These plants may worsen air pollution on a warming planet, says study

On an already warming planet, plants like oaks and poplars will emit more of a compound that exacerbates poor air quality, contributing to problematic particulate matter and low-atmosphere ozone, claims a study.

Interestingly, the same compound, called isoprene, can also improve the quality of clean air while making plants more resistant to stressors including insects and high temperatures.

"Do we want plants to make more isoprene so they're more resilient, or do we want them making less so it's not making air pollution worse? What's the right balance?" asked Tom Sharkey, a Professor in the Plant Resilience Institute at Michigan State University in the US.

Isoprene from plants is the second-highest emitted hydrocarbon on Earth, only behind methane emissions from human activity.

Yet most people have never heard of it, Sharkey said, in the paper published in the journal Proceedings of the National Academy of Sciences.

Isoprene interacts with nitrogen oxide compounds found in air pollution produced by coal-fired power plants and internal combustion engines in vehicles. These reactions create ozone, aerosols and other byproducts that are unhealthy for both humans and plants.

In the study, the team worked to understand the biomolecular processes plants use to make isoprene. The researchers are particularly interested in how those processes are affected by the environment, especially in the face of climate change.

Prior to the study, researchers understood that certain plants produce isoprene as they carry out photosynthesis. They also knew the changes that the planet is facing were having competing effects on isoprene production.

That is, increasing carbon dioxide in the atmosphere drives the rate down, while increasing temperatures accelerate the rate.

One of the questions behind the new study was essentially which one of these effects will win out.

"The crux of the paper is that we identified the specific reaction slowed by carbon dioxide, CO2," Sharkey noted.

"With that, we can say the temperature effect trumps the CO2 effect," he said.

"By the time you're at 95 degrees Fahrenheit -- 35 degrees Celsius -- there's basically no CO2 suppression. Isoprene is pouring out like crazy."

In their experiments, which used poplar plants, the team also found that when a leaf experienced warming of 10 degrees Celsius, its isoprene emission increased more than tenfold, the team said. The discovery will help researchers better anticipate how much isoprene plants will emit in the future and better prepare for the impacts of that. But the researchers also hope it can help inform the choices people and communities make in the meantime.