Plants are not simple bystanders in the environment, soaking up sun and otherwise engaging in a passive existence. They’re actually active communicators and engage in a complex relationship with their environment.
Not only do plants communicate with each other but they also take steps to protect themselves from predators. About 200 plant species, for instance, manufacture a glue-like substance that attracts sand or soil.
The resulting “sand armor,” which is created in a process called psammophory, has been the subject of numerous theories. Some researchers have suggested plants coat themselves in sand as a form of camouflage or for added protection during sandstorms.
Others have posited it may have to do with water retention or protection for radiation. New research published in Ecology has revealed what may be its true underlying purpose, however, which is to discourage predators from taking a bite.1
Plants Use “Sand Armor” to Prevent Being Eaten
Researchers from the University of California, Davis studied two different plants that coat themselves in sand: the sand verbena and the honeyscented pincushion plant. In one experiment, they gently removed the sand from parts of wild-growing verbena plants then kept track of any damage from predators.
They also added sand to wild pincushion plants and compared them to pincushion plants that remained sand-free. The results were quite revealing. The sand-free verbena plants had twice as much damage from herbivores than sand-coated plants.
The sand-covered pincushion plants, however, largely escaped predation; only one out of 19 was eaten compared to eight of 18 that were sand-free. Next the researchers wanted to find out if sand’s ability to camouflage the plant was making a difference.
So they covered some of the plants in green sand, which would therefore make them stand out more in the environment compared to ordinary brown sand. No difference was found among the green- or sand-colored hues, which suggests the role of psammophory isn’t to camouflage but instead is to deter predation.2
Music and Healing Energy Changes the Way Plants Grow
If there were any doubt that nature is an active participant, and recipient, to its environment, consider the fascinating research that shows music and noise both influence the growth of plants. As explained in The Journal of Alternative and Complementary Medicine:3
“Plants are complex multicellular organisms considered as sensitive as humans for initial assaying of effects and testing new therapies. Sound is known to affect the growth of plants. Seeds are sometimes treated with ultrasound to help start the germination process …
Foliage planted along freeways to reduce noise pollution often grows differently than foliage planter in a quiet environment … Sound vibration can stimulate a seed or plant.”
In a series of five experiments that used okra and zucchini seeds germinated in acoustically shielded, thermally insulated chambers, researchers measured the biologic effects of music, noise and healing energy on the seeds’ growth.
They compared untreated controls with seeds exposed to musical sound, pink noise and healing energy. The seeds exposed to music and those exposed to healing energy both germinated faster than the control seeds or those exposed to noise. According to the study:4
“This group of experiments indicates that both the musical sound and healing energy used in this study had replicable and significant effects on the germination of two different types of seeds when compared to an untreated control.
The differences in germination rates between different conditions cannot be explained by mean temperature, temperature differences between chambers, petri dish position, growth chamber position, or persons scoring the seeds.”
Plants Warn Each Other About Pest Attacks
Plants communicate with each other. When a plant becomes infested with a pest like aphids, for example, it warns surrounding plants of the attack via a network of mycorrhizal fungi.5
These fungi form a symbiotic relationship with the plant, colonizing the roots and sending extremely fine filaments far out into the soil that act as root extensions.
Not only do these networks sound the alarm about invaders, but the filaments are more effective in nutrient and water absorption than the plant roots themselves.
In research published in Ecology Letters, the mycorrhizal fungi were found to act as “a conduit for signaling between plants, acting as an early warning system for herbivore attack.”
Even more amazing, the warning led to systemic changes, particularly it caused the plant to increase production of volatile chemicals that repel aphids while attracting wasps, which are aphids’ natural enemy.6
In bean plants where the researchers had removed the mycorrhizae connecting them together, the plants quickly succumbed to the infestation, presumably because they didn't receive the warning to mount their defenses.
Another 2010 study published in PLOS One detailed the interplant communication of tomato plants, explaining:7
"CMNs [common mycorrhizal networks] may function as a plant-plant underground communication conduit whereby disease resistance and induced defense signals can be transferred between the healthy and pathogen-infected neighboring plants …
… suggesting that plants can 'eavesdrop' on defense signals from the pathogen-challenged neighbors through CMNs to activate defenses before being attacked themselves."