Plant Conversations: Green Leaf Volatiles

Being outdoors for many of us means flowers blooming, walking under a tree, and that comforting and evocative scent of green from freshly mown grass. For plants, that same smell means protection and warning. Many of the volatile chemicals that we perceive as the smell of growing are actually produced by plants to defend themselves. Whether from a chewing caterpillar, a munching grasshopper, bark beetle, pathogen, or a lawn mower, the green fragrance released by plants often signals injury. Visualize a grasshopper chewing holes along the edges of a leaf. The plant is able to sense the damage and immediately begin producing chemicals to communicate danger.

Grasshoppers on Thistle Plant

Plants communicate via these volatile organic chemicals or VOCs, generally within the plant itself (internally or leaf to leaf) but also as a warning to neighboring plants, either on purpose or by being eavesdropped on. Early research on this led scientists to use the term ‘talking trees’ to refer to such plant conversations. In the context of plants, this is mainly a way of understanding the dynamics of communication. Plants are putting out signals and receiving signals through four steps – production of the signal by the emitter plant, transport of the signal through the air, absorption of the signal, and perception by the receiver plant. When humans speak, we call it hearing or listening—with plants the simplest concept is to call it communication. Is it the same thing?

Tall Grasses (photobombed by a sandhill crane)

Green leaf volatiles also communicate to predators that will respond by approaching the plant to prey on the herbivores chewing on leaves or flowers. Within the plant, responses include production of extrafloral (other places than flowers) nectar that attracts predators to control the herbivores as a defense mechanism. Or the plant may move nutrients from leaves and tops of plants, areas likely to be munched on, further inwards or towards the roots to avoid loss.

Insect Damage

Next time you are outside, use your nose to sense what the plants are communicating. Fresh and floral often means attraction for pollinators, resinous and citrusy provides protection, and bright green may mean herbivores in the neighborhood—or just your neighbor mowing their lawn and the plants protesting.

For more on talking trees, see Baldwin et al. “Volatile Signaling in Plant-Plant Interactions: ‘Talking Trees’ in the Genomics Era” in Science Feb. 2006

I enjoyed our conversation about green leaf volatiles during my book signing at Dolly’s Bookstore in Park City Utah.