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Calcium: an essential plant nutrient
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Calcium: an essential plant nutrient
Essential nutrients - mineral nutrients that are crucial for plant growth
1.C, H, O – absorbed as gases. Carbon and Oxygen from atmospheric fixation in the photosynthetic reaction and respiration. Hydrogen and Oxygen too, from water hydrolysis.
2. N,P,K,Ca, Mg, S – Macro elements. Absorbed from soil solution. Needed in high ratio, their concentration in tissue is measured by percentages.
N,P,K – Major macro elements.
Ca, Mg, S – Secondary macro elements.
Plant's nutrients
Roots absorb plant-available nutrients from the soil as positively or negatively charged ions
A divalent cation belonging to the group of alkali metals (similar to magnesium)
Found in high concentrations in all soils types except very acidic soils
Example of main ions in nutrients solution – Mexico
Typical Ca, Mg and S requirements
In acidic soils, calcium availability is disturbed
Balanced nutrition
All nutrients must be supplied at appropriate rates, to prevent imbalances that may limit plant growth
Plant’s calcium needs
Calcium strengthens the cell walls of plants.
Calcium should be available continuously in soluble form to ensure adequate absorption.
Calcium and nitrogen are about half of all nutrients absorbed by the plant.
Concentration in the plant 0.1% - 5 %.
Highest concentrations is found in mature leaves.
Lowest concentrations is found in young leaves , fruits & flowers .
Most Ca is found in the Apoplast – cell walls, xylem, middle lamella.
Apoplastic transport, occurs through the apoplast (the region of continuous cell walls among cells).
Transport through vascular channels
Xylem (apoplastic movement):
Regulated by the xylem flow.
The driving force for this flow is water potential differences between soil, leaf and atmosphere.
Movement from low to high water potential.
The xylem flow is controlled by transpiration during the day, and by root pressure at night.
Calcium moves in the plant’s transpiration stream and is deposited mainly in the older leaves.
Deficiencies are found in the youngest leaves and growing points, which have low rates of transpiration.
Emerging leaves appear scorched and distorted and may cup downwards because the leaf margins have failed to expand. Fully mature and older leaves are generally unaffected.
With a severe deficiency, flowers can abort, and the growing point may die.
Fruits from calcium-deficient plants are smaller and tasteless, and may fail to develop normally at the blossom end rot.
The roles of calcium
Activates enzymes, is a structural component of cell walls.
Influences water movement in cells and is necessary for cell growth and division.
Some plants must have calcium to take up nitrogen and other minerals. Calcium is easily leached.
Calcium, once deposited in plant tissue, is immobile (nontranslocated) so there must be a constant supply for growth.
Deficiency causes stunting of new growth in stems, flowers and roots. Symptoms range from distorted new growth to black spots on leaves and fruit. Yellow leaf margins may also appear.
Calcium takes a key role in the structure and functioning of cell membranes and the strength of cell walls. Calcium also reduces plant susceptibility to diseases.
Most calcium-related disorders of crops are caused by unfavorable growing conditions and not by inadequate supply of calcium to the roots.
Rapidly growing crops in hot windy conditions are most at risk. Deficiencies can also develop when cucumbers grow quickly under continuously humid conditions, as in a greenhouse.
Other contributing factors are waterlogging, soil salinity, high potassium or ammonium supply, and root diseases.
Structural control -> High demand during the growth period.
Stability
Structural factor: a component of middle lamella
Stabilizing factor: Strengthening, stabilizing and regulating macromolecules in the cell wall
Maintaining cell membranes
Stabilizing factor
Maintaining the selective properties of cell membranes
Activity in the cytoplasm
Calcium is the 2nd messenger in the cell
The calcium moves only in the xylem
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