Soil pH influences availability of soil nutrients.

Soil pH influences availability of soil nutrients.

Fine roots and root hairs “mine” the soil for

nutrients. Mycorrhizal hyphae do

this even better.

4. Roots and mineral nutrient acquisition

Roots

Provide large surface area for nutrient uptake

- Root hairs

Why are fine structures like hyphae and root hairsparticularly effective at nutrient absorption?

For a given volume (or mass) of roots, what size rootpresents the most surface area?

Surface area of a cylinderSA = circumference x length

SA = x diam x lengthSA = x 2r x length

Volume = area x lengthVol = 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.

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.

Fig. 5.7

Depletion zones - regions of lowernutrient concentration -developaround roots

A depletion zone of low concentration forms near the rootwhen the rate of nutrient uptake exceeds the rate of diffusion

Mycorrhizae“fungus -

root”Symbiosis with fungi

Nutrient Uptake and Mycorrhiza

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-mycorrhiza2. EctomycorrhizaOther types

ericoidorchid endomycorrhiza

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

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 hyphaeeven connecting different plants

AM

Arbuscule of Glomus mosseae – branching provides large surface area

Outside of root network of hyphae and spores

2. Ectomycorrhiza (EM)

• Ascomycetes and Basiodiomycetes – form large fruiting bodies

• 5000 species interact with 2000 plant species

• Interaction with trees: angiosperms and all Pinaceae

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 hyphaeeven connecting different plants

Ectomycorrhizal root tip

Mantle Hyphae

Hartig Net

Why mycorrhiza?

• Roots and root hairs cannot enter the smallest pores

Why mycorrhiza?

Root hair Smallest hyphae

• 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

Inoculated with mycorrhizae

Not inoculated with

mycorrhizae

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

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 --> C – C + NH3

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

For usmore 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 Nconcentration of leaves and photosynthesis?

Nitrogen - the most limiting soil nutrient

Evidence - factorial fertilization experiments (N, P, K, etc.)

show largest growth response to N.

1. 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.

The inorganic forms of nitrogen in soils.

1.NH4+, ammonium ion. A cation that is bound to clays.

2.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

-?

SoilOrganic N

NH4+

Plant N

NO3-

NH4+ uptake

Mineralization

NH4+

immobilization

Nitrification

NO3-uptake

NO3-

immobilization

NO, N2O

N2

Leaching

Denitrification

N Fixation

Atmospheric N2

The Nitrogen Cycle

SoilOrganic N

NH4+

Plant N

NO3-

NH4+ uptake

Mineralization

NH4+

immobilization

Nitrification

NO3-uptake

NO3-

immobilization

NO, N2O

N2

Leaching

Denitrification

N Fixation

Atmospheric N21. Emissions to

atmosphere

Dead organismsand tissues

Pathways of N loss from ecosystems

2.