Plant Nutrition Notes

Plant Nutrition - Chapter 36

Key Topics Discussed

  • What nutrients do plants need?

  • What nutrients limit growth?

  • Soils & nutrient sources

  • How do plants take in nutrients?

  • How else do plants get nutrients?

    • Nitrogen fixation

    • Symbiotic fungi

    • Parasitism and carnivory

Where Does the Mass of Plants Come From?

  • Experiment by Jean-Baptiste von Helmont (Early 1600s)

    • Setup:

    • A 5 lb willow sapling planted in 200 lb of soil.

    • Duration: 5 years.

    • Results:

    • Initial weight (tree): 5 lb

    • Final weight (tree): 169 lb 3 oz

    • Final weight of soil: 199 lb 14 oz

    • Conclusion:

      • The mass of a growing plant comes primarily from water.

    • Later Determination:

    • This conclusion turned out to be incorrect.

Composition of Plant Biomass

  • Elements in Dry Weight (%):

    • Carbon: 45%

    • Oxygen: 45%

    • Hydrogen: 6%

    • C, H, O constitute 96% of a plant's dry mass.

    • Most plant biomass derived from both CO2 and H2O.

    • These elements are the major components of organic compounds (e.g., cellulose).

Macronutrients (1.5% or Less of Plant Mass)

  • Essential Macronutrients:

    • Nitrogen (N)

    • Critical for amino acids, nucleic acids, and chlorophyll.

    • Deficiency Symptoms: Stunted growth and yellowing of leaves.

    • Phosphorus (P)

    • Key for nucleic acids, ATP, phospholipids.

    • Deficiency Symptoms: Developmentally slow and stunted plants.

    • Potassium (K)

    • Necessary for enzyme activity, protein synthesis, and closing/opening of stomata.

    • Deficiency Symptoms: Curled, necrotic leaves.

    • Calcium (Ca)

    • Important for cell walls and membranes.

    • Magnesium (Mg)

    • Part of the chlorophyll molecule.

    • Sulfur (S)

    • Required for amino acids.

Nutrient Functions and Limits

  • Limiting Nutrients in Plant Growth:

    • Nitrogen, Phosphorus, and Potassium are the major limiting factors in plant growth.

  • Fertilizer Analysis Example:

    • Glorion Deluxe Fall Fertilizer

    • Guaranteed Analysis: 10-18-10

      • Total Nitrogen (N): 10.0%

      • Available Phosphoric Acid (P2O5): 18%

      • Soluble Potash (K2O): 10%

      • Sulfur (S): 0.10%

    • Nutrient Sources: Ammonium Phosphate, Ammonium Sulfate, Muriate of Potash.

Micronutrients (Less than 0.01% Dry Weight)

  • Essential Micronutrients:

    • Chlorine (Cl): Osmosis and ionic balance.

    • Iron (Fe): Essential for chlorophyll and cytochromes.

    • Manganese (Mn): Enzyme activator.

    • Zinc (Zn): Enzyme activator.

    • Boron (B): Carbohydrate synthesis.

    • Copper (Cu): Enzyme activator.

    • Nickel (Ni): Enzyme cofactor.

    • Molybdenum (Mo): Important for nitrogen fixation.

Source of Nutrients

  • Plants acquire nutrients primarily through soil, which is formed by the weathering of rocks and organic matter decomposing over time.

  • Soil Composition:

    • Classified by particle size:

    • Clay: < 0.002 mm

    • Silt: 0.002-0.02 mm

    • Sand: 0.02-2.0 mm

    • Gravel: > 2.0 mm

Soil Layers

  • Topsoil: Contains most organic matter (humus).

  • Subsoil: Mostly mineral weathering.

  • Bedrock: The substance that gradually breaks down into soil.

Nutrient Uptake Mechanisms

  • Ionic Interactions in Soil:

    • Organic matter and clay have a slight negative charge.

    • Positive ions interact with soil and are harder for plants to access.

    • Negatively charged ions are in solution and more accessible but prone to leaching.

  • Active Transport Mechanisms:

    • Active transport is used to move ions in/out of plant cells to acquire nutrients:

    • Active Transport Process:

      • Utilizes ATP to pump protons (H+) across the membrane.

    • Cotransporters (Symporters): Move substances simultaneously, often taking advantage of H+ gradients.

    • Antiporters: Move substances in opposite directions across the membrane.

Exclusion Mechanisms

  • Active transport is also employed to eliminate toxins, ensuring plant resilience in salty environments.

  • Some plants (e.g., Saltgrass, mangroves) manage salt overload through specialized mechanisms.

  • Sequestration Mechanism:

    • Vacuoles can sequester toxins, aiding in tolerance to high salinity.

Nutritional Interactions between Species

  • Plant nutrient acquisition often involves symbiotic relationships.

    • Types of Interactions:

    • Symbiotic: Both species benefit.

    • Commensal: One species benefits; the other is neutral.

    • Parasitic: One benefits, while the other is harmed.

Nitrogen Fixation

  • Plants require ammonia (NH3) for the synthesis of amino acids, but most lack the ability to convert atmospheric N2 to ammonia.

  • Symbiotic Relationships with Bacteria:

    • E.g., Legumes host nitrogen-fixing bacteria.

Mycorrhizae

  • About 90% of vascular plants engage in mutual symbiotic associations with fungi (mycorrhizae).

    • Types of Mycorrhizae:

    • Arbuscular Mycorrhizae: Hyphae penetrate outer cells of plant roots.

    • Ectomycorrhizae: Hyphae surround roots but don’t penetrate; associated often with trees.

    • Mycorrhizal relationships enhance root surface area for nutrient acquisition significantly.

Parasitic and Carnivorous Plants

  • Parasitic Plants:

    • Such as Indian pipe, which steals carbon from mycorrhizae associated with nearby plants.

    • Mistletoe uses haustoria to penetrate host xylem.

  • Carnivorous Plants:

    • E.g., Pitcher plants and Sundews

    • These plants trap insects to supplement their nutrient intake.

    • Found in nutrient-poor environments, often nitrogen limited.