Ion uptake and Transport Mechanism

Ion uptake mechanism

Mechanism:  Ion uptake mechanism is a two way processes
Step­ 1: The first step of the ion uptake by the growing plants is the Adsorption of ions by the Ca­pectate layer of the cell wall of roots and then cytoplasm. 
Step2:  The  second  phase  of  ion  uptake  mechanism  is  the  transfer  of  adsorbed  ions  through  cytoplasm  and  into  the  cell  sap.  This process occur, where metabolic energy is required. The metabolic energy is produced from respiration and the ion transformation occur against osmosis.
1. Plants uptake nutrients cation (+) in exchange of H+ excreted by plant roots.
2.  Plants uptake nutrients anion in exchange of HCO3­ excreted by plant roots. 

Ion Transport Mechanism 

The dissolved nutrients in the soil solution have to come in contact with plants roots for absorbing by plant. Following 3 mechanism / ways by which nutrients come in contact with plant roots are-
1.  Mass flow. 
2.  Diffusion.
3.  Root interception. 

1. Mass flow

Mass flow is occurred when soil water contains nutrients ion. Mass flow is the process in which the ions of plant nutrients elements in soil move to the plants with water flow. Water flow is produced by transpiration in plants and nutrient ion and dissolved food materials are moved through water. It can be expressed by following formula
Q= V X C 
Here, Q = mass flow rate. 
V = water flow rate. 
C = Ionic concentration in soil solution. 
Ca, Mg, S, N and most of micro nutrients move to the plants by mass flow. 

2. Diffusion

By the action of thermal flow, diffusion occurs when ion moves from an area of higher concentration to the area of lower concentration. It happens without movement of soil water. Mass flow and diffusion occur simultaneously. 
Specially, K and P move to plant roots by diffusion. Factors influencing in mass flow and diffusion flow are given below-
Soil texture – If it is sandy soil, mass flow and diffusion occur limit but in clay soil is more.
Soil moisture – If it is high moisture, the mass flow and diffusion should be low.
Soil temperature – In Low temperature movement is low, In Warm temperature movement is high. 

3. Root interception

While the root system of plants spread out in soil, the structure of soil destroyed. As a result, soil solution and adsorbed ions of its surface come in contact to the root surface. Finally, ions are absorbed in roots by contact exchange theory.

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