Mycorrhizal Fungi

July 24, 2011

Photographer: Phil Lachman
Summary Author: Phil Lachman

The photo above shows a lovely group of mushrooms nestled against the trunk of a eucalyptus tree. The association between the fungi and the tree however is no accident. This is a mutualistic relationship, where the two species assist each other, and in fact probably would be poorer without each other. Mutualism is any relationship between two species of organisms that benefits both species. Up to a quarter of the mushrooms you see while walking through the woods actually make their living through a mutualistic relationship with the trees in the forest. Remember of course that the mushroom is just the reproductive structure of a far more extensive organism consisting of a highly intertwined mass of fine white threads called a mycelium.

The word mycorrhiza is derived from the Classical Greek words for "mushroom" and "root." In a mycorrhizal association, the fungal hyphae of an underground mycelium are in contact with plant roots but without the fungus parasitizing the plant. While it's clear that the majority of plants form mycorrhizas, the exact percentage is uncertain, but it's likely to lie somewhere between 80 and 90 percent. When the fungus’ mycelium envelopes the roots of the tree the effect is to greatly increase the soil area covered by the tree’s root system. This essentially extends the plant’s reach to water and nutrients, allowing it to utilize more of the soil’s resources. This mutualistic association provides the fungus with a relatively constant and direct access to carbohydrates, such as glucose and sucrose, supplied by the plant. In return the plant gains the benefits of the mycelium's higher absorptive capacity for water and mineral nutrients (due to comparatively large surface area of mycelium-to-root ratio), thus improving the plant's mineral absorption capabilities. Photo taken on May 7, 2011.

Photo details: Camera Maker: Canon; Camera Model: Canon EOS 50D; Focal Length: 70.0mm; Aperture: f/10.0; Exposure Time: 0.013 s (1/80); ISO equiv: 1250; Exposure Bias: -1.00 EV; Metering Mode: Matrix; Exposure: aperture priority (semi-auto); White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.