Grasses in Arid and Semi-Arid Lands: The Multi-Benefits of the Indigenous Grasses Grasses in Arid and Semi-Arid Lands: The Multi-Benefits of the Indigenous Grasses

Drought regions are the most critical areas of the world. The challenging environmental conditions create severe concerns in arid and semi-arid lands. Consequently, the management task is crucial to face the proposed complicated ecological conditions. The main objective of this chapter is to focus on the vital roles of the indigenous grasses in drought areas and how the same could be a perfect solution in the urban planning of such places sustainably. Examples of the indigenous grasses of arid and semi-arid regions from the Poaceae family will be illustrated along their multi-economic values. In addition, promis- ing innovative approaches required to face the demanding future of the agricultural sector will be presented and discussed.


Introduction
Arid and semi-arid lands are regions of the world that have harsh environmental conditions, including high temperatures, high evapotranspiration rates, low precipitation rates, and scarcity of freshwater resources. Consequently, the management task of such regions is a challenging mission, especially with the growing concerns of climate change, population explosion, and food security.
This chapter provides insights into how the indigenous grasses can be a perfect candidate to rescue the future of the agricultural sector in arid and semi-arid regions sustainably, focusing on the major role of grasses in urban planning. In addition, examples of predominant grass communities that have multi-economic benefits of add value in arid and semi-arid areas will be discussed. In addition, the chapter offers promising innovative approaches in such drought regions.

Drought regions
Tropical desert (TBWh) is the global ecological zone (GEZ) that is characterized by severe ecological conditions including high summer temperatures, high evapotranspiration (ET), and low and irregular precipitation [1]. The sandy soil texture is predominant with high porosity, high water permeability, low water holding capacity, poor nutrient content, and thus low fertility [2][3][4][5][6].
Under such conditions certain vegetation can adapt and survive [5][6][7]. Such flora was for centuries a free resource that provides free ecological services including shelter, food, and medication [5].

Global concerns and the demanding future
Currently, there are major concerns threatening the future of the agricultural sector in many regions around the world, particularly in arid and semi-arid areas. Concerns are associated with the sharp global population growth, depletion of natural resources (e.g., fresh water), pollution (e.g., air, water, and soil), and climate change and global warming [8,9]. Since 1960, global population is dramatically increasing, reaching 7.442 billion in 2016 with sharp growth projections [10], which are expected to reach over 9 billion by 2050. More people means more natural resources required to cover the basic life requirements, such as water, food, medication, and accommodation [8,9].
The concerns are more serious in the era of climate change, where regions with scarcity in freshwater resources are subjected to worse drought conditions, associated with extreme ecological events of severe implications on the limited available natural resources and thus on food productivity. Particularly, the same synchronized with the sharp expansion in industrial activities, urbanization, and population. Consequently, it could be highly expected that the drought regions could be much more susceptible and sensitive to any further environmental challenges [2].
The situation is more critical in developing countries, which have limitations on the environmental resources (e.g., water, land, and energy) and thus have high risks of hunger and poverty. Based on the Food and Agriculture Organization of the United Nations (FAO), the global demand for cereals will increase by 70% in 2050 compared to the current rates and would be doubled in many low-income nations [11]. Also, the demand for food will sharply grow in high-income countries, which have high per capita food consumption rates [12].

Indigenous grasses of drought regions
The indigenous plants including the indigenous grasses can play a significant role in mitigating the demanding future of arid and semi-arid lands. Special attention should be given to the industrial gasses that can bring extra economic value by each water drop to the drought regions [8,13]. Such plants can provide maximum benefits with minimal inputs, as illustrated in Figure 1.
There are many desert grasses that have the capability of producing expensive secondary metabolites (e.g., terpenes) as their defense phytochemicals. Such natural compounds have many therapeutic applications in the traditional herbal practices [13].
For example, Cyperus rotundus L. (English name: Coco grass) from Cyperaceae (Sedges family) is a perennial grass that is widespread in sandy and saline soils, like in the central areas of Tunisia, northern parts of the United Arab Emirates, Southern Africa, and Northern India. This grass is not used as a forage grass only, but it is also eaten to treat worm infections and regulate menstruation. Its seeds are heated with oil and used as ear drops to soften earwax. Besides, this grass is an ingredient in tooth powder to whiten teeth. Moreover, C. rotundus is used by Greek as a diuretic, to break up stones, and to treat uterine disorders. The herbal extract of C. rotundus rhizomes is found to be rich in sesquiterpenes and monoterpenes and proven to be a rich source of antioxidants and antibacterial bioactive compounds [14,15].
Besides the healing benefits, there are many grass species that have excellent landscaping and urbanization potentials. The same is due to their unique shapes, textures, and colors which is totally opposite of the general concept of the desert plants by the public community. For example, Cyperus arenarius Retz. (English name: Dwarf sedge), which is a perennial grass of the Cyperaceae family, has high value as a landscaping grass in the urbanization activities of sandy and coastal saline habitats [16,17].
Consequently, while the indigenous grasses of the arid and semi-arid regions can be cultivated to provide various therapeutic, nutraceutical, and health-care applications, they also could be employed to sustain the landscaping beauty and to conserve a balanced ecosystem. Examples of potential grasses from the Poaceae family are provided in Table 1.
On the other hand, cultivating exotic grasses, which are originally from other regions (e.g., temperate region), requires enormous amounts of inputs (e.g., water and soil nutrients) to survive and grow [32]. Even with the application of the modern irrigation technologies, which save 60% of the watering amounts [11], most of these grasses have high watering requirements, lack adaptation mechanisms, and disturb the natural balance of the desert ecosystem.
In additional, to the high irrigation requirements, exotic grasses are labor intensive (e.g., adding fertilizers and maintenance) leading to expensive environmental and economic costs. Due to these, the cultivation of exotic grasses is restricted or even banned in some areas [32].
Similarly, some indigenous grasses in the drought regions that consume high amount of water should be cultivated wisely. For example, Rhodes grass (Chloris gayana Knuth.), which is a perennial grass from the Poaceae family, has high value as a forage grass in warm regions. However, since it is a water-intensive grass, growing it as a forage grass has been banned in many countries (e.g., in United Arab Emirates) [32].

Morphophysiological characteristics
Cultivating the indigenous grasses could greatly mitigate the water scarcity situation with robust adaptation strategies to survive the drought conditions. Over the time, these desert grasses have developed diverse morphophysiological mechanisms to adapt to arid environmental conditions, as illustrated in Table 2 [4,13]. These environmental conditions include high intensity of sunlight, high wind speed, rapid loss of water through evaporation or evapotranspiration, low amount of precipitation, low soil moisture content, low soil waterholding capacity, high rate of water permeability, high level of soil salinity, and deficiency in soil nutrients [33,34].
Many indigenous grasses of the drought regions belong to the xerophytes and/or halophytes as indicated in Table 1, which are adapted to water scarcity and soil salinity, respectively [33,34].
In addition, the following morphological properties enable desert plants to adapt to the prevailing harsh environmental condition: seeds dormancy, long root system, light green color, small leaf area, succulent plant parts, presence of hairy surface and thorns, short growth rate, and short life cycle (ephemerals) [33,34].
Physiological adaptation of grasses in drought regions is another adaptation mechanism that enables the plant either to reduce the amount of water loss, "transpiration," or increase the ability of the grass to uptake more water. The same is achieved by different physiological and biochemical modifications [19].
For example, some grasses have the ability to control stomatal opening during the day, thus controlling transpiration rates and reducing water loss. Also, controlling the osmotic pressure of plant cells in drought and saline habitats is another important physiological adaptation mechanism that reduces the osmotic potential of plant cell solutes to lower levels compared to the water potential of the surrounding environment, which enables the roots to uptake more water and enhances plant water-use efficiency. Proline accumulation is another adaptation mechanism to survive stress factors, like water limitation. The accumulation of such organic compounds inside plant cells helps in reducing the osmotic potential, thus enhancing soilwater uptake. Besides, the capability of plant cell components to have higher rates of water bound plays a major role in reducing water loss during transpiration [19].
Photosynthesis carbon fixation pathways of C4 and CAM plants are vital mechanisms to adapt to hot and arid environments. Such pathways are associated with higher rates of water-use efficiency, thus a better water conservation strategy. Most indigenous grasses from drought regions are following these carbon fixation pathways [19]. Examples of such grasses that are following the C4 pathway are illustrated in Table 1, that include Cynodon dactylon L., Paspalum vaginatum Sw., Cenchrus ciliaris L., Pennisetum setaceum (Forssk.) Chiov, Desmostachya bipinnata L., Cymbopogon schoenanthus L., and Cymbopogon jwarancusa (Jones) Schult.  [26,18] Note: Plant photos are taken by authors of this work. Table 2.
Adaptation characteristics of common perennial grasses from Poaceae family.

Sustainable value
Grasses are the most plentiful species in the plant kingdom with enormous socio-economic potentials. Growing the indigenous grasses in drought regions can provide the community with great sustainable values, including the cultural, environmental, and economic values as discussed below:

Cultural benefits
There is no doubt that the indigenous grasses provide great cultural and social values for the local community. In the old times, such plants had been greatly used in traditional medicine, as the only available resources for therapeutic and medication purposes, which established a strong relationship between these plants and the Bedouin people who historically inhabited the desert regions [4,35].
For example, Buffel grass (Cenchrus ciliaris L.) has been used in the Zulu traditional herbal practices as a pain reliever and to cure many diseases, such as menstrual disorders, urinary infections, kidney pain, tumors, sores, and wounds [36]. Also, oil grass (Cymbopogon jwarancusa (Jones) Schult.) has been used by Indians to treat blood disorders, vomiting, skin problems, unconsciousness, and abdominal tumors [37].

Ecological benefits
Grasses play a major role in the fight against desertification. It is a cost-effective method of soil binding and fixation to mitigate land degradation in dry lands. It is of particular interest in urban planning to cultivate the indigenous grasses of the drought regions, which conserve natural resources and maintain a balanced and healthy ecosystem [38]. For example, dwarf sedge (Cyperus arenarius Retz.) from the Cyperaceae family provides major ecological services in the sandy, saline, and coastal habitats [17].

Economic benefits
There are a lot of grass species in drought regions that can offer multi-economic benefits, including food and nutritional resource, medicinal, cosmetic, flavoring, and fragrance. Examples of selected grasses and their benefits are shown in Table 1.

Innovative technologies and approaches
Certainly, the agricultural sector in drought regions has to adopt the best agricultural practices and irrigation methods in cultivating selected indigenous grasses that can best survive the harsh conditions and at the same time provide multi-economic benefits. Such agricultural practices include deficit irrigation and irrigation scheduling, which reduce watering volumes, increase water-use efficiency and thus increase water productivity. Studies need to be done to determine an optimized amount (model) of irrigation schedule, in order to apply the minimum amount of water which returns in maximum possible yield considering the prevailing and expected change in climate [32,39].
Undoubtedly, it is very important to imitate the natural and original environment of the drought areas, through focusing on planting the indigenous grass species from the xerophytes and halophytes. Besides, the adoption of hardscaping and xeriscaping plays an essential role in reducing the heavy pressure on the limited available water resources [5,13,32].
On the other hand, exotic grasses have to be restricted or even banned since most of these grasses require high amounts of irrigation water and labor for maintenance and fertilization; they thus pose very expensive environmental and economic costs. It is, therefore, recommended to replace these exotic grasses with salt and drought-tolerant species, which substantially reduce water requirements and sustainably maintain a balanced and healthy ecosystem [32].
New approaches are applied to reduce water loss and enhance plant soil-water uptake. One of these approaches is the application of hydrophobic sand, which is originally beach sand coated with chemically treated pure silica. According to Salem et al. [40], mixing the hydrophobic sand with the agricultural soil improves soil and plant characteristics and conserves water use without causing any adverse effects to the cultivated plants. Successful initiatives were reported with Bermudagrass (Cynodon dactylon L.), showing better growth rates, while keeping the plant mineral composition (e.g., Cd, Mo, Pb, and Se) within acceptable limits [40].

Conclusion
It is crucially needed to use each drop of expensive freshwater resource in drought regions cautiously and wisely. This could be done through focusing on cultivating the indigenous industrial gasses that can best adapt and mitigate the harsh environmental conditions, and still produce expensive raw materials of great applications (e.g., food and pharmaceuticals), offering potential ecological and/or landscaping services sustainably. Cultivating the indigenous grasses of drought lands should be synchronized with the best agricultural practices and the most recent innovations of soil-plant water use efficiency.
The demanding future of the greenery sector in the arid and semi-arid regions does not rely on how to enlarge the available freshwater resources (which are already limited and scarce), as much as relying on how to best employ such limited resources to gain maximum economic benefits to arid and semi-arid regions sustainably.