4
1.3 Water Scarcity Induces Water Stress
Water stress can be defined as the absence of adequate moisture necessary for normal plant growth to complete its life cycle (Zhu 2002). The lack of adequate moisture that leading to water stress is a common occurrence in rain fed areas, brought
about by infrequent rains and poor irrigation (Wang et al. 2015). Similarly, in irrigated agriculture water stress could be also induced by water scarcity. Water stress
affects every aspect of plant growth, including anatomy, morphology, physiology,
and biochemistry (Zhu 2002). Decreasing water availability under drought generally results in limited nutrients uptake (Davari 2016). Another important effect of
water deficit is the reduction of nutrient acquisition by the root and its transport to
shoots (Farooq et al. 2009). Lowered absorption of the inorganic nutrients could
result from interference in nutrient uptake and the unloading mechanism, which
reduces transpiration flow (Garg 2003). Influence of drought on plant nutrition may
also be related to limited availability of energy for assimilation of nitrate, phosphate, and sulfate (Baligar et al. 2001).
Under water stress, plants close their stomata to prevent dehydration, thus drastic
reduction in transpiration rates occur (Taiz and Zeiger 2004), and production of
abscisic acid increases by as much as 50-fold in leaves, which decreases leaf area
due to lower-turgor-pressure cells, stomatal closure, the induction of senescence
and ethylene production (Taiz and Zeiger 2013). Water stress also affects many
important biochemical processes such as osmotic adjustment, antioxidant enzyme
defense system, abscisic acid production, and lipid peroxidation (Sarto et al. 2016).
The increase in Si in the plant can increase the efficiency of water use by some
grasses (Sarto et al. 2017).
Under severe stress, the dehydration in mesophyll cells inhibits photosynthesis
and water use efficiency decreases as a result (Taiz and Zeiger 2004). A reduction in
water availability in plants leads to the reduction of cell solutes thus increasing the
solute concentration. This causes the plasma membrane to become thicker, affecting
the turgidity processes of cells, reducing the leaf area and causing stomatal closure.
This results in a reduced rate of photosynthesis, influencing the plant development
(Dias 2008).
At present, nearly 80% of the world’s population is exposed to high levels of
threat to water security (Bunn 2016). The misuse of water resources (Ouda and
Zohry 2018a), and the lack of infrastructures to supply water (Abou Zeid 2002) are
some of the main reasons for scarcity of water. Many parts of the world experience
acute water scarcity and that requires increasing the effectiveness of agricultural
water resources usage and reduces the excessive irrigation for enhanced food security (FAO 2007). To cope with water scarcity without reducing the irrigated area,
different options are available. One of these options is better forecasting of soil
moisture and requirement of crops for water through combining weather predictions
and hydrological modeling, supported by data using new technologies for environmental monitoring and Earth observations from space (Ravazzani et al. 2017).
S. Ouda and A. E.-H. Zohry
1.3 Water Scarcity Induces Water Stress
Water stress can be defined as the absence of adequate moisture necessary for normal plant growth to complete its life cycle (Zhu 2002). The lack of adequate moisture that leading to water stress is a common occurrence in rain fed areas, brought
about by infrequent rains and poor irrigation (Wang et al. 2015). Similarly, in irrigated agriculture water stress could be also induced by water scarcity. Water stress
affects every aspect of plant growth, including anatomy, morphology, physiology,
and biochemistry (Zhu 2002). Decreasing water availability under drought generally results in limited nutrients uptake (Davari 2016). Another important effect of
water deficit is the reduction of nutrient acquisition by the root and its transport to
shoots (Farooq et al. 2009). Lowered absorption of the inorganic nutrients could
result from interference in nutrient uptake and the unloading mechanism, which
reduces transpiration flow (Garg 2003). Influence of drought on plant nutrition may
also be related to limited availability of energy for assimilation of nitrate, phosphate, and sulfate (Baligar et al. 2001).
Under water stress, plants close their stomata to prevent dehydration, thus drastic
reduction in transpiration rates occur (Taiz and Zeiger 2004), and production of
abscisic acid increases by as much as 50-fold in leaves, which decreases leaf area
due to lower-turgor-pressure cells, stomatal closure, the induction of senescence
and ethylene production (Taiz and Zeiger 2013). Water stress also affects many
important biochemical processes such as osmotic adjustment, antioxidant enzyme
defense system, abscisic acid production, and lipid peroxidation (Sarto et al. 2016).
The increase in Si in the plant can increase the efficiency of water use by some
grasses (Sarto et al. 2017).
Under severe stress, the dehydration in mesophyll cells inhibits photosynthesis
and water use efficiency decreases as a result (Taiz and Zeiger 2004). A reduction in
water availability in plants leads to the reduction of cell solutes thus increasing the
solute concentration. This causes the plasma membrane to become thicker, affecting
the turgidity processes of cells, reducing the leaf area and causing stomatal closure.
This results in a reduced rate of photosynthesis, influencing the plant development
(Dias 2008).
At present, nearly 80% of the world’s population is exposed to high levels of
threat to water security (Bunn 2016). The misuse of water resources (Ouda and
Zohry 2018a), and the lack of infrastructures to supply water (Abou Zeid 2002) are
some of the main reasons for scarcity of water. Many parts of the world experience
acute water scarcity and that requires increasing the effectiveness of agricultural
water resources usage and reduces the excessive irrigation for enhanced food security (FAO 2007). To cope with water scarcity without reducing the irrigated area,
different options are available. One of these options is better forecasting of soil
moisture and requirement of crops for water through combining weather predictions
and hydrological modeling, supported by data using new technologies for environmental monitoring and Earth observations from space (Ravazzani et al. 2017).
S. Ouda and A. E.-H. Zohry