**2. Chemical and physical water properties**

The two hydrogen atoms bonded by covalent brigs to an oxygen atom makes water molecule [10]. A water molecule is a polar molecule meaning that it is electro negatively charged (around oxygen atoms) at one end and electro positively charged (about two hydrogen atoms) at the other end [11]. When water molecules are interconnected, the positively charged end of one molecule (hydrogen atom) connected by a hydrogen bond to the negatively charged end (oxygen atom) to another water molecule [11]. The phenomenon of attracting water molecules is called cohesion [10]. Due to its properties (polarity and the formation of hydrogen bonds), water participates in many interactions and plays a major role in the plant organism (because it makes up between 80 and 95% of the mass of plant tissue) [10]. Polarity makes water the most widespread and most important solvent in nature. The polarity property allows the dissolution of ionic substances and organic molecules containing polar groups (OH− , NH4 + , and COO− ) [10]. Hydrogen bonds formed between water molecules and ions/polar substances reduce electrostatic interactions

**75**

*Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

between charge-carrying substances and thus allow them to dissolve. The polar parts of the water molecule can form an aqueous mantle (hydration mantle) around the charged particles of the macromolecules, thereby reducing the interactions and binding of the macromolecules, thereby increasing their solubility in water. Due to the large number of hydrogen bonds that connect water molecules, it can absorb heat without large changes in temperature, making it an ideal medium for thermoregulation. As the temperature rises, water molecules movement accelerates. Compared to others liquids, to increase the water, temperature required a relatively large amount of energy (to break hydrogen bonds). From this fact arises one of the basic functions of water in the plant and that is the regulation of plant temperature (thermoregulation) [10]. Since cells contain large amounts of water, they can receive or lose heat with minimal temperature changes. This property can serve to protect organisms from sudden changes in temperature, because organisms that contain larger amounts of water in their tissues were better protected from temperature changes caused by oscillations in heat. Water exists in three different states: ice, liquid, and as steam or water vapor [12]. Water conversion into water vapor requires break down of hydrogen bonds. Therefore, a large amount of energy is used to evaporate the water, which allows the plants to cool efficiently [12]. On the contrary, low temperatures make water molecules approaching. They are closest at 4° C, although they are still moving. At temperatures below 4° C, the molecules just vibrate and the hydrogen bridges become open and rigid [10]. Water in solid state (ice) has a lower density than in liquid, so it floats on the water surface. This property allows many organisms to survive under the frozen water sheet [10]. Water molecules also have a pronounced surface tension. In order to increase the contact area between water and air, it is necessary to break down hydrogen bridges between water molecules [12]. This process requires energy investment, and this energy represents the surface tension. Surface tension has a major role in the transport (movement) of water in the soil-plant system. In addition to surface tension, cohesion and adhesion forces were important in water transport. The attraction between two water molecules is a force called cohesion, while adhesion causes water molecules to adhere to another solid (e.g., a cell wall) [10]. Cohesion, adhesion, and tension allow the appearance of capillarity, that is, the rise of water column through a narrow pipe—capillary, where the water level in the capillary is higher compared to the water level in the source that supplies the capillary [11]. Capillary occurs in various media (soil, root/stem tissue) due to: (1) the attraction of water molecules to the cell wall (adhesion), (2) mutual attraction of

water molecules (cohesion), and (3) surface tension of water [13].

membranes. Water is the basic constituent of protoplasm.

The plant tissue consists mostly of water and to a lesser extent of inorganic substances that plants receive from the soil, organic substances formed by photosynthesis and the products of their conversion. Water makes up 80–95% of the mass of metabolically active plant tissue. Majority of the contained water in plant tissue serves for transpiration and less than 1% was used for metabolic activity [14, 15]. High water content is an essential feature of all metabolically active cells. Relative water content reduction up to 70–80% in most plant cells results in the inhibition of central metabolic functions, such as respiratory processes and photosynthesis. In the process of photosynthesis, water is the carrier of electrons and protons. The role of water in plant tissue is multiple. In addition to being the best and most common solvent, water is also a medium for the movement of molecules inside and between cells. It greatly affects the molecular structure and properties of proteins; nucleic acids and other macromolecules indirectly affect the property of cells plasma

Water is essential for most of biochemical reactions in plant cells. Water is directly involved in number of chemical reactions, for example, hidrolysis and dehydratation reaction (e.g., ADP phosphorylation is actually dehydration of the

#### *Water Plant and Soil Relation under Stress Situations DOI: http://dx.doi.org/10.5772/intechopen.93528*

*Soil Moisture Importance*

while about 21% used for public supply and about 11% accounted for by industry process. Water use around the world has increased six-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by agriculture and irrigation [1]. Water is an important component in every plant's life helping them to obtain their nutrients (through the process of photosynthesis), growth (cell division, mitosis), respiration (cellular respiration), and turgidity (up standing form). Water helps plants to maintain their formation by transporting water and dissolved nutrients, amino acids, and other osmotic active substances from soil to aboveground plant part. Water help plants to perform the most important process, for them, the photosynthesis. In this chapter, we focused in water cycle and its importance for soil to plant life. The soil consists of different horizons, different thicknesses formed under the influence of pedogenetic factors, and processes that have been going on for millions of years and that are constantly going on. Soil system is consisting of solid (soil particles), liquid (water), and gaseous phases (air). A porous space was built between the soil particles of different shape and dimensions in which there is water, air, or some other gas. Vegetable production largely depends on the quality, type, and types of soil, and the necessary factor for plants is water. It is therefore not surprising that all civilizations in the development of human society have settled in the river valleys. Water is constantly present in the soil or on its surface. Its content in the soil is constant changing and depends on weather conditions and the needs of the plant world. The water is in constant circling, and this movement was called the hydrological cycle. Due to the movement of water in the soil and variable content, there are two major problems. One of those problems is excess water in the soil, so due to such water-air regime, unfavorable living conditions for plants occur. Another problem was the lack of water in the soil for normal growth and development of plants that was negatively reflected on yield. The fact is that producers were increasingly faced with prolonged droughts during the growing season. The only measures to combat the consequences of such troubles are the introduction of programs of the irrigation through reclamation measures as a necessary item for the future of agricultural production and reduction of far-reaching consequences if not prepare for the changes that have taken place. The biggest challenge of today's agriculture is how to ensure sufficient water needs for growing crop. This entails to identify critical plant growth phase in order to meet their water needs. Defining the period, form, role, and amount of available moisture for plants could be useful for obtaining the optimal yields.

**74**

containing polar groups (OH−

**2. Chemical and physical water properties**

The two hydrogen atoms bonded by covalent brigs to an oxygen atom makes water molecule [10]. A water molecule is a polar molecule meaning that it is electro negatively charged (around oxygen atoms) at one end and electro positively charged (about two hydrogen atoms) at the other end [11]. When water molecules are interconnected, the positively charged end of one molecule (hydrogen atom) connected by a hydrogen bond to the negatively charged end (oxygen atom) to another water molecule [11]. The phenomenon of attracting water molecules is called cohesion [10]. Due to its properties (polarity and the formation of hydrogen bonds), water participates in many interactions and plays a major role in the plant organism (because it makes up between 80 and 95% of the mass of plant tissue) [10]. Polarity makes water the most widespread and most important solvent in nature. The polarity property allows the dissolution of ionic substances and organic molecules

, and COO−

between water molecules and ions/polar substances reduce electrostatic interactions

) [10]. Hydrogen bonds formed

, NH4 + between charge-carrying substances and thus allow them to dissolve. The polar parts of the water molecule can form an aqueous mantle (hydration mantle) around the charged particles of the macromolecules, thereby reducing the interactions and binding of the macromolecules, thereby increasing their solubility in water. Due to the large number of hydrogen bonds that connect water molecules, it can absorb heat without large changes in temperature, making it an ideal medium for thermoregulation. As the temperature rises, water molecules movement accelerates. Compared to others liquids, to increase the water, temperature required a relatively large amount of energy (to break hydrogen bonds). From this fact arises one of the basic functions of water in the plant and that is the regulation of plant temperature (thermoregulation) [10]. Since cells contain large amounts of water, they can receive or lose heat with minimal temperature changes. This property can serve to protect organisms from sudden changes in temperature, because organisms that contain larger amounts of water in their tissues were better protected from temperature changes caused by oscillations in heat. Water exists in three different states: ice, liquid, and as steam or water vapor [12]. Water conversion into water vapor requires break down of hydrogen bonds. Therefore, a large amount of energy is used to evaporate the water, which allows the plants to cool efficiently [12]. On the contrary, low temperatures make water molecules approaching. They are closest at 4° C, although they are still moving. At temperatures below 4° C, the molecules just vibrate and the hydrogen bridges become open and rigid [10]. Water in solid state (ice) has a lower density than in liquid, so it floats on the water surface. This property allows many organisms to survive under the frozen water sheet [10]. Water molecules also have a pronounced surface tension. In order to increase the contact area between water and air, it is necessary to break down hydrogen bridges between water molecules [12]. This process requires energy investment, and this energy represents the surface tension. Surface tension has a major role in the transport (movement) of water in the soil-plant system. In addition to surface tension, cohesion and adhesion forces were important in water transport. The attraction between two water molecules is a force called cohesion, while adhesion causes water molecules to adhere to another solid (e.g., a cell wall) [10]. Cohesion, adhesion, and tension allow the appearance of capillarity, that is, the rise of water column through a narrow pipe—capillary, where the water level in the capillary is higher compared to the water level in the source that supplies the capillary [11]. Capillary occurs in various media (soil, root/stem tissue) due to: (1) the attraction of water molecules to the cell wall (adhesion), (2) mutual attraction of water molecules (cohesion), and (3) surface tension of water [13].

The plant tissue consists mostly of water and to a lesser extent of inorganic substances that plants receive from the soil, organic substances formed by photosynthesis and the products of their conversion. Water makes up 80–95% of the mass of metabolically active plant tissue. Majority of the contained water in plant tissue serves for transpiration and less than 1% was used for metabolic activity [14, 15]. High water content is an essential feature of all metabolically active cells. Relative water content reduction up to 70–80% in most plant cells results in the inhibition of central metabolic functions, such as respiratory processes and photosynthesis. In the process of photosynthesis, water is the carrier of electrons and protons. The role of water in plant tissue is multiple. In addition to being the best and most common solvent, water is also a medium for the movement of molecules inside and between cells. It greatly affects the molecular structure and properties of proteins; nucleic acids and other macromolecules indirectly affect the property of cells plasma membranes. Water is the basic constituent of protoplasm.

Water is essential for most of biochemical reactions in plant cells. Water is directly involved in number of chemical reactions, for example, hidrolysis and dehydratation reaction (e.g., ADP phosphorylation is actually dehydration of the ADP molecule, is a donor of hydrogen in photosynthesis). In addition, as water has a high heat capacity, its presence in the plant ensures that temperature changes occur slowly. The polarity and ability to form hydrogen bonds allows water to participate in a number of interactions. Water molecules were arranged around ions or charged groups of macromolecules and cover their charge. This reduces the interactions between the charged substances and increases their solubility. Therefore, water is the best solvent for ionic substances. Water is in liquid phase and medium in which all enzymatic reactions take place. Various substances can enter into a chemical reaction with each other only if they dissolve in water. The uptake of solutes is possible only from an aqueous solution. As the water content in the plant organism decreases, so does the vital activity. Water regulates turgor pressure and upright visual appearance and cell size. A large number of metabolic functions of water were realized by the processes of uptake and release (transpiration).
