Plants in forest emit
aspirin chemical to deal with stress; discovery may help agriculture
Plants in a
forest respond to stress by producing significant amounts of a
chemical form of aspirin, scientists have discovered. The finding, by
scientists at the National Center for Atmospheric Research (NCAR),
opens up new avenues of research into the behavior of plants and their
impacts on air quality, and it also has the potential to give farmers
an early warning signal about crops that are failing.
who are advised to take aspirin as a fever suppressant, plants have
the ability to produce their own mix of aspirin-like chemicals,
triggering the formation of proteins that boost their biochemical
defenses and reduce injury," says NCAR scientist Thomas Karl, who
led the study. "Our measurements show that significant amounts of
the chemical can be detected in the atmosphere as plants respond to
drought, unseasonable temperatures, or other stresses."
For years, scientists
have known that plants in a laboratory may produce methyl salicylate,
which is a chemical form of acetylsalicylic acid, or aspirin. But
researchers had never before detected methyl salicylate in an
ecosystem or verified that plants emit the chemical in significant
quantities into the atmosphere.
The team of
scientists reported its findings last week in Biogeosciences.
The research was funded by the National Science Foundation, NCAR's
Researchers had not
previously thought to look for methyl salicylate in a forest, and the
NCAR team found the chemical by accident. They set up specialized
instruments last year in a walnut grove near Davis, California, to
monitor plant emissions of certain volatile organic compounds (VOCs).
These hydrocarbon compounds are important because they can combine
with industrial emissions to affect pollution, and they can also
influence local climate.
scientists used specially equipped towers to measure plant
emissions above the forest canopy of a walnut grove.
When the NCAR
scientists reviewed their measurements, they found to their surprise
that the emissions of VOCs included methyl salicylate. The levels of
methyl salicylate emissions increased dramatically when the plants,
which were already stressed by a local drought, experienced
unseasonably cool nighttime temperatures followed by large daytime
temperature increases. Instruments mounted on towers about 100 feet
above the ground measured up to 0.025 milligrams of methyl salicylate
rising from each square foot of forest per hour.
Karl and his
colleagues speculate that the methyl salicylate has two functions. One
of these is to stimulate plants to begin a process known as systemic
acquired resistance, which is analogous to an immune response in an
animal. This helps a plant to both resist and recover from disease.
The methyl salicylate
also may be a mechanism whereby a stressed plant communicates to
neighboring plants, warning them of the threat. Researchers in
laboratories have demonstrated that a plant may build up its defenses
if it is linked in some way to another plant that is emitting the
chemical. Now that the NCAR team has demonstrated that methyl
salicylate can build up in the atmosphere above a stressed forest,
scientists are speculating that plants may use the chemical to
activate an ecosystem-wide immune response.
show tangible proof that plant-to-plant communication occurs on the
ecosystem level," says NCAR scientist Alex Guenther, a co-author
of the study. "It appears that plants have the ability to
communicate through the atmosphere."
Guenther examines leaves in a California walnut grove where a
team of NCAR scientists discovered plant emissions of methyl
The discovery raises
the possibility that farmers, forest managers, and others may
eventually be able to start monitoring plants for early signs of a
disease, an insect infestation, or other types of stress. At present,
they often do not know if an ecosystem is unhealthy until there are
visible indicators, such as dead leaves.
signal is a very sensitive way to detect plant stress, and it can be
an order of magnitude more effective than using visual inspections,"
Karl says. "If you have a sensitive warning signal that you can
measure in the air, you can take action much sooner, such as applying
pesticides. The earlier you detect that something's going on, the more
you can benefit in terms of using fewer pesticides and managing crops
The discovery also
can help scientists resolve a central mystery about VOCs. For years,
atmospheric chemists have speculated that there are more VOCs in the
atmosphere than they have been able to find. Now it appears that some
fraction of the missing VOCs may be methyl salicylate and other plant
hormones. This finding can help scientists better track the impact of
VOCs on the behavior of clouds and the development of ground-level
ozone, an important pollutant.
Corporation for Atmospheric Research manages the National Center for
Atmospheric Research under sponsorship by the National Science
Foundation. Any opinions, findings and conclusions, or recommendations
expressed in this publication are those of the author(s) and do not
necessarily reflect the views of the National Science Foundation.