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Plant Nutrition and Interaction with Environment

Important Focus Points

  • Types of nutrients critical to plants and their roles.
  • Impact of changes in nutrient availability on plants.
  • Role of microbes in nutrient availability for plants.

Essential Inorganic Nutrients

  • 17 essential elements are necessary for plant growth and reproduction.
    • Macronutrients: Required in large amounts (9 total)
    • Micronutrients: Required in smaller amounts (8 total)
  • Both macronutrients and micronutrients are vital for plant functions.

Macronutrients

  • Constituents of plant weight (99.7%)
    • Carbon (C) - Integral part of organic compounds
    • Oxygen (O) - Integral part of organic compounds
    • Hydrogen (H) - Integral part of organic compounds
    • Nitrogen (N) - 45% of plant weight, crucial for proteins and nucleic acids
    • Potassium (K) - Regulates stomatal movement
    • Calcium (Ca) - Cell wall component, maintains membrane structure
    • Magnesium (Mg) - Component of chlorophyll
    • Phosphorus (P) - Nucleic acids, ATP
    • Sulfur (S) - Component of proteins

Micronutrients

  • Needed in tiny quantities (0.3% of plant weight)
    • Molybdenum (Mo)
    • Iron (Fe) - Component of proteins in electron transport chains
    • Manganese (Mn)
    • Boron (B)
    • Zinc (Zn)
    • Copper (Cu)
    • Chlorine (Cl)
    • Nickel (Ni)
    • Sodium (Na) - Required by some plants only

Fertilizers

  • Nutrient availability in soil is critical for plant health.
  • Common nutrient deficiencies:
    • Nitrogen deficiency (most common)
    • Phosphorus deficiency (second most common)
  • Fertilizer types:
    • Inorganic chemical fertilizers
    • Organic compost
  • Fertilizers help alleviate nutrient deficiencies.

Soil Conservation

  • Cultivation practices can degrade soil health.
    • Irrigation can increase salinity.
    • Erosion from plowed lands can remove topsoil.
    • Chemical fertilizers can contaminate groundwater.
  • Good soil management practices:
    • Water-conserving irrigation
    • Erosion control measures
    • Prudent use of fertilizers and herbicides.

Role of Microbes in Plant Nutrition

  • Most plants depend on soil bacteria for nitrogen supply.
    • Nitrogen in the atmosphere (N2) cannot be directly absorbed.
    • Nitrogen-fixing bacteria convert atmospheric N2 to ammonia (NH3).
    • Ammonifying bacteria decompose organic matter to supply ammonium (NH4+).
    • Nitrifying bacteria convert ammonium to nitrates (NO3-), the form plants uptake.

Symbiotic Relationships

  • Plants often form symbioses with fungi (mycorrhizae):
    • Increase root area for absorption.
    • Aid in absorbing phosphates and minerals.
    • Release growth factors and antibiotics.
  • Leguminous plants (e.g., peas, beans) form root nodules with nitrogen-fixing bacteria (Rhizobium):
    • These associations lead to nitrogen richness in plants.

Parasitic and Carnivorous Plants

  • Some plants may evolve to become:
    • Parasitic (e.g., mistletoe): Absorb nutrients from host plants.
    • Carnivorous (e.g., sundew, Venus flytrap): Capture insects for nutrients in poor soil.
    • Epiphytes (e.g., orchids): Grow on other plants to absorb water and minerals.

Summary

  • Importance of understanding plant nutrients, their availability, microbial interactions, and adaptations in diverse environments.