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Sick fir warns its neighbors
The neighbors become more resistant to disease. The signals travel through the underground fungal network that also moves carbon, nutrients, and water between trees, a web in which the biggest, oldest trees are the most highly connected.
If the neighbor is a birch, the fir also benefits from antibiotic-producing bacteria associated with the shared network. Together this works like a public immunization system.
The finding answered a question about whether a tree that is stressed or diseased could benefit from the health of its neighbors. Experiments showed that it can.
How do trees send warnings underground?
The warning travels as chemical signals through the fungal threads that link roots. In a 2010 study in PLOS ONE, Yuan Yuan Song and colleagues grew tomato plants connected by a shared fungal network. When they infected one plant with a leaf blight fungus, healthy neighbors on the same network raised their defense enzymes. Plants that were not connected through the network showed no such response.
How do root bacteria protect plants from disease?
Soil bacteria that live around roots and fungal threads can produce antibiotic compounds that suppress disease-causing microbes. They also crowd out pathogens by using up the space and food on root surfaces. Bacteria of the genus Streptomyces are especially prolific producers of such compounds. Streptomycin, one of the first antibiotics used in medicine, was isolated from a soil Streptomyces in 1943.
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