Plant Nutrition

• • Most plants are considered autotrophs, making their own sugars
  • Sugar alone insufficient for growth - amino acids, pigments, nucleic acids, enzymes needed, obtained from soil
• Plant Composition

  • Most higher order vascular plants contain a minimum of 17 essential elements
  • 3 elements make up 96 % of the dry mass of the plant - carbon (from CO2), hydrogen (from water), oxygen (from O2, H2O)
  • Macronutrients - required in large amount - N, P, K, Mg, Ca, S
  • Micronutrients - Fe, Mn, Zn, Cu, B, Mo, Cl, Ni - deficiency evident with phenotypic display in plant
  • Enzymes function to speed up reactions, require micronutrients as cofactors
• Mobile Nutrient

  • N, P, K
  • If lacking in plant, then older leaves give them up to newer leaves
  • Fertilizers, components of nucleic acids, proteins, and phospholipids
• Immobile Nutrients

  • Ca, Fe
  • Deficiency shown in newer leaves
• Soil Texture

  • Affects root growth, ability to penetrate soil
  • Impacts ability of soil to retain water & make it available to plants
  • Impacts availability of oxygen access for roots (for cellular respiration)
  • Generally, best soil for plant growth is loams - equal amount of sand, silt, clay, and high amount of humus (decaying organic matter)
• Anions in Soil

  • Usually dissolve in water as they interact with water molecules via hydrogen bonding (polarity)
  • Readily available to plants for absorption
  • Easily washed out of the soil by rain leaching - loss of nutrients by movement of water through soil
• Cations in Soil

  • Generally difficult for plants to acquire, so immobile
  • Dissolve in water because of polarity
  • Not immediately available with plant because they interact with negative charges on soil particles, particularly clay particles (cations stick to clay particles)
  • Organic matter can also have many negatively charged particles, binding up cations
• Soil pH

  • Soil pH influences availability of elements
  • More hydrogen ions, lower pH, more acidic
  • Acidic soils in conifer forests - decomposition of organic matter produces carbonic, phosphoric, or nitric acid - alkaline soils in regions with limestone bedrock
  • Plants can influence soil pH around their roots
  • Roots release CO2, CO2 reacts with water in soil to form carbonic acid, acid releases protons
  • CO2 reacts with water to form carbonic acid, which releases protons
• Nutrient Absorption

  • If plant grows in soil, most nutrient absorption happens though root hairs (small and thin, lots of surface area)
  • Zone that absorbs most of it is cellular maturation, that’s where the root hairs are
• The cell wall is fairly porous and permeable to water and nutrients.
• The cell membrane (lipid bilayer) is selectively permeable and will not allow charged molecules to pass through because it is made of fatty acids (hydrophobic, non-polar).
• Ions enter the cell using transporters in the cell membrane made of protein, using an electrochemical gradient.
• Mycorrhizal Fungi

  • Mycorrhizae - a symbiotic relationship plants have with fungus in soil
  • Evolved together with vascular plants
  • Fungus helps plants access nutrients in soil like nitrogen
  • Fungi gets sugars produced by plant through photosynthesis
  • Mycorrhizae protect the plant from pathogenic microorganisms by creating a physical barrier and by production of antibiotics
  • Stimulate root growth by producing auxins (plant hormone)
  • Networks of fungal hyphae increase surface area for absorption by up to 700%
• Ion Exclusion

  • Plants exclude extra nutrients using passive or active exclusion
  • Passive: root doesn’t have ability to take them up
  • Lack membrane protein transporter required
  • Vary number of protein transporters regulate uptake
  • Casparian strip blocks ions that entered via apoplectic route
  • Active: plants uses energy
  • Plants use energy to make metallothioneins and phytochelatins that bind metal ions and prevent poisoning - metals attracted to them
  • Storage via tonoplast - vacuole, double lipid bilayer - membrane proteins actively move toxic substances into the vacuole for storage