Sound Waves Can Influence Soil Health and Diversity, According to New Study

When we typically think about ecosystem restoration, we imagine planting more native trees or perhaps reintroducing lost or declining species. Yet, one of the most critical approaches to ecosystem recovery lies in soil biodiversity. Soil fauna like earthworms and microbes like bacteria and fungi are primary contributors to the overall functioning of an ecosystem.

In a search to boost soil health, researchers have discovered a unique method to increase the growth of fungal biomass and organic matter decomposition – through playing soundscapes! Acoustic stimulation has shown promise in promoting a more dynamic and resilient soil microbiome, which can ultimately improve the overall health of an ecosystem in a non-invasive way.

How sound affects fungi

While fungi are unable to hear like we can due to the lack of auditory organs, research has found evidence that they can still respond to sound. For instance, one study discovered that 5kHz sound waves inhibited mycelium growth and spore production in a pathogenic fungi called Botrytis cinerea. The results indicated that high-frequency sounds could be used as a natural alternative to chemical pesticides (1).

In contrast, another study found that lower-frequency sounds could actually be beneficial to fungal growth. The fungi in the study that were treated with ultrasonic and acoustic sounds had larger growth and yields compared to ones without sound (2). 

Although sound is often overlooked as a contributing environmental factor, it heavily influences several ecological processes and shapes ecosystem dynamics. However, no studies have examined the effect of man-made sounds on soil microbes and plant growth. To fill this gap in missing information, researchers tested the potential of acoustic stimulation on important soil components to determine if the method could one day be used to aid ecosystem restoration.

Study findings

Using compost and tea bags, researchers played 70 and 90-decibel soundscape treatments at 8kHz, 8 hours a day for 14 days. “The humble teabag is often used in ecological studies to get information about soil decomposition,” explains Dr. Jake Robinson, a microbial ecologist at Flinders University and the study’s lead author, during an interview with Cosmos. “Green tea bags are more leafy, and the rooibos is more woody. [We wanted] to see if that had different effects on the decomposition rate, because you’d expect woody stuff to decompose slightly slower.”

Teabags treated with acoustic simulation were shown to have increased biomass and greater decomposition compared to the untreated control group. Though no fungi were directly added to the teabags, the preexisting microbial activities in the compost appeared to be significantly enhanced by the sound treatments. This suggests that sound waves at specific frequencies can stimulate the activity of soil microorganisms, leading to a more rapid breakdown of organic matter.

A second test was also conducted on a common soil fungus called Trichoderma harzianum, applying a monotone soundscape (80 decibels at 8kHz) over the course of five days. Once again, sound was shown to have a similar beneficial effect on microbial growth (3).

According to Robinson, “This fungal species is known to be beneficial for plants. We cultured it in petri dishes, and then did the same thing: we applied sound to the petri dishes, and we found that it significantly increased growth rate.”

Possible mechanisms and future research

As promising as the study’s results are, researchers are still unaware of how sound influences fungal growth. There are several hypotheses as to why this phenomenon occurs. 

One theory is the piezoelectric effect, which is caused by the generation of an electrical charge due to mechanical stress or pressure as a result of sound waves. Researchers believe that this electrical stimulation can enhance microbial activity and also lead to changes in the physical structure of the soil. These structural changes may increase the soil’s capacity to retain nutrients and water, leading to a more favorable environment for fungal growth. 

Furthermore, fungi possess mechanoreceptors that can detect and respond to physical stimuli like vibrations or mechanical pressure from soundwaves. It is hypothesized that when these receptors are activated, they trigger a cascade of cellular signals within the fungi, including growth-promoting responses like increased enzyme activity, enhanced nutrient uptake, or accelerated cell division. These responses would be beneficial to both the fungi’s growth rate and its ability to decompose organic material more efficiently.

“We don’t know too much about it yet. The next step is trying to understand the mechanisms, and where we can select for different sounds to promote different communities in the soil,” says Robinson.

The study proposes that future research focuses on determining the optimal acoustic stimulation for plant microbes and directly testing these sound treatments in natural and farming environments to improve their health and function. More studies will also be needed to study potential unintended consequences on microbial communities; however, the work is still a significant stride forward in using sound as a tool for restoring soil ecosystems. 

References

1. Binti Hasnoel Mazidi, Mazlin Nur Iman, Roshita Ibrahim, and Tan Soon Teck. 2020. “Comparison of Ultrasonic and Acoustic Sound Treatments on Grey Oyster Mushroom (Pleurotus Sajor-Caju) Cultivated on Sawdust and Kenaf Waste.” IOP Conference Series: Materials Science and Engineering 932 (December): 012005. https://doi.org/10.1088/1757-899x/932/1/012005.
2. Jeong, Mi-Jeong, DongWon Bae, Hanhong Bae, Soo In Lee, Jin A. Kim, Sung Chul Shin, Sung Han Park, and Soo-Chul Park. 2013. “Inhibition of Botrytis Cinerea Spore Germination and Mycelia Growth by Frequency-Specific Sound.” Journal of the Korean Society for Applied Biological Chemistry 56 (4): 377–82. https://doi.org/10.1007/s13765-013-3088-7.
3. Robinson, Jake M, Christian Cando-Dumancela, and Martin F Breed. 2024. “Sonic Restoration: Acoustic Stimulation Enhances Soil Fungal Biomass and Activity of Plant Growth-Promoting Fungi.” BioRxiv, January. https://doi.org/10.1101/2024.01.11.575298.