Nature Roundup: Plants, Auroras, Jellyfish


New Research Opens a Window on the Minds of Plants

My fake plants died because I did not pretend to water them.

- Mitch Hedberg

With the help of a little paint, this tree appeared to be keeping an eye on traffic as cars passed by it in Dover, Kentucky.
Photo/The Ledger Independent, Terry Prather

by Patrik Jonsson

Raleigh – Hardly articulate, the tiny strangleweed, a pale parasitic plant, can sense the presence of friends, foes, and food, and make adroit decisions on how to approach them.  Mustard weed, a common plant with a 6-week life cycle, can't find its way in the world if its root-tip statolith - a starchy "brain" that communicates with the rest of the plant - is cut off.  The ground-hugging mayapple plans its growth 2 years into the future, based on computations of weather patterns.  And many who visit the redwoods of the northwest come away awed by the trees' survival for millenniums - a journey that, for some trees, precedes the Parthenon.

As trowel-wielding scientists dig up a trove of new findings, even those skeptical of the evolving paradigm of "plant intelligence" acknowledge that, down to the simplest magnolia or fern, flora have the smarts of the forest.  Some scientists say they carefully consider their environment, speculate on the future, conquer territory and enemies, and are often capable of forethought - revelations that could affect everyone from gardeners to philosophers.  Indeed, extraordinary new findings on how plants investigate and respond to their environments are part of a sprouting debate over the nature of intelligence itself.

"The attitude of people is changing quite substantially," says Anthony Trewavas, a plant biochemist at the University of Edinburgh in Scotland and a prominent scholar of plant intelligence.  "The idea of intelligence is going from the very narrow view that it's just human to something that's much more generally found in life."  To be sure, there are no signs of Socratic logic or Shakespearean thought, and the subject of plant "brains" has sparked heated exchanges at botany conferences.  Plants, skeptics scoff, surely don't fall in love, bake souffl├ęs, or ponder poetry.  And can a simple reaction to one's environment truly qualify as active, intentional reasoning?

But the late Nobel Prize-winning plant geneticist Barbara McClintock called plant cells "thoughtful."  Darwin wrote about root-tip "brains."  Not only can plants communicate with each other and with insects by coded gas exhalations, scientists say now, they can perform Euclidean geometry calculations through cellular computations and, like a peeved boss, remember the tiniest transgression for months.

To a growing number of biologists, the fact that plants are now known to challenge and exert power over other species is proof of a basic intellect.  "If intelligence is the capacity to acquire and apply knowledge, then, absolutely, plants are intelligent," agrees Leslie Sieburth, a biologist at the University of Utah in Salt Lake City.  For philosophers, one of the key findings is that two cuttings, or clones, taken from the same "mother plant" behave differently even when planted in identical conditions.

"We now know there's an ability of self-recognition in plants, which is highly unusual and quite extraordinary that it's actually there," says Dr Trewavas.  "But why has no one come to grips with it?  Because the prevailing view of a plant, even among plant biologists, is that it's a simple organism that grows reproducibly in a flower pot."

But here at the labs on the North Carolina State campus, where fluorescent grow-rooms hold genetic secrets and laser microscopes parse the inner workings of live plants, there is still scepticism about the ability of ordinary houseplants to intellectualise their environment.  Most plant biologists are still looking at the mysteries of "signal transduction," or how genetic, chemical, and hormonal orders are dispersed for complex plant behaviour.  But sceptics say it's less a product of intelligence than mechanical directives, more genetic than genius.  Some see the attribution of intelligence to plants as relative - an oversimplification of a complex human trait.

And despite intensifying research, exactly how a plant's complex orders are formulated and carried out remains draped in leafy mystery.  "There is still much that we do not know about how plants work, but a big part of intelligence is self-consciousness, and plants do not have that," says Heike Winter Sederoff, a plant biologist at North Carolina State.

Still, a new NASA grant awarded to the university to study gravitational effects on crop plants came in part due to new findings that plants have neurotransmitters very similar to humans' - capable, perhaps, of offering clues on how gravity affects more sentient beings.  The National Science Foundation has awarded a $5 million research grant to pinpoint the molecular clockwork by which plants know when to grow and when to flower.

The new field of plant neurobiology holds its first conference - The First Symposium on Plant Neurobiology - in May in Florence, Italy.

The debate is rapidly moving past the theoretical.  In space, "smart plants" can provide not only food, oxygen, and clean air, but also valuable companionship for lonely space travellers, say some - a boon for astronauts if America is to go to Mars.  Research on the workings of the mustard weed's statolith, for example, may one day yield a corn crop with 13/8 the gravitational force of earth.  Some earth-bound farmers, meanwhile, see the possibility of communicating with plants to time waterings for ultimate growth.  A new gene, Bypass-1, found by University of Utah researchers, may make that possible.

Still, it can be hard for the common houseplant to command respect - even among those who study it most closely.  "When I was a postdoc, I had a neighbour who watched me buy plants, forget to water them, and throw them out, buy them and throw them out," says Dr Sieburth.  "When she found out I had a PhD in botany, I thought she was going to die."

Source: csmonitor.comChristian Science Monitor 3 March 2005

Potted Plants Are Nicer to Their Siblings

Bejimg - A recent study reveals plants potted with siblings are kinder to each other than when potted with strangers.  When plants share a pot with strangers, they develop a competitive streak.  "The ability to recognise and favour kin is common in animals, but this is the first time it has been shown in plants," said Susan Dudley of McMaster University in Canada.

Roots branch out in search of water and nutrients after plants are potted.  But when several plants of the same species are potted together, each plant extends its root growth to try and gobble up available resources - unless the plants came from the same mother plant, in which case they become very accommodating, allowing each other ample root space.  Because the interactions between related and unrelated plants only happened when plants were in the same pot, where root space is limited, root interactions are likely what gives plants the cue that their neighbour is related.  Dudley observed this behaviour in sea rocket (Cakile edentula), a member of the mustard family that is native to North America beaches.  The findings, detailed in the 12 June issue of Biology Letters, may not come as a surprise to seasoned gardeners.

"Gardeners have known for a long time that some pairs of species get along better than others, and scientists are starting to catch up with why that happens," Dudley said.  "The more we know about plants, the more complex their interactions seem to be."

Source: 15 June 2007


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The Good and the Bad: But Will It Get Ugly?

Jellyfish-Like Creatures May Play Major Role in Fate of Carbon Dioxide in the Ocean

A chain of salpa aspera (Photo by Larry Madin, Woods Hole Oceanographic Institution)

Transparent jellyfish-like creatures known as salps, considered by many a low member in the ocean food web, may be more important to the fate of the greenhouse gas carbon dioxide in the ocean than previously thought.  In the May issue of Deep Sea Research, scientists report that salps, about the size of a human thumb, swarming by the billions in "hot spots" may be transporting tons of carbon per day from the ocean surface to the deep sea and keep it from re-entering the atmosphere.  Salps are semi-transparent, barrel-shaped marine animals that move through the water by drawing water in the front end and propelling it out the rear in a sort of jet propulsion.  The water passes over a mucus membrane that vacuums it clean of all edible material.

The oceans absorb excess CO2 from the atmosphere, some from the burning of fossil fuels.  In sunlit surface waters, tiny marine plants called phytoplankton use the CO2 to grow.  Animals then consume the phytoplankton and incorporate the carbon, but most of it dissolves back into the oceans when the animals defecate or die.  The carbon can be used again by bacteria and plants, or can return to the atmosphere as heat-trapping CO2 when it is consumed and respired by animals.

Biologists Laurence Madin of Woods Hole Oceanographic Institution (WHOI) and Patricia Kremer of the University of Connecticut and colleagues have conducted four summer expeditions to the Mid-Atlantic Bight region, between Cape Hatteras and Georges Bank in the North Atlantic, since 1975.  Each time the researchers found that one particular salp species, Salpa aspera, multiplied into dense swarms that lasted for months.  One swarm covered 100,000 square kilometers (38,600 square miles) of the sea surface.  The scientists estimated that the swarm consumed up to 74% of microscopic carbon-containing plants from the surface water per day, and their sinking fecal pellets transported up to 4,000 tons of carbon a day to deep water.

"Salps swim, feed, and produce waste continuously," Madin said.  "They take in small packages of carbon and make them into big packages that sink fast."

In previous work, Madin and WHOI biologist Richard Harbison found that salp fecal pellets sink as much as 1,000 metres (3,280 feet) a day.  The scientists also showed that when salps die, their bodies also sink fast — up to 475 metres (1,575 feet) a day, faster than most pellets.  If salps are really a dead-end in the food web and remain uneaten on the way down, they could send even more carbon to the deep.

Salpa aspera swims long distances down in daylight and back up at night in what is known as vertical migration.  Madin, Kremer and colleagues Peter Wiebe and Erich Horgan of WHOI and Jennifer Purcell and David Nemazie of the University of Maryland found that the salps stay at depths of 600 to 800 metres (1,970 to 2,625 feet) during the day, coming to the surface only at night.  "At the surface," Madin said, "salps can feed on phytoplankton.  They may swim down in the day to avoid predators or damaging sunlight.  And swimming up at night allows them to aggregate to reproduce and multiply quickly when food is abundant."  Because of this behaviour, salps release fecal pellets in deep water, where few animals eat them.  This enhances the transport of carbon away from the atmosphere.

In 2004 and 2006, Madin and Kremer studied salp swarms in a different ecosystem, the Southern Ocean near Antarctica.  Some scientists have reported larger salp populations there in warmer years with less sea ice.  If this proves true, and if Antarctica's climate warms, salp swarms could have a greater effect on phytoplankton and carbon in the Southern Ocean ecosystem.

Funding for this study was provided by the National Science Foundation, National Oceanic and Atmospheric Administration, and the Access to the Sea program at Woods Hole Oceanographic Institution.

Source: 30 June 2006 Woods Hole Oceanographic Institution

Heavy Fishing Blamed for Jellyfish "Explosion" off Namibia

Scientists in Scotland have blamed heavy fishing for an "explosion" in jellyfish in the Benguela Current that streams past Namibia in the South Atlantic Ocean.  "Because fish and jellyfish essentially compete for similar food resources, a dramatic decline in fish populations could theoretically contribute to a substantial increase in the abundance of jellyfish," Andrew Brierley, head of the pelagic ecology research group at the University of Saint Andrews, said Tuesday.  "This type of shift has been predicted as a consequence of 'fishing down the food web'."

Jellyfish have been increasing in the Benguela Current off Namibia for some time but a lack of hard data on their numbers has until now hampered understanding of their likely impact on the ecosystem.  Researchers from the University of St Andrews in Scotland carried out an in-depth quantitative analysis after striking changes were reported in numbers of the large jellyfish species Chrysaora hysoscella (Compass jellyfish) and Aequorea forskalea (Medusa).

The team's findings appeared Tuesday in the journal Current Biology.

"We estimate the total biomass of jellyfish in the region to be 12.2 million metric tons, most of which is due to A.forskalea, while the biomass of fish accounts for only 3.6 million metric tons," Brierley said.  "In the past this region has offered abundant fish stocks, thanks largely to the fact that it is served by cool, nutrient rich upwelling waters," he added, referring to the Benguela Current, which originates in the Southern Ocean.  Fish stocks, including sardines and anchovies, have been heavily exploited there since the 1960s and their numbers have fallen significantly as a result, he said.

The jellyfish population in the northern stretch of the Benguela Current not only outnumbers fish in the region but is now so large that it significantly interferes with fishing operations and industrial water uptake systems, the Scottish researchers found.  The team used scientific echosounders to sample jellyfish and fish in an area of more than 30,000 nautical square miles along the Namibian shelf, between the borders of Angola and South Africa.  Brierley said there could be other factors contributing to the increase in jellyfish there.  "Jellyfish biomass has risen in numerous locations worldwide, possibly as a consequence of fishing, but it is possible that climatic changes could also contribute to jellyfish population increases.  Also, jellyfish have few predators.  Once jellyfish become established it may be very difficult to revert to previous fish domination because jellyfish are predatory on fish eggs and juveniles."

Source: 11 July 2006

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