Some of the good fungus among our plants

On January 13 National Public Radio presented a segment on forests investigations by Suzanne Simard, a forestry ecologist, who worked out how trees in the forest can communicate and share resources by use of underground connections via fungi mycelium. It was very fascinating and the presentation is on TED  One has to wonder if such communications and sharing of resources happen outside of forests, but we do know that fungus and plants go together.

What is mycelium one might ask? Mycelium is the vegetative part of a fungus or fungus-like bacterial colony consisting of a mass of branching, thread-like hyphae. These vegetative components of fungi are less conspicuous than the reproductive fruiting stages that we recognize as mushrooms, but the mycelium often forms symbiotic relationships with the plants in our gardens. They also are important in breaking down material in ecosystems and in our compost piles. It can be seen in the compost pile as light grey threads. Mycelium is good at breaking down lignin, the woody parts of plants. In compost piles they operate best at temperatures less than 120 ºF. They are also good at breaking down and detoxifying hydrocarbons often found in industrial wastes such as oil and pesticides.

The mycelium, when in a symbiotic plant relationship, is termed mycorrhizae. The term comes from the Greek word ‘mykos’ meaning fungi and ‘riz’ referring to root and hence describes the symbiotic relationship between a fungus and the root of a vascular plant. There are actually two kinds of relationships; endomycorrhizae actually invade the plant root cells whereas ectomycorrhizae form a sheath around the root, but do not invade root tissues. Endomycorrhizae are also referred to in the literature as arbuscular mycorrhizae.

The fungi benefits from sugars that the plant produces and the plant benefits because the fungi shares phosphate, nitrogen, iron, copper and other minerals with the plant. The host plant may donate between 4 and 20% of its photosynthetically fixed carbon to the mycorrhizal fungus. Mycorrhizae also help increase the surface area of the plant root system because hyphae can spread beyond the nutrient depletion zone. The benefits of the mycorrhizae are most evident on poor soils where plants are nutrient challenged. Mycorrhizae also help protect plants from root pathogens and help plants withstand drought.

Fossil records indicate that these symbiotic relationships have been around for 400 to 450 millions years and these fungi are widespread in our environment. They likely helped plants adapt to a terrestrial existence as they colonized the earth. Approximately 80 % of all known land plant species form mycorrhizal interactions with these ubiquitous soil fungi. However, there can be situations where the mycorrhizae are not present because of construction or other soil disturbances. This is where entrepreneurs have come to the rescue by providing a variety of mycorrhizae for use in compost, greenhouses, agriculture, turf and other situations.

In doing research for this article, I came across a study made by a master gardener in another county were the MG had planted a variety of plants in the same soil mixture but with and without mycorrhizae. The test of the difference caused by the mycorrhizae was to measure the height of the plants. It actually did show differences, but they were small except for the Cardoon which with mycorrhizae was twice as tall as the one without the mycorrhizae. I think the study would have been more successful if they had used poorer soil for growing medium instead of the rich medium they used. This would perhaps have enhanced the effect the mycorrhizae. It is also unknown if they used the best mycorrhizae for the plants grown because there are lots of species.

However I have seen other studies where the plant size was markedly greater when mycorrhizae were present versus plants were it was absent. For example, potatoes grown with mycorrhizae present yielded 33 percent more by weight than potatoes grown without mycorrhizae. Cabbages and its relatives are one of the few plants that don’t have mycorrhizae helping them grow. For more information on kinds of mycorrhizae see: It is good to know that the fungus among us is not all bad and in fact vital to good gardening success.

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website:

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    Lee Miller

    Lee Miller is a University of Delaware graduate and retired fisheries biologist, he gardens on 10 acres and makes wine each year with the help of a cadre of friends. However, his first love is gardening and he grows various fruit trees, heirloom ... Read Full

    Marcy Sousa

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