Sound is a fundamental aspect of the environment and is vital to ecosystems. One study found that playing sound effects to a common, plant-boosting fungus in the soil caused it to grow faster than fungi not exposed to the sound. This novel "ecoacoustic" approach holds the promise of restoring damaged ecosystems.
Studies have found that plants perceive sound as a mechanical stimulus that can facilitate the flow of nutrients, promote growth and strengthen the immune system. Now, a new study from South Australia's Flinders University suggests the same may be true for soil.
Researchers investigated how acoustic stimulation affects a soil-resident, plant-growth-promoting fungus, and whether it might be possible to use sound to restore damaged ecosystems.
"More than 75% of the world's soils are already degraded, so we need to take fundamental steps to reverse this trend and start restoring biodiversity," said Jake Robinson, first and corresponding author of the study. "This study surprised us by showing that the initial number of spore cell biomass of a common plant growth-promoting fungus increased almost fivefold compared to a control group where sound waves were at ambient levels."
The researchers began by burying regular green tea bags and rooibos tea bags underground to encourage the growth of fungal biomass, a renewable organic material from plants and animals. The tea bags were placed in a soundproof box and exposed to a monotonic sound field of 70 dB or 90 dB at 8 kHz. At the beginning of the experiment, no fungal biomass was visible in any tea bag, but after 14 days of acoustic stimulation, a large amount of dense fungal biomass was evident in the green and black tea bags in the 70 dB and 90 dB treatment groups, as well as on the inside and outside of each tea bag. In the control tea bags with ambient sound levels below 30 decibels, fungal biomass was much less visible.
The researchers then repeated the experiment in a laboratory setting, using petri dishes containing cultures of Mucor. Mucor is an effective biological control agent that kills a variety of soil pathogens and promotes plant growth. Twenty petri dishes were stimulated by 80 decibel monotonic sound waves with a frequency of 8 kilohertz for five days; 20 petri dishes were not stimulated at all. By day five, a strong effect of acoustic stimulation on fungal growth, spore growth, and spore density was observed. In petri dishes exposed to sound, spore activity increased approximately fivefold.
"Our laboratory's research on restoration ecology is paving the way for improved regrowth of native vegetation, including the reintroduction of lost species," said study co-author Martin Breed. "Our research into the potential to stimulate soil microbial activity taps into other innovative possibilities to help restore nature."
After revegetation, soil microorganisms take decades to fully recover. This study offers a potential "ecoacoustic" approach to speeding up this process. Further research is needed to investigate the mechanisms of sound effects on fungal growth and to determine whether certain sound parameters can target specific fungal species.
A preprint of the study is available on bioRxiv.