Soil pH influences availability of soil nutrients.

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Soil pH influences availability of soil nutrients.
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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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Roots
Provide large surface area for nutrient uptake -
Root hairs
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Why are fine structures like hyphae and root
hairs particularly effective at nutrient
absorption?
For a given volume (or mass) of roots, what size
root presents the most surface area?
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Surface area of a cylinder SA circumference x
length SA ? x diam x length SA ? x 2r x
length Volume area x length Vol ? x r2 x
length SA/Vol (? x 2r x length)/(? x r2 x
length) SA/Vol 2/r
As the radius decreases, the surface area per
volume increases.
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Minirhizotron photos of yellow birch roots in the
Hubbard Brook Experimental Forest (New Hampshire)
in April (left) and June (right). 0.3 mm in
diameter.
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Depletion zones - regions of lower nutrient
concentration -develop around roots
Fig. 5.7
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A depletion zone of low concentration forms near
the root when the rate of nutrient uptake exceeds
the rate of diffusion
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Nutrient Uptake and Mycorrhiza
Mycorrhizaefungus - root
Symbiosis with fungi
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Roots and Mycorrhiza an old symbiosis

• Mutual benefit
• Carbohydrates for the fungus
• P, Zn, Cu, water, N for plant
• Different types
• 1. Vesicular-arbuscular mycorrhiza
  VA-mycorrhiza
• 2. Ectomycorrhiza
• Other types
• ericoid
• orchid endomycorrhiza

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• 1. Vesicular arbuscular mycorrhiza (AM)
• Glomales (130 species infects 300.000 plant
  species)
• Found on roots of herbaceous angiosperms, most
  trees, mosses, ferns
• not present on Cruciferae, Chenopodiaceae,
  Proteaceae
• small biomass compared to roots

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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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AM
Arbuscule of Glomus mosseae branching provides
large surface area
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Outside of root network of hyphae and spores
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• 2. Ectomycorrhiza (EM)
• Ascomycetes and Basiodiomycetes form large
  fruiting bodies
• 5000 species interact with 2000 plant species
• Interaction with trees angiosperms and all
  Pinaceae

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• Ectomycorrhiza
• Inside root
• Intercellular hyphae
• Does not enter cells
• Outside root
• Thick layer of hyphae around root
• Fungal sheath
• Lateral roots become stunted
• Hyphae
• Mass about equal to root mass
• Forms extensive network of hyphae
• even connecting different plants

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Ectomycorrhizal root tip
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Mantle Hyphae
Hartig Net
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Why mycorrhiza?

• Roots and root hairs cannot enter the smallest
  pores

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Why mycorrhiza?

• Roots and root hairs cannot enter the smallest
  pores
• Hyphae is 1/10th diameter of root hair
• Increased surface area
• Surface area/volume of a cylinder
• SA/vol 2/radius

Root hair
Smallest hyphae
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Why mycorrhiza?

• Roots and root hairs cannot enter the smallest
  pores
• Hyphae is 1/10th of root hair
• Increased surface area
• Extension beyond depletion zone

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Why mycorrhiza?

• Roots and root hairs cannot enter the smallest
  pores
• Hyphae is 1/10th of root hair
• Increased surface area
• Extension beyond depletion zone
• Breakdown of organic matter

C C NH2 --gt C C NH3
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• Summary on mycorrhizae
• Symbiosis with mycorrhiza allows greater soil
  exploration,
• and increases uptake of nutrients (P, Zn, Cu,
  N, water)
• Great SA per mass for hyphae vs. roots
• Mycorrhiza gets carbon from plant
• Two main groups of mycorrhiza Ectomycorrhiza
  and VA-mycorrhiza

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• For us
• more on nitrogen nutrition
• Why is N so important for plant growth?
• What percentage of the mass of plant tissues is
  N?
• What kinds of compounds is N found in?
• Why is there a strong relationship between the N
• concentration of leaves and photosynthesis?

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• Nitrogen - the most limiting soil
  nutrient
• Evidence - factorial fertilization experiments
  (N, P, K, etc.)
• show largest growth response to N.
• Required in greatest amount of all soil nutrients
• 2. A component of proteins (enzymes, structural
  proteins,
• chlorophyll, nucleic acids)
• 3. The primary photosynthetic enzyme, Rubisco,
  accounts
• for a 25 to 50 of leaf N.
• Photosynthetic capacity is strongly correlated
  with
• leaf N concentration.
• 4. Availability in most soils is low
• 5. Plants spend a lot of energy on N acquisition
  - growing
• roots, supporting symbionts, uptake into roots,
  biochemical assimilation into amino acids, etc.

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• The inorganic forms of nitrogen in soils.
• NH4, ammonium ion. A cation that is bound to
  clays.
• NO3-, nitrate ion. An anion that is not bound to
  clays.
• Nutrient mobility in soils refers to the rate
  of diffusion,
• which is influenced by nutrient ion interactions
  with soil particles.
• Would you expect NH4 or NO3- to diffuse more
  rapidly?
• Would you expect a more pronounced depletion zone
  for NH4 or NO3-?

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The Nitrogen Cycle
 
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Pathways of N loss from ecosystems
1. Emissions to atmosphere
2.
Dead organisms and tissues