Visions from nature

Plant wars

By Anders L Kolstad

«Plant must be the most peaceful life form on earth. What if anything could they have to fight over?» One might think that life for plants is easy. Air, water and sunlight is in a way the whole recipe for life. But the reality is quite different, and some of the strategies used by some species is not far behind on aggressiveness in comparison to things like parasites or ferocious carnivores. Perhaps because everything happens is such a relatively slow pace, we don’t think much about this.

Kreklingen er ikke så fredelig som den ser ut. For å hindre at andre planter skal komme for nær, skiller den ut stoffer som virker hemmende på vekst og frøspiring. Det er en av grunnene til at den kan dominere over store arealer.
The black crowberry is not as peaceful as you might think. To stop other plants from crowding its space it secretes a chemical toxin that suppress their growth and germination. This is one of the reasons why this plant can often dominate over large areas. Photo: Jason Hollinger CC BY 2.0.

Conflict over resources

Of the three factors sunlight, water and air, only air comes free to plants. Light on the other hand is often a limitation for plant growth, simply because they overgrow each other. In other words, the plant compete for a spot in the sun. Also below ground, the plants are pushing and shoving as the root systems of different individuals are all after the same water and the same nutrients. To win in this constant fight for space, plants have evolved many strategies to impair and weaken their neighbors.

 

War in slow motion. Here we see a leafy lichen aggressively moving on a patch of moss, slowly overgrowing it. The fight for light is life or death for these species. Photo: Anders L. Kolstad, NTNU University Museum CC BY-SA 4.0.

The crowberrys’ own weed killer

A fascinating example come from the black crowberry. This species is widely distributed in the world and often dominate in areas where it is found. It’s doing quite well for itself. Researchers have found that one of the reasons behind its success is due to its ability to displace other species. It does this by excreting a chemical toxin that becomes trapped in the soil below it. This compound act to reduce the growth and germination of its neighbors. In the crowberries eyes, I guess it’s a herbicide.

Different tolerances

The crowberries neighbors, or the plants often found growing around it, all have different tolerances or susceptibility, to this toxin. For example, it looks as if heather and birch are really sensitive, whereas pine and European goldenrods are not. This could be because of different predispositions to the toxin, or from the different evolutionary pressure laid upon the species to overcome this warfare tactic.

Perhaps after reading this you won’t think of plants as simply innocent anymore.

 

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