Chapter 37: Plant Nutrition

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Chapter 37 Plant Nutrition
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Where does mass come from?

• Mineral nutrients-- essential elements
• minimal contribution to mass
• Water 80-85 of herbaceous plants
• over 90 lost via transpiration
• Retained H2O solvent, maintain turgidity
• Assimilated CO2 makes up most of organic
  molecules mass.

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How do plants get nutrients?
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Dry Weight

• 95 organic (carbs, CHO, cellulose).
• 5 inorganics
• nitrogen, sulfur, and phosphorus
• Found in many organics

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Plant Nutrients

• Essential nutrients-- required for a plant to
  grow from a seed and complete the life cycle.
• Plants require 9 macronutrients and 8
  microsnutrients
• Hydroponic cultures identify essential nutrients

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Hydroponics
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Macronutrients

• Needed in large quantities
• 9 macronutrients
• carbon, oxygen, hydrogen, nitrogen, sulfur, and
  phosphorus (found in organics)
• potassium, calcium, and magnesium (ions)

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Micronutrients

• Needed in very small amounts
• 8 micronutrients
• iron, chlorine, copper, zinc, magnanese,
  molybdenum, boron, and nickel.
• Cofactors of enzymatic reactions.
• Lacking micronutrients can kill/sicken a plant.

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Mineral Deficiencies (ex Chlorosis)

• Since Mg and Fe are involved in the production of
  chlorophyll, their deficiencies are marked by
  yellow leaves (chlorosis)

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Mineral Deficiencies

• Mobile Nutrients
• symptoms of the deficiency will appear first in
  older organs
• Ex chlorosis affects older leaves first
• Immobile Nutrients
• affect young parts of the plant first
• Older tissue adequate supplies for shortages

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Soil

• The type of soil (composition/texture) determines
  the plants that can survive
• Originates from weathered rock (minerals)
• Topsoil (product of weathering)
• Rich in decaying organic material (humus),
  bacteria and rock
• Horizons ? Horizontal layers of soil

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Soil
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Soil Texture

• Depends on the size of its particles (coarse
  sand to microscopic clay)
• Loams
• Most fertile soils (equal silt/sand/clay)
• fine particles large surface area for retaining
  minerals and water
• course particles air spaces that supply oxygen
  to the root (respiration)

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Waterlogged Soil ? Too much H2O

• Water in air spaces can suffocate a plant
• Unfavorable molds can grow and attack plant.
• Mangroves have long, hollow, tube roots that
  allow them to survive in marshland.

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Topsoil Organisms

• 1 teaspoon approx. 5 billion bacteria.
• Organisms alter the physical and chemical
  properties of the soil.
• Earthworms aerate soil (burrowing) add mucus
  holds fine particles together.
• Bacteria (ie nitrogen fixation)
• Plants extract nutrients, affect soil pH, and
  reinforce the soil

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Humus

• Decomposing organic material
• Formed by the action of bacteria and fungi on
  dead organisms, feces, leaves, etc.
• Crumbly soil -- retains water, porous enough for
  aeration of roots
• Rich in minerals from decomp.

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How does Soil Hold Water?

• Electrostatic attraction between soil particles
  and water molecules.
• Plants extract the more loosely bound water
  molecules
• Surface of soil is charged (hydrophilic)

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How does Soil Hold Minerals

• Positively charged minerals (K, Ca2, Mg2 are
  not leached out by rain because they adhere to
  negative surface of clay (remember origins!)
• Negatively charged mineral ions (NO3-, H2PO4-,
  SO42-) leach out more easily.

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Cation Exchange

• () mineral ions are made available to the plant
  when H ions in the soil displace the mineral
  ions from the clay particles.
• cation exchange
• roots secrete H and compounds that form acids in
  the soil solution

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How does Soil Hold Water?
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Soil Mismanagement

• The Dust Bowl (1930s)
• Farmers removed grasses that held soil in place
  during droughts
• Topsoil was blown away and soil useless

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Fertilizers

• Agriculture requires a lot of minerals
• Fertilizers replace the minerals in the soil
• 10-12-8 Fertilizer 10 nitrogen, 12
  phosphorus and 8 potassium
• Used to increase crop yield
• Organic Fertilizers (ie manure)
• Too much pollution of groundwater

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Water Availability and Irrigation

• Top limiting factor for plant growth
• Irrigation bring water to dry areas (ie desert)
• Irrigated water that evaporates leaves salt
  behind.
• Lowers soil H2O potential
• plasmolysis

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Wind and Erosion

• Wind destroys topsoil of many crops.
• Planting trees or other crops (alfalfa) in rows
  between fields.
• Acts as a windbreak for soil

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Wind and Erosion
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Sustainable Agriculture

• The goal is to eventually develop farming
  techniques that are maximally conservation
  minded, environmentally friendly, and profitable.

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Human Influence

• Humans have made many areas uninhabitable for
  both flora and fauna
• contamination and/or overdevelopment.
• Phytoremediation Use of plants that utilize
  toxic contaminants to clean up our mess
• Ex alpine pennycress (Thlaspi caerulescens)
  accumulates zinc in its shoots

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Nitrogen Fixation

• Atmosphere 80 nitrogen, yet plants suffer from
  deficiencies
• Plants cant use N2 (g) directly
• Must be taken as NH4 or NO3-
• Decomp. of humus by microbes releases usable
  nitrogen into the soil

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Denitrifying Bacteria

• Convert NO3- (usable) into N2 (not usable) which
  diffuses into atmosphere
• Denitrifying bacteria remove usable nitrogen from
  the soil

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Nitrogen-Fixing Bacteria

• Nitrogen Fixation
• Soil microbes convert N2 (not usable) into NH3
  (will be usable)
• Nitrogen fixation restocks the soil with usable
  forms of nitrogen (specifically ammonia)
• Nitrogenase complex of enzymes catalyze rxns

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Nitrogen Cycle in the Soil
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Nitrogen Fixation

• Once bacteria release NH3, it picks up extra H
  to become NH4 which plants can assimilate
  directly
• Much NH4 oxidized to NO3- (also absorbed)
• Once absorbed, plants incorporate nitrogen into
  amino acids and organics

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Symbiosis

• When a species participates in a direct
  relationship with an individual of another
  species.
• Often involve microorganisms.
• Can be good, bad, or neutral for one or both of
  the organisms.

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Nitrogen-Fixing Root Nodules

• Rhizobium bacteria exist in specialized
  projections in roots of legumes
• The bacteria fix nitrogen into usable forms.
• The plant supplies nutrients to the nodule
  through xylem and phloem.
• Relationship is good for both.
• Plant gets nitrogen, the bacteria obtains
  nutrients.

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Root Nodules
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Root Nodules
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Mycorrhizae

• Symbiosis b/t fungi and root of nearly all
  plants.
• Early evolutionary adaptation??
• Fungi gets a good (protected) environment with
  nutrients from plant
• Plant Benefits
• Fungus surface area and absorbs minerals in
  the soil and supplies them to the plant.
• Fungi secretes growth factors that stimulate root
  growth.
• Fungi produce antibiotics

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Plant Modifications

• Parasites Plants that steal nutrients from
  other plants (ie tap into vascular tubes)
• Carnivores Plants that eat meat (ex venus fly
  trap)