We can finally find out what makes one of the world’s largest organisms so resilient

With huge networks of black tentacles stretching for miles beneath the ground, the Armillary group of fungi includes some of the largest organisms known to our planet.

An 8,500-year-old specimen of Armillaria ostoyae in Oregon covers 2,385 acres (3.7 square miles) with its mass of rhizomorphic tentacles and its weight is estimated to be around 7,500 to 35,000 tons – a mass and coverage that makes it a competitor for the world’s largest organism .

This incredible mass allows it to join the category of organisms of breathtaking size, like the magnificent grove of interconnected aspen clones known as Pando in Utah. And yet the huge mushroom largely appears to us as clusters of cute, independent mushrooms.

Armillary is a pathogenic vampire-type fungus that feeds on trees. It can drain the life of 600 types of woody plants and thus decimate the vegetation, causing farmers millions of dollars in damage.

(Debora Lyn Porter / University of Utah)

Above: Once inside a tree, branching white filaments grow from the penetrating rhizomorph which sucks water and nutrients from the flesh of the plant.

The ability of this parasitic fungus to grow so massive is in part due to its hardiness. Armillary is incredibly resistant to many biological control methods – typical fungicides can even stimulate its growth. It can also survive dormant in the soil for a remarkably long time without any food.

“These networks of mycelia and rhizomorphs have been shown to be dormant for decades in the environment when living hosts are not available, becoming active again as new hosts return,” explains the mechanical engineer at the University of Utah, Debora Lyn Porter and colleagues. in a recently published article, in which they investigated what makes the fungus so resistant.

Porter and his team used chemical analysis, mechanical testing, and modeling to take a close look A. ostoyae – compare samples cultivated in the laboratory and collected in nature from its tentacle-shaped rhizomorphs.

They found that only the wild fungus produced rhizomorphs with a shield layer that can protect the most sensitive tendrils from both chemicals and mechanical forces.

(Porter et al., Journal of the Mechanical Behavior of Biomedical Materials, 2021)

Above: Rhizomorph grown in the laboratory (blue arrows) compared to harvested rhizomorphs (red arrows).

“This outer layer is pretty tough,” said mechanical engineer Steven Naleway. “It’s kind of like hard plastic. For the natural world, it’s pretty sturdy.”

This layer has been darkened by melanin – a pigment known to provide fungi with various benefits, such as binding calcium ions which help neutralize toxins, such as insect acids. The wild fungal shield also had much smaller pores than those seen in lab grown rhizomes and had a more cohesive structure that left no room for weak spots.

“If you want to have some kind of human biocontrol, you have to fight this calcium and better penetrate this outer surface”, noted Naleway.

These properties provide the fungal tentacles with the force to apply enough pressure, with the help of enzymes, to pierce hard woody roots and steal nutrients from trees. And, with enough time, turns into a huge mass of mushrooms rivaling the largest living things on Earth.

Their research has been published in the Journal of the Mechanical Behavior of Biomedical Materials.

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