The Secret Life of Plants

[Billy]

.. . . Since the development of time-lapse
photography, it has been possible to
document the dances and scuffles in densely
populated plant communities: saplings on
the forest floor compete for space to stretch
their roots and shoots; fallen [Only registered and activated users can see links. ] provide
young ones with nourishment; vines lash
around desperately searching for a trunk
they can climb to reach the light; and
wildflowers race each other to open their
blooms in springtime and compete for the
attention of pollinators. To truly understand
the secret social life of plants, however, you
must look and listen more closely.

A good place to start is underground in
the rhizosphere - the ecosystem in and
around plant roots. Beneath the forest floor,
each spoonful of dirt contains millions of
tiny organisms. These bacteria and fungi
form a symbiotic relationship with plant
roots, helping their hosts absorb water and
vital elements like nitrogen in return for
a steady supply of nutrients.

Now closer inspection has revealed that
fungal threads physically unite the roots of
dozens of trees, often of different species, into
a single mycorrhizal network. These webs .
sprawled beneath our feet are genuine social
networks. By tracing the movement of
radioactive carbon isotopes through them,

"Plants don't go out to
parties or to watch the
movies, but they do have
a social network"

Simard has found that water and nutrients
tend to flow from trees that make excess food
to ones that don't have enough. One study
published in 2009, for example, showed that
older Douglas firs transferred molecules
containing carbon and nitrogen to saplings
of the same species via their mycorrhizal
networks. The saplings with the greatest
access to these networks were the healthiest
(Ecology, vol 90, p 2808).

As well as sharing food, mycorrhizal
associations may also allow plants to share
information. Biologists have known for a
while that plants can respond to airborne
defense signals from others that are under
attack. When a caterpillar starts to munch
on a tomato plant, for example, the leaves
produce noxious compounds that both repel
the attacker and stimulate neighboring
plants to ready their own defenses.

Yuan Yuan Song of South China Agricultural
University in Guangzhou and colleagues
investigated whether similar chemical alarm
calls travel underground. They exposed one
group of tomato plants to a pathogenic fungus
and monitored the response in a second group
connected to the first via a mycorrhizal >

26 March 20111 NewScentist 147

network. The diseased plants were sealed
inside airtight plastic bags to prevent any
communication above ground. Nevertheless
the healthy partners began producing defense
chemicals, suggesting that the plants detect '
each other's alarm.,calls via their mycorrhizal
networks (PLoS One,\vol 5, p e13324).

Another recent discovery, one which may
be connected with Song's finding, is that
some plants recognize members of their own
species and apparently work together for the
common good. Amanda Broz of Colorado
State University in Port Collins paired spotted
knotweed plants inside a [Only registered and activated users can see links. ] either
with other knotweeds or with blue
bunchgrass. She then simulated an attack
by spraying them with methyl jasmonate, a
chemical many plants release when wounded.
The knotweed's response depended on its
neighbours. When growing near members
of its own species, it produced leaf toxins to
boost its defences. But it chose to focus on leaf
and stem growth when its neighbours were
bunchgrass {BMC Plant Biology, vol 10, p 115).

Such discrimination makes sense because,
in the knotweed's native environment, dense
clusters of a single plant tend to attract large
numbers of insects to an all-you-can-eat
buffet. So cooperating with other knotweed
plants helps stave off an attack. However,
when knotweed is surrounded by bunchgrass,
a better strategy is to leave defense to its
neighbours and concentrate on aggressive
growth -which might also help explain why
knotweed is such an effective invasive species.

Broz's research was published just last year,



and it remains unclear how knotweed, or any
other plant, could be recognizing members

of its own species. However, one instance of
a plant with family values has been more
thoroughly explored.

In a landmark paper published in 2007,
Susan Dudley from McMaster University in
Ontario, Canada, reported the first case of
plants recognizing and favoring their kin
(Biology Letters, vol 3, p 435). Her studies of
American sea rocket, a scraggly weed that
grows along the shorelines of the Great Lakes,
showed that a plant potted with an unrelated
individual did not hesitate to spread its roots
and soak up as much water and nutrients as
it could. However, when Dudley planted sea-
rocket siblings in the same pot, they exercised
restraint, taming their eager roots to better
share resources. Siblings and strangers that
grew near each other but did not share pots
showed no differences in root growth,
indicating that sea rocket relies on
underground chemical signaling to
identify its kin. They don't seem to be using
mycorrhizal networks, though.

In subsequent research with Meredith
Biedrzycki from the University of Delaware
in Newark, Dudley discovered that the signals
take the form of' exudates" - a cocktail of
soluble compounds including phenols,
flavonoids, sugars, organic acids, amino acids
and proteins, secreted by roots into the
rhizosphere. How these indicate relatedness
is still a mystery, though (Communicative &
Integrative Biology, vol 3, p 28).

In the past few years, kin recognition has
been discovered in of "Arabidopsis and a kind
of lmpatiens called pale jewelweed. This has
led some botanists to argue that plants,
like animals, are capable of kin selection-
behaviours and strategies that help
relatives reproduce. Kin selection has an
evolutionary rationale because it increases
the chances that the genes an individual
shares with its relatives will be passed to the
next generation, even if altruistic behaviour
comes at a cost to one's own well-being.

"There's no reason to think plants wouldn't
get the same benefits from kin selection that
animals do," says Dudley.

Recognizing siblings and restraining one's
growth in response certainly looks like kin
selection, but that still leaves the question
of whether such interactions also improve
the survival prospects of related plants.
Research by Richard Karban at the University
of California, Davis, goes some way to
answering that.

Karban studied a desert shrub called
sagebrush, which emits a pungent bouquet
of chemicals to deter insects. When he clipped
an individual plant's leaves to simulate an
attack, he found that it mounted a more
robust defence if it was growing next to
its own clone than if its neighbour was
unrelated. What's more, for a period of five
months afterwards, the neighbouring clones
suffered far less damage from caterpillars,
grasshoppers and deer than did unrelated
neighbours (Ecology Letters, vol 12, p 502).

Studying kin selection and other plant
interactions doesn't just improve our
knowledge of basic plant biology and
ecology. "There are a lot of people really
interested in it, because it's not just an
intellectually neat puzzle," says James Cahill
at the University of Alberta in Edmonton,
Canada. "There are many potential
applications, especially for agriculture."

One obvious area is in companion
planting - the strategic positioning of
different crops or [Only registered and activated users can see links. ] plants so they
benefit one another by deterring pests,
attracting pollinators and improving nutrient
uptake. This ancient technique, which
traditionally relies on trial and error and close
observation, can be highly effective. For
example, beans fix nitrogen that boosts
growth in some other plants, and when
Europeans arrived in America in the 15th
century, they discovered that Native
Americans used corn as a natural trellis for
bean plants. Our modern understanding of
plant interactions suggests we could find new,
more subtle and potentially beneficial
relationships, which could help us overcome
a major drawback of modern monoculture
farming. Since a single pathogen can wipe
out an entire crop of genetically similar- and
therefore equally vulnerable - plants, farmers
make heavy use of pesticides. But instead of
picturing an endless stretch of corn or wheat,
imagine something more like a jungle of
diverse species that work together above
and below ground.

Breeding cooperation

Cahill has another idea. "Fertilizers aren't
always spread evenly," he says. "Maybe we
could breed plants to cooperate more
effectively with their neighbours to share
fertilizer." Meanwhile, Simard thinks the
recent discoveries about mycorrhizal
networks have implications for both
agriculture and forestry. Hardy old trees
should not be removed from forests so hastily,
she says, because saplings depend on the
mycorrhizal associations maintained by these
grandparent trees. She also suggests that
farmers should go easy on fertilization and
irrigation because these practices can damage
or destroy delicate mycorrhizal networks.

Clearly, we do not yet have all the
information we need to start deploying such
tactics. "What we want to do next is develop
more advanced techniques to watch roots
grow, to really see what they do with each
other and how they interact in space," Dudley
says. She also wants to figure out what genetic
factors control plant interactions and look at
how they change survival and reproduction.
"The molecular aspects are perhaps the most
challenging," she adds, "but we have made
some big leaps."

The idea that plants have complex
relationships may require a shift in mindset. ,
"For the longest time people thought that
plants were just there," says Biedrzycki. "But
they can defend themselves more than we
thought and they can create the environment
around them. It turns out they have some
control over what is going on through this
chemical communication." Passive and silent
though plants may seem, their abilities to
interact and communicate should not come
as such a shock. "Some incredibly simple
organisms - even one-celled organisms - can
recognize and respond to each other," says
Broz. "Why is it so bizarre to think that plants
could have this same kind of ability?"

March 25, 2011 NewScientist
--
- Billy

E pluribus unum
<http://www.rollingstone.com/politics/news/the-great-american-bubble-machine-20100405>

[Steve Peek]

"Billy" <Wildbilly@withouta.net> wrote in message
news:Wildbilly-04CD75.21093714112011@c-61-68-245-199.per.connect.net.au...


Perhaps the forest is being grown by a benevolent fungus?

Steve

[Gary Woods]

"Steve Peek" <speek@ioa.com> wrote:


Paging Mr. Aldis!


--
Gary Woods AKA K2AHC- PGP key on request, or at home.earthlink.net/~garygarlic
Zone 5/4 in upstate New York, 1420' elevation. NY WO G