Both humans and plants inhale other chemicals in the air around them and exhale chemicals produced inside them—coffee breath for some people, pine scents for some trees.

Unlike humans, however, leaves breathe in and out at the same time, constantly taking in and releasing atmospheric gases.

Clues from over a century of research

In the early 1900s, scientists studying trees in heavily polluted areas discovered that those chronically exposed to pollution from coal-burning had black granules clogging the leaf pores through which plants breathe. They suspected that the substance in these granules was partly created by the trees, but due to the lack of available instruments at the time, the chemistry of those granules was never explored, nor were the effects on the plants’ photosynthesis.

Most modern research into wildfire smoke’s effects has focused on crops, and the results have been conflicting.

For example, a study of multiple crop and wetland sites in California showed that smoke scatters light in a way that made plants more efficient at photosynthesis and growth. However, a lab study in which plants were exposed to artificial smoke found that plant productivity dropped during and after smoke exposure—though those plants did recover after a few hours.

There are other clues that wildfire smoke can impact plants in negative ways. You may have even tasted one: When grapes are exposed to smoke, their wine can be tainted.

Taken together, studies suggest that wildfire smoke interacts with plants, but in poorly understood ways. This lack of research is driven by the fact that studying smoke effects on the leaves of living plants in the wild is hard: Wildfires are hard to predict, and it can be unsafe to be in smoky conditions.

Accidental research—in the middle of a wildfire

We didn’t set out to study plant responses to wildfire smoke. Instead, we were trying to understand how plants emit volatile organic compounds—the chemicals that make forests smell like a forest, but also impact air quality and can even change clouds.

Fall 2020 was a bad season for wildfires in the western U.S., and thick smoke came through a field site where we were working in the Rocky Mountains of Colorado.

What our months of data told us is that some plants respond to heavy bouts of wildfire smoke by shutting down their exchange with outside air. They are effectively holding their breath, but not before they have been exposed to the smoke.

We hypothesize a few processes that could have caused leaves to close their pores: Smoke particles could coat the leaves, creating a layer that prevents the pores from opening. Smoke could also enter the leaves and clog their pores, keeping them sticky. Or the leaves could physically respond to the first signs of smoke and close their pores before they get the worst of it.

It’s likely a combination of these and other responses.

The long-term impact is still unknown

The jury is still out on exactly how long the effects of wildfire smoke last and how repeated smoke events will affect plants—including trees and crops—over the long term.

With wildfires increasing in severity and frequency due to climate change, forest management policies and human behavior, it’s important to gain a better understanding of the impact.

Delphine Farmer is a professor of chemistry at Colorado State University.

Mj Riches is a postdoctoral researcher in environmental and atmospheric science at Colorado State University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.