My labmate is doing research on the interaction between the plant circadian rhythm and the plant immune system. Their various immune hormones (along with all kinds of other things) are modulated by a rhythm that anticipates the diurnally-varying likelihood of fungal infection and can be phase-shifted not just by light but by humidity. The hormones that modulate this are systemic and get carried throughout the plant and can easily be taken up through roots.
After poking his plants in the lab he came up with the idea of getting our tomato plants we were growing together this summer to sacrifice a little bit of biomass in favor of fungus resistance by watering them with dilute aspirin (a slightly modified version of a plant immune system hormone originally extracted from willow bark) in the early mornings, and we discovered that other people had been doing this successfully for decades without any particular known mechanism. That chemical is easy enough for them to make and some plants (like willows) are absolutely full of it. Would not be surprised if they secreted it into the soil and if it bled over into adjacent plants. They also do not limit their interactions to other plants—I have seen research to the effect that most plants actively secrete sugars into the soil around their roots to attract bacteria which break down minerals and nutrients into forms they can absorb, and that they actively allow many symbiotic fungi into their roots without mounting immune responses.
My labmate is doing research on the interaction between the plant circadian rhythm and the plant immune system. Their various immune hormones (along with all kinds of other things) are modulated by a rhythm that anticipates the diurnally-varying likelihood of fungal infection and can be phase-shifted not just by light but by humidity. The hormones that modulate this are systemic and get carried throughout the plant and can easily be taken up through roots.
After poking his plants in the lab he came up with the idea of getting our tomato plants we were growing together this summer to sacrifice a little bit of biomass in favor of fungus resistance by watering them with dilute aspirin (a slightly modified version of a plant immune system hormone originally extracted from willow bark) in the early mornings, and we discovered that other people had been doing this successfully for decades without any particular known mechanism. That chemical is easy enough for them to make and some plants (like willows) are absolutely full of it. Would not be surprised if they secreted it into the soil and if it bled over into adjacent plants. They also do not limit their interactions to other plants—I have seen research to the effect that most plants actively secrete sugars into the soil around their roots to attract bacteria which break down minerals and nutrients into forms they can absorb, and that they actively allow many symbiotic fungi into their roots without mounting immune responses.