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.

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Alpinia zerumbet (Zingiberaceae) is a unique ornamental and medicinal plant primarily used in food ingredients and traditional medicine. While organic amendments such as biochar (BC) and compost (Co) have been demonstrated to improve plant productivity, no studies have examined their effects on the growth, physiology, and secondary metabolites of A. zerumbet. This study evaluated the impact of the amendment of BC, Co, or a biochar and compost mixture (BC+Co) on modifying and improving the growth, photosynthesis, antioxidant status, and secondary metabolism of A. zerumbet grown on sandy loam soil. The morpho-physiological and biochemical investigation revealed variation in the response of A. zerumbet to organic amendments. The amendment of BC and BC+Co significantly increased net photosynthetic rates of plants by more than 28%, chlorophyll a and b contents by 92 and 78%, respectively, and carboxylation efficiency by 50% compared with those grown in the sandy loam soil without amendment. Furthermore, the amendment significantly decreased plant oxidative stress, measured as leaf free proline and glycine betaine. Enzymatic antioxidant activity, total phenols, and flavonoids also varied in their response to the organic amendments. In conclusion, this study shows that BC and/or Co amendments are an efficient and sustainable method for improving the metabolite contents and reducing oxidative stress in A. zerumbet.

Plant photosynthesis and biomass production are closely associated traits but critical to unfavorable environmental constraints such as salinity and drought. The relationships among stress tolerance, photosynthetic mechanisms, biomass and ethanol yield were assessed in Phragmites karka. The growth parameters, leaf gas exchange and chlorophyll fluorescence of P. karka were studied when irrigated with the control and 100 and 300 mM NaCl in a nutrient solution and water deficit conditions (drought, at 50% water holding capacity). The plant shoot fresh biomass was increased in the low NaCl concentration; however, it significantly declined in high salinity and drought. Interestingly the addition of low salinity increased the shoot biomass and ethanol yield. The number of tillers was increased at 100 mM NaCl in comparison to the control treatment. High salinity increased the photosynthetic performance, but there were no significant changes in drought-treated plants. The saturated irradiance (Is) for photosynthesis increased significantly in low salinity, but it declined (about 50%) in high salt-stressed and (about 20%) in drought-treated plants compared to the control. The rates of dark respiration (Rd) and compensation irradiance (Ic) were decreased significantly under all treatments of salinity and drought, with the exception of unchanged Rd values in the control and drought treatments. A-Ci curve analyses revealed a significant improvement in the Jmax, Vc, max, and triose-phosphate utilization (TPU) at lower salinity levels but decreased at 300 mM NaCl and drought treatments compared to the control. In the chlorophyll fluorescence parameters (Fv/Fm, maximum photochemical quantum yield of PSII, and Y(NO)), the non-photochemical yields were not affected under the salt and drought treatments, although an effective photochemical quantum yield (YII) and electron transport rate (ETR) were significantly enhanced in water deficit compared to control plants. P. karka regulates an efficient photosynthesis mechanism to grow in saline and arid areas and can therefore be used as a sustainable biofuel crop.

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.

Summary.Over two-thirds of Morocco can be classified as semiarid, arid and desert with low and variable rainfalls. While the country is subject to frequent drought, groundwater resources are predominantly consumed by irrigated agriculture leading to the depletion of water resources and degradation of soil quality. Application of bio-resources wastes to soils after pyrolysis process is well documented to help retain water and nutrients in soils. In this study, three bio-resources wastes derived from argan shells, wood chip, a blend of paper sludge and wheat husks are characterized for physical and chemical properties. To determine the potential impact of salt stress and toxic substances the second part of this study focused on the effect these bio-resources wastes have on germination of salad and barley respectively. The three bio-resources obtained from different biomass showed some unique properties compared to the soil, such as high electrical conductivity (EC), high content of K, Na and Mg, low content of heavy metals. Moreover, the water holding capacities increased with increasing application of bio-resources wastes. Concerning the phytotoxic tests, no negative effect was observed neither for salad (Lactuca sativa L.) nor for barley (Hordeum vulgare) indicating that the three bio-resources could be safely used for agriculture. Collectively, the use of these bio-resources wastes as a soil amendment is anticipated to increase both water and nutrient and could provide the potential for a better plant growth mainly in semiarid, arid and desert climatic conditions like the case of Morocco in which the agricultural practices reserve a majority of the water resources to be used for irrigation.

T HREE SWEETPOTATO cultivars, Abees, Mogamba and Santo Amaro, were subjected to moderate (-0.5MPa) and severe drought stress (-2.5MPa) or to salt treatments up to 200mM NaCl, respectively. Patterns of leaf polyamine contents were analyzed to verify whether these metabolites could be used as early traits of tolerance. Physiological parameters like leaf relative water content, total chlorophyll content, leaf electron conductance, stomata resistance and transpiration rate were used to indicate stress conditions of the plants and growth parameters were applied to identify the level of tolerance among the used cultivars. In all three cultivars, drought led to an increase of putrescine (Put) and decrease of spermidine (Spd) concentrations while spermine (Spm) was decreased only in the Santo Amaro cultivar. The most tolerant cultivar was Mogamba followed by Santo Amaro and Abees. However, this descending order was not reflected by the specific changes in polyamine levels but it is altered under drought as well as under salinity in both sensitive and tolerant cultivars. More investigations are needed to figure out if polyamines behave as a response of stress and/or a protective mechanism.