Picky Plants: Do They "Choose" The Best Fungal Partner?

Many plants form partnerships with fungi that live in the soil. Attached to the plant's roots, the fungus provides the plant with nutrients needed for growth---usually phosphorus—and the plant provides the fungus with something it needs, usually carbon. Many plants show increased growth when they team up with a fungus, but all fungi are not created equal. Depending on the environment, one fungus may cost the plant more or less carbon in exchange for the nutrients the fungus makes available to the plant.

And according to a paper to be presented at the annual meeting of the Ecological Society of America on Aug. 8 by U-M doctoral student Miroslav Kummel, "plants may be actively 'choosing' the species of fungus that supports the highest growth for the plant."

Depending on environmental factors such as soil type or amount of light, fungi differ in their effects on plant growth, and a plant living in the shade may be better off with a different fungus than a plant living in the sun. "Of course this is the result of long-term selection," says Deborah Goldberg, a professor of ecology and evolutionary biology and one of Kummel's faculty advisers, "but the consequences are the same as if it were a cognitive choice, and that's pretty cool."

Kummel looked at the distribution pattern of different types of fungi growing on balsam fir seedlings in an area with light conditions ranging from full sun to full shade. He found that a fir seedling living in the shade associates with a different fungus than a fir seedling living in the sun, and that it teams up with the fungus that "costs" the least, while still benefiting the plant.

The mechanism by which the plant "chooses" the fungus is not yet known. It could result from the plant selectively aborting roots that associate with the more "expensive" fungus or from selective growth of new root tips. By isolating pure cultures of different fungi to more closely examine the exchange of nutrients between plant and fungus, Kummel hopes to unravel this mechanism. These experiments are in progress. Ultimately, Kummel's work could have implications for the timber industry, as many of our pulp crops and commercial hardwoods also form associations with fungi.