Mushrooms are the visible manifestations (sexual organs, actually) of microscopic, soil-dwelling fungi that form mutually-beneficial partnerships with plants.
Since these filamentous fungi interact with the roots of plants, such symbiotic relationships are called mycorrhizae, literally “fungus root”.
Fossil evidence supports the idea that these plant-fungal partnerships are as old as the emergence of terrestrial plants (about 500 million years ago).
Indeed, some scientists believe that mycorrhizae may have been critical for the successful colonization of land by plants.
The plants benefit because the mycorrhizal fungal network effectively increases the root surface area. This may help the plant take up water and mineral nutrients, such as phosphorus and nitrogen. The fungus gets sugars (carbohydrates) from the plants.
Over 90% of native plant species examined form mycorrhizae. That means in a typical forest or meadow, most of the plants’ roots are connected to fungal networks.
Is it possible that plants are inter-connected by these weblike fungal networks? Moreover, could chemical signals travel throughout this network?
Such questions have long intrigued plant scientists interested in mycorrhizae.
In 1997, a scientific paper was published that certainly stimulated interest in these questions. This report, by Dr. Suzanne Simard and colleagues, provided experimental evidence showing that radioactively-labeled carbon from one tree seedling could pass to an adjacent tree seedling via the mycorrhizal fungal network.
If carbon compounds such as sugars could travel from plant to plant via the mycorrhizal fungal network, then could small signaling molecules, such as plant hormones, also travel this way?
Where does this story stand today?
The initial report of carbon flow from plant to plant via mycorrhizal fungi has been tempered by subsequent research (such as this) that doesn’t support this idea.
Scientists are refining their techniques in order to provide unequivocal results regarding carbon flow via mycorrhizal networks under natural conditions in the field. This is a very challenging endeavor, indeed.
Though some new evidence (see ref. 1 below) suggests that carbon compounds may indeed travel from tree to tree via mycorrhizal networks, it is still uncertain whether such resource transfer is an important mechanism underlying tree seedling establishment.
Although it is unlikely that chemical signals, such as plant hormones, travel from plant to plant via common mycorrhizal networks (CMN), a recent report provides evidence that plant wound signals may do so (see ref. 2 below).
Bottom line: Despite tantalizing evidence that plants may “talk” via the “wood-wide web”, I think most plant scientists would agree that the jury is still out on this very interesting question.
1. Philip, L., S. Simard and M. Jones (2011) “Pathways for below-ground carbon transfer between paper birch and Douglas-fir seedlings.” Plant Ecology & Diversity, Vol. 3, pp. pp. 221-233. (Full Text)
2. Song, Y.Y., et al. (2010) “Interplant communication of tomato plants through underground common mycorrhizal networks.”, PLoS ONE, Vol. 5: e13324. (Full Text)
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