By Celia Llopis-Jepsen
A burgeoning billion-dollar industry woos farmers and gardeners with promises of achieving better, more environmentally friendly harvests through symbiotic fungi that bond with plant roots.
These fungal bonds can help plants thrive and can lock carbon that came from the atmosphere into the soil. But evidence has been piling up that shows buyers ought to eye with some skepticism the products that promise to produce them.
Now, University of Kansas scientists have combed through 250 commercial product trials detailed in peer-reviewed journals. Most of those trials checked to see if the promised fungi materialized on plant roots and helped the plants grow. And 88% of the time, the answer was no.
Problems that have cropped up in peer-reviewed studies at KU and elsewhere include:
- Some commercial products contain a pathogen that harms plants.
- Some contain undisclosed chemical fertilizer.
- Some don’t contain any spores for the beneficial fungi they’re meant to produce.
- Some contain spores that aren’t viable.
“These fungi can do awesome things,” lead author Liz Koziol said. “But not when they’re dead.”
Koziol is an assistant research professor at the Kansas Biological Survey and Center for Ecological Research, where she works with the world’s largest collection of the kind of symbiotic fungi that so many growers want in their soil. These are called arbuscular mycorrhizal fungi.
The paper in New Phytologist concluded with a plea for improving the industry. It said the U.S. “fully lacks regulations” on the quality of these products and on importing or exporting them. And it said these products could pose a risk of introducing invasive species.
“There is a pressing need for mandatory global regulation on product quality control,” the authors wrote.
Though it would cost money to enforce rules and independently evaluate products, researchers said they see significant potential for savings compared to how much money farmers and gardeners may be wasting.
Symbiotic fungi give plants vital nutrients. They also help the ground absorb water better, which improves resilience against both drought and heavy rain. They help plants cope with attacks from insects. And they protect against erosion, which is significant because U.S. farmland is losing soil faster than new soil forms.
All these benefits pique the interest of farmers and gardeners, but how can they browse the dizzying array of fungal inoculants for sale — and pick something that works?
“We need to have more transparency,” said Kirsten Hofmockel, a soil ecologist not involved in the KU research. She’s a senior scientist at the Pacific Northwest National Laboratory and recently served as president of the international Soil Ecology Society.
“There’s not a lot that the consumer can do at this moment without that transparency,” she added.
The microbiome ‘moment’
Eco-friendly soil products are a booming market for a reason.
“In a lot of ways, the microbiome is coming of age,” Hofmockel said, referring to microscopic life in the ground. “Soil health is having its moment.”
Scientific understanding of what makes soil productive has expanded greatly in recent decades. It’s amply clear that microbes play key roles. This has growers eager to explore beneficial bacteria and fungi. Many are seeking an alternative to chemical fertilizers.
“There’s a lot of legitimate concern about synthetic fertilizers,” Hofmockel said. “A lot of frustration about the cost and the environmental effects.”
The U.S.’ heavy reliance on these fertilizers since World War II boosted yields but exacerbated greenhouse emissions, polluted groundwater and surface water and fed a dead zone in the Gulf of Mexico.
Today, farmers and gardeners worldwide buy billions of dollars in microbe products each year, according to business analysts. They have linked this fast-growing market to the rising interest in organic and eco-friendly methods. Symbiotic fungi alone account for about $1 billion annually.
KU scientists published two studies this fall that focus on arbuscular mycorrhizal fungi (also called endomycorrhizal fungi on product labels).
One is their analysis of trials conducted by other scientists internationally. The other one, published in Applied Soil Ecology, laid out the results of a product study at KU.
For her research, Koziol bought 16 products on Amazon that were top sellers at the time of purchase. She also picked up two products stocked by one of the country’s biggest retailers of home improvement supplies. And she chose two from sellers that are building a niche market by targeting their soil health products to cannabis growers.
The study involved scouring the products for fungal spores, as well as testing the products in pots containing soil and seedlings for vegetables and grains.
Some of the packages didn’t contain spores. Some did but still failed to produce mycorrhizae.
On the whole, the study found commercial products bonded with roots at much lower rates than when academic scientists used fungi that they grow in-house.
Koziol said a product could underperform for a variety of reasons. Some companies may inadvertently expose their products to extreme temperatures during transport or warehouse storage, for example. Some may mix in other ingredients in ways that can harm the fungi.
Sellers generally don’t disclose their methods in detail, she said, but she wants the problems to get identified and resolved so consumers can tap into the potential of beneficial fungi.
One step that would help, she said, is for more companies to test whether their products are still good after they reach consumers.
“I don’t think that’s necessarily being done,” she said, “because as the end user of these products, they weren’t viable.”
In her papers, Koziol disclosed a potential conflict of interest. She runs a private business selling a mycorrhizal inoculant. The other authors on KU’s studies have not reported any potential conflicts of interest.
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