Beyond average: Risk sensitivity in an annual plant

Background/Question/Methods

Plants are known to discriminate between soil patches with different resource levels and tend to allocate more roots to rich patches. We tested the hypothesis that in addition to their ability to discriminate in response to mean differences in resource availability, plants can also discriminate in response differences in habitat variance.  Split-root Pisum sativum plants were grown in two separated pots. While one of the root-systems was subjected to a constant nutrient supply (constant fertilizer concentrations throughout the season) the other experienced temporal variability in nutrient availability (randomly changing fertilizer concentrations). Overall, mean nutrient availability was equal for both root systems. Since theoretical models of risk sensitivity predict an energy-status dependent response, the experiment was replicated 3 times, with plants of low, medium and high energy-status.

Results/Conclusions

Root allocation was dependent on the plants energy-status. Plants of low energy-status developed significantly more roots in the variable pot (25% more biomass). In contrast, plants of high energy-status developed significantly more roots in the constant pot (58% more biomass).  These results are in agreement with the energy budget rule and suggest that in addition to their ability to notice mean differences plants are also able to perceive within season environmental variability. This ability might enable plants to manage their risks while foraging in variable environments.