Hey, Jasmine, come and meet Robert and Violet

Fied Bindweed - Convolvulus arvensis - busy doing what?

Field Bindweed – Convolvulus arvensis – busy doing what?

Common sense, ‘facts’, things taken for granted, taken as read: the history of science shows that all these can be swept aside like old toys by some confident new research. The idea of unchanging, fixed species?  Darwin saw to that.  Solid matter? Smashed by nuclear physics.  In botany? Well, Darwin and evolutionary theory are still transforming our view of how plants came to be what they are today.  However, considering that much less funding goes to botanical research than other sciences, I wonder if other surprises still await us. Yes, the way a seed germinates and grows is clever, but after that, plants just stand there alone, stupid, blind, waiting to be picked, or eaten, or trodden on, or strimmed – don’t they? Isn’t that how they’re different from animals?

I’d like to hazard a guess at what a new surprise might be: plants have a social life. Since I’ve taken more time to observe plants and read about them in the last year or so, my view of them has changed.  Here are some examples.

Plants communicate. Not in the ‘talk to your geranium’ sense, or the ‘scream when they’re cut’ sense, but more commonly with chemicals. In the book I reviewed in my last post, Weeds, Richard Mabey writes that

The air and the soil are busy with constant streams of chemical messages – plant pheromones – designed to deter predatory insects, seduce pollinators, kill off competitors, encourage companion plants and warn other plants of insect attack.

These pheromones can be volatile compounds evaporating from the leaves or soluble chemicals exuding from the roots into the water in the soil. The roots of field bindweed (Convolvulus arvensis – in photo at top) secrete something which inhibits the germination of most grain crops.  The seeds of the striking thornapple (Datura stramonium ) can release chemicals which inhibit cabbages and tomatoes.

Thornapple - Datura stramonium - the poisonous weed that looks like a garden flower

Thornapple – Datura stramonium – the poisonous weed that looks like a garden flower

The growing tip of the plant dodder, which is parasitic on tomatoes, spirals round till it senses tomato leaf chemicals and then grows straight toward their source.

Plants are interdependent. Gardeners often use the phrase ‘companion plants’ to describe plants which grow well together: my Agenda du jardinier bio (organic gardener’s diary) lists dozens under ‘Voisinage favorable’: plant garlic near tomatoes but away from artichokes, celery near beetroot but away from salads etc. Pheromones may be at work here too.

An even closer association is between plant roots and beneficial fungi – I had heard of truffle oaks of course, but I was surprised to read in a botany textbook that ‘most higher plants have an association with soil fungi’. Yes, ‘most higher plants’: estimates are as high as 95%.  A root which cohabits (‘is infected with’ seems too value-laden a term) with a symbiotic fungus is called a mycorrhiza. The fungal threads can cover a huge area and help the plant source scarce minerals such as phosphates and nitrates, as well as water.  In return the fungus receives carbohydrates from the green plant. This short clip shows how it works:

A plant that combines many of these features is Cistus monspeliensis, which I wrote about on this blog here. As well as helping absorb nutrients, the fungus on its roots secretes a toxin which stops other seeds germinating – and it’s true that each Cistus usually sits in a bare patch of ground.

To give a few more examples, they’re also particularly important in trees of northern temperate areas, such as oaks, birches and conifers; and in heathers – Erica and Arbutus. Many orchids can’t even germinate without a particular fungus, which may account for their appearance in patches, from seeds germinating within the area of ground which contains fungus.  This makes evolutionary sense: plants originated in the seas and first colonised wet areas.  Fungal help would have been invaluable in spread to drier habitats, and once the solution was found, why evolve another?

Here’s forestry specialist Professor Suzanne Simard explaining that a forest is really a community, whose members have different roles:

You can make the most of mycorrhizae in organic gardening by inoculating your seeds and plants with fungal spores: see here:

One point I came across often is that industrial-scale grain growing goes against this process: the grain-bearing species are the least likely to have mycorrhizae; they therefore need higher levels of chemical fertiliser than other crops; and application of fungicides and other processes further reduce the biological activity of the soil.  All in all, we’re getting some insights in how to live with Nature, which, as Richard Mabey has said, is bigger than us.

In the second part of this theme, I’ll look at the lifestyles of plants – and their relationship with humans. Meanwhile, what more appropriate song title for this post than Stevie Wonder’s 1979 ‘Secret life of plants’?

 

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11 Comments

Filed under Cistus, Convolvulus, Datura, Himantoglossum, Orchis

11 responses to “Hey, Jasmine, come and meet Robert and Violet

  1. Interesting! I recently read this article about flowers communicating with bees
    http://phenomena.nationalgeographic.com/2013/02/21/bees-can-sense-the-electric-fields-of-flowers/
    haven’t head that song before, not Stevie’s best…..

  2. Ceridwen

    So interesting!
    Anyone who studies fungi in the wild quickly notices that it’s rare to find two separate species growing in close proximity with each other, as if they create a sort of exclusion zone. On the other hand the known mycorrhizal associations means that you don’t bother to look for fungi under sycamores, and the demise of the English elm made searching for morels very problematic.
    Also see here
    http://www.medicaldaily.com/articles/10247/20120611/plants-communication-survival.htm
    for the posibility that plants communicate acoustically.

    • Just catching up on comments that came in after we left home – thanks for your expert knowledge of fungi. The acoustic communication article is interesting, but my old science training makes me want a fuller picture, particularly about how plants might respond to what are called here, rather anthropomorphically, ‘warnings’ of predators or drought. No matter how many Google pages I’ve been through, you always seem to find something I haven’t seen!

  3. jan

    We were once given some Datura seeds, and they grew, but then the winter killed them off. Thank goodness!

  4. Pingback: Made in the shade: Limodorum abortivum (Violet limodore) | an entangled bank

  5. if there is a social life of plants (and i think there should be), then lichen would perhaps come under the heading of long-term vegetative state, no? what would the mycobion call its photobiont (or vice versa)? husband, wife, live-in-lover, life-partner, significant other?

  6. Pingback: Something’s Got a Hold of my Root: Broomrape (Orobanche) | an entangled bank

  7. Pingback: Going against the flow | an entangled bank

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