Plant-Water Relations

Introduction

The hydration of the plant cells are related to the plant-water relations. It includes collecting water from the soil, transporting it within the plant and leaving evaporation. Generally, the term “water potential” is used for expressing the water status of the plant. Some questions arise about plants regarding water such as, What’s the role of water in plants?  Can plants synthesize food through photosynthesis only within the presence of water in their system. Today, in this article, we will talk about Plant-Water Relations and other related topics in detail. Without any further ado, let’s get started! 

Role of Water in Plant

Water is significant for the life and survival of all plants. Water plays a significant role in the transportation of essential nutrients from the soil to the root and food from leaf to other parts of the plant. Almost all physiological activities of plants require water. Water acts as an excellent solvent and helps in the uptake and distribution of minerals, nutrients and other solutes for growth. The protoplasm of the cells is nothing but water in which thousands of different molecules are dissolved and several more particles are suspended. Most of the herbaceous plants have 10 to 15 percent of their fresh weight, as dry matter and rest water. A watermelon contains more than 92 percent water. The distribution of water within the plant varies from organ to organ.

Land plants absorb a huge quantity of water daily from the soil. Only a fraction of the absorbed water is utilized in various metabolic activities by the plants, while most of it is lost to the atmosphere through transpiration. A mature corn plant absorbs almost three liters of water a day, while a mustard plant loses as much water as its own weight in about 5 hours because of this high demand. Water is often a limiting factor for plant growth and productivity in both agriculture and natural environments.

Result of a Plant When Watered with Different Liquid Other than Water

Every time you tend to grow plants using several methods that include other liquids than water, the molecules formed look different as compared to the water molecules, the process of photosynthesis does not take place. As a result, plant growth is affected. Plants need three main elements so as to grow: water, sunlight and CO2. 

Effect of Plants in Flow of Water

Plants are referred to as the phenomenal hydraulic engineers. By using the necessary physics laws along with the simple mechanical energy manipulation, plants have the power to move water to a height of a 116-meter-tall tree. Plants even use hydraulics for getting enough force for separating buckles and rocks sidewalks. 

Removal of Liquid Water Rather than Vapor

As per Sterling, the method of turning water into the vapors cools down the plant. As water can be transpired, the roots are drawing extra essential nutrients from the soil. This water availability in the soil provides immense support to the plant .

Water potential

The difference in the free energy or chemical potential of water in a system and that of pure water at the same temperature and pressure is called water potential. Water molecules possess kinetic energy and in liquid and gaseous form they are in consonant motion, which is both rapid and constant. The greater the concentration of water in a system, the greater its ‘kinetics energy’ or its ‘water potential’.  Hence, it is obvious that pure water will have the greatest water potential. If two systems containing water are in contact such as soil and air, or cell and solution, random movement of water molecules will result. In movement of water molecules from the system with higher energy to the one with lower energy, there is a movement of water from the system containing water at higher water potential to one having low water potential. This process of movement from down a gradient of free is called diffusion. Water potential is denoted by the Greek symbol Psi (ψ), and is expressed in pressure units such as Pascal’s (Pa). 1 megaPascal (mPa) = 10 bars. By convention, the value is considered to be the highest.

A positive hydrostatic pressure in a plant cell is also called turgor pressure. Loss of water produces a negative hydrostatic pressure or tension. It develops in xylem due to loss of water in transpiration. This is very important in transport of sap over long distances in plants.

Water potential is affected by both solute potential (ψs) and pressure potential( ψp). The relationship between them is as follows.

                 ψ = ψs + ψp

Key Points

• Once plants are turgid, they perform the best. As a result, the water within their cells starts to incorporate a positive hydrostatic pressure
• Leaves tend to transpire multiple times in their own water volume with each passing, however, the overall loss is mostly small because of the water inflow caught up the plant from the soil which is termed as ‘transpiration stream’
• The plant’s water status is expressed by ‘water potential’. Whereas the water’s chemical potential is divided by the amount of 1 mole of water to relinquish units of pressure
• The water flow through the soil and plant is mostly because of the gradients present in the hydrostatic pressure creating the differences in water potential in the semipermeable membranes
• Resistance to those flows, and also the factors that are influencing them varies markedly as the transpiration stream starts to move from the soil, longitudinally inside the xylem, across the roots and finally, through tissues of leaves till the evaporating surfaces inside the leaf

Conclusion 

Water acts as an excellent solvent and helps in the uptake and distribution of minerals, nutrients and other solutes for growth. The protoplasm of the cells is nothing but water in which thousands of different molecules are dissolved and several more particles are suspended. Most of the herbaceous plants have 10 to 15 percent of their fresh weight, as dry matter and rest water. A watermelon contains more than 92 percent water. The distribution of water within the plant varies from organ to organ.