When fungi spread through a fallen log, they leave behind a web of tiny threads that quietly break down wood and recycle nutrients. For a long time, scientists assumed most of that network simply stayed behind as the fungus moved on.
But new research shows that some forest fungi don’t just grow forward – they tear down and reuse large parts of their own threadlike networks as they expand.
Instead of abandoning old growth, they pull nutrients back in and redeploy them. This newly discovered recycling strategy could reshape how scientists estimate forest carbon storage.
If some fungi leave less material behind in the soil than expected, it changes how much carbon forests ultimately lock away over time.
Inside the fungal network
Inside clear chips carved with microscopic channels, fungal networks left behind visible traces of which threads stayed alive and which were stripped back.
By tracking those changes over weeks, Dr. Dimitrios Floudas at Lund University documented how certain species actively reclaimed older growth while continuing to expand.
In several cases, fungi that appear slow and steady on tree trunks recycled their internal resources faster than short-lived species that colonize twigs and branches.
That split between recyclers and leavers sets up a larger question about how different fungal lifestyles shape what ultimately remains in forest soils.
Wasteful vs. frugal fungi
Across each colony, the frugal fungi pulled resources back through mycelium – the living web of fungal filaments – before pushing into new territory. The study captured how quickly that recycling happened as the networks expanded outward.
“The results show that the studied fungi can be divided into groups based on two clear strategies,” said Floudas.
“There is a ‘wasteful’ group that leaves large amounts of inactive mycelium behind, and a ‘frugal’ group that quickly recycles the major part of its mycelium during growth.”
Those labels describe a trade-off between leaving behind empty cell walls and reclaiming nutrients for the next push forward – and that trade-off plays out differently depending on the wood the fungi inhabit.
On fallen twigs and small branches, fast colonizers often run out of time before recycling can help them. Short-lived wood patches push those fungi to keep moving, even if they abandon nutrients behind them.
Across bigger logs and standing trunks, long-lived species regained nutrients by dismantling older growth and reducing food for grazers.
That link between habitat and thrift suggests forest carbon storage may depend on which fungi arrive first and dominate.
Recycling without collapse
Under magnification, the slow-looking trunk fungi recycled fastest, pulling nutrients back even while the colony still expanded.
Using microfluidic chips – lab devices that steer liquid through tiny channels – researchers watched the network thin without killing it.
Small pockets of living threads stayed behind as a reduced network, ready to restart growth when resources improved. Such persistence could help a fungus hold its territory on a log, even after a lean spell.
Fungi adapt to tough food
The type of food available in the chips changed how the fungi behaved – even when the same species grew in the same space.
When simple sugars were available, the fungi kept growing longer and didn’t need to tear down as much of their network to reuse the nutrients.
But when the only option was a tougher, wood-like material similar to cellulose, the fungi recycled their older growth more aggressively.
Breaking down that harder food takes more effort, so they had to manage their resources more carefully.
This shows that a single fungal species can act differently depending on what it’s eating – growing more freely when food is easy, and becoming more frugal when nutrients are harder to extract from real wood.
Hungry neighbors compete
Around a fungal network, tiny animals and microbes treat fresh growth as food – and they take what they can. By recycling internally, a frugal fungus pulls nutrients out of older strands, leaving less for springtails and mites.
Wasteful species leave more inactive material behind, giving competitors more places to invade and more material to graze.
Those side effects can steer decomposition rates, since consumers and rival microbes often determine how long fungal presence persists. But the story does not end when fungi thin out or die.
Dead fungal material does not vanish at once. Its chemistry can influence carbon sequestration – the long-term storage of carbon in biomass or soil.
In forest soils, necromass – dead microbial remains that can linger for years – makes up about 35 percent of soil carbon, and roughly two-thirds of that comes from fungi.
Some fungal cell walls contain melanin, a dark pigment that strengthens the walls, slows decay, and keeps carbon in soil longer.
If wasteful fungi leave more material behind, forests may gain short-term soil carbon even while those fungi spend nutrients freely.
Predicting carbon with fungi
In climate models, small assumptions about fungi add up fast, because forests span huge areas and store enormous carbon.
To predict long-term storage, modelers need traits like how quickly mycelium is recycled instead of left behind. Data from lab chips can sort species into behavior groups, but only if scientists test many more fungi.
Real forests add uneven wood, drought, and competition, so field checks will decide how well these patterns hold.
Balance on the forest floor
Across a forest floor, many fungi share the same fallen wood, and each one handles leftovers in its own way.
When frugal recyclers dominate, they keep nutrients circulating inside living growth, limiting what other organisms can siphon away.
“Fungi play a crucial role in carbon sequestration in our forests,” said Dr. Floudas.
Because forest fungi do not all manage their networks the same way, those differences can ripple into how much carbon ultimately remains stored.
Keeping a mix of fungal strategies may steady forest carbon outcomes, since each leaves a different legacy in the soil.
More tests in real wood – with animals and rival microbes present – will help clarify where recycling boosts carbon storage and where it does not.
The study is published in the journal New Phytologist.
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