By now we have become familiar with the concept of a garden as an ecosystem or as a community with all sorts of associates, including plants, birds, insects and others. All of them complement each other and compete with each other. If you pull one thread of this tapestry, you can feel the repercussions in near and distant parts. But many times we don’t think about the partners underground. Their interconnections are just as complex, or even more so. I talked about the fungi called mycorrhizae in my recent post “Root Partners, Mycorrhiza”and want to take the subject a little further.
There are thousands of species of mycorrhizal fungi. They often intertwine with each other and with the roots of numerous plant partners of the same or different species. They also associate with soil bacteria, including valuable nitrogen-fixing bacteria. So they form an intricate network which can cover vast expanses of land. Some workers feel that the whole forest is one enormous partnership, which they call the “Wood Wide Web“. Such inter-connectivity confers tremendous resilience to a system.
A beautiful explanation of this web of life is the illustration “A Thousand Words” of the Australian Fungi Website. Although to me it is worth far more than a thousand words.
Let us skip #1 for now:
2 (green) and 3 (violet): Two mycorrhizal fungi, one produces above-ground mushrooms and the other below-ground truffles as fruiting bodies. The mycelium of #2 reaches three different trees, while that of #3 connects with just two trees. Both mycelia are surrounded by symbiotic bacteria.
4: A small tree, growing shaded under the canopy of larger ones. It may be getting some nourishment indirectly from them by means of the interconnecting mycelia.
5 (orange): Another type of mycorrhiza. It forms a different kind of fruiting bodies called corticioid; flat structures seen on decaying wood or on mosses. We see them as disease or decay, but more often than not corticioid fungi are mycorrhizal and thus significant parts of the plant community. This is another example of a largely ignored member of ecosystems. Who would think of their beneficial function with such plain appearance?
1: Finally, what would a society be without a few freeloaders? Two kinds are illustrated here.
1 (red): A parasitic mushroom, drawing food from a tree and returning nothing.
1 (black): Another kind of parasite; this time a flowering plant, such as Indian pipe. These plants have lost all chlorophyll and are dependent on fungi, not only parasitic ones as the one illustrated here but also mycorrhizal. So, indirectly they parasitize the trees.
You may be wondering what the bushy tailed little rascal perched on a pine tree is doing in an article on mycorrhizae. Squirrels, as well as other animals, are an integral part of a community. Many fungi need helpers to spread their spores. This is similar to the association between flowering plants and pollinators. The fleshy mushrooms provide food for small creatures such as squirrels, chipmunks and beetles. Truffles, being underground, resort to strong aromas to attract hungry seekers. In some cases, these odors resemble sexual pheromones, driving some male animals to distraction. Flying squirrels are very effective at finding truffles. Spores have a tough, acid-proof coating so they can survive the trip through the intestines if they get eaten and end up being deposited some distance from the parent organism.
A community made entirely of native organisms has evolved an optimal balance of the parts above and below ground. Disturbed soils have lost more than the flora above ground; they have also lost much of their native mycorrhizae and soil bacteria. Many invasive plants do well without these soil components (probably that is why they are so invasive). Non-natives, such as garlic mustard and thistle illustrate this situation. They prosper and prevent the growth of mycorrhizae and, by extension, the restoration of native plants. This is another tragic example of the ecological disruption caused by non-natives. In some cases it may be necessary to inoculate mycorrhizae when trying to restore disturbed soils.
I never cease to marvel at the constellation of relationships in a garden. It includes native plants, the insects that feed on them, the wildlife that feed on such insects, the pollinators, the birds that spread seeds, and, last but not least, the mycorrhizae, other soil organisms, and the animals that take care of the mycorrhizae reproduction.
More on mycorrhizae:
The Use of Mycorrhizal Fungi in Erosion Control Applications
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