Plant Grapevine

We are slowly learning thatplants do communicate information and do make decisions.  A huge amount of this activity takes place inthe plants root space.  Recall that theroot system typically matches the mass of the above ground mass.

This all supports research into protocolsthat take advantage of this behavior for agriculture.

For instance, using so calledhills rather than rows promises to be far superior as a growing method simplybecause it assures maximum communication between the plants. 

The traditional three sisters mixedcorn and beans in a hill with the odd squash plant thrown in to provide weedsuppression.  Obviously the beansprovided nitrogen.

At present, that is the onlyclever combination that I know of and it would be good practice to reestablishit, provided there is a way to mechanize the laying down of the hillsthemselves.  It certainly should beapplied in the family garden and perhaps we need to think out a lot of otherprospective combinations.  The nitrogenequation alone needs to be better exploited.

Any given hill for any particularplant type can be set with a core of peas or beans to do that.  Instead of growing radishes and beets and carrotsin rows, we set them in the borders of hills that also have peas or beans atits core.

Then of course, while we are atit, we throw in a handful of biochar to help eliminate leaching.  Have to get that pitch in there.

Heard it on the grapevine: The secret society of plants

29 March 2011 by Ferris Jabr

http://www.newscientist.com/article/mg20928051.500-heard-it-on-the-grapevine-the-secret-society-of-plants.html

The botanical underground is a social network of powerful alliances andnepotism. Decoding its messages could lead to radical change in farms andforests

Every autumn swarms of dusty grey moths engulf the mountainside birchforests of northern Scandinavia, laying theireggs on twigs so that, come springtime, the newly hatched larvae can feast uponbudding leaves. It looks like a battle that the trees, with no naturaldefences, are doomed to lose, but some have a secret weapon. They form analliance with a neighbouring plant, a kind of rhododendron, borrowing wafts ofits volatile insecticides as a sort of olfactory camouflage. "This kind ofinteraction has never been observed in the field before," says JarmoHolopainen at the University of Eastern Finland in Kuopio, who made the discovery ( New Phytologist, vol 186, p 722). His study is oneof the latest to demonstrate the unexpectedly complex relationships betweenplants

We've known for some time that plants respond to one another, but onlynow are we realising how subtle and sophisticated their interactions can be.Plants continually eavesdrop on each other's chemical chatter - sometimessympathetically, sometimes selfishly. Some plants, like the Scandinavianrhododendron, assist their neighbours by sharing resources. Others recogniseclose relatives and favour them over strangers. And at least one parasiticplant homes in on its host's telltale chemical scent (see"Scent of a victim").

"Plants don't go out to parties or to watch the movies, but theydo have a social network," says Suzanne Simard, a forest ecologist at the University of British Columbia in Vancouver, Canada."They support each other and they fight with each other. The more we lookat plant signalling and communication, the more we learn. It's reallyincredible."

Since the development of time-lapse photography, it has been possibleto document the dances and scuffles in densely populated plant communities:saplings on the forest floor compete for space to stretch their roots andshoots; fallen trees provide young ones with nourishment; vines lash arounddesperately searching for a trunk they can climb to reach the light; andwildflowers race each other to open their blooms in springtime and compete forthe attention of pollinators. To truly understand the secret social life ofplants, however, you must look and listen more closely.

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

Now closer inspection has revealed that fungal threads physically unitethe roots of dozens of trees, often of different species, into a singlemycorrhizal network. These webs sprawled beneath our feet are genuine socialnetworks. By tracing the movement of radioactive carbon isotopes through them,Simard has found that water and nutrients tend to flow from trees that makeexcess food to ones that don't have enough. One study published in 2009, forexample, showed that older Douglas firstransferred molecules containing carbon and nitrogen to saplings of the samespecies via their mycorrhizal networks. The saplings with the greatest accessto these networks were the healthiest (Ecology, vol 90, p 2808).

As well as sharing food, mycorrhizal associations may also allow plantsto share information. Biologists have known for a while that plants can respondto airborne defence signals from others that are under attack. When acaterpillar starts to munch on a tomato plant, for example, the leaves producenoxious compounds that both repel the attacker and stimulate neighbouringplants to ready their own defences.

Yuan Yuan Song of South China AgriculturalUniversity in Guangzhou and colleagues investigated whethersimilar chemical alarm calls travel underground. They exposed one group oftomato plants to a pathogenic fungus and monitored the response in a secondgroup connected to the first via a mycorrhizal network. The diseased plantswere sealed inside airtight plastic bags to prevent any communication aboveground. Nevertheless, the healthy partners began producing defence chemicals,suggesting that the plants detect each other's alarm calls via their mycorrhizalnetworks (PLoS One, vol 5, p e13324).

Another recent discovery, one which may be connected with Song'sfinding, is that some plants recognise members of their own species andapparently work together for the common good. Amanda Broz of Colorado StateUniversity in Fort Collins paired spotted knotweed plantsinside a greenhouse either with other knotweeds or with blue bunchgrass. Shethen simulated an attack by spraying them with methyl jasmonate, a chemicalmany plants release when wounded. The knotweed's response depended on itsneighbours. When growing near members of its own species, it produced leaftoxins to boost its defences. But it chose to focus on leaf and stem growthwhen its neighbours were bunchgrass (BMC PlantBiology, vol 10, p 115).

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

Broz's research was published just last year, and it remains unclearhow knotweed, or any other plant, could be recognising members of its ownspecies. However, one instance of a plant with family values has been morethoroughly explored.

In a landmark paper published in 2007, Susan Dudley from McMaster Universityin Ontario, Canada, reported the first case ofplants recognising and favouring their kin (Biology Letters, vol 3, p 435). Her studies of Americansea 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 tospread its roots and soak up as much water and nutrients as it could. However,when Dudley planted sea-rocket siblings in thesame pot, they exercised restraint, taming their eager roots to better shareresources. Siblings and strangers that grew near each other but did not sharepots showed no differences in root growth, indicating that sea rocket relies onunderground chemical signalling to identify its kin. They don't seem to beusing mycorrhizal networks, though.

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

In the past few years, kin recognition has been discovered in otherplants, including the botanical "lab rat" Arabidopsis and akind of Impatiens called pale jewelweed. This has led some botaniststo argue that plants, like animals, are capable of kin selection - behavioursand strategies that help relatives reproduce. Kin selection has an evolutionaryrationale because it increases the chances that the genes an individual shareswith its relatives will be passed to the next generation, even if altruisticbehaviour comes at a cost to one's own well-being. "There's no reason tothink plants wouldn't get the same benefits from kin selection that animalsdo," says Dudley.

Recognising siblings and restraining one's growth in response certainlylooks like kin selection, but that still leaves the question of whether suchinteractions also improve the survival prospects of related plants. Research byRichard Karban at the University of California, Davis,goes some way to answering that.

Karban studied a desert shrub called sagebrush, which emits a pungentbouquet of chemicals to deter insects. When he clipped an individual plant'sleaves to simulate an attack, he found that it mounted a more robust defence ifit 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 clonessuffered far less damage from caterpillars, grasshoppers and deer than did unrelatedneighbours (Ecology Letters, vol 12, p 502).

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

One obvious area is in companion planting - the strategic positioningof different crops or garden plants so they benefit one another by deterringpests, attracting pollinators and improving nutrient uptake. This ancienttechnique, which traditionally relies on trial and error and close observation,can be highly effective. For example, beans fix nitrogen that boosts growth insome other plants, and when Europeans arrived in America in the 15th century, theydiscovered that Native Americans used corn as a natural trellis for beanplants. Our modern understanding of plant interactions suggests we could findnew, more subtle and potentially beneficial relationships, which could help usovercome a major drawback of modern monoculture farming. Since a singlepathogen can wipe out an entire crop of genetically similar - and thereforeequally vulnerable - plants, farmers make heavy use of pesticides. But insteadof picturing an endless stretch of corn or wheat, imagine something more like ajungle of diverse species that work together above and below ground.

Breeding cooperation

Cahill has another idea. "Fertilisers aren't always spreadevenly," he says. "Maybe we could breed plants to cooperate moreeffectively with their neighbours to share fertiliser." Meanwhile, Simardthinks the recent discoveries about mycorrhizal networks have implications forboth agriculture and forestry. Hardy old trees should not be removed fromforests so hastily, she says, because saplings depend on the mycorrhizal associationsmaintained by these grandparent trees. She also suggests that farmers should goeasy on fertilisation and irrigation because these practices can damage ordestroy delicate mycorrhizal networks.

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

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

See gallery: "Plants thatact like people"

Scent of a victim

Many of the social interactions of plants seem to involve a form ofsharing or cooperation mediated by chemical signals. However, some chemicalcommunication is far from benevolent, as research on a parasitic vine calleddodder has found.

Dodder contains almost no chlorophyll - the green molecule that allowsplants to produce sugars from sunlight, water and carbon dioxide. Instead,after sprouting as a leafless tendril, it searches for a victim into which itsinks its nozzles and sucks out the sugary sap. "We knew how it createsnozzles and gets resources from the host, but nobody knew how dodder found itshost," says Consuelo De Moraes at PennsylvaniaState Universityat University Park.

Some plants identify neighbours by sensing sunlight refracted off theirleaves, but time-lapse video suggests that dodder uses a different technique.The footage shows that when the tendril searches for a host it twirls aboutlike a snake tasting the air. Could it be searching for a chemical, wondered DeMoraes?

To test this idea, she and her colleagues hid a variety of plantsaround a corner from a dodder tendril. If the vine were really using chemicalsensing to find its victims, it should be able to home in on its hosts usingthe volatile chemicals they naturally produce.

That is exactly what they found. In fact, dodder even showed dietarypreferences based on the different airborne chemicals, almost always choosingsucculent tomatoes over twiggy wheat, and favouring healthy hosts by avoidingthe chemicals given off by damaged plants (Science, vol 313, p 1964). "Not only does dodder usechemical cues to find a host," says De Moraes, "it can distinguishbetween hosts of different qualities. It knows which plants are healthier andgoes after them."