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 and transfer of its N to host plant.

C – C – NH2 --> C – C + NH3

Are mycorrhizae always beneficial?

Probably not!!

Mutualistic Neutral Parasitic

Mycorrhizal interaction continuum(Nancy Johnson & Co)

What conditions influence where on the continuum agiven interaction falls?

Mycorrhizal response (MR) of various plant species at ambient and elevated CO2.

MR > 0 means better growth with AM than without AMMR < 0 means better growth without AM than with AM

0

1

2

3

4

5

6 Agropyron repens

- Nitrogen + Nitrogen

Plant growth is reduced by a full soil community that includes mycorrhizal fungi (filled bars) compared to the partial community (open bars). Added N significantly reduces the stunting of plant

growth by the full soil community.T

ota

l pla

nt m

ass

, g

Full Partial Full Partial Full Partial Full Partial

Soil Community

Are soil organisms competing with plants for nitrogen?

Summary on mycorrhizae

• Symbiosis with mycorrhiza allows greater soil exploration, and increases uptake of nutrients (P, Zn, Cu, N, water)

• Mycorrhiza gets carbon from plant

• Great SA per mass for hyphae vs. roots

• Not all mycorrhizal associations benefit the 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

Solute Transport (Ch. 6)

1. The need for specialized membrane transport systems.

2. Passive vs. Active Transport

3. Membrane Transport Mechanisms

Fig. 1.4

Why the need for specialized transport systems?

Fig. 1.5A

Fig. 6.6

That the permeability of biological membranes differsfrom that of a simple phospholipid bilayer indicates

that transporters are involved.

Passive vs. Active Transport

Passive transport requires no energy input, G < 0Active transport requires energy, G > 0

Whether active or passive transport is required is determined by the chemical potential of a solute on either side of a membrane.

We can use the G concept to understand the chemical potential.

Hydrostatic

Chemical potential difference

1.Concentration component2.3 RT log (Cj

i/Cjo)

What is the concentration influence on wherethe solute will tend to move spontaneously?

2. Electrical componentzjFE

What is the electrical influence on wherethe solute will tend to move spontaneously?

Movement along electrical and concentration gradients(from Lecture 3)

G = zF Em + 2.3 RT log(C2/C1)

At equilibrium (G = 0) can rearrange this as:

Em = -2.3(RT/zF) log(C2/C1)

Nernst potential•The difference in electrical potential (voltage) between two compartments at equilibrium with respect to a given solute.

•The membrane electrical potential at which the concentration and electrical influences on a solute’s movement are exactly balanced, so there is no net movement.

Ej = 2.3RT (log Cjo/Cj

i) zjF

•At equilibrium, the difference in concentration of an ion between two compartments is balanced by the voltage difference between the compartments.

Cjo Cj

i

Plasmamembrane and the tonoplast are sites of much ion transport.

Fig. 6.4

Maintenance of cell membrane potential requires energy produced by respiratory metabolism

Fig. 6.7

Fig. 6.8

Fig. 6.9

even

Transport of a solute against its concentration gradient can occur by coupling it to proton transport with its concentration gradient.