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INTRO: Hello and welcome to Mind Full of Everything with me, Agrita, a podcast giving an insight to the minds of deep thinkers, where in each episode I’ll be discussing various thoughts and questions deep thinkers often find themselves “mind-full” of, from topics such as climate change to self-development and everything else in between. So, let the journey of mind unraveling begin now!
Today I’m going to be starting off my Beautiful Planet series! I posted about this a few weeks back. The current pandemic has definitely made us forget quite a lot of things, especially taking care of the planet and also the beautiful planet that we have that we are just not thinking about or have forgotten about. It does make sense of course, we do need to focus on our health, on our security, keeping in check with the lockdown measures, etc. but I think it’s also really, really important to appreciate what is out there. Even though we can’t explore it and we can’t see it in first person at the moment, I think it’s still really important to at least appreciate and just celebrate what our planet has to offer. So, every single episode, I’m going to be talking about one aspect of the planet that I really, really appreciate, cherish, love, and I think you should really as well. Every single episode, I’m going to be trying to pick out something that’s really important in the planet, in our world, that we do depend on for it to exist and just kind of the beauty of the planet. Whether that will be in the form of a particular species I find really interesting, or a phenomenon that exists in the planet. Today’s episode is going to be just on how trees communicate with each other, so without wasting any more time, let’s begin today’s episode!
Language is one of the most powerful tools of communication we have. Language dates back to a long, long time, the time where we didn’t even have proper tools, we didn’t have any sorts of technology or digital advances. We just depended on language as our way to communicate. This is not just present in humans, of course, is present across kingdoms in species, individuals. It’s really essential for survival, and it really, really symbolizes how every single species is not independent in that sense. As soon as we are born, we enter a really complex web of connections where children really, really depend on people to care for them. The more connections and more relations that a child has, the healthier their childhood would be compared to a child that doesn’t really have many people looking after it. Of course, excluding the fact that many relations does not equate to quality relations.
Our perception of communication, in particular language, is really based off a fundamental principle essentially, and that is sound. What we can hear really, really plays a major role in how we communicate with each other, and it’s the same for species. Let’s say if you go out to a park and you hear birds chirping, you immediately identify that as them communicating with each other. If dogs are barking at other dogs that they haven’t seen before, we think that they’re communicating with those dogs. Even looking at prey animals, they sound their special alarm calls when a predator is nearby to alert their community that a threat is nearby. So, this is all different forms of communication that is really based off sound, so essentially for us, sound equals communication. But what if our perception of language, our perception of communication is partially true or maybe not even true at all? What if we’ve just defined language based off what we as humans know and what we as humans identify it as, instead of what it really is and the different forms of communication that occur in ecosystems and the planet as a whole.
Today’s episode is just going to be talking about one aspect of communication, a form of communication that many of us may be aware of, but we don’t know how complex it actually is. And that is within the plant kingdom, the silent, immobile organisms that we perhaps see as one of the simplest forms of life today in terms of the visible life forms that we can see. So, how can plants like trees actually communicate? Trees really communicate their needs by sending nutrients to each other through a network of fungi called mycelium; it’s almost like the neural systems in a brain. It’s like they’re sending signals to each other and it’s not just restricted to resource transfers. It also includes things like defense signals and also kin recognition. So, this makes trees and plants in general, much more complex than what people know them to be. Yes they aren’t mobile, yes they don’t of course use sounds to communicate, but they communicate through an underground network of fungi.
This occurs globally. All trees have a symbiotic interaction going on below ground that we can’t see, but it really does exist, and it really helps them to survive. So, the mycelia are able to colonize the soil and connect to trees’ roots and really just absorb any nutrients like phosphorus, nitrogen and also water that they can bring back to the plant and exchange that for a substance called photosynthate, which is a type of sugar made from photosynthesis. Of course, fungi can’t photosynthesise because they’re underground, so there really depends on this exchange for them to survive. And also, the trees rely on the fungi to bring them essential nutrients so that they can continue on growing. What makes these networks complex is that the phone guy is not just connected to one tree, it’s connected to many others. So these nutrients, water, etc. is really being shared amongst many other trees. A really good example of this is the Douglas fir and paper birch experiment, which was carried out by Suzanne Simard (I’ve put the link of that experiment to my website). The experiment really showed how the fir and birch were able to share carbon based on shading in summertime, which is a really important ecological factor that helped in distributing resources equally. The more shading the Douglas fir got in the summertime, the more excess carbon was received by the far from the birch. In autumn when the birch started losing its leaves, the Douglas fir got excess carbon because it was able to photosynthesize. So, the net transfer of the carbon went from the birch to the fir. This carbon partitioning was all able to happen just because of the existence of mycelium.
The fungal network is not just limited to nearby trees or nearby plants. It can really spread across large distances. So for example, a tree in your garden could actually be connected to a distant bush in a nearby park just because of the mycelium network that exists. These fungal systems are actually so widespread that some scientists actually refer them to the Earth’s natural internet. In fact, Avatar got inspiration by this, where all the organisms are connected on the forest moon and communicate through the roots of trees. Of course, this is a bit too far-fetched, but the fundamental idea is correct. The fungus is of course, not really doing it for the benefit of the trees, it’s doing it for its own livelihood to ensure that it has a secure food base, but the trees really, really depend on it for resource partitioning and for many, many other things that help them to survive. This connectivity with the mycelium really makes trees have a symbiotic interaction with each other.
There’s actual evidence to show that older trees help out younger ones instead of outcompeting them using this fungal internet. For example, seedlings in the shade usually get more carbon donated to them by larger trees, compared to those in out in sunlight. It really, really contradicts the Darwinian theory of survival of fittest, where tall trees would always out-compete smaller ones, because of the vast amount of time they’re in the shade. But here, instead of being individuals competing for themselves and for their seedlings, they’re actually just helping each other to survive. So it’s not just individual plants competing as we know, the kind of simple interaction that we know. Alongside competing and of course competing for resources for space, etc. plants are really also helping each other to survive and that will in the end, benefit them, but also benefit many, many other plants. It’s also really important to note, however, that the extent of these transfers and how important these transfers are for the overall survival of plants is really unknown. But the fact that these networks exist, and really encourages symbiotic interactions to happen, this just symbolizes how complex the plant kingdom is and how interdependent plants are.
Not only does this natural internet help in resource partitioning etc., it also helps boost immune system of host plants. As the fungus initially starts colonising the plant’s roots, this triggers a production of defense-related chemicals, so that makes the plants more able to prepare themselves for future attack compared to plants that don’t have a mycelium network. Not just for themselves, but also neighbouring plants as well. In 2010, a study by Ren Sen Zeng from South China Agricultural University found that if plants had a harmful fungi attached to them, they were able to release chemicals into the mycelia that warned neighbouring plants that they were being attacked, and those plants could be attacked as well. Really showing that this mycelia, this natural internet, is not just for resource transfers, is also to help other plants realize when a threat is nearby like fungal attacks. Zeng’s team was able to show this through tomato plants; so they grew pairs of tomato plants in parts, some of the plants were allowed to grow mycelia and others weren’t. Once the network was formed in some of the plants and some of the plant pots, one plant from each pair was sprayed with Alternaria solani, which is a fungus that causes blight disease, and the plants were covered with air tight bags to prevent any airborne signaling happening between the plants. After 65 hours, Zeng tried infecting the second plant that wasn’t infected by disease, and he found that the second plant was much, much less likely to get blight and have much less of damage caused than the plants that did not have the mycelium. So, this really symbolized that during those 65 hours, the plant that was infected was able to send signals, defense signals to the second plant that it has been infected by blight disease and that plant was able to become resistant to that disease. I think that is just amazing. We humans can’t do that, but plants definitely can.
Another study done by David Johnson from the University of Aberdeen showed similar results with broad beans and aphids this time. So the seedlings, which weren’t affected by aphids, but were connected to the, mycelium network activated defense mechanisms for the aphids. The plants that weren’t infected by the aphids, they weren’t being attacked by the aphids, they were producing the same defense mechanisms as the plants that were infected when the mycelia network was there. When the network wasn’t there, plants that weren’t infected by aphids weren’t producing those defense mechanisms. So that clearly shows that a secret sort of communication was happening just because of the mycelium.
So far, it’s all looking good. It all looks positive. The fungus is getting the nutrients it needs, and the plants are surviving well that they’re able to signal to each other in terms of threats and also partitioned resources. But just like how the internet has a dark side to it, for example we have security breaches, cyber-crimes, viruses being spread to softwares, there are also many harmful aspects to fungal connections, and it’s not just the pathogenic fungus that I’m talking about here. Many species actually use this internet to steal from each other. A common example is a phantom orchid, which can’t photosynthesize because it doesn’t have chlorophyll, so it takes carbon from neighboring plants through the mycelia that they’re both connected to. What’s worse is that some plants use the mycelium network to harm other plants and to prevent their growth as part of competition. So, some plants can release harmful chemicals to their competitors; it’s really common in many, many species of trees, and it’s known as allelopathy. So trees like acacias, some species of eucalyptus and sycamores, they release chemicals to either reduce the spread of microbes around neighbouring trees’ roots, or reduce chances of new plants being established nearby to make sure that only their seedlings can be established.
Again, we don’t know the extent of which this is really useful for plants and how strong these chemical releases will actually be for the survival of the plant compared to another one, but it does exist. There is evidence for it. A study was carried out in 2011 where marigolds were grown in containers; half of them had the mycelia (it was allowed to form) and half didn’t have them. The soils would then be tested to see if these harmful toxins, the substances would be released. Two substances were tested for: one for killing nematode worms and another for reducing the growth of other plants. In the half that had the network, it was found that 179% of more substance to reduce plant growth and 278% more of the substance to kill nematode worms were found in the plants that were allowed to make the mycelium network compared to the plants that didn’t have them [mycelium]. The experiment was then repeated with lettuce seedlings; after 25 days of growing the seedlings in the toxic soil that had the mycelium, it was found that they weighed 40% less than those seedlings that did not have the mycelia present, just because of the toxic chemicals that were released by the plants for reducing growth and killing the worms. So, this symbolises that mycelia were extremely important for competition, in terms of transporting these toxins and reducing the growth of other species. The fact that you found more than a hundred percent increase in the release of these substances really shows that plants clearly rely on releasing chemicals and toxins to help them compete better. So, it’s not just about symbiosis, it’s also about competition. It’s a bit of both really, whatever helps the plants survive the best. This is not just present in lab experiments. Experiments in the wild were also carried out, for example, the black walnut tree reflects the same sorts of tactics. It inhibits the growth of many plants like potatoes and cucumbers through releasing these toxic chemicals. One such chemical is jugalone, and many, many other species do the same, just so that they can compete better and get more resources.
All of these pieces of evidence have led many biologists to label this communication between trees, between plants as the wood-wide web. A language system that happens on the ground that we aren’t able to see but really does exist and really, really helps each tree part of the mycelia network, each plant part of the mycelia network to survive. Whether that’s through competing, whether that’s through stealing resources, whether that’s through providing other resources for other species. It’s all of course for survival, but the fact that this “wood-wide web” exists shows how complex the plant kingdom really is, and without the presence of these fungal networks, we wouldn’t have the trees that we do have. We wouldn’t have a surviving plant kingdom without this interconnectivity. So what’s really important to take out of all of this is that because these complex fungal networks exist, it really helps us shift away from the mindset that plants are very simple life forms, all they do is produce seeds and grow in essentially one place, to acceptance that our plants are very, very complex individuals just like us, just like any other organism in this world, and really without sustaining these networks they won’t be able to grow. They won’t be able to function and support all the ecosystems that we do need supporting of. I think labeling this communication as “language of trees” or “language of plants” is really important because if we kind of see them in the light that we see other people and other organisms, then we will definitely respect them more.
We would definitely value them, and the more similarities essentially that we pick out between us and plants and other organisms, the more we will be able to value them and the more we are able to relate to them as well. This underground internet, this natural internet, really shows that just like how a single organism within a community is essential and needs to be there in order to provide the necessary functions of an ecosystem, each and every plant within this mycelia network is essential for the functionality of the plant community within an ecosystem. So next time you go to a park and you see trees close to each other, or just a single tree, just imagine how beautiful their communication is, the fact that the existence of just a single tree helps the wellbeing of so many others.
OUTRO: Thank you for listening. I hope you’ve gained a little more insight to what it’s like to be “mind-full of everything”. If you haven’t already, hit the subscribe button on your favourite podcast app to be up to date with episode releases, and go over to my website mindfullofeverything.home.blog to get more information. This is Agrita with the Mind Full of Everything podcast, and I shall see you next time!
- Allelopathy: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027195
- Phantom orchids: https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2000.00592.x
- Bean plants resistant to aphid attack: https://onlinelibrary.wiley.com/doi/abs/10.1111/ele.12115
- Tomato plants and blight disease: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0013324
- Douglas fir and paper birth experiment: https://www.nature.com/articles/41557