Plants Can Hear Themselves Being Eaten, and Can Communicate the Threat to Their Neighbors

Plants Can Hear Themselves Being Eaten, and Can Communicate the Threat to Their Neighbors

The interconnectedness between soil, microbes, plants, pests, and ultimately human health, is a fascinating area of study.

With the rapid evolution of technology, much of what used to be common-sense farming and gardening knowledge was lost. However, science is starting to reaffirm age-old wisdoms, showing that nature is far smarter than we may have given it credit for.

For example, we now know that plants are capable of communicating with each other via extensive and complex networks, and can warn each other of the presence of pests. In response, the plants will mount natural defenses against the infestation.

This is an important part of chemical-free agriculture. We don’t need to combat pests with chemical warfare… We just have to create the optimal growing conditions so the plant can respond with its own defenses.

We’re also starting to realize how microorganisms in soil and the human gut are interconnected, and work to create health in very similar ways.

Researchers have also discovered that plants can actually “hear” when they’re being chewed on, and in response, they can launch a chemical defense to minimize the destruction. In truth, whether we’re eating meat, fish, fowl, or plants, we’re taking sustenance from something that is (or was) very much alive…

How Plants Hear

As reported by IFL Science,1 when a bug such as a caterpillar chews on a plant’s leaf, the plant actually “hears” the vibrations of the chewing, and produces a phytochemical to defend itself from further harm.

I never realized that this happened but after reading the study, I went out to my edible landscape and found many of the plants had been nibbled on, but just in one small section of leaves. The rest of the leaves were fine. This seemed to confirm the observation of the study.

The study was published in the journal Oecologia2 and involved recording plant responses to vibrational sounds by placing reflective tape on a leaf. Using a laser beam, they were able to measure the leaf’s response when a caterpillar chewed on it.

They also played a recording of the near-inaudible vibrational sound of a caterpillar chewing, and interestingly enough, plants that had been previously exposed to these feeding sounds released higher amounts of chemicals that deters bugs.

Even more interesting, these phytochemicals are also what give a plant many of its medicinal qualities, such as glucosinolates, which have anti-cancer properties, and other antioxidants. When a plant has increased levels of these chemicals, insects will not feed on it.

In a nutshell, the vibrational sound of a bug chewing on a plant’s leaf causes a change in the cellular metabolism of the plant, creating chemicals that repel the attacker.

Many view pests as an unavoidable nuisance very similar to disease. But actually they serve a valuable role and destroy sick or damaged plants. This is why healthy plants typically don’t have a problem with pests.

Interestingly, this research even suggests that minor pest attacks may play an important role in encouraging plant growth that have higher levels of (to humans) important nutrients! In a press release,3 one of the researchers stated:

“This research also opens the window of plant behavior a little wider, showing that plants have many of the same responses to outside influences that animals do, even though the responses look different.”

How Plants Communicate

As mentioned earlier, plants also communicate with other plants—even with plants of other species—through a complex underground network that includes:

• The plants’ rhizosphere (root ball)
• Aerial emissions (volatile gasses emitted by the plants)
• Mycelial networks in the soil

These three systems work together forming a “plant internet,” if you will, where information about each plant’s status is constantly exchanged. One of the organisms responsible for this amazing biochemical highway is a type of fungus called mycorrhizae.

The name mycorrhiza literally means fungus root.4 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—mycorrhizae increase the nutrient absorption of the plant 100 to 1,000 times.5

In one thimbleful of healthy soil, you can find several MILES of fungal filaments, all releasing powerful enzymes that help dissolve tightly bound soil nutrients, such as organic nitrogen, phosphorus, and iron.

This is one of the major reasons why tilling the soil is deleterious to gardening or farming as it damages these fragile fungal filaments. The last thing any gardener or farmer should be doing is tilling the soil.

That is one of the reasons why wood chips are so useful as they not only eliminate tilling but effectively feeds the fungi. One of the best things you can do for your garden is to put a four inch layer of wood chips (not bark) around your plants to encourage this fungal growth and attract earthworms so they can create vermicompost.

Plant Communications Network Combats Pest Infestation

Previous research6 has shown that when a plant becomes infested with a pest like aphids for example, it warns surrounding plants of the attack via this network of mycorrhizal fungi.

This “heads up” gives the other plants time to mount their chemical defenses in order to repel the aphids. Mycorrhizae fungi can even connect plants of different species, perhaps allowing interspecies communication.7

The study in question used bean plants and aphids, and in this case, the alerted bean plants deployed not only aphid-repelling chemicals, but also produced other chemicals that attract wasps, which are aphids’ natural predators!

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 2012 article in the Journal of Chemical Ecology8 describes mycorrhizae-induced resistance as part of plants’ systemic “immune response,” protecting them from pathogens, herbivores, and parasitic plants. And in 2010, Song et al published a report about the interplant communication of tomato plants, in which they wrote:9

“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.”

More than 90 percent of plant species have these naturally occurring symbiotic relationships with mycorrhizae, but in order for these CMNs to exist, the soil must be undisturbed. Erosion, tillage, cultivation, compaction, and other human activities simply destroy these beneficial fungi networks, and they are slow to colonize once disrupted.10 Therefore, cultivated or tilled farmed plants don’t develop mycorrhizae and are typically less healthy, as a result.

Healthy Soil Makes for Healthy People

Mycorrhizae aren’t the only organisms harmed by our modern chemical- and technology-heavy agricultural methods. Soil and plant health also depends on many other microbes and critters living in the soil. This includes bacteria, fungi, protozoa, microscopic roundworms called nematodes, and earth worms.

We now understand that it is the cooperation between these microorganisms—the soil’s biome—and the plants’ roots that is ultimately responsible for allowing the plant to absorb nutrients from the soil in which it’s grown. Insects and weeds also have their place. They only really reach “pest” status when the balance is shifted in such a way that they’re able to get the upper hand. Otherwise, insects actually serve a very important role as nature’s “garbage collectors.” Thanks to their specialized digestive systems, they remove that which is not fit for us to eat—things we cannot digest.

Once you start to connect all these dots, you begin to understand the depth of nature’s intelligence, which always strives to maintain balance. This balance is what leads to healthy soils, healthy plants, a healthy environment, and, ultimately, healthy bodies. You are beautifully “plugged into” this system. We, as caretakers of the earth, have the free will to either protect and nurture it or destroy it. The fact that if we choose to poison the earth, we poison ourselves, can be seen as an expression of nature’s self-regulatory capacity… Since soil health connects to everything up the food chain, our health therefore originates in the soils in which our food is grown.

Besides deepening our understanding of the importance of nurturing and maintaining healthy soil microbes, research into the plant kingdom really helps explain why synthetic chemicals are unnecessary. It also tells us that most of our modern agricultural “advances” are actually killing the very foundation of food production and human health—the microbiome in the soil. I believe that as responsible stewards, it is our duty to act on such information, and to make the necessary changes to ensure mankind’s survival on this planet. The arguments for organic farming go far beyond nostalgic notions of preserving a way of life; it’s about self-preservation!

Taking Matters Into Your Own Hands…

If you support and nurture the microbiome in soil, it in turn will provide you with good nutrition and optimal health through the food grown in it. Three basic principles of biological gardening that will make your soil hospitable for beneficial microorganisms, which in turn will allow plants to flourish, are the following:

• Correct nutrient balance in your soil, ideally through simple and inexpensive methods like applying woodchips. Once established, the chips will optimize soil pH and minerals without the need for testing or expensive fertilizers. It will also radically decrease the time you spend weeding, increase fungal networks in the soil and attract earthworms to further improve your soil.
• Soil inoculation. This can be done by adding soil probiotics or basic fermentation products such as compost tea. This will generate and support the proliferation of beneficial bacteria much in the same way you can boost the probiotics in your fermented vegetables by using a starter culture. I have learned that compost tea used alone is relatively worthless. It works far better if you have a cover of woodchips that help preserve the organisms in the tea and help them to colonize the soil.
• Provide a hospitable habitat for microbes to thrive in. Once you’ve added soil probiotics, the microbes need a proper “home” to hang out and multiply in. Biochar is excellent for this, and research11 shows that the addition of biochar can more than double a plant’s yield.
  Besides microorganisms such as bacteria, earthworms also play an important role in maintaining the health of the soil. Pesticides, which are commonly sprayed on crops to protect them against being ravaged by pests, have a devastating effect on earthworms, which is yet another reason to avoid chemical gardening. Research shows that earthworms exposed to pesticides grow to only half their normal weight. Pesticide exposure also has a detrimental impact on their ability to reproduce, and untreated soils can contain as much as two to three times as many earthworms as treated soils.
• Proper food (fertilizer) for the microorganisms to consume and thrive. Note that it’s the microbiome that you need to feed, not the plant directly. The microbes in turn will then feed the proper nutrients to the plants grown in that soil. Without these bioorganisms, your plants cannot get the nutrients they need. The better you’re able to fertilize the microbes, the healthier your plants will be, and the fewer plant diseases, pest infestations and weed problems you’ll have as well.

Helpful Resources

A whole host of environmental and human health problems could be corrected by addressing how we grow our food. Therefore, I cannot encourage you to support the small family farms in your local area strongly enough. They, and by extension you, are part of the solution. Here are some great resources to obtain wholesome food that supports not only you but also the environment:

1. Alternative Farming Systems Information Center, Community Supported Agriculture (CSA)
2. Farmers’ Markets — A national listing of farmers’ markets.
3. Local Harvest — This Web site will help you find farmers’ markets, family farms, and other sources of sustainably grown food in your area where you can buy produce, grass-fed meats, and many other goodies.
4. Eat Well Guide: Wholesome Food from Healthy Animals –– The Eat Well Guide is a free online directory of sustainably raised meat, poultry, dairy, and eggs from farms, stores, restaurants, inns, and hotels, and online outlets in the United States and Canada.
5. Community Involved in Sustaining Agriculture (CISA) — CISA is dedicated to sustaining agriculture and promoting the products of small farms.
6. FoodRoutes — The FoodRoutes “Find Good Food” map can help you connect with local farmers to find the freshest, tastiest food possible. On their interactive map, you can find a listing for local farmers, CSAs, and markets near you.