PHOTO: RALF GEITHE/ISTOCK.COM14 7 JANUARY 2022 • VOL 375 ISSUE 6576 science.org SCIENCENEWS | IN DEPTHI
nventorying the plants in a tract of woods
or fields or searching for invasive species
can take days of hot, hard work slogging
through thorny brush and tick-infested
grass. Now, researchers have shown that
simply capturing and analyzing the DNA
plants release into the air can work as well
as putting boots on the ground—and in some
cases even better.
“Airborne DNA could be a game changer
in our ability to monitor and study bio-
diversity,” says Kristine Bohmann, a molecu-
lar ecologist at the University of Copenha-
gen who was not involved with the work.
The approach could help track how climate
change is altering the makeup of
plant communities, researchers say,
and provide early warning of invad-
ing species.
Reported last month in BMC Eco-
logy and Evolution, the work takes
the study of environmental DNA
(eDNA)—genetic material shed, def-
ecated, coughed up, or otherwise re-
leased into the environment—into a
new realm. Aquatic eDNA is now a
proven tool for identifying fish and
other marine and freshwater organ-
isms, with no need to catch them. In
soil, eDNA can reveal the presence
of people and animals, current or
ancient. “The time is right to look at
another source,” says Elizabeth Clare,
a molecular ecologist at York Univer-
sity who has tracked animal species
with airborne eDNA.
Plants already emit airborne
tracers that are familiar to anyone with al-
lergies: windborne pollen. The grains’ dis-
tinctive shapes make it possible to identify
unseen species simply by capturing their
pollen. But pollen surveys have their limits.
They can only detect plants whose pollen is
spread by wind (other types depend on pol-
linating insects and other animals), require
well-trained experts, and don’t always pro-
duce species-specific identifications. Mark
Johnson, a graduate student at Texas Tech
University, wanted to know whether study-
ing the eDNA that is shed into air not only
as pollen but also in minuscule fragments of
leaves or flowers would work better.
He and his colleagues developed better
ways to collect plant eDNA in dust traps, andin 2019 they demonstrated that the filters
capture DNA-bearing traces from all sorts of
plants. “We could find species not flowering,
not pollinating, or when they are not active
like in the winter,” Johnson says.
Now, he has shown how eDNA can in-
ventory an entire plant community. He and
his colleagues mounted dust traps in nine
places across a well-studied short grass prai-
rie owned by his university. They collected
the dust every couple of weeks for 1 year,
extracted the DNA, and sequenced a gene
that varies among plant species, serving as
a “DNA barcode” for identifying them. In the
spring and again in the fall, his team also
pulled on their boots and surveyed plants
along 27 100-meter transects. They com-pared the results of the two kinds of surveys.
The traditional surveys detected 80 spe-
cies and the air eDNA study 91, the team
reported. Both surveys uncovered the
same 13 grass species, but the eDNA work
found an additional 13. Among nonwoody
flowering plants, both approaches yielded
a total of 60 species, but each detected
20 or so that the other missed. eDNA was
better at finding easily overlooked species
with small flowers, such as weakleaf bur
ragweed. But people were better at spot-
ting plants too rare to release much eDNA,
particularly when they had showy flowers,
such as the chocolate daisy.
Airborne DNA also revealed tree of
heaven, an invasive plant not detectedby the survey. That’s encouraging, says
Loren Rieseberg, a plant evolutionary bio-
logist at the University of British Colum-
bia, Vancouver. “I think [airborne eDNA]
will be especially useful for detecting in-
vasive species before they become wide-
spread and difficult to get rid of.”
The technique recorded how the
abundance of different species changed
through time, including the rapid bloom
and growth of the tansy mustard in early
spring, which ground surveys missed.
“This [report] might encourage more re-
searchers to take up dust traps to comple-
ment” other kinds of surveys, particularly
at long-term study sites, says Fabian Roger,
an ecologist at ETH Zürich who was not
involved with the work.
Along with plant DNA, the filters
picked up DNA from fungi, and
other researchers have captured
insect, earthworm, and slug DNA
from the air. “Potentially air DNA
is incredibly diverse and represen-
tative of the full diversity of living
organisms,” Roger says. His own
eDNA survey of insects in the wild
detected just a fraction of the spe-
cies known to be present, but he ex-
pects sensitivity to improve with a
better understanding of how wind
and other conditions affect DNA
collection, and better technology.
Existing traps typically rely on
natural air flow to carry in particles
carrying eDNA, but the concentra-
tions can be very low. More efficient
filters, or traps with fans to suck in
air, could work better. “You need a
good system to trap the air,” agrees Crystal
Jaing, a molecular biologist at Lawrence
Livermore National Laboratory who has
been assessing high-altitude airborne mi-
crobes from specially equipped airplanes.
Joseph Craine, co-owner of Jonah Ven-
tures, a company commercializing eDNA
surveys, thinks the technology isn’t ideal
for large areas. “I can’t see the applica-
tion,” he says. Finely tuned spectroscopic
measurements from space are a better ap-
proach to surveying plants, he says.
But others point to how far aquatic eDNA
studies have come in recent years and think
air eDNA can do the same for monitoring
terrestrial life. Roger says: “Air has the po-
tential to be the ‘water’ over the land.” jPlants fill the air with their DNA, encased in the windblown pollen
seen here, as well as in tiny particles of leaves and flowers.By Elizabeth PennisiE C O L O GYPlant diversity is blowing in the wind
DNA in air reveals the plants below—and requires no tromping through bushes