Fabulous Friendly Fungi
Marion Jay

Have you ever grubbed around beneath a pine tree and found yourself unearthing a curious, whitish substance which seems woven into the soil? Then you have chanced upon one of the most essential components of life on Earth. Mycorrhizal fungi are a diverse array of ancient organisms, some 460 million years old, which evolved alongside the development of plant roots. The name derives from the Greek ‘myco’ (fungus) and ‘rhiza’ (roots).

A mycorrhiza is technically a symbiotic association between a fungus and a vascular plant system. There is a mutually beneficial relationship between the two organisms. The plant feeds the fungus via its roots, using carbohydrates translocated from its leaves. In return, the fungus offers access to a large surface area of mycelium (underground, threadlike fibres) with which to absorb water and nutrients, a far wider network than the plant’s own root-system. The net result is that the plant is healthier, has better disease resistance and increased drought tolerance.

Mycorrhizal fungi colonise plants in two ways; endomycorrhizal, occurring within the plant’s cell walls, and ectomycorrhizal which appears externally, in the rhizosphere (amongst the plant’s roots). One sugar-cube of soil can contain up to 20 metres of ectomycorrhizal mycelium.

Mycorrhizal fungi are vital in helping plants access nutrients normally ‘locked up’ in the soil, such as phosphorus, gathering the element in large quantities and producing enzymes which convert it into a usable form. This access to nutrients is particularly useful to plants growing in poor soils, and in fact it is in natural, uncultivated soils that mycorrhizal fungi are mainly to be found. Digging, manuring and fertilising the soil suppresses the fungus; it hates disturbance and adding nutrients appears to nullify its own productive function.

Approximately 80% of plants on earth take advantage of mycorrhizal fungi. Conifers would not exist without it (hence the mould under the pine tree), and orchid seeds cannot germinate without infection by a fungus. In the latter case, the fungus simply provides enough food for the seeds to grow. Many trees have symbiotic relationships with particular strains of mycorrhizal fungi. Alders, for example, are colonised by the boletus toadstool and several trees, including oak and hazel, host the mycorrhizal fungus responsible for producing truffles.

Recently, programmes such as Gardeners’ World have brought mycorrhizal fungi to the attention of gardeners, with Monty Don demonstrating the use of Rootgrow, an RHS product designed to ‘inoculate’ the soil with mycorrhiza at the time of planting. When I was a garden design student in the ‘90s, my tutor explained the benefits of symbiotic fungi long before the idea was commonly accepted. He advised us to take a handful of conifer litter containing the white mould and add it to the soil each time we planted a conifer. I have always done so, and nowadays I routinely sprinkle Rootgrow into the hole each time I plant anything. I have noticed a much quicker rate of establishment as a result, and the plant mortality rate is virtually nil.

Without mycorrhizal fungi, the world would not exist as we know it. There is a lot more research to be done into these symbiotic relationships. No doubt those of us interested in growing healthy plants will have our ears to the ground.

First published in the Hertfordshire Group Newsletter Autumn 2013
and subsequently in Cornucopia Issue 34.
© Copyright for this article: Marion Jay

This article was taken from a copy of Cornucopia that was published in 2014. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.