Plants are at the trophic base of most ecosystems, embedded in a rich network of ecological interactions. While their limited range and speed of motion precludes animal-typical behavior, plants are accomplished chemists, producing thousands of specialized metabolites which may convey information, or even to manipulate others’ physiology. Using genetically modified lines of the wild tobacco Nicotiana attenuata planted into experimental populations in their native habitat, we investigated community-level effects of diversity in defensive chemistry, for populations of otherwise isogenic plants. In a separate set of experiments, we investigated direct effects of neighbor volatile emission on seedling growth. We focused on the volatile phytohormone ethylene (ET) which regulates components of the shade avoidance syndrome and, at very high concentrations, can initiate neighbor shade avoidance; and the green leaf volatiles (GLVs) responsible for the odor of cut grass and other wounded leaves, which are ubiquitous damage-associated volatiles in plants. GLVs act as defenses and are perceived and even co-opted by neighbor plants, but were not known to affect growth.
Results/Conclusions
We found that the number of plants in a population emitting specific volatiles interacted with plants’ total chemical defense capacity to determine whether the plant volatiles had a positive or a negative effect on plant infestation rates, indirect defense via predator recruitment, and mortality. Using wild-type (WT) emitter plants or emitters rendered deficient in these components of their volatile profile via RNAi, we observed that N. attenuata seedlings exposed to realistic emissions of GLVs from wounded neighbor plants increased their leaf area expansion rates, independently of neighbor ET emission. To determine if responsiveness to GLVs was linked with plants’ ability to produce them, we supplemented the headspace of irLOX2 seedlings and empty vector (EV) controls with synthetic GLV blends in open-flow experimental chambers, and in natural field conditions. Our results indicate that seedling leaf growth promotion by neighbor GLVs depends on a ratio to internal growth-inhibiting oxylipin pools, such as traumatins, which are reduced in LOX-deficient plants. Interestingly, measurements of seedling ET emission indicated that changes in ET signaling, also known to be affected by traumatins, are part of the GLV growth response.