plant symbiosis

I consider agriculture as practiced by civilization, where plants grow up without interaction with underground fungal networks, a diverse variety of root bacteria and exposure to other plants to be a violation of the rights of plants.

There’s a study that was recently done that looked at the responses of plants to volatile organic compounds, which are produced by plants in response to insects eating from their leaves.

The scientists assumed that a mixture of plant chemicals would trigger other plants to produce defensive mechanisms, but rather, a single chemical called (Z)-3-Hexenol (also referred to as leaf alcohol) led tomato plants to start producing HexVic, which is the chemical name of a compound that kills insects exposed to it in the long run.

That’s interesting, because (Z)-3-Hexenol can be produced by most plants. More interesting is the fact that the leaf alcohol that attacked plants emitted was directly converted into Hexvic by plants that received it. In other words, the plants that are attacked emit a chemical that other plants directly use to defend themselves. In addition, it was found that not just tomatoes produce HexVic, but so do sorghum and rice. Also important to note is that plants produce more leaf alcohol, when exposed to small amounts of volatile organic compounds of other plants over a longer period of time.

That’s all nice and well so far, but what makes it so interesting are the apparent implications. Plants produce chemicals that provide benefits to other plants. They produce these chemicals when environmental triggers indicate they are potentially at risk, thus there is some sort of cost for these plants when it comes to producing these chemicals, as they only produce them when there are indicators of risk. What makes it really interesting is the apparent indiscriminate aspect of the mechanism. Practically any plant can produce leaf alcohol, and a variety of species can transform leaf alcohol into a pesticide that harms the insects, benefiting all other species.

What we find thus is essentially a mechanism of apparent cooperation at the level of an entire community of plants. Plants aid other plants of different species nearby them that we would expect to be their competitors. I’m not really surprised by this, as it fits in with everything else I’ve learned about plants. Plants are highly dependent upon one another, especially plants of other species.

Some species such as the dandelion are capable of growing thick roots that dig up nutrients that are not accessible to other species, thus benefiting other species when they die. Other species, such as the stinging nettle and the giant hogweed, produce skin reactions on mammals, thus causing mammals to avoid areas where they grow. That’s very interesting, because what giant hogweed and the stinging nettle have in common is that they only have a competitive edge over other plant species, when there are relatively high concentrations of nitrogen in the soil. High concentrations of nitrogen in the soil are caused by a large number of mammals defecating in the general area. You can confirm this for yourself, you will notice that these plants tend to grow in places where people take out their dogs, you generally won’t find many of them in actual forests.

What it leaves us with however, is an apparent contradiction. These plants chase away the animals that made their growth possible in the first place, by enriching the soil with excessive amounts of nitrogen. How could a plant possibly benefit from that, doesn’t this act of destroying your own niche contradict natural selection? The best explanation I can come up with is as following: The reason this occurs is because of selection occurring at the level of ecosystems. Only those ecosystems survive where different plant species are not selfish, but rather, attempt to cooperate and do not attempt to dominate the entire ecosystem for themselves. Ecosystems where different plant species do not manage to cooperate destroy themselves from within.

What would happen if the giant hogweed and the stinging nettle decided to be selfish instead and stop chasing away mammals? More animals would visit these areas, other soils would deplete at the cost of a small area, this would reduce humidity in the air as fewer plants grow in those areas, species diversity begins to decline in the ecosystem and eventually the plants that dominate are hit by a pathogen or suffer drought, die off and as a result leave the soil exposed and without roots. The sudden lack of biomass makes it easy for the soil to blow away, which in turn makes it impossible for the plants to grow. A boom ensures a bust that ends in extinction, whereas selfless cooperation leads to long term survival.

Taking this a step further, plants may very well be happier surrounded by a diversity of other species, whereas they experience a situation where they are surrounded by members of their own species as rather stressful. I consider agriculture as practiced by civilization, where plants grow up without interaction with underground fungal networks, a diverse variety of root bacteria and exposure to other plants to be a violation of the rights of plants. It’s arguable that it only sounds less horrifying to me than the experience of children who grow up forcibly drugged to sit quiet in their desks and memorize arbitrary factoids because of my own anthropocentric bias. Finally, taking this thought a final step further, it has to be asked: Are we a selfish plant?Are we the poor species that kills its own ecosystem to temporarily sustain a higher population density at the cost of our own quality of life as well as any future we otherwise might have had?


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