I've always suspected that a family of living beings that are as
prolific as plants must be smarter than we give them credit for being.
After all, we can't even communicate very well with animals that we
KNOW are intelligent. Science is finally catching up with a gardener's
intuition.
Plants engage in self-recognition and can communicate danger to their
"clones" or genetically identical cuttings planted nearby, says
professor Richard Karban of the Department of Entomology, University of
California, Davis, in groundbreaking research published in the current
edition of Ecology Letters.
Sagebrush exhibits communication only when air contact is
allowed, says Rick Karban, shown here bagging sagebrush. When air
contact is blocked with plastic bags there is no indication that
communication has occurred.
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Karban and fellow scientist Kaori Shiojiri of
the Center for Ecological Research, Kyoto University, Japan, found that
sagebrush responded to cues of self and non-self without physical
contact.
The sagebrush communicated and cooperated with other branches of
themselves to avoid being eaten by grasshoppers, Karban said. Although
the research is in its early stages, the scientists suspect that the
plants warn their own kind of impending danger by emitting volatile
cues. This may involve secreting chemicals that deter herbivores or
make the plant less profitable for herbivores to eat, he said.
What this research means is that plants are "capable of more
sophisticated behavior than we imagined," said Karban, who researches
the interactions between herbivores (plant-eating organisms) and their
host plants.
"Plants are capable of responding to complex cues that
involve multiple stimuli," Karban said. "Plants not only respond to
reliable cues in their environments but also produce cues that
communicate with other plants and with other organisms, such as
pollinators, seed disperses, herbivores and enemies of those
herbivores."
In their UC Davis study, Karban and Shiojiri examined the
relationships between the volatile profiles of clipped plants and
herbivore damage They found that plants within 60 centimeters of an
experimentally clipped neighbor in the field experienced less leaf
damage over the season, compared with plants near an unclipped
neighbor. Plants with root contact between neighbors, but not air
contact, failed to show this response.
"We explored self-recognition in the context of plant
resistance to herbivory," he said. "Previously we found that sagebrush
(Artemisa tridentata) became more resistant to herbivores after
exposure to volatile cues from experimentally damaged neighbors."
The ecologists wrote that "naturally occurring herbivores caused
similar responses as experimental clipping with scissors and active
cues were released for up to three days following clipping. Choice and
no-choice experiments indicated that herbivores responded to changes in
plant characteristics and were not being repelled directly by airborne
cues released by clipped individuals."
In earlier research, Karban found that "volatile cues are
required for communication among branches within an individual
sagebrush plant. This observation suggests that communication between
individuals may be a by-product of a volatile communication system that
allows plants to integrate their own systemic physiological processes."
The scientists made cuttings from 30 sagebrush plants at the UC
Sagehen Creek Natural Reserve and then grew the cutting in plastic
pots. They grew the cuttings at UC Davis and then placed the pots near
the parent plant or near another different assay plant (control group)
in the field.
The research, "Self-Recognition Affects Plant Communication and Defense," is online.
Their grant was funded by the U.S. Department of Agriculture Hatch
Project and the Japan Society for the Promotion of Science (JSPS).