Plant Nutrition: Types, Macro and Micro Nutrients, Deficiency Symptoms, Hydroponics

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Plant Nutrition: The basic needs of all living organisms are essentially the same. They require macromolecules, such as carbohydrates, proteins and fats, and water and minerals for their growth and development.

All living organisms require food. Plants can synthesise food for themselves but animals including humans cannot. They get it from plants or animals that eat plants. Thus, humans and animals are directly or indirectly dependent on plants

Hydroponics-

• In 1860, Julian von Sachs (German Botanist) demonstrated that plants could be grown to maturity in defined nutrient solution in the absence of solution. This is hydroponics.
• This involves aerated mineral solution (Culture of plants in Soil free).
• Require purified water and mineral nutrient salts.
• Commercial production of vegetables (tomato, seedless cucumber, lettuce)

Plant Nutrition- Essential Mineral Elements-

• Some plant species accumulate selenium and some gold, while some grow near nuclear test sites takes radioactive strontium.
Criteria for essentiality –
• Element must be necessary for average growth and reproduction. In absence, don’t complete life cycle.
• Requirement must be specific, mustn’t be replaceable.
The deficiency of one can’t be met by another.
• Should be directly involved in metabolism.
• Divided in two, based on quantitative requirement-

(a). Macronutrient – Present in large amounts (over 10 mmole/kg of dry matter). E.g., C, H, O, N, P, S, K, Ca, Mg. C, H, O (from Co2, H2o)
(b). Micronutrient – Tiny amount (also trace element). (Less than 10 mmole/kg of dry matter). E.g., Fe, Mn, Cu, Mo, Zn, B, Cl, Ni, Na, Si, Co, selenium is required by higher plants.

Divided in 4, based on functions-
I. As a component of biomolecule – Structural element of cells (E.g., C, H, O, N)
II. Component of energy-related chemical compound – Mg in chlorophyll & P in ATP.
III. Activate or inhibit enzymes – Mg2+ – activator of ribulose bisphosphate. Carboxylase oxygenase and phosphoenolpyruvate carboxylase (photosynthetic C fixation); Zn2+- activator of alcohol dehydrogenase & no of Nitrogenase during Nitrogen metabolism.
IV. Alter osmotic potential of cell – K (Opening – closing of stomata)

Mechanism of Hydroponic in Plant Production –

• Plants are grown in a tube placed on a slight incline. A pump circulates nutrient solution from the reservoir to the high end of the tube. The solution flows down tube and returns to the reservoir due to gravity. Inset shows plants whose roots are continuously bathed in an aerated nutrient solution.

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Role of Macro and Micro Nutrients –

• Nitrogen – Greatest amount, absorbed mainly as NO3-, sometimes as NO2- or NH4-, Required by all especially meristematic & metabolically active cell, a major constituent of proteins, nucleic acid, Vitamins, Hormones.
• Phosphorus – From Soil in the form of phosphate ions (H2PO4 or HPO42-), a constituent of the cell membrane, proteins, nucleic acids, nucleotides, phosphorylation reactions.
• Potassium – Absorbed as K+, mainly by meristematic tissue, bud, leaves, root tips, helps maintain anion cation balance, protein synthesis, opening and closing of stomata, activation of enzymes, turgidity of the cell.
• Calcium – From Soil in the form of Ca2+, synthesis of the cell wall during cell division (Ca pectate in middle lamella), formation of spindle fibre, accumulates in older leaves, normal functioning of the cell membrane.
• Magnesium – Inform of divalent Mg2+, activates respiration enzymes, photosynthesis, Synthesis of DNA & RNA, a constituent of the ring structure of chlorophyll, ribosome structure.
• Sulphur – Inform of sulphate (SO42- ), present in 2 amino acids- cysteine & methionine, a constituent of coenzyme, vitamin (thiamine, biotin) ferredoxin.
• Iron – Inform of ferric ions (Fe3+), large amount, transfer of e like ferredoxin & cytochrome, reversibly oxidized from Fe2+ to Fe3+ during electron transfer, activates catalyze EnzymeEnzyme, formation of chlorophyll.
• Manganese – In the form of Mn2+, activates EnzymeEnzyme involved in photosynthesis, respiration, nitrogen metabolism, best function- water splitting to liberate O2 during photosynthesis.
• Zinc – In the form of Zn 2+, activates carboxylases, synthesis of auxins.
• Copper – Absorbed as Cu2+, Overall metabolism, associated with EnzymeEnzyme involved in redox, reversibly oxidized from Cu+ to Cu2+.
• Boron – Absorbed as BO3- or B4O72-, uptake and utilization of Ca2+, membrane functioning, pollen germination, cell elongation, cell differentiation, Carbohydrate translocation.
• Molybdenum – In the form of MoO2+, a component of Enzymes like Nitrogenase & nitrate reductase (Nitrogen metabolism).
• Chlorine – Inform of Cl-, determine the solute concentration, anion – cation balance, water-splitting reaction in Photosynthesis, O2 evolution.

Deficiency Symptoms of essential elements –

• Critical concentration – Concentration of essential elements below which plant growth is retarded.
• Element is different when present below critical concentration.
• This shows morphological changes which indicate deficiency called deficiency symptoms.
• If deprivation continues, it may lead to death.
• Elements that are actively mobilized in plants and exported to young developing tissues.
• Example – Deficiency symptoms of N, K, Mg are visible first in senescent leaves. The biomolecule containing these elements is broken in older leaves, making elements available for mobilizing to young leaves.
• Deficiency symptoms first appear in young tissue when elements are relatively immobile and not transported.
• Example – S and Ca (structural component) are not quickly released.

Deficiency Symptoms –

• Chlorosis -Loss of chlorophyll leading to yellow leaves by N, K, Mg, S, Fe, Mn, Zn, Mo, deficiency.
• Necrosis or death – due to deficiency of Ca, Mg, Cu, K
• Imbibition – Lack or low level of N, K, S, Mo
• Delay flowering – Deficiency of N, S, Mo

Toxicity of Micronutrient –

• Moderate decrease in micronutrient case deficiency symptom & toxicity.
• Mineral ion Concentration in tissue that reduces the dry weight of tissues by 10 % is toxic. Its symptoms are different to identify.
• Excess of one may inhibit the growth of the other.
• Example – a symptom of non-toxicity is the appearance of a brown spot surrounded by chlorotic veins. It competes with Fe & Mg for uptake and binding with EnzymeEnzyme. It inhibits Ca translocation in the shoot apex.
• So, excess Mn cause deficiency of Fe, Mg & Ca.

Mechanism of absorption of Elements –

• Carried out in the isolated cell, tissue or organ.
• In the first phase, the initial rapid uptake of ions into the free or outer cell- apoplast is passive. It occurs through ion-channel transmembrane protein (function as selective pore).
• In the second phase, ions are taken in slowly into inner space- simplest. Entry or exit required expenditure of energy, so active.
• Movement of ions is flux. Inward movement – Influx, outward movement – efflux.

Translocation of solutes –

Though xylem along with ascending stream of water pulled through plants by transpiration pull.

Soil as a reservoir of essential elements –

• Weathering & breakdown of rocks enrich Soil with dissolved ions & inorganic salts. So, called mineral nutrition.
• It not only supplies minerals but harbours N fixing bacteria, holds water, supplies air to the root, acts as a matrix that stabilizes the plant.
• As deficiencies of some elements affect crop yield, so need fertilizers.

Plant Nutrition Citation

Plant nutrition: Rooting for more phosphorus

Mineral nutrition of plants: a short history of plant physiology

The critical role of potassium in plant stress response

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