Question

With the help of a neat and labeled diagram explain VAM (vesicular-arbuscular mycorrhizae).

Answer 1

Hint: Arbuscular mycorrhiza is a type of mycorrhiza in which the symbiotic fungus (AM fungi, or AMF) penetrates the cortical cells of the arbuscle- forming roots of a vascular plant. Arbuscular mycorrhizas are characterized by the formation by fungi of the phylum Glomeromycota of unique structures, arbuscules, and vesicles.

Complete answer:
- The AM fungi are compulsory symbionts. They have limited saprobic capacity and rely on the plant for their carbon nutrition. The products of photosynthesis of the plant host are taken up as hexoses by AM fungi.
- Carbon transfer can occur via the arbuscules or intraradical hyphae from plant to fungi.
- Increased absorption of nutrients, particularly phosphorus, has been attributed to the key benefit of mycorrhizas in plants.
- This may be due to increased soil- contact surface area, increased nutrient transfer into mycorrhizae, a changed root environment, and increased storage.
- Mycorrhizal activity increases the available concentration of phosphorus in the rhizosphere.
- By selective uptake of ammonium-ions and by releasing protons, mycorrhizae lowers the root zone pH. The solubility of phosphorus precipitates is increased by decreased soil pH.
- Hyphal ammonium absorption also increases the supply of nitrogen to the plant as the inner surfaces of the soil accumulate and disperse ammonium through diffusion.
- AM fungal colonies and relationships between AM fungi and their plant hosts are influenced by global climate change.

Note:
- In recent analyses, under drought conditions, AM fungi have been shown to increase plant biomass and decrease plant biomass under simulated studies of nitrogen deposition.
- In reaction to elevated atmospheric carbon dioxide, arbuscular mycorrhizal fungi themselves have been shown to increase their biomass.
- Brassicaceae members do not create arbuscular mycorrhizal fungi on their roots.