I just can't get enough of the seemingly implausible social life of plants. Plants do not only actively communicate with each other, with insects and also with animals. Plants are also aware of who their siblings are. And by that I don't mean that a plant knows there are plants from the same species around her. She actually clearly recognises a sister from the same mother plant. And she will help her sister to survive, but will not do the same for other plants of the same species.
Susan Dudley at the McMaster University on Hamilton, Ontario has demonstrated that the Hooded Skullcap will actively adjust her root growth when a sister is growing next to her as opposed to a stranger. When grown next to a stranger, she will grow an extensive root network under her neighbour, stealing its water and nutrients. Yet when grown next to a sister, she will avoid growing roots under her sister, giving her a better chance of survival. This strategy helps both sister plants to save energy by not growing roots that compete each other - thus giving both of them a better chance of growing up and spreading their genes.
And plants do not only recognise their own kin, they also know what other plants are growing around them and adjust their response to predators accordingly.
Amanda Broz at the Colorado State University in Fort Collins grew knotweeds in isolation and together with fescue grass. Broz then simulated an insect attack by spraying a specific fragrance over the plants. The knotweed's response to the attack depended on who his neighbours were. When surrounded by other knotweeds, he would produce a toxin in his leafs to kill the insects. If however the knotweed was surrounded by fescue grass, he would put all his energy into growing as quickly as possible and leave the defence against the invader to the surrounding fescue grass.
This complex social behaviour of plants clearly demonstrates that plants are not just "biological machines". We have clearly underestimated them until now.
For more interesting plant stories, check out Florianne Koechlin's new Book "Jenseits der Blattränder - Eine Annäherung an Pflanzen".