Altruistic plants?

There’s been a thoughtfulness* of books recently that reflect on aspects of plant intelligence – e.g. Daniel Chamovitz’s What a Plant Knows, Anthony Trewavas’ Plant Behaviour & Intelligence, Richard Karban’s Plant Sensing and Communication , and Stefano Mancuso and Alessandra Viola’s Brilliant Green.

Monks collecting alms
Monks collecting alms during Bun Vat Phou 2012. Image: GuillaumeG / Wikipedia.

Whilst the concept or meaning of plant intelligence is debated, let’s muddy the waters by introducing work by Deshan Zhang et al. on roots and phosphorus ( P ) acquisition. Working with maize (Zea mays) and faba bean (Vicia faba) they demonstrated that maize had longer root length and greater shoot biomass and P content when grown with faba bean than with maize alone.

Although this maize behaviour is ultimately attributed to increased P availability in the soil, P availability is enhanced by exudates of citric acid and acid phosphatase from the faba bean. Understandably (it’s a study in a serious, sober scientific journal, after all), the paper’s authors discuss the results in the context of new insights into root/rhizosphere interactions “in developing strategies for rhizosphere management through optimizing plant combinations and soil nutrient supply to increase crop productivity and nutrient-use efficiency”.

But, there’s another aspect to these insights; can the faba bean’s actions be considered an example of altruism (“altruism or selflessness is the principle or practice of concern for the welfare of others. … “Altruism in biological organisms can be defined as an individual performing an action which is at a cost to themselves … , but benefits, either directly or indirectly, another third-party individual, without the expectation of reciprocity or compensation for that action”)? If so, why?? And isn’t altruism ‘stupid’, and therefore a sign of low intelligence on the part of the faba bean (and therefore a vote for those who deny plants intelligence…)?

If the faba bean also benefits, then it’s not true altruism, but quite intelligent – cunning even – behaviour on its part. And, if it’s not intentional altruism**, but the maize just capitalises on the enhanced P availability, then surely that’s clever, intelligent behaviour on behalf of the maize? Do different plant species differ in their levels of intelligence? Is it beyond the reach of mere humans to understand these plant actions and interactions?

Why is botany so philosophical these days? [Ed. – botany has always been a philosophical activity, at least as far back as Aristotle [Ancient Greek philosopher in 384– 322 BC] who proposed that plants – and animals! – have souls.]

[Ed. – in related rhizosphere-relevant work Jun Yuan et al. show that “organic acids from root exudates of banana help root colonization of PGPR (plant growth promoting rhizobacteria) strain Bacillus amyloliquefaciens NJN-6“.]

* If you can think of a more appropriate collective noun, please contact me.

** And one recognises that altruism may not be the most appropriate word, but I wasn’t sure where on the spectrum of symbiosis this relationship should be placed – it isn’t mutualism, it’s not parasitism, and it’s not amensalism