Fungal diversity and its relationship to the future of forests
If
you indulge in truffles, or porcini and chanterelle mushrooms, you have enjoyed
a product of ectomycorrhizal fungi. Forming symbiotic relationships with plants
-- including pine, birch, oak and willow tree species -- these fungi have existed
for millions of years, their sprawling filaments supporting ecosystems
throughout their reach.
According
to research from Stanford University, published Jan. 21 in the Journal
of Biogeography, by the year 2070, climate change could cause the local loss
of over a quarter of ectomycorrhizal fungal species from 3.5 million square
kilometers of North American pine forests -- an area twice the size of Alaska.
"These
are critical organisms for the functioning and the health of forests,"
said Kabir Peay, associate professor of biology in Stanford's School of
Humanities and Sciences and senior author of the study. "We have evidence
to suggest that these fungi are as susceptible to climate change as other kinds
of organisms and their response may be even more important."
Previously,
the Peay lab had mapped the global distributions of forests where trees
associate with different types of symbiotic fungi, finding that over 60 percent
of all trees on Earth currently associate with ectomycorrhizal fungi. Now, by
learning more about the communities these fungi form in different climates, the
researchers projected how climate change might affect them in the future.
Microbial maps
Over
several years, the Peay lab has gathered about 1,500 soil samples from 68 pine
forests, which represent a swath of North America from Florida to Alaska. In
past work, they sequenced DNA in each sample to understand what fungal species
live in that soil, and in what abundance. Their results, published previously,
suggested that fungi were different in each region, contradicting a common
assumption that those communities would look similar in most places in the
world. They followed that up by mapping the associations between trees and
symbiotic microbes around the world.
For
their latest paper, Brian Steidinger, a postdoctoral scholar in the Peay lab,
explored the relationship between these geographical fungi patterns and
historical climate data.
"We
took soil from the cores and climatic data unique to each site," said
Steidinger, who was lead author of the study. "We found that climate was
by far the most important predictor of contemporary fungal diversity patterns
across North America."
Steidinger
also found that different regions of North America had unique optimal
temperatures for fungal diversity. For example, cold boreal forests had a
diversity peak around 5 C mean annual temperature, while Eastern temperate
forests peaked in diversity near 20 C.
The
researchers then applied these data to predict future diversity, given
projections of climate change produced by the Intergovernmental Panel on
Climate Change. Because of the regional differences in optimal climate for
fungal diversity, some forests, particularly those in the North and Northwest,
could experience major decreases in fungal diversity.
"According
to our models, climate change over the next 50 years could eliminate more than
a quarter of ectomycorrhizal species inside 3.5 million square kilometers of
North American pine forests," said Steidinger. "That's an area twice
the size of Alaska."
Other
regions, such as the Eastern temperate forests, could experience gains of 30 to
50 percent -- assuming it is as easy to develop new species as to lose them.
"One
of the things that's kind of shocking and a little bit scary is that we predict
there will be some pretty significant decreases in diversity in western North
America, well known culturally for fungal diversity and for people who are
interested in collecting edible mushrooms," Peay said.
Buffering against climate change
Ectomycorrhizal
fungi form a sheath around their hosts' roots, which can help prevent erosion
and protect roots from damage and disease. The fungi seem to boost carbon
storage in soil by slowing down decomposition and encouraging the buildup of
soil. They also help their host trees grow more quickly -- and therefore take
in more carbon -- by improving their ability to take in nitrogen, which they
need in order to grow.
"In
terms of ecosystem function, particularly buffering the atmosphere against
climate change, ectomycorrhizal fungi are among the last microbes you want to
lose," said Steidinger. "We're expecting to lose the species that
seem to be the most functionally intense -- the ones with the greatest enzyme
activity, the ones that forage out the farthest."
Building
on this work, the researchers are considering studying forests with low
diversity of fungi and conducting experiments to better understand how these
altered fungal communities might function in the future.
"For
microbiome work, I feel like we're in a new era of discovery," said Peay.
"Like Darwin and Wallace getting on ships and going to new places and
seeing new things and changing the way they view the world, that is what is
happening in this field."
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