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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