Mg 2+ and Na + but such generalizations could not be made in case of anions. Potassium sulfate was inhibitory than Mg 2+ salts for seed germination. A better germination recovery from salt stress was found in 10/20oC. More seeds recovered when transferred from NaCl to distilled water at all temperature regimes. Seeds treated with magnesium sulfate showed better recovery at 10/20 oC, while recovery in Na2SO4 and MgCl2 treated seeds was better in moderate temperatures. The salts did not affect viability of seeds which probably entered into dormancy.

An unsustainable supply of fossil fuel necessitates the need to look for suitable alternatives. One solution lies in using plant biomass, which can be converted into a wide range of biofuels. To avoid conflict between feed and fuel, the crops available for human consumption being used presently as biofuel feedstock may be replaced with halophytes, which have the potential to thrive in saline lands and can be irrigated with brackish water; some can even tolerate seawater salinity. This approach will help in producing sustainable fuel without encroaching on the good quality land and water resources needed for food crops. A candidate species should preferably be perennial, having high yield in saline lands with minimum inputs. Other attributes include cellulose/hemicellulose >25–30%, lignin <10%, low salt load in foliage and a non-invasive nature. The unexplored aspects of agronomy of these wild plants need careful study, especially with regards to land degradation and ecological consequences, before large-scale cultivation.