Listening in on the Language of Soil

In soil, word gets around.

While we scroll through our newsfeeds to stay updated, plants and microbes tap into a network of underground chemical signals to get the latest dirt on their surroundings.

But how do we find out who’s talking? And why?

Laura Meredith, an assistant professor for the School of Natural Resources and the Environment, is listening in on what’s driving these plant-microbe interactions.

Meredith’s Lab, located at the BIO5 Institute, studies how the gaseous subset of these signals, volatile organic compounds (VOCs), are processed and what they mean for soil microbiome health and composition.

Picture of Parker Geffred at the lab bench
Parker Geffre, a biochemistry junior at the University of Arizona, conducts research in Dr. Laura Meredith’s lab. Meredith’s research examines how microbial life affects soil-atmosphere emissions.

As microbes and plants live, they cycle nutrients, respond to stress, and adapt. VOC gases are released as a byproduct of these processes. Indirectly, VOCs send information about how, where, and why they were created due to them being process specific.

The scent of a fresh cut lawn is a familiar VOC example. While it may be a refreshing smell – in reality, it’s a harrowing distress call that tells neighboring plants damage has occurred to the VOC source. Grass roots, when exposed to these types of VOCs, grow thicker and more durable in response.

But VOCs can play a variety of roles beyond just acting as signals. Many VOCs are released only by certain species of microbes or plants. As a result, there’s evidence VOCs can also predict what organisms are in the soil, and detail what they consume and release into the air.

Following these developments, VOCs are being used more and more to communicate the importance of the soil microbiome’s role in large-scale environmental changes – like region wide responses to climate change, according to Meredith.

“We sometimes forget that a gram of soil contains billions of microbes. VOCs already play an important role in air quality and climate, but increasingly we are recognizing that in addition to plants, microbial life in soil can cycle VOCs in ways that impact the atmosphere,” Meredith said.

Yet listening in, identifying, and quantifying these signals is no easy feat. Soil VOC gases are released only in trace amounts, requiring highly sensitive and expensive sensors. Often, these detectors are unfit to function in real-world soil environments, such as outside in fields or other large areas.

“We are talking about trying to find a drop in a lake, a scale of parts per billion. State-of-the-art VOC detectors can cost the price of a new house – around $400,000,” explained Parker Geffre, a biochemistry junior and undergraduate of Meredith lab.

For the past summer, VOC detection has driven Geffre’s research in the Meredith lab. Affordable science is accessible science, and one of Meredith lab’s key goals is to assist in the development of low-cost soil VOC sensors for future research.

Meredith lab has partnered with Aerodyne Research Inc. and QuantAQ, Inc., industry leaders in atmospheric monitors. Together, their partnership focuses on developing new VOC measurement capabilities and demonstrating them in field deployment.

Like with any trend of technological development, shrinking the size of the sensor’s components and working with artificial intelligence is on the docket

“Instead of using a single expensive VOC sensor to analyze a large area, many low-cost sensors are going to be linked together. This expansive web of data will be analyzed and processed using advanced data techniques, like machine learning,” Geffre said.

Currently, Geffre is examining how sensitive and reliable the novel sensor’s VOCs detection capabilities are at Aerodyne’s headquarters in Boston, MA.

By developing a network of VOC detectors, it could change how researchers measure and classify VOCs in real-time. Meredith believes this new sensor data could also elevate the importance of investigating the microbiome’s effect on soil-to-atmosphere emissions.

While development and testing of the sensor is in its infancy, it’s already had immediate and positive effects in bridging academia and industry VOC research together – opening up new opportunities for undergraduates.

“One of the thrusts of my NSF CAREER award is to develop an industry internship for UA undergraduate students at companies on the forefront of sensor research and development. This was inspired by my own career path, where an industry internship at a large chemical company helped refine my educational and research goals,” Meredith expressed.

For Geffre, having the chance to explore different research settings has positively impacted her educational career, helping her discover her passion for science and research.

“I don’t believe in going through any experience with tunnel vision. I’m grateful that I’ve been able to experience research outside of my interests in biochemistry or forensics. Traveling to do work out-of-state has opened my eyes to the opportunities available to me, and other ways I can make an impact with my education,” Geffre said.

Meredith and Geffre’s research is supported by the National Science Foundation and the UA’s Undergraduate Biology Research Program.