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Mineral Nutrition: 1. Introduction to Mineral Nutrition: - Mineral nutrients are elements absorbed by plants primarily as inorganic ions from the soil. - Plants act as "miners" of Earth's crust, absorbing and translocating mineral elements to various parts for numerous bio...

Mineral Nutrition: 1. Introduction to Mineral Nutrition: - Mineral nutrients are elements absorbed by plants primarily as inorganic ions from the soil. - Plants act as "miners" of Earth's crust, absorbing and translocating mineral elements to various parts for numerous biological functions. - Water absorption and mineral nutrient uptake are closely related processes in plants. - Other organisms like mycorrhizal fungi and nitrogen-fixing bacteria often assist roots in nutrient acquisition. 2. Essential Mineral Elements: - Criteria for an element to be considered essential (Arnon and Stout, 1939): a) The plant must be unable to complete its life cycle without the element. b) The element's function cannot be replaced by another mineral element. c) The element must be directly involved in plant metabolism (e.g., as a component of an enzyme or required for a distinct metabolic step). - Beneficial elements: Mineral elements that can compensate for the toxic effects of other elements or replace nutrients in less specific functions like maintaining osmotic pressure. 3. Classification of Essential Elements: - Macronutrients: Required in larger quantities (e.g., nitrogen, phosphorus, potassium) - Micronutrients: Required in smaller quantities (e.g., iron, manganese, zinc) 4. Nutritional Study Techniques: - Historical context: Researchers like Nicolas-Théodore de Saussure, Julius von Sachs, Jean-Baptiste-Joseph- Dieudonné Boussingault, and Wilhelm Knop conducted early experiments on plant growth without soil. - Hydroponics: - Definition: Growing plants with roots immersed in a nutrient solution without soil. - Also called solution culture (Gericke 1937). - Requires large volumes of solution or frequent adjustments to maintain nutrient concentrations and pH. - Vigorous air bubbling provides oxygen to roots. - Used in commercial greenhouse crop production. - Forms of Commercial Hydroponic Culture: 1. Plants grown in supporting materials (sand, gravel, vermiculite, expanded clay) with nutrient solutions flushed through. 2. Nutrient film technique: Roots lie on the surface of a trough with a thin film of nutrient solution flowing over them. - Aeroponics: - Plants grown with roots suspended in air and sprayed continuously with nutrient solution. - Hoagland solution: - Named after Dennis R. Hoagland, a prominent researcher in mineral nutrition. - Contains all known mineral elements needed for rapid plant growth. - Concentrations set at the highest possible levels without causing toxicity or salinity stress. 5. Mineral Deficiencies: - Inadequate supply of an essential element results in characteristic deficiency symptoms. - Symptoms are expressions of metabolic disorders due to insufficient supply of an essential element. - Five main categories of deficiency symptoms: 1. Stunted growth 2. Chlorosis (general yellowing) 3. Interveinal chlorosis 4. Purplish-red coloring 5. Necrosis - Specific symptoms:  - Stunting: Common for many deficient nutrients due to their roles in various plant functions. - Chlorosis: Affects photosynthesis and chlorophyll production. - Interveinal chlorosis: Occurs with deficiencies in B, Fe, Mg, Mn, Ni, and Zn. - Purplish-red discoloration: Due to anthocyanin accumulation, can be difficult to diagnose as it's also caused by other stressors. - Necrosis: Later stages of deficiency, causing browning and death of affected plant parts. - Mobility of elements within plants affects symptom location: - Mobile elements (e.g., N, P, K): Deficiency symptoms appear first in older leaves. - Immobile elements (e.g., B, Fe, Ca): Deficiency symptoms appear first in younger leaves. 6. Symbiotic Relationships: - Mycorrhizal fungi and nitrogen-fixing bacteria assist in nutrient acquisition. Mineral nutrient deficiencies in plants: 1. Mobile Nutrients: a) Nitrogen (N): - Function: Production of proteins, nucleic acids, and chlorophyll. - Deficiency symptoms: - General chlorosis of lower leaves - Stunted and slow growth - Necrosis of older leaves in severe cases - Early maturation, reduced crop quality and yield - In cereals: Yellow 'V' shaped discoloration from leaf tip - In potatoes: Leaf curling and small tubers b) Phosphorus (P): - Function: Development of ATP, sugars, and nucleic acids. - Deficiency symptoms: - Dark green leaves and stems - Stunted appearance - Purplish discoloration in older leaves - Delayed maturity - Inhibited leaf expansion and surface area - In small grains: Predisposition to root rot diseases - In alfalfa: Upward tilting of leaflets - In potatoes: Leaves curling upward, brown internal specks in tubers - In corn: Purple leaves in young plants c) Potassium (K): - Function: Enzyme activation, photosynthesis, protein formation, sugar transport. - Deficiency symptoms: - Reduced growth rate (initially) - Chlorosis and necrosis in later stages - Mottled or chlorotic areas with leaf burn at margins of older leaves - Reduced straw/stalk strength in grains and corn - Reduced disease resistance and winter-hardiness - In small grains: Excessive tillers, shriveled grain low in protein - In alfalfa: White spots on leaf edges - In root crops: Small tubers d) Chloride (Cl): - Function: Leaf turgor and photosynthesis. - Deficiency symptoms: - Chlorotic and necrotic spotting along leaves - Wilting of leaf margins - Highly branched root systems (mainly in cereal crops) e) Magnesium (Mg): - Function: Central molecule in chlorophyll, co-factor for ATP production. - Deficiency symptoms: - Interveinal chlorosis - Yellow or reddish-purple leaf margins with green midrib - In wheat: Distinct mottling as yellowish-green patches - In alfalfa: Leaf curling and reddish undersides - In sugar beets and potatoes: Stiff and brittle leaves, twisted veins f) Molybdenum (Mo): - Function: Enzyme activity and nitrogen fixation in legumes.  - Deficiency symptoms: - Resembles nitrogen deficiency (stunted growth and chlorosis in legumes) - Pale leaves that may be scorched, cupped, or rolled - Thick or brittle leaves that eventually wither 2. Immobile Nutrients: a) Sulfur (S): - Function: Constituent of amino acids and proteins. - Deficiency symptoms: - Light green to yellow younger leaves - Pale green entire plant in later growth - Spindly and small plants with thin stems b) Boron (B): - Function: Cell wall formation and reproductive tissue. - Deficiency symptoms: - Chlorotic young leaves - Death of the main growing point - Dark brown, irregular lesions progressing to leaf necrosis - Brittle and distorted leaves and stems - Thickened and curled leaf tips - Poor flower formation and seed viability - In alfalfa and canola: Rosetting, yellowing of upper leaves, poor flowering - In sugar beets: Stunted growth, curled and discolored young leaves, crown and root rot c) Iron (Fe): - Function: Respiratory and photosynthetic reactions. - Deficiency symptoms: - Interveinal chlorosis in young leaves - Sharp distinction between veins and chlorotic areas - Whitish-yellow entire leaf in advanced stages - Slow plant growth d) Zinc (Zn): - Function: Growth hormone production, internode elongation. - Deficiency symptoms: - Interveinal chlorosis in middle leaves - Striping effect and possible mottling - Gray-white leaves that fall prematurely or die in severe cases - Severe stunting - Poor flowering and seed set - In alfalfa: Smaller leaf size - In small grains: Gray or bronze banding, reduced tiller production e) Calcium (Ca): - Function: Component of cell walls, regulates cell wall construction. - Deficiency symptoms: - Distorted young leaves with abnormally dark green color - Dry or brittle leaf tips that eventually wither and die - Weak stems - Poor germination f) Copper (Cu): - Function: Chlorophyll production, respiration, protein synthesis. - Deficiency symptoms: - Chlorosis in younger leaves - Stunted growth - Delayed maturity - Lodging - Melanosis (brown discoloration) - Poor grain production and fill - Increased susceptibility to diseases g) Manganese (Mn): - Function: Important for chloroplast function. - Deficiency symptoms: - Interveinal chlorosis in young leaves (diffuse effect) - Grey speck in oats - Marsh spot in peas - White streak in wheat - Interveinal brown spot in barley h) Nickel (Ni): - Function: Proper seed germination, and nitrogen metabolism in legumes. - Deficiency symptoms: - Chlorosis and interveinal chlorosis in young leaves - Necrosis of plant tissue - Poor seed germination - Decreased crop yield 1. Nutrient Toxicities: a) General Causes: - Over-application of fertilizers or manure - Use of irrigation water high in micronutrients or salts - Abnormally high soil micronutrient concentrations (e.g., in mining areas) b) Macronutrient Toxicities: - Nitrogen (N): * Deep green color and delayed maturity * Tall plants with weak stems, prone to lodging * Succulent new growth and high transpiration * Burning effect under dry conditions * Ammonium toxicity: reduced growth, lesions on stems and roots, downward-rolling leaf margins - Phosphorus (P): * Indirect effects by reducing Fe, Mn, and Zn uptake * Most commonly causes Zn deficiency - Potassium (K): * Can cause Mg deficiency, and sometimes Ca deficiency, due to cation imbalance c) Micronutrient Toxicities: - Boron (B): * Narrow range between sufficiency and toxicity * Chlorosis followed by necrosis, starting at leaf tips and margins * Older leaves appear scorched and fall prematurely * In sugar beets: yellow-tinted band around leaf margins - Copper (Cu): * Displaces Fe and other metals, causing chlorosis and stunted growth - Manganese (Mn): * Blackish-brown or red spots on older leaves * Uneven chlorophyll distribution, chlorosis, and necrotic lesions - Molybdenum (Mo): * Stunted growth with yellow-brown leaf discolorations * Excess in forage can be toxic to livestock - Nickel (Ni): * Displaces Fe, causing interveinal chlorosis in new leaves and stunted growth - Zinc (Zn): * Dark green leaves, chlorosis, interveinal chlorosis * Reduced root growth and leaf expansion * May induce Fe deficiency 2. Soil as a Nutrient Reservoir: a) Soil Colloids: - Inorganic and organic soil particles that retain and release nutrients - Present large negatively charged surface areas  - Important for retaining and exchanging cations b) Cation Adsorption: - Follows the lyotropic series: Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+ - Influenced by ion valence and hydrated size - Reversible process known as ion exchange 3. Root-Microbe Interactions: a) Rhizosphere: - Area of soil influenced by living roots - Site of numerous associations between roots and soil microorganisms b) Bacterial Contributions: - Nitrogen fixation - Conversion of ammonium to nitrate - Influence on root growth and morphology (e.g., proteoid roots) c) Mycorrhizal Fungi: - Widespread associations between fungi and plant roots - Facilitate nutrient uptake by extending the reach of root systems d) Types of Mycorrhizae: 1. Ectotrophic Mycorrhizal Fungi: * Form thick sheath around roots * Penetrate between cortical cells but not into them * Form Hartig net * Primarily associated with tree species 2. Vesicular Arbuscular Mycorrhizal (VAM) Fungi: * Grow between and into root cortical cells * Form highly branched arbuscules within cells * Occasionally form vesicles * Increase surface area for nutrient exchange * Do not actually invade the cell protoplast 4. Importance of Mycorrhizae: - Improve nutrient absorption capacity of roots - Extend beyond nutrient-depleted soil near roots - Increase cytoplasmic volume in host cells - Provide large surface area for nutrient exchange between plant and fungus