A million trees and counting have been inoculated with native fungi by a US start-up aiming to make the trees grow faster and store more carbon. Outside researchers say this could be effective, but they have concerns about disturbing microbial diversity in soil.
“On the scale they’re talking about, that’s a crapload of soil,” says at the University of British Columbia in Canada.
The forestry industry has long experimented with ways to improve growth by inoculating trees with species of mycorrhizal fungi, which exchange nutrients with tree roots. But results with single-species inoculants have been mixed. “These cookbooked, one-size-fits-all inoculants don’t really perform like wild-type inoculants do,” says at Funga, the Texas-based company behind the inoculations.
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Funga’s approach is to inoculate seedlings with wild soil collected from areas similar to where the trees will be planted. The idea is that a diversity of well-adapted microbial species will be more effective than generic inoculants, especially if the trees are planted in places where microbial diversity is depleted.
Bigger, faster-growing trees also pull more carbon from the atmosphere. Funga plans to sell carbon credits based on the additional growth attributed to the inoculation.
In February 2023, the company completed its first test plantings in Georgia. It has since inoculated around a million loblolly pine (Pinus taeda) seedlings, planting them in small plots across the south-east US. Ware says inoculated trees have seen a 30 to 60 per cent increase in growth compared with trees planted in the same plots without inoculation; smaller-scale experiments have shown similar changes in growth, although not always reliably.
The company now plans to inoculate millions more seedlings this year by with a seedling company called PRT-IFCO, which grows more than 600 million seedlings a year in nurseries across North America. “We see a product that allows trees to be bigger, stronger, sooner,” says , the company’s CEO.
To inoculate millions of trees at once, soil is first collected from forested donor sites that company surveys have found contain a diversity of microbes. This soil is then mixed with water and sprayed across seedlings at a nursery.
This approach could be effective in some contexts, says Hart. However, she is sceptical that it will work at large scales, given that native microbes are often already in the soil when trees are planted. “There’s absolutely no evidence we would need to manipulate the biodiversity in forested systems,” she says.
at the University of Kansas, who founded a start-up called MycoBloom that grows native mycorrhizae in the lab, thought Funga’s approach was promising. But she adds that collecting large amounts of soil from donor sites risks depleting the source of that native microbial diversity, and warns using “whole soil” inoculant could spread along with the beneficial fungi.
So far, Funga’s inoculations have only used soil collected from managed forests and tree farms where the soil would have been disturbed when the trees were harvested anyway, and Ware says they are careful to avoid depletion.
But disturbing soils could be a concern as they scale up, he says. “We don’t just want to be monetising topsoil. That seems like a slippery place to be.”
