What is the role of mycorrhizal fungi in plant nutrition, and how might a gardener inoculate new plantings?

• A. They extend the root network and improve water and nutrient uptake; inoculate with commercial mycorrhizal products or soil inoculants
• B. They deter pests; apply pesticides
• C. They photosynthesize for the plant; spray with fertilizer
• D. They fix atmospheric nitrogen; use compost tea

Answer: (A)

Mycorrhizal fungi form a mutualistic relationship with plant roots, effectively extending the plant’s root system through their network of hyphae. This expanded network increases the surface area for water and nutrient uptake, especially phosphorus and certain micronutrients, and can help plants tolerate drought and poor soils. In return for sugars produced by the plant, the fungi receive energy to sustain this partnership.

When planting new plants, inoculating can give these beneficial fungi a helping hand. Use a commercial mycorrhizal inoculant or a soil inoculant labeled for your plant group, and apply it at planting—either by coating the roots, mixing with the planting medium, or placing it in the planting hole around the root zone. For best results, choose an inoculant appropriate for the plant type (many garden plants form arbuscular mycorrhizae, while some trees form ectomycorrhizae) and follow the product’s instructions. It’s good to know that native soils often already contain mycorrhizal fungi, so inoculation is especially useful when soil has been disturbed or sterilized, or for plants that have establishment difficulties. Also, avoid using fungicides that can kill beneficial fungi while the new roots are trying to establish.

Pests are not the primary role of these fungi, so treating with pesticides isn’t how they function. They don’t photosynthesize for the plant, nor do they provide nitrogen by fixing atmospheric N2; their benefit is mainly in nutrient and water uptake through the expanded root network. Inoculation, coupled with good soil health and watering practices, helps plants access nutrients more efficiently and establishing a thriving root system.