Plant–microbe mutualism: Which statements about mycorrhizae and their effect on plant nutrition and water uptake are correct?

Introduction / Context:
Mycorrhizae are among the most important mutualisms in terrestrial ecosystems. They enhance plant growth, drought tolerance, and nutrient acquisition, especially phosphorus and micronutrients.

Given Data / Assumptions:

• Fungus–root association is mutualistic.
• Hyphae extend far beyond the root depletion zone.
• Benefits include improved water and nutrient uptake.

Concept / Approach:
Arbuscular mycorrhizal fungi form arbuscules inside cortical cells to exchange carbon for nutrients; ectomycorrhizae form mantles and Hartig nets around roots. In both cases, hyphae significantly increase effective absorptive area and access microsites inaccessible to roots, improving P, Zn, and water uptake.

Step-by-Step Solution:
Identify the nature of the association: mutualism benefiting both partners. Recognize the functional role: hyphal networks deliver nutrients and water. Attribute the benefit to increased surface area and soil exploration. Select the comprehensive choice including all correct statements.

Verification / Alternative check:
Field trials show improved shoot biomass and phosphorus content in mycorrhizal plants versus non-mycorrhizal controls under limiting P conditions.

Why Other Options Are Wrong:
Each individual statement is correct; “None” contradicts extensive evidence.

Common Pitfalls:
Assuming mycorrhizae only affect phosphorus; they also influence water relations and pathogen resistance.

Final Answer:
All of the above.