BIO 2600 - Unit 14: Mutualism

Mutualism

Interactions between individuals of different species that benefit both partners

Facultative mutualism

Occurs when a species can live without its mutualistic partner

Obligate mutualism

Occurs when a species is dependent on a mutualistic relationship

Plants benefit from mutualistic partnerships with a widevariety of

Bacteria, fungi and animals

_________ are the center of mutualistic relationships that affect structure and processes of terrestrial ecosystems

• Nitrogen fixation.

• Nutrient absorption.

• Pollination.

• Seed dispersal

Plants

Mycorrhizal fungi provide plants with

Greater access to inorganic nutrients (K, Cu, Zn, N).

Two most common types of mycorrhizae

Arbuscular mycorrhizal fungi (AMF) and Ectomycorrhizae (ECM)

Arbuscular mycorrhizal fungi (Endomycorrhizae)

Fungus produces arbuscules (exchange sites), hyphae (fungal filaments), and vesicles (energy storage organs). in 85% of plant species, including grains and legumes.

Ectomycorrhizae

Fungal mycelium forms dense sheath over surface of root. Hyphae form a network in apoplast, but do not penetrate root cells walls

Ectomycorrhizae is in

10% of plant families including pine, spruce, oak, walnut, birch, willow and eucalyptus

Apoplast

The network of cell walls and intercellular spaces within a plant body that permits extensive extracellular movement of water within a plant

Why is in Endomycorrhizae in so many plant species?

Because both the plant and the fungus benefit, so evolution kept this partnership.

Arbuscules

Specialized branching hyphae that are found in some mutualistic fungi and exchange nutrients with living plant cells.

Do ectomycorrhizal fungi penetrate root cells?

No, they only surround the root and stay outside cells.

Do endomycorrhizae penetrate the root cell wall?

Yes, but they do not cross the plasma membrane.

What structure do endomycorrhizae form inside root cells?

Arbuscules (sites of exchange).

Hyphae

Fungal filaments that extend into soil for absorption.

What are vesicles in arbuscular fungi?

Fungal energy-storage organs

Why do plants with mycorrhiza grow better?

Fungi increase water and phosphorus access

What happened when nutrients were added to soil in nutrient experiment?

Plants with mycorrhiza had higher shoot mass.

Inflorescence

A group of flowers tightly clustered together.

When did plants make inflorescences in nutrient experiment?

Only when nitrogen was added.

What happened with fungi from fertilized soil in nutrient experiment?

They produced fewer flowers than fungi from unfertilized soil

What do acacia trees give ants?

Thorns for shelter, nectar, and Beltian bodies

What do ants give acacia trees?

Protection from herbivores and competing plants.

What happened to acacias without ants?

More herbivores, slower growth, lower survival

Why don't acacia flowers produce nectar?

To avoid attracting ants that would interfere with pollinators.

What organisms live inside corals?

Zooxanthellae (dinoflagellate algae).

What do corals give zooxanthellae?

Nutrients and a protected place to live.

What do zooxanthellae give corals?

Organic carbon made from photosynthesis

Zooxanthellae give corals _______ fixed carbon

90-99%

When will mutualism evolve?

When benefits > costs.

Successful mutualist

One that gives and receives benefits.

Nonmutualist

A species that gives nothing and receives nothing.

Unsuccessful mutualist

Gives but does not receive benefits

When will plants evolve to attract ants?

When ant protection saves more energy than nectar costs