Chapter 37 Plant Nutrition

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Chapter 37Plant Nutrition
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Nutritional Requirements of Plants

• Mineral nutrients- essential chemical elements
  absorbed from the soil in the form of inorganic
  ions. (i.e. nitrogen)

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Essential Nutrients

• Essential nutrient- chemical element that is
  required for a plant to grow and complete the
  life cycle. There are 17 elements that are
  essential to all plants.
• Essential nutrients can be dividend into two
  categories, macronutrients and micronutrients.

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Macronutrients

• Macronutrients are elements required by plants in
  relatively large amounts. There are 9 total.
  They are Carbon, Oxygen, Hydrogen, Nitrogen,
  Sulfur, Phosphorus, Potassium, Calcium, and
  Magnesium.

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Micronutrients

• Micronutrients are elements a plant needs in
  very small amounts. They are Iron, Chlorine,
  Copper, Manganese, Zinc, Molybdenum, Boron, and
  Nickel.
• These elements function in plants mainly as
  cofactors of enzymatic reactions. (i.e. Iron is a
  metallic component of cytochromes, the proteins
  that function in the electron transport chains).
  

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Symptoms of Mineral Deficiency

• A deficiency of magnesium, which is an ingredient
  in chlorophyll, causes the yellowing of the
  leaves, or chlorosis.
• If nutrients move freely from one part of the
  plant to another, symptoms of deficiency will
  show up in the older parts.
• If the nutrients do not move freely, they
  generally appear in the newer parts of the plant.

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The Role of Soil in Plant Nutrition

• Factors that will determine what types of plants
  can grow in the region
• 1. Texture
• 2. Composition
• 3. Availability of soil water and nutrients
• 4. Climate

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Texture and Composition of Soil

• Horizons are layers of soil that are often
  visible in vertical profiles.
• Topsoil is a mixture of particles derived from
  rock, living organisms, and humus, a residue of
  partially decayed organic material.
• The texture of the topsoil depends on the size of
  the particles, ranging from coarse sand to
  microscopic clay particles.
• The most fertile soil is loams, made up of
  roughly equal amounts of sand, silt, and clay.

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Availability of Soil Water and Nutrients

• Water stays in smaller spaces in the soil because
  of its attraction for the soil particle which
  have electrically charged surfaces.
• The minerals in the soil-especially the
  positively charged minerals, such as potassium,
  calcium, and magnesium-adhere by electrical
  attraction to the negatively charged surfaces.
• Minerals that are negatively charged, such as
  nitrate, phosphate, and sulfate, are not bound as
  tight to the soil and are leached away more
  quickly.
• Positively charged minerals are made more
  available when the hydrogen ions in the soil
  displace the mineral ions from the clay
  particles. This process, called cation exchange,
  is stimulated by the roots, which discrete the
  hydrogen.

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The Availability of Soil Water and Materials
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Soil Conservation

• Agriculture uses up the nutrients in the soil. To
  preserve them, farmers must use a variety of
  techniques to increase the amount on minerals in
  the soil.
• Farmers use fertilizers to enrich the soil.
  Fertilizers generally contain the three elements
  most commonly deficient in the soil, nitrogen,
  phosphorus, and potassium.
• The numbers on fertilizer bags represent the
  percentage of these elements in the fertilizer.
  (I.e. a bag marked 10-12-8 has 10 nitrogen, 12
  phosphorous, and 8 potassium)
• Farmers must also pay attention to the conditions
  of the soil to fertilize properly. A plant in a
  field with a pH of 8 can absorb calcium, but
  cannot absorb iron.

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Soil Conservation

• Irrigation is a problem for the soil. In an arid
  climate, irrigation can make the soil so salty
  that it becomes infertile. Eventually, salt left
  in the lowers the water potential of the soil,
  which causes the plant to lose water. Farmers
  now use drip irrigation and are trying to develop
  varieties of plants that require less water.
• Topsoil is lost due to wind and water erosion.
  To stop this, farmers use trees as wind breakers,
  and terracing a hill side to prevent soil from
  washing away during a heavy rain.
• The goal is sustainable agriculture, using
  farming methods that are environmentally safe and
  profitable.

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Soil Bacteria Makes Nitrogen Available to Plants

• 80 of the air is nitrogen, yet plants suffer
  from nitrogen deficiency because they are not
  able to absorb the N2.
• For plants to absorb the nitrogen, it must be
  converted to ammonium or nitrate.
• Nitrogen-fixing bacteria convert N2 to
  NH3(ammonia) through a metabolic process called
  nitrogen fixation.
• N2 8e 8H 16 ATP --gt2 NH3 H2 16 ADP
  16P
• Nitrogenase reduces N2 to NH3 by adding
  electrons with hydrogen ions. Nitrifying
  bacteria oxidize ammonium into NO3.

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Nitrogen-Fixing Bacteria
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Symbiotic Relationships

• Legumes roots have swellings called nodules
  containing nitrogen-fixing bacteria of the genus
  Rhizobium. Legumes are peas, beans, soybeans,
  peanuts, clover, and alfalfa.
• The nodules contain bacteroids, which have
  vessels formed by the root cell.
• Farmers use plant rotation to replenish nitrogen.
  One year they plant a nonlegume plant, such as
  corn, and the next year, a legume. The legume
  plant is often mowed down and then allowed to
  decompose.

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Soybean Root Nodule
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Mycorrhizae

• Mycorrhizae, fungus roots, are modified roots
  consisting of symbiotic associations of fungi and
  roots.
• There are two main types of Mycorrhizae
  ectomycorrhizae and endomycorrhizae.
• Ectomycorrhizae forms a dense mantle over the
  surface of a root, which increases the surface
  area for absorption.
• Endomycorrhizae have hyphae, which extend into
  the root by digesting small patches of the cell
  wall. They have arbuscles, knotlike structures,
  where nutrients pass from fungi to plant.

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Parasitic and Carnivorous Plants

• Some plants get their nutrition by using
  projections called haustoria to siphon xylem sap
  from the host tree. Mistletoe, dodder, and
  Indian pipe are parasitic.
• Carnivorous plants make their carbohydrates by
  photosynthesis, but get their nutrients by
  killing and digesting insects. This includes the
  Venus Flytrap and Pitcher plants.