New research shifts model on how forests contribute to carbon sequestration

If you hear the words “carbon sequestration,” you might well think of dense forests filled with mighty trees.

But Ecologist Karina Clemmensen’s new research reported in Science magazine suggests that tiny fungi in the soil may deserve a little more credit for fighting global warming.

Clemmensen, of the Swedish University of Agricultural Sciences in Uppsala, says the primary way people thought carbon entered the soil was through leaves and branches that fall off of trees and are decomposed by fungus. But Clemmensen’s new research on boreal forests says there’s another group of fungi that also play an important role in sequestering carbon in the environment: Mycorrhiza fungi.

“They sit on the tree roots and receive carbon directly from the tree, which makes carbon into photosynthesis,” she said. “And they use that carbon to grow in the soil and produce biomass. And in return, as part of the symbiosis, they return nutrients and water to the tree. So they basically have the capacity to add carbon to the soil at depth.”

So the tree harvests the sunlight for the fungi, and the fungi does the processing to sequester the carbon.

These fungi aren’t the type that hikers would be familiar with. These fungi are growing like little threads in the soil.

“If you look closely on the root tips of the tree, you can see that the tips are normally rounded, and they can have different colors — and that’s the fungus that form those structures,” she said.

In her recent, Clemmensen learned that 50 to 70 percent of the carbon in the environment comes from these small, unseen fungus.

And these boreal forests are incredibly important to storing carbon in the environment.

“If you consider the boreal forest only, it’s 16 percent of the carbon stored in soil globally,” Clemmensen said.

But these fungus are also active in the Arctic forests — another major source of carbon storage.

“We think that those fungi have an equally big role in carbon sequestration in those areas,” she explained.

Through her research, Clemmensen learned that forests will continue to sequester carbon far into the future, if left undisturbed. Over even 1,000 years, she said, the forests will continue to harvest carbon from the environment.

That contradicts previous theories that said full-grown trees stopped absorbing carbon from the environment.

“A general thing to say here would be, OK, clear cutting in forest management would probably not be good for carbon sequestration,” she said.