The document discusses the mechanisms and factors influencing water absorption in plants, emphasizing the role of root systems and moisture extraction patterns. It distinguishes between active and passive absorption processes, detailing how factors like soil type, water concentration, and temperature affect water uptake. Additionally, it highlights the importance of rooting characteristics in determining moisture availability and discusses the overall significance of water movement within the soil-plant-atmospheric system.

1. Water absorption, factors affecting water absorption,
rooting characteristics, Moisture extraction patterns
and SPAC

2. • Introduction
• Plant absorbs moisture from soil through their root system.
• The method and quantity of water absorption varies with crops and their rooting pattern.
• The moisture extraction pattern revels about how the moisture is extracted and how much quantity is
extracted at different depth level in the root zone.
• The moisture extraction pattern shows the relative amount of moisture extracted from different
depths within the crop root zone

3. • Mechanism of water absorption
• In plants, water is absorbed through roots and root hairs which are in contact with soil water.
• The wall of the root hairs are permeable and consists of pectic and cellulose substances which are strongly hydrophilic
(water loving ) in nature.
• There are two types of absorption.
• a) Active absorption b) Passive absorption
• a) Active Absorption
• Active transport depending on expenditure of metabolic energy mass flow move same diretion in mass.
• Here the process of osmosis plays an important role.
• The soil plant water movement can be effected due to forces of imbibition, diffusion and osmosis

4. • Imbibition
• The first process in the absorption of water by the plant is the imbibition of water by the cell walls of root
hairs.
• Diffusion
• Movement of diffusing particles from higher concentration to lower concentration is called diffusion.
• It is an essential step in exchange of gases in respiration and photosynthesis and stomatal transpiration.
• Osmosis
• The movement of water molecules from a solution with a high concentration of water molecules to a
solution with a lower concentration of water molecules, through a cell's partially permeable membrane.
• Significance of Osmosis
• Large quantities of water are absorbed by roots from soil by osmosis.
• Cell to cell movement of water and other substances takes place through this process.
• Opening and closing of stomata depends upon the turgor pressure of guard cells.
• Due to osmosis the turgidity is maintained and give a shape to the plants.

5. • b) Passive absorption of water
• It is mainly due to transpiration and the root cells do not play active role.
• Passive absorption takes place when rate of transpiration is very high.
• Rapid evaporation from the leaves during transpiration creates a tension in water in the xylem of the leaves.
• These tension is transmitted to the water in xylem of roots through the xylem of stem.
• Due to this, water rises upward to reach the transpiring surface.
• As a result, soil water enters into the cortical cells through the root hairs to reach xylem of the roots to maintain the
supply of water.
• The force for this entry of water is created in leaves due to rapid transpiration and hence the root cells remain passive
during this process.
• It is otherwise known as transpiration pull.

6. • Difference between Active absorption and Passive absorption
Sr.
No.
Active absorption Passive absorption
1 Active absorption refers to the absorption of
water by roots with the help of adenosine tri-
phosphate, generated by the root respiration: as
the root cells actively take part in the process.
The sort of absorption that occurs through the
transpiration pull is known as passive
absorption.
2 Rate of absorption depends on diffusion
pressure deficit (DPD).
Tension (force) is created by the transpiration
pull, which aids in the upward passage of
water into the xylem sap.
3 Energy is required Energy isn't required.
4 The rate of absorption is slow. The faster the rate of transpiration, the greater
the water absorption.
5 Absorbed through the symplast pathway and
transmembrane pathway.
Water passes through the apoplast pathway,
symplast pathway and transmembrane
pathway.
6 Absorption due to the activity of root hair cells. Absorption due to the activity of the leaves

7. • Factors affecting absorption of water
• Available soil water
• Capillary water is available to plants. Hygroscopic water and gravitational water are not available to plants. The
capillary water is absorbed by the plants which inturn reduces the soil water potential. Hence the water from
higher potential area tends to move to lower potential area and root will absorb this water. This is the chain of
process involved in water uptake.
• Concentration of soil solutions.
• High concentration affects the process of osmosis.
• Soil air
• Sufficient amount of O2 should be there and excess amount of CO2 affects the availability of water by root
suffocation.
• Soil Temperature
• Upto 30oC favours absorption. Very low and very high temperature affects absorption.
• Soil texture
• Clay - neither good nor bad
• Sand – Not good for absorption
• Loamy - good for absorption

8. • Moisture extraction pattern
• The moisture extraction pattern revels about how the moisture is extracted and how much quantity is extracted at
different depth level in the root zone.
• The moisture extraction pattern shows the relative amount of moisture extracted from different depths within the
crop root zone.
• It is seen that about 40% of total moisture is extracted from first quarter of the root zone, 30% from second quarter,
20 % from third quarter and 10 % from last quarter.
• This indicates that in most of the crops the effective root zone will be available in the 1st quarter.

9. • Rooting characteristics
• The root system is extremely variable in different crop plants. The variability exists in rooting depth, root length
and horizontal distribution of roots. These are further influenced by environmental factors and the genetic
constitution. The roots of cereals apparently occupy more surface area of the soil than other crops. For example, it
has been proved that cereals’ roots extend to 200-400 cm of soil surface area as against 15-200 cm/m2 for most
graminaceous plants.
• The amount of soil moisture that is available to the plant is determined by the moisture characteristics of the soil
depth and the density of the roots. The moisture characteristics of soil like FC and PWP cannot be altered so easily
and greater possibilities lie in changing the rooting characteristics of plants system to go deeper and denser and
more proliferation to tap water from deeper layer of soil as well as from the larger surface area. Plants vary
genetically in their rooting characteristics. (Figures) vegetable crops like onion, potato, carrot etc., have very
sparse rooting system and unable to use all the soil water in the root.
• Rice, grasses, Sorghum, maize, sugarcane have very fibrous dense root system which can extract much water from
soil. Millets, groundnut, grams are moderately deep rooted.
• Maize, sorghum, Lucerne, cotton and other perennial plants have deep root system and can utilize effectively the
moisture stored in root zone as well as in the unexploited deeper zones. Crops which have dense and deep root
system like cotton, sorghum, red gram tolerate high reduction of soil water content. Shallow rooted crops like rice,
potato, tomato tolerate low level of soil water reduction. Moderately deep rooted crops like millets, ground nut,
grams tolerate medium level of soil water reduction.

10. • The root growth of the crop plants is affected by
• Genetic nature
• High water table
• Shallow nature of soil and permeability of soil layer.
• Soil Fertility
• Salt status of soil
• Effective root zone depth
• It is the depth in which active root proliferation occurs and where maximum water absorption is taking place. It is
not necessary that entire root depth should be effective.
Shallow
( 60 cm)
Medium to deep
(90 cm )
Deep
(120 cm)
Very deep
(180 cm)
Rice
Potato
Cauliflower
Cabbage
Lettuce
Onion
Wheat
Ground nut
Carrots
Soybean
Pea
Bean
Maize
Cotton
Sorghum
Pear millet
Sugar beet
Chillies
Sugarcane
Citrus
Coffee
Sunflower

12. • Water movement in soil-plant –atmospheric system
• The total quantity of water required for the essential physiological functions of the plant is usually less than 5 per
cent of all the water absorbed. Most of the water entering the plant is lost in transpiration. But failure to replace
the water loss by transpiration results in the loss of turgidity, cessation of growth and death of plants due to
dehydration.
• The following are the main areas of water movement in plant system:
• Water adsorption
• Water absorption
• Water conduction and translocation
• Water loss on transpiration
• The path of water movement may be divided into four sequential processes as follows:
• The supply of liquid to root surface – Adsorption
• The entry of water into the root-Absorption
• The passage of water in the conducting tissues – (Xylem) Translocation or conduction.
• Movement of water through and out of leaves – Transpiration or loss of water.
• The rate of water movement is directly proportional to potential gradient i.e. higher potential to lower potential and
inversely proportional to the resistance to flow.

13. Soil – Plant – Atmospheric- Continuam