Communication between plants: this time it's real.

Of course, neighboring plants in natural communities interact: we usually think of plants competing for sunlight and soil nutrients. Few topics in plant ecology have inspired so much excitement and controversy, however, as communication between plants. The idea, simply put, is that rooted and immobile plants might act to increase their levels of defense by responding to cues from neighbors that are being attacked by herbivores or pathogens. As some authors have suggested, perhaps 'listening trees' is a better descriptor than 'talking trees', but, in either case, the interaction holds unquestionably fascinating natural history. Communication is so prevalent and important among animals that its presence in plant communities could be revolutionary. In addition, if the phenomenon is real, it poses important questions about community evolution, including altruism (although the interaction might only benefit the listener). Unfortunately, the first demonstrations of these phenomena were trashed and disregarded by ecologists because of methodological inadequacies and the lack of realism in the experimental designs. Recent interest in volatile compounds produced by plants, such as jasmonate (known as the 'queen of aroma' in the perfume industry) and salicylate, has provided potential mechanisms for interplant communication. Three recent papers resurrect interplant communication by conducting rigorous and far-reaching studies spanning gene expression, physiology and field ecology. Dolch and Tscharntke 1 show that defoliation of single trees at ten sites in Germany caused natural herbivory to increase with distance from the defoliated tree. This result was confirmed in laboratory experiments reducing the possibility of associational resistance causing the field result. This effect might be due to airborne or soilborne cues. Karban et al. 2 demonstrated, over several years, that damaged sagebrush plants cause neighboring native tobacco plants to be more resistant to herbivores than tobacco plants next to undamaged sagebrush. This interaction is correlated with induced production of volatile methyl jasmonate in the sagebrush and increased polyphenol oxidase (a putative defense) in the tobacco. The communication was not mitigated by removing soil contact between plants, but was mitigated by bagging the damaged sagebrush plants. Arimura et al. 3 examine specific signals released by bean leaves attacked by herbivores and the activation of five putative defense genes. Indeed, at least three volatile terpenoids induced by herbivory, not by mechanical wounding, caused neighboring leaves to induce these genes and the induction was similar to that caused by exposure to jasmonate. Critics are going to love these studies: two of …