Wood Wide Web
Agricultural scientists Yuan Yuan Song and coworkers at Guangzhou showed how tomato plants use their fungal internet to warn neighbors of attack. The researchers cultivated tomato plants in a shared plot, inoculated with the mycorrhizal fungus Glomus mosseae. Glomus forms particularly intimate arbuscular fungal connections that insert “arbuscules” or microscopic tree-like projections into the cytoplasm of host cells. When one of the tomato plants was infected with a pathogen, the fungal-connected neighbor plants proved resistant. The neighbor plants got the message from their internet, quickly producing anti-pathogenic enzymes for defense.
Other plants actually warn each other of aphid attack. David Johnson’s group at Aberdeen showed how fava beans fungal tweet their neighbors to repel aphids. The aphid-infected plants send signals via fungal connectors telling their neighbors to make salicylates, all-purpose aspirin-like defense molecules that repel aphids but attract aphid parasitoids.
What does an arboreal internet look like in nature? Real nature, that is, off the set of Avatar. Canadian and New York scientists mapped the fungal network for a plot of Douglas firs. The firs are linked at the roots by Rhizopogon fungi, known for forming mycorrhizal connections among roots. The scientists examined the pattern of fungal connections to characterize their network model. In a 30 x 30 meter plot, every tree was connected to every other, connected by no more than three fungal links. The modeled network was random and scale-independent, thus assuring the trees general access to fungal connections at all levels of forest size.
Most interesting, it seems that larger, older trees have greater numbers of fungal connectors, thus helping support the younger trees. This fungal support role implies the special importance of older trees, like hometree, for Eywa’s forest stability.