Most plants use safety methods to protect themselves from danger. When we cut grass or when bugs eat grass, the blades of grass produce chemicals to warn surrounding grass. But is there any use?
It’s all explained in the following answers we gathered from the internet.
They aren’t warning other grass.The chemicals being released do a couple things.They help heal the grass, help seal the grass so that it’s a bit more resistant to damage (doesn’t do shit against a steel blade, but helps against a caterpillar).And it can help to call certain bugs that feed on the bugs that feed on the grass.Some grasses will also release certain chemicals that make their leaves taste awful to bugs.Some grasses can also concentrate nutrients into their roots to better rebuild.
The smell may also be a chemical warning to other grass to preemptively taste bad, but its far more likely that other grass is warned via the Wood Wide Web
People like to think that it’s an animal trait to like to stay alive, and protect and defend themselves, and plants are just totally inert. But that isn’t true. Unlike animals, plants can’t run away and escape danger, but plants are every bit as opposed to being killed and eaten as any animal is. Instead of running, plants engage in physical warfare: spikes and tough exteriors and all kinds of other things, and chemical warfare: releasing a number of different chemicals in response to being attacked by an herbivore. These responses fall into three main categories:
- Direct defense. Some chemicals released by plants are intended to directly harm the predator eating it. Many plants, such as clover for example, use cyanide as their poison of choice. Sometimes, to prevent poisoning themselves by accident, they’ll even compartmentalize their cyanide into a two-part weapon system, storing a harmless, nontoxic cyanide precursor inside their cell cytoplasms, and storing an enzyme in their cell walls that breaks down that precursor into active, deadly cyanide. Getting munched on by a herbivore breaks the cell wall and mixes these ingredients, poisoning the predator. Plants can also harm their herbivore attackers indirectly too, through things like producing an analog of the mating pheremones of the herbivore’s natural predator.
- Local repair. Some chemicals that plants release when they’re damaged, such as jasmonic acid, serve as plant hormones that signal the rest of the plant to brace and prepare for damage. Plants constrict their water channels to avoid losing water through their damaged parts, produce saps and sticky coagulants to block off the damage, produce antibacterials and antifungals to protect against infection, increase cell replication to heal faster, and start producing bitter, foul-tasting molecules that discourage herbivores from continuing to eat them, as well as enzymes that block digestion, making itself less nutritious.
- Remote signaling. Many of the same chemicals that direct plants to start repairing themselves, such as jasmonic acid, are also highly volatile, and signal neighboring plants to start bracing for impact and preparing themselves as well. In response to distress signals given off by nearby plants that are being eaten, plants will produce bitterants and digestion-blockers, making themselves unpalpatable to their herbivore predators. In fact, this is the reason that giraffes have to be nomadic creatures: you never see a giraffe herd strip a tree completely bare, because after munching on a tree for some time, the tree becomes bitter and inedible, and depending on wind conditions, other trees for miles around become so too. So the herd has to keep moving, trying to stay ahead of the chemical cloud of anguished screaming their leaf-munching inspires, in order to keep finding new trees which are still delicious and haven’t yet hardened themselves.
Of course, plants can’t tell the difference between an animal’s teeth and a lawnmower’s blade, so against us, all their chemical screams, poisons, and distress calls don’t do them much good, and make a pleasant summertime perfume for us instead.
I can’t speak for grass, but tomatoes under attack by caterpillars can boost defensive chemicals that make their leaves taste horrible, causing caterpillars to eat each other instead and save the plant.
Incredibly, some plants are capable of ramping up their defences simply by hearing the sounds of caterpillars chewing.