Plant Behavior

Monte Amiata, Italy (September 16, 2009)

One of the best use I have for the iPad is to watch PBS (the US public TV) programs. In a country where everything is extremely commercialized, PBS is one of the gems of public service (another one being NPR, the public radio). Being public doesn't mean that PBS and NPR are entirely paid by the government. In fact only 15 to 20% of their funding comes from the federal government, the rest being provided by micro-donations from the public, as well as sponsorship of individual programs from foundations and corporations. The reason why I like PBS and NPR is not (just) that they are free and devoid of commercials, but most importantly that their programming is very high quality and touches topics that are generally avoided by commercial broadcasters. Some of these topics are of course not the favorite of a certain political side, and in this crazy-cut-it-all mania PBS and NPR have been repeatedly threatened of being defunded (most infamously by a certain presidential candidate during an electoral debate). Among my favorite programs are NOVA (science), Frontline (investigative journalism) and Nature (you guess this one).

I am writing about this because the Nature program I saw a couple of nights ago was simply mind-boggling. The title was "What Plants Talk About", and the topic was plants behavior. Plants what? Yes behavior like in animal behavior. It turns out that even if plants do not possess a nervous system like animals, they have a range of mechanisms to interact actively with their environment, and to communicate one with the other. We usually don't see all this because it happens on a time scale significantly longer than animal interactions, but the the program show an impressive array of cases in which plants have a very animal-like behavior.

New Zealand forest

What would you think if I say that plants tend their young? This is what Douglas fir trees in a British Columbia forest appear to be doing, by providing nutrients to its seedlings through their root system. Or how other plants share resources with genetically related individuals while at the same time compete fiercely with unrelated plants (how do they know who is family)? Or how plants' roots forage like animal herbivores? That's what the roots of plants filmed at high speed appear to do, snaking around and "tasting" the soil, stopping temporarily only when they find a patch of nutrients to absorb. Or that some plants cry for help when under attacks, alerting their neighbors and calling for reinforcements? This is what the wild tobacco plant does, changing from a nocturnal to a diurnal flowering plant depending on the kind of predators that are around (and "telling" the other plants around to do the same before they are attacked), and tagging the offending insects with a substance that attracts their own predators. The fact that all these behaviors happen through chemical signaling, rather than through the "senses" that we associate with animal communications, and that the processes that are involved in plants decision-making are also based on chemical reactions, rather than electrochemical signals as in animals' nervous system, does not make all this less impressive. It actually makes it even more remarkable, considering that we are talking about organisms that are essentially stuck where their roots are, and despite this limitation had developed survival strategies that are very complex and sophisticated.

I found the best part of the program towards the end. Dr. Suzanne Simard of the University of British Columbia, the one working on the Douglas fir trees nurturing their young, tells how one day she went to the theatre to see the Avatar movie. The film has a scene in which the protagonists seek refuge under a "mother three" that keeps alive the whole ecosystem in the Avatar world. She said that once she saw that scene she exclaimed "they have read my papers!". The movie was perfectly describing what she sees every day when she work in the forest, and discovers how these trees communicate one with the others, sharing resources through an underground network that touches all the other creatures in the forest, making it like a huge interconnected multi-organism. Like Pandora.