We can’t hear it, but scientists are finding that in the apparently silent world of plants, a whole lot of communication is going on.
At the University of Western Australia (UWA), researchers recently found that seeds recognise “good” or “bad” neighbouring seeds – even when there is a plastic sheet between them.
And in the United Kingdom, researchers have found that plants also maintain sophisticated underground signaling networks through mycorrhizal fungi. If a plant is attacked by a pest, the attack is telegraphed to other plants connected by the fungi. Those “alerted” plants can then produce repellent compounds ahead of the pests’ arrival.
The new information helps explain why the long-established gardener’s practice of companion planting, or the permaculture principle of planting in plant “guilds”, has an effectiveness that goes beyond visible evidence of competition and community. Mixed plant communities compete for resources like water and light, but helpful interactions also play out: nitrogen fixing, pest control or the attraction of desirable insects like pollinators. The interactions we know about are the ones we can see, like the shading effects of taller plants on those below.
Monica Gagliano and colleagues at UWA looked at whether some other form of invisible communication was going on. To their interest and bemusement, it seems there is. In an exploratory study, the researchers first looked at the interactions between chili and fennel. Chili doesn’t like fennel: when grown next to each other, the volatile chemicals of fennel hinders the germination rate of chili seeds. But when the researchers blocked all known light, chemical and touch signals between the plant seeds – using a sheet of black plastic – the same suppression of chili germination occurred.
“This demonstrated that plants were able to sense their neighbours even when all known communication channels are blocked, and most importantly, recognise the potential for the interfering presence of a ‘bad neighbour’ and modify their growth accordingly,” Dr Gagliano wrote.
The next step was to look at the effect of “good” plant neighbours: in this case, basil and chili. Basil, Dr Gagliano wrote, has the capacity to act as a natural insecticide, and to produce secondary and organic volatiles inhibiting germination and root growth of common competitive weeds like barnyard grass and lambsquarter. “Besides, gardeners commonly regard it as the ideal companion to chili plants by virtue of its ability to keep the soil moist and act as organic living mulch.”
In their experiments, basil proved to have a positive effect on chili germination and growth – and again, it didn’t matter whether the plants were in visible contact or all known sources of communication had been masked. Dr Gagliano speculated that even at the seed stage, plants have evolved the ability to sense their neighbours in the soil.
Ref: Matthew Cawood p18. The Land 23 May, 2013
Love thy neighbour: facilitation through an alternative signalling modality in plants
See also The Secrets Life of Plants by Phil Callahan