can plants talk?

thescientist |  It’s every plant’s worst nightmare. In the fall of 2009, in a Victorian greenhouse at the Cruickshank Botanic Garden at the University of Aberdeen in Scotland, Zdenka Babikova sprinkled vegetation-devouring aphids on eight broad bean plants and sealed each plant’s leaves and stems inside a clear plastic bag. This was no act of malice, though; it was all in the name of science. 

Babikova, a PhD student at the University of Aberdeen, knew that aphid-infested bean plants release odorous chemicals known as volatile organic compounds (VOCs) into the air to warn their neighbors, which respond by emitting different VOCs that repel aphids and attract aphid-hunting wasps. What she didn’t know was whether the plants were also sounding the alarm beneath the soil surface.

Five weeks earlier, Babikova filled eight 30 cm–diameter pots with soil containing Glomus intraradices, a mycorrhizal fungus that connects the roots of plants with its hyphae, the branching filaments that make up the fungal mycelium. Like a subterranean swap meet, these hyphal networks facilitate the trade of nutrients between fungi and plants. In each pot, Babikova planted five broad bean plants: a “donor” plant surrounded by four “receiver” plants. One of the receivers was allowed to form root and mycorrhizal contact with the donor; another formed mycorrhizal contact only, and two more had neither root nor mycorrhizal contact. Once the mycorrhizal networks were well established, Babikova infested the donor plants with aphids and sealed each plant in a separate plastic bag that allowed for the passage of carbon dioxide, water, and water vapor but blocked larger molecules, such as the VOCs used for airborne communication.

Four days later, Babikova placed individual aphids or parasitoid wasps in spherical choice chambers to see how they reacted to the VOC bouquets collected from receiver plants. Sure enough, only plants that had mycorrhizal connections to the infested plant were repellent to aphids and attractive to wasps, an indication that the plants were in fact using their fungal symbionts to send warnings.¹