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{Nature_and_Environment.122.16}: Jay Hoffman {resist} Sun, 06 Dec 2020 12:38:26 CST (82 lines)

Trees appear to communicate and cooperate through subterranean
networks of fungi

Trees and fungi form partnerships known as mycorrhizas: Threadlike
fungi envelop and fuse with tree roots, helping them extract water and
nutrients like phosphorus and nitrogen in exchange for some of the
carbon-rich sugars the trees make through photosynthesis. Research had
demonstrated that mycorrhizas also connected plants to one another and
that these associations might be ecologically important, but most
scientists had studied them in greenhouses and laboratories, not in
the wild.

By analyzing the DNA in root tips and tracing the movement of
molecules through underground conduits, Suzanne Simard has discovered
that fungal threads link nearly every tree in a forest — even trees of
different species. Carbon, water, nutrients, alarm signals and
hormones can pass from tree to tree through these subterranean
circuits. Resources tend to flow from the oldest and biggest trees to
the youngest and smallest. Chemical alarm signals generated by one
tree prepare nearby trees for danger. Seedlings severed from the
forest’s underground lifelines are much more likely to die than their
networked counterparts. And if a tree is on the brink of death, it
sometimes bequeaths a substantial share of its carbon to its

Before Simard and other ecologists revealed the extent and
significance of mycorrhizal networks, foresters typically regarded
trees as solitary individuals that competed for space and resources
and were otherwise indifferent to one another. Simard and her peers
have demonstrated that this framework is far too simplistic. An old-
growth forest is neither an assemblage of stoic organisms tolerating
one another’s presence nor a merciless battle royale: It’s a vast,
ancient and intricate society. There is conflict in a forest, but
there is also negotiation, reciprocity and perhaps even selflessness.
The trees, understory plants, fungi and microbes in a forest are so
thoroughly connected, communicative and codependent that some
scientists have described them as superorganisms. Recent research
suggests that mycorrhizal networks also perfuse prairies, grasslands,
chaparral and Arctic tundra — essentially everywhere there is life on
land. Together, these symbiotic partners knit Earth’s soils into
nearly contiguous living networks of unfathomable scale and

Depending on the species involved, mycorrhizas supplied trees and
other plants with up to 40 percent of the nitrogen they received from
the environment and as much as 50 percent of the water they needed to
survive. Below ground, trees traded between 10 and 40 percent of the
carbon stored in their roots. When Douglas fir seedlings were stripped
of their leaves and thus likely to die, they transferred stress
signals and a substantial sum of carbon to nearby ponderosa pine,
which subsequently accelerated their production of defensive enzymes.

Forests function as some of the planet’s vital organs. The
colonization of land by plants between 425 and 600 million years ago,
and the eventual spread of forests, helped create a breathable
atmosphere with the high level of oxygen we continue to enjoy today.
Forests suffuse the air with water vapor, fungal spores and chemical
compounds that seed clouds, cooling Earth by reflecting sunlight and
providing much-needed precipitation to inland areas that might
otherwise dry out. Researchers estimate that, collectively, forests
store somewhere between 400 and 1,200 gigatons of carbon, potentially
exceeding the atmospheric pool.

When a seed germinates in an old-growth forest, it immediately taps
into an extensive underground community of interspecies partnerships.
Uniform plantations of young trees planted after a clear-cut are
bereft of ancient roots and their symbiotic fungi. The trees in these
surrogate forests are much more vulnerable to disease and death
because, despite one another’s company, they have been orphaned.

Diverse microbial communities inhabit our bodies, modulating our
immune systems and helping us digest certain foods. The energy-
producing organelles in our cells known as mitochondria were once
free-swimming bacteria that were subsumed early in the evolution of
multicellular life. Through a process called horizontal gene transfer,
fungi, plants and animals — including humans — have continuously
exchanged DNA with bacteria and viruses. From its skin, fur or bark
right down to its genome, any multicellular creature is an amalgam of
other life-forms. Wherever living things emerge, they find one
another, mingle and meld.


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