Plant Nutrition

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Plant Nutrition

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• Mineral Nutrition
• How plants acquire and use mineral nutrients
• 1. Why is mineral nutrition important?
• 2. What are the essential mineral nutrients?
• classification systems
• 3. Mineral nutrients in the soil
• nutrient availability
• adsorption to soil particles
• effects of pH
• 4. Roots and mineral nutrient acquisition
• root structure
• depletion zones
• 4. Mycorrhizae
• 5. Nitrogen - the most limiting soil nutrient

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• Why is mineral nutrition important?
• 2. In most natural soils, the availability of
  mineral nutrients limits plant growth and primary
  productivity.
• Nutrient limitation is an important selective
  pressure and plants exhibit many special traits
  related to the need to acquire and use mineral
  nutrients efficiently.

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2. What are the essential mineral
nutrients? Macronutrients - present in
relatively high concentrations in plant
tissues. N, K, P, Ca, Mg,S, Si Nitrogen is
most commonly limiting to productivity of natural
and managed soils. Phosphorus is next most
limiting, and is most limiting in some tropical
soils. Micronutrients - present in very low
concentrations in plant tissues.
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There are 17 essential elements required for
plant growth

• What defines an essential element?
• In its absence the plant cannot complete a normal
  life cycle
• The element is part of an essential molecule
  (macromolecule, metabolite) inside the plant
• Most elements fall into both categories above
  (e.g., structural vs. enzyme cofactor)
• These 17 elements are classified as
• 9 macronutrients (present at gt 10 mmol / kg dry
  wt.)
• 8 micronutrients (lt 10 mmol / kg dry wt.)

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All mineral nutrients together make up less than
4 of plant mass, yet plant growth is very
sensitive to nutrient deficiency.
Not considered mineral nutrients
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Micronutrients are present in very low
concentrations
ppm
Very low concentrations, but still
essential because of specialized roles in
metabolism
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I. Plant Nutrients

• C. Macro/Micronutrients
• Hydroponics allowed us to see what was needed
• The necessary nutrients are those the plant can
  not grow with out
• Come in two categories
• 1. Macronutrients (C, O, H, N, S, P, K, Ca, Mg)
• Majority of the time used for the main organic
  compounds
• 2. Micronutrients (Cl, Fe, B, Mn, Zn, Cu, Mo,
  Ni)
• Mostly cofactors for particular enzymes (Fe -gt
  Cytochromes

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Hydroponic culture techniques come in different
flavors
Fig. 12.1

• Main disadvantage of simple solution culture ? as
  plant grows, it selectively depletes certain
  minerals
• When one becomes limiting, growth will slow
  significantly
• Can grow in vermiculite/perlite (inert,
  non-nutritive) and refertilize daily
• Commercially, it is often cheaper and easier to
  continuously bathe roots in a nutrient solution
  (nutrient film technique)
• Aerates
• Standard nutrient level maintained
• Continuous process monitoring
• To define essential, researchers need inert
  materials contributing low levels of nutrients
  (NO METAL PARTS!)

Fig. 12.2
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Soils particles are generally negatively charged
and so bind positively charged nutrient ions
(cations). Cation Exchange Capacity refers to a
soils ability to bind cations.
NH4, NO3-, Cl-, PO4-2, SO4-2
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Soil pH influences availability of soil nutrients.
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Roots
Provide large surface area for nutrient uptake -
Root hairs
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Root hairs
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Depletion zones - regions of lower nutrient
concentration -develop around roots
Fig. 5.7
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Root hairs
Root hairs
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4. Roots and mineral nutrient acquisition
Fine roots and root hairs mine the soil for
nutrients. Mycorrhizal hyphae do this even
better.
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K
K
K
Clay particle
H
K
K
K
K
K
Root hair
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• Vesicular Arbuscular Mycorrhiza
• Inside root
• Intercellular mycelium
• Intracellular arbuscule
• tree-like haustorium
• Vesicle with reserves
• Outside root
• Spores (multinucleate)
• Hyphae
• thick runners
• filamentous hyphae
• Form extensive network of hyphae
• even connecting different plants

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Mycorrhizae
Ectotrophic mycorhizae
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Why mycorrhiza?

• Roots and root hairs cannot enter the smallest
  pores

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Nitrogen fixing bacteria Genus Rhizobium
N2 NH4
Supply of electrons
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Ion uptake
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Active uptake
Proton pumps establish an electrochemical
gradient.
Outside cell (positive)
Net positive charge
Net negative charge
Inside cell (negative)
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Cations enter root hairs via channels or carriers
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Anions enter root hairs via cotransporters.
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Concept of critical concentration illustrated

• Above critical concentration, there is no net
  benefit (e.g., yield increase) if more nutrient
  is supplied
• Below critical concentration, nutrient level
  limits growth!
• Not shown on diagram all elements eventually
  become toxic at very high concentrations

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Analysis of plant tissues reveals mineral
deficiencies
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The absence of essential elements causes
deficiency symptoms

• Essential because of their metabolic functions
• Characteristic deficiency symptoms shown because
  of these roles
• Typical deficiency responses are
• Chlorosis yellowing precursor to
• Necrosis tissue death
• Expressed when a supply of an essential
  metabolite becomes limiting in the environment
• Element concentrations are limiting for growth
  when they are below the critical concentraion
• This is the concentration of nutrient in the
  tissue just below the level giving maximum growth

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Limiting nutrient levels negatively affect growth

• Plant responses to limiting nutrients usually
  very visible affects yield/growth!
• Again, chlorosis and necrosis of leaves is
  typical
• Sometimes straightforward relationship
• e.g., in chlorosis (lack of green color),
• N chlorophyll component
• Mg cofactor in chlorophyll synthesis

Ctrl
- P
- N
- Fe
- Ca
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Chlorosis
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Necrosis
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Stunted growth