Air pollution impedes plant-to-plant communication, but what is the signal?

Since the first reports that undamaged plants gain defensive benefits following exposure to damaged neighbors, the idea that plants may signal to each other has attracted much interest. There has also been substantial debate concerning the ecological significance of the process and the evolutionary drivers. Part of this debate has centered on the distance over which signaling between plants occurs in nature. In a recent study we showed that an ozone concentration of 80 ppb, commonly encountered in nature, significantly reduces the distance over which plant-plant signaling occurs in lima bean. We went on to show that degradation of herbivore-induced plant volatiles by ozone is the likely mechanism for this. The key question remaining from our work was that if ozone is degrading the signal in transit between plants, which chemicals are responsible for transmitting the signal in purer air? Here we present the results of a small scale experiment testing the role of the two most significant herbivore-induced terpenes and discuss our results in terms of other reported functions for these chemicals in plant-plant signaling.