What is the role of mycorrhizal fungi in horticulture?

• A. They fix atmospheric nitrogen for the plant.
• B. They extend the root system, improving water and nutrient uptake, especially phosphorus.
• C. They increase leaf chlorophyll production directly.
• D. They cause roots to become toxic to soil organisms.

Answer: (B)

Mycorrhizal fungi extend the plant’s root system with their hyphae, vastly increasing the area available to explore soil for water and nutrients. This is especially important for phosphorus, which moves slowly through soil and is frequently limited; the fungal network reaches tiny soil pores that roots alone can’t access, delivering more phosphorus and other nutrients to the plant. In return, the plant supplies the fungi with sugars, forming a beneficial symbiosis that also helps with drought tolerance and overall vigor. The fungi don’t fix atmospheric nitrogen themselves, so they don’t directly supply nitrogen to the plant, and they don’t directly cause leaves to become more chlorophyll-rich. They also aren’t used to make roots toxic to soil organisms; in many cases they help protect roots from pathogens. In horticulture, this symbiotic role is why inoculants are used to improve establishment and nutrient uptake, particularly in phosphorus-poor soils.