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The Secret Handshake of Plants

November 30, 2014
The scientist enters the forest.

The harbinger.

A wayward scientist bounces inside his off-road buggy on his way to his research site. Stopping well before his destination, he disembarks and hikes his way to the pristine research site. His fluorescent little flags mark his territory. He slows his walk and carefully wades through his subjects, a herd of grass, ready to be measured.

This budding experimenter may not be doing enough to mitigate his affects on his subjects. The grass has sensed his presence and has already begun the stampede, or at least the plant equivalent of one. Motionless and secretive, the plants fortify and call the alarm for the perceived danger: the invasive species of the sapien. The experimenter sees nothing but the wind on the leaves and soon begins fiddling with measuring instruments.


There is a world unknown, and seldom accounted for, pulsing in plant life. Plants have a high level of communication that necessitates a more conciliatory approach towards how our interactions, as observers, affect plants. Plant communication crosses species and even kingdoms. Plants have not just developed these mechanisms as peculiarities, but as significant systems of reactive and proactive actions. This communication is vital to their existence and energy consumption. This notion of plant communication has been around a while, but has only recently in the last decade become a focus of attention. This subject opens up new aspects of plant life that must be considered/accounted for in experimentation. Plants are talking during an exam and affecting their neighbor’s test scores. Care must be taken when it comes to plant-plant communication: it has vast influence. Interconnectedness means vast influence by disturbance from researchers. This affects measurements in ways we still do not know. Are we triggering plants to behave differently? Is the observed plant “listening” and responding to us?

Due to their silent and immobile nature plants appear to be quite the dullards. But, the level that plants are communicating with each other is greater than one may think. In an attempt to draw you into the scale of this, I will describe: root interactions, airborne signals, underground fungal networks, insect luring, and acoustic methods of communications.

Kin recognition

In a study on American Searocket published in Biology Letters, it was found that this annual, when grown near siblings, had less fine root mass than those placed near stranger plants. This plant is dedicating more energy in root growth to compete with strangers for underground resources. And “because sibling groups avoided this potential cost” (Dudley et al. 2007) of root production, there is increased fitness. This means that because the plant was able to sense that its neighbors were kin, it was able to spend its precious resources towards tasks like growing or reproducing faster. It did not need to focus on root competition.

A broken limb.

This limb has something to say about what you’ve done.

A broken limb a day keeps the herbivore away

Airborne communication between sagebrush individuals has been documented. “With air contact, branches became more resistant to herbivory when neighboring branches of the same or a different individual were clipped” (Karban et al. 2006). This means that plants downwind of sagebrush are exposed to an airborne chemical released by the broken sagebrush branch. Those exposed to the airborne chemicals react. Tomato and tobacco plants have been “observed to respond to cues released by sagebrush” (Karban et al. 2006). Sagebrush is communicating with other species of plants. This has implications in the field. Moving through the forest and disrupting the floor of flora may also upset the roof. Something even more interesting is that plants are able to communicate with insects as well.

Fungi dials 1-800-555-WASP

Forms of fungi worm their way throughout the soil and create networks by connecting up with plant root systems. These networks have been found to act like buried telephone lines between plants. Signals between plants, only connected by this network, “elicited emission of… [chemicals] that are repellent to A. pisum aphids but attractive to a key natural enemy, the parasitoid wasp” (Babikova et al. 2013). These plants were able to tell their neighbors to make themselves more toxic and call for a predator.

A song for the roots

Probably the strangest and least studied aspect of plant communication is sound. Some budding studies have found “evidence about plant’s ability [to detect] vibrations and [exhibit] frequency-selective sensitivity” (Gagliano et al. 2012). While more research in this aspect of communication is needed, it is an interesting thought that plants may react to vibrations in the soil.

With each step, we break their limbs and agitate their soil networks. A human in a forest is like a bull in a china shop. With the realization that we are affecting our observations just by setting foot near our specimens, we realize that scientific methods must take into account, or at least acknowledge, that plants are talking behind our backs.


References

Babikova Z, Gilbert L, Bruce TJ, Birkett M, Caulfield JC, Woodcock C, Pickett J, Johnson D (2013) Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. Ecology Lett 16:835-843. doi: 10.1111/ele.12115

Dudley SA, File AL (2007) Kin recognition in an annual plant. Biology Lett 3:435-438. doi: 10.1098/rsbl.2007.0232

Gagliano M, Mancuso S, Robert D (2012) Towards understanding plant bioacoustics. Trends in Plant Science 17:323-325. doi: 10.1016/j.tplants.2012.03.002

Karban R, Shiojiri K, Huntzinger M, Mccall AC (2006) Damage-Induced Resistance In Sagebrush: Volatiles Are Key To Intra- And Interplant Communication. Ecology 87:922-930. doi: 10.1890/0012-9658(2006)87[922:DRISVA]2.0.CO;2

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