A forest often reverberates with the sounds of its inhabitants, especially after rainfall. Birds coo and caw, insects chirp and buzz, frogs squeak and roar.
But not all conversations in the woods can be heard – and not all of them include animals.
In a new study, scientists in Japan found intriguing evidence that rain may prompt some fungi to communicate using underground electrical signals.
The researchers focused on small, light brown mushrooms known as two-colored impostors (Laccaria two-tone), which they found growing on the floor of a secondary mixed forest at the Kawatabi Field Science Center of Tohoku University in Japan.
L. two-tone is an ectomycorrhizal fungus that forms symbiotic relationships with certain plants, including many large trees such as oaks and pines. It increases their supply of water and nutrients in exchange for carbohydrates.
In fact, previous research suggests L. two-tone may help some trees feeding animals indirectlylure insect relatives called springtails and possibly kill them with a toxin, sharing the animal’s nitrogen with their host trees.
While some mycorrhizal fungi invade the cell walls of their host plants, ectomycorrhizal fungi such as L. two-tone instead, build underground “sheaths” around the outside of a tree’s roots.
These sheaths are made of hyphae, the root-like filaments that fuel the growth of a fungus. When the hyphae of mycorrhizal fungi connect underground, they form interconnected systems known as mycorrhizal networks. It has been proposed that such underground networks act as a kind of “wood-wide web”, where entire forests communicate via chemical signals along tree roots and mycorrhizal fungi.
While mycorrhizal networks are real, there is too little evidence to know if they reach the scale and complexity often attributed to wood-wide webs. Many popular stories about this phenomenon are exaggerated, some scientists say.
Nevertheless, this study adds to a growing body of research that digs into the details of these relationships and reveals fascinating details about how they work.
Previous studies have shown that fungi produce variations in electrical potentials seemingly in response to changes in their environment, with evidence that these signals serve as a form of communication.
For example, a 2022 study found patterns of nervous electrical activity in some fungi that appear similar to the structure of human speech. The study identified up to 50 different “words,” or groups of spikes in electrical activity, generated by fungal networks.
Previous research has also shown that plants can send secret electrical signals underground, possibly even without the help of mycorrhizal fungi.
While spikes of electrical potential have been observed before in fungi, sometimes in response to water or other stimuli, most studies have focused on limited species of fungi grown on artificial media or collected from the field under laboratory conditions, the authors of the new paper say. study note .
In the new study, researchers attached electrodes to a cluster of six L. two-tone mushrooms they found growing on the side of a forest path.
The mushrooms were located near a jolcham oak (Quercus serrata) and a loose-flowered hornbeam (Carpinus laxiflora), both represent potential symbiotic tree species L. two-tone.
The researchers monitored the mushrooms’ electrical potential, measured in megavolts (mV), for about two days in late September and early October 2021.
However, that changed on October 1 when Typhoon Mindulle brought 32 millimeters of rain. One to two hours after the rainfall, the mushrooms started to show new signs of activity.
“In the beginning the mushrooms showed less electrical potential and we narrowed that down to the lack of precipitation,” say microbial ecologist Yu Fukasawa of Tohoku University. “However, the electrical potential began to fluctuate after rain, sometimes exceeding 100 mV.”
This fluctuation correlated with changes in both precipitation and temperature, according to Fukusawa and colleagues, whose analysis suggests that the electrical signal after rainfall showed evidence of signal transport between mushrooms.
This signal transport was especially strong between mushrooms closer together on the forest floor, the researchers report, and showed directionality.
While the new study is far from definitive, it adds another intriguing piece to the puzzle of what role fungi play in the oft-overlooked ecosystems hidden beneath forest floors.
“Our results confirm the need for further investigation of fungal electrical potentials in a real ecological context,” Fukasawa say.
The study is published in Fungus ecology.