An international team of scientists from Oxford University, UK, and Tel-Hai College, Israel, has shown that pea plants can demonstrate sensitivity to risk - namely, that they can make adaptive choices that take into account environmental variance, an ability previously unknown outside the animal kingdom. In the study, published in the journal Current Biology, pea plants were grown with their roots split between two pots, thus facing the decision of which pot to prioritise. 

In a preliminary experiment, the researchers showed that the plants grew more roots in a pot endowed with higher levels of nutrients - an adaptive response similar to animals allocating greater foraging effort to richer food patches. In a series of follow-up experiments, they then split the roots of each plant between two pots that had equal average nutrient concentrations, but where one pot had a constant level and the other a variable level, asking whether plants would 'prefer' to grow more roots in one or the other.

Based on theoretical analyses of how decision makers such as humans or animals respond to similar choices, the researchers predicted that plants might prefer the variable pot (ie be risk prone) when the average nutrient level was low, and the constant pot (ie be risk averse) when average nutrient level was high. 

This is because when the average nutrient level is below what is required for the plant to thrive, the variable option at least offers the chance to 'gamble' on a run of good luck. On the other hand, when average conditions are good, it makes sense to take the safe option. 

The researchers found that this is exactly what the pea plants did.

Co-author Professor Alex Kacelnik, of the Department of Zoology at Oxford University, said: 'To our knowledge, this is the first demonstration of an adaptive response to risk in an organism without a nervous system. We do not conclude that plants are intelligent in the sense used for humans or other animals, but rather that complex and interesting behaviours can theoretically be predicted as biological adaptations - and executed by organisms - on the basis of processes evolved to exploit natural opportunities efficiently. 

'We do not yet know how the plants' sense variance functions, or even if their physiology is specifically adapted to respond to risk, but the findings lead us to look even at pea plants as dynamic strategists and to model their decision processes just as one would model an intelligent agent.'