What plants’ aerosol alarms tell their neighbors

A plant can’t flee when a hungry animal chomps down on its leaves, stem, or roots. It can, however, release a cloud of volatile organic compounds (VOCs) to dissuade predation and cry out to its neighbors, “Start armoring up!”

But herbivory-induced VOCs have a life of their own in the atmosphere. Researchers know that plant VOCs readily transform into secondary organic aerosol (SOA), a mixture of aqueous or semisolid particles that form when gases are oxidized. Whether these particles participate in plant-to-plant communication has been a mystery. Newly published work may change that.

“We found for the first time that secondary organic aerosol can actually have a role in mediating interactions between plants,” says chemical ecologist James Blande of the University of Eastern Finland (Science 2024, DOI: 10.1126/science.ado6779).

To study SOA-mediated plant communication, Blande and his team captured the VOCs emitted by Scots pine seedlings whose roots were besieged by largepine weevils. As the bugs chewed, the plants released α-pinene, 3-carene, and many other monoterpenes, all of which were trapped inside a glass chamber surrounding the seedling. The team then siphoned away the VOC-laden air, oxidized the volatiles to form SOA, mixed those particles into ultrapure water, and sprayed the mixture onto a separate group of noninfested plants—the damaged plants’ “neighbors.”

Nonstressed plants also emit low levels of VOCs, so Blande and his team formulated a spray to represent the SOA that would form from nonstressed plants. They sprayed this on another group of neighboring pine seedlings.

Only the seedlings sprayed with stress-generated SOA responded. Their responses were similar to those caused by stress-induced VOCs, suggesting that the information VOCs convey is preserved when they transform into SOA, “which is very interesting,” says ecologist Velemir Ninkovic of the Swedish University of Agricultural Sciences. “This is a groundbreaking study that puts plant-plant interactions via volatiles in another perspective,” he says.

“The greatest implication here relates to the ability of SOAs to travel further than volatiles,” Mj Riches, an atmospheric chemist at Colorado State University studying plant VOCs, writes in an email. “This could help explain why plants further away from initial herbivory-induced stress have time to build their defenses.”