A start-up has begun planting fungi and other microbes in soil collected from intact forests at a tree plantation in the state of Georgia. The effort to “rewild” the soil microbiome may help to grow healthier trees that store more carbon.
Fungi and other microbes in soil are important factors for tree growth and health. Many species of mycorrhizal fungi, for instance, have evolved to form symbiotic partnerships with certain tree species, helping roots access nutrients in exchange for food in the form of carbohydrates produced by the trees.
“They’re completely dependent on the photosynthetic products coming from the tree,” says , an ecologist at ETH Zürich in Switzerland and founder of Funga, the company behind the Georgia project. Disruptions from agriculture such as clear-cutting can kill these symbiotic fungi and alter the soil’s microbial diversity.
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With Funga, Averill is using soil from intact forests to inoculate newly planted trees to make them grow bigger and faster, generating carbon credits the company can sell. The concept is similar to faecal transplants for gut microbiome disorders, says Averill. “But we apply it to the forest.”
In mid-February, planters started inoculating soil on 40 hectares of a commercial loblolly pine plantation near Lexington, Georgia. The planting itself is straightforward: a scoop of soil from an area of intact forest is added to a hole where a sapling is planted. Identifying precisely which soil to scoop is more complicated.
“If you just plunk a tree in and inoculate it with some random fungus, it might work or it might not,” says at the University of British Columbia in Canada, who wasn’t involved in the project.
Over the past year, Funga researchers analysed tree growth rates and sequenced the DNA of soil microbes in 500 loblolly pine forests around the south-eastern US to determine which composition of microbes is associated with the most growth. They then collected these candidate microbes from the test site in Lexington and inoculated new saplings.
Averill says they also planted trees without the added soil to establish a baseline against which to compare any additional carbon stored by the inoculated trees.
Results won’t be available until the end of 2023, but Averill says similar methods increased forest productivity between 30 and 70 per cent at a research plot where he works in Wales.
He and his colleagues also analysed 81 experiments that examined how inoculating soil with wild microbiomes affected various types of plants in different ecosystems. They found a range of effects, from a small reduction of biomass to a more than 700 per cent increase. On average, plant biomass increased 64 per cent.
“It’s going to do something,” says at Boston University, though she says how much depends on a lot of factors, such as how degraded the soil is to begin with. She also says the effects of soil restoration are better understood with saplings than with older trees. “When they get older, will that initial inoculant be enough?”
Sourcing the soil poses another challenge, says Prescott. Many species of fungi can’t be cultured, and at larger scales, soil extraction could degrade the collection sites.
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