CR

8, Plant Nutrition Study Notes

Plant Nutrition Summary Notes

Soils: The Substrate on Which Plants Depend

  • Definition: Soil is the highly weathered outer layer of the Earth’s crust, composed of a mixture of sand, rocks, clay, silt, humus, air, and other organic and mineral materials.

  • Elements Present: Contains approximately 92 naturally occurring elements, primarily found in inorganic compounds known as minerals.

  • Microorganisms: Soil is rich in microorganisms that play key roles in nutrient cycling.

Topsoil

  • Importance: Most plant roots are located in the topsoil, which is crucial for plant nutrition and growth.

  • Composition: Consists of various mineral particles, living organisms, and humus, characterized by amounts of sand, silt, and clay.

  • Soil Composition Effects: Determines the binding capacity of water and nutrients to soil particles, influencing plant health.

Mineral Availability

  • Dissolution in Water: Only minerals dissolved in soil water are available for plant uptake by roots.

  • Membrane Potential: Roots maintain charge by pumping H+, directly affecting nutrient absorption and water po

  • tential (Yw).

  • Osmosis: A difference in water potential helps pull water and ions into the roots.

Pores in Soil

  • Soil Volume: Approximately 50% of soil volume is pores filled with air or water, affecting water accessibility to plants.

  • Water Availability: Water in small pores is easily accessible, whereas larger pores may drain quickly due to gravity.

Topsoil Loss

  • Consequences: Loss of topsoil negatively affects water retention and nutrient availability.

  • Historical Context: Drought and poor farming practices in the 1930s contributed to the Dust Bowl phenomenon in the Great Plains.

Erosion Prevention

  • Erosion Causes: Disruption of vegetative cover increases susceptibility to wind and water erosion.

  • Prevention Techniques:

    • Intercropping: Mixing different plant species in one field.

    • Conservation Tillage: Includes practices such as no-till agriculture and retaining crop stubble.

Fertilizer Runoff Prevention

  • Issue: Overusing fertilizers can cause significant water pollution and algal blooms in water bodies (e.g., Lake Erie 2011).

  • Impact: Excess nutrients lead to deterioration of aquatic ecosystems and freshwater quality.

Acid Soils

  • pH Influence: Soil pH affects mineral availability; low pH can release toxic aluminum to plants.

  • Optimal Conditions: Most plants thrive at slightly acidic pH levels. Efforts are ongoing to breed acid-tolerant plant varieties.

Saline Soils

  • Salt Accumulation: Typically from overwatering, leading to loss of water and turgor in plants due to altered water potential.

  • Commonality: More prevalent in dry regions where salts are concentrated through irrigation.

Plant Nutrients

  • Sources: Major source of plant nutrition is photosynthesis, utilizing CO2 and solar energy.

  • Types of Nutrients:

    • Macronutrients: Required in large amounts (e.g., C, O, H, N, K, Ca, Mg, P, S).

    • Micronutrients: Required in trace amounts (e.g., Cl, Fe, Mn, Zn, B, Cu, Mo).

  • Deficiencies: Lack of any nutrient can severely affect plant growth.

Hydroponics

  • Concept: Soilless systems that provide nutrients and support, allowing year-round plant growth.

Food Security

  • Global Issue: Addressing starvation through enhanced plant nutrient uptake and fortification.

  • Research Areas: Includes GMOs designed to increase mineral absorption and secretion.

Special Nutritional Strategies

  • Nitrogen Needs: Plants require ammonia (NH3) or nitrate (NO3-) for amino acids but cannot convert atmospheric N2 directly.

  • Symbiotic Relationships: Nitrogen-fixing bacteria like Rhizobium form nodules in legumes, assisting in nitrogen acquisition.

Mycorrhizae

  • Role: Symbiotic fungi that enhance nutrient uptake, especially phosphorus, by expanding root surface area.

Carnivorous Plants

  • Adaptations: These plants trap and digest insects for nitrogen, crucial for survival in nitrogen-poor acidic soils.

Ghost Pipe

  • Characteristics: A parasitic plant without chlorophyll that accesses nutrients from host trees via mycorrhizal fungi.

Carbon-Nitrogen Balance and Global Change

  • Issues: Increasing CO2 levels can disrupt carbon-to-nitrogen ratios, crucial for plant and herbivore health.

Free Air CO2 Enrichment (FACE) Studies

  • Methodology: Towers release CO2, allowing ecosystem-level studies to understand plant responses to increased CO2.

Phytoremediation

  • Mechanisms: Utilizes plants to absorb, degrade, or stabilize contaminants in soil, such as trichloroethylene and heavy metals.

    • Types: Includes phytodegradation, phytovolatization, and phytoaccumulation, addressing various soil contaminants.

  • Concerns: Risk of heavy metal accumulation in edible plants poses health risks to herbivores and humans.